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Journal of Sea Research 43 (2000) 183–197
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Review Paper
Physiological aspects of the production and conversion of DMSP in
marine algae and higher plants
J. Stefels
Department of Marine Biology, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands
Received 20 April 2000; accepted 9 May 2000
Abstract
Dimethylsulphoniopropionate (DMSP) is a compound produced in several classes of algae and higher plants that live in the
marine environment. Considering its generally high intracellular concentrations, DMSP has a function in the osmotic protection
of algal cells. Due to the relatively slow adaptation of its intracellular concentrations upon salinity shifts, DMSP should,
however, not be considered as an osmoticum in the strict sense of being responsible for osmotic balance, but rather as a
constitutive compatible solute. Besides salinity, other factors also appear to affect cellular DMSP quotas, but the exact
regulatory mechanisms are still unclear. In this review, a brief discussion is given of the three pathways of DMSP biosynthesis
that are currently distinguished. This is followed by an overview of the factors that affect DMSP biosynthesis (light, salinity,
temperature and nitrogen limitation) in relation to its physiological functions. A new hypothesis is presented in which DMSP
production is described as an overflow mechanism for excess reduced compounds and for energy excess. Finally, the possible
functionality of the enzymatic cleavage of DMSP is discussed in the context of an overflow mechanism. 䉷 2000 Elsevier
Science B.V. All rights reserved.
Keywords: dimethylsulphoniopropionate; DMSP; dimethylsulphide; DMS; DMSP lyase; biosynthesis; global climate; sulphur assimilation
1. Introduction
Since the 1970s, interest in the production of the
volatile organic sulphur compound dimethylsulphide
(DMS) and its precursor dimethylsulphoniopropionate (DMSP) by marine organisms has been fuelled
by the realisation that marine DMS emissions could
close the global sulphur budget (Lovelock et al.,
E-mail address: [email protected] (J. Stefels).
Abbreviations: AdoMet, S-adenosylmethionine; APS, adenosine 5 0 phosphosulphate; DMS, dimethylsulphide; DMSP, dimethylsulphoniopropionate; GBT, glycine betaine; GSH, glutathione; MMPA,
methylmercaptopropionate; MTOB, 4-methylthio-2-oxobutyrate;
MTHB, 4-methylthio-2-hydroxybutyrate; DMSHB, 4-dimethylsulphonio-2-hydroxybutyrate; PAPS, adenosine 3 0 -phosphate 5 0 -phosphosulphate; SMM, S-methylmethionine
1972). Moreover, it was hypothesised that marine
DMS emissions are involved in the biological regulation of climate (Bates et al., 1987; Charlson et al.,
1987). The oxidation products of atmospheric DMS
may act as condensation nuclei, thereby affecting the
radiative properties of skies and clouds, with subsequent implications for climate. Since then, an increasing amount of research has been performed in a
variety of environments and with a variety of organisms (see e.g. Kiene et al., 1996). Although we now
know a lot more on the qualitative aspects of the
marine sulphur cycle (Kiene et al., 2000) the factors
that control the various pathways are still largely
unknown.
In plants, sulphur is present in a variety of organic
compounds. Most of it occurs in proteins, specifically
1385-1101/00/$ - see front matter 䉷 2000 Elsevier Science B.V. All rights reserved.
PII: S1385-110 1(00)00030-7
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J. Stefels / Journal of Sea Research 43 (2000) 183–197
SO4 2out
in
ATP + SO4 =
ADP
sulfolipids
sulfate esters
glycolysis
carbohydrates
ATP
PAPS
APS
3-phosphoglycerate
2 GSH
GSSG
SO326e-
phosphoenol pyruvate
GS–SO3-
GSSG
GSH
GSH
tra n sa mi na tio n
6e-
GS–S -
pyruvate
serine
2e-
acetyl-CoA
CO2
S 2-
a na pl er oti c
CO2 fixa tio n
O-acetylserine
aspartate
cysteine
glutathione
tra n ssu lfu ra tio n
protein
oxaloacetate
O-phosphohomoserine
Krebs cycle
cystathione
homocysteine
CH 3
DMSP
ATP
PP i + Pi
S-adenosylmethionine
methionine
tr a n sme th yl a ti o n s
S-adenosylhomocysteine
S-methylmethionine
other CH3
acceptors
homocysteine
Fig. 1. Schematic representation of the processes involved in the assimilatory sulphate reduction and biosynthesis of DMSP. No attempt has
been made to represent stoichiometries. Explanation is given in the text. This figure is extracted from references discussed in the text and from
Quispel and Stegwee (1983) and Salisbury and Ross (1992).
in the amino acids cysteine and methionine. Other
important compounds that contain sulphur are
coenzyme-A, glutathione, the vitamins thiamine and
biotin and sulpholipids. The production of DMSP is
almost exclusively confined to a few classes of marine
micro- and macroalgae (Reed, 1983; Keller et al.,
1989; Blunden et al., 1992). Observations of DMSP
production in higher plants are rare, with the
J. Stefels / Journal of Sea Research 43 (2000) 183–197
exception of a few Spartina species, some sugarcanes
and the coastal strand plant Wollastonia biflora (Van
Diggelen et al., 1986; Dacey et al., 1987; Pakulski and
Kiene, 1992; Hanson et al., 1994; Mulholland and
Otte, 2000).
On a global scale, the main producers of DMSP are
phytoplankton species confined to the classes Dinophyceae (dinoflagellates) and Prymnesiophyceae
(including the coccolithophorids) (Keller et al.,
1989). Some members of the Chrysophyceae and
Bacillariophyceae (diatoms) can also produce
significant amounts of DMSP. Intracellular
concentrations of DMSP may vary between zero
and 1–2 M in a few dinoflagellates (Keller et al.,
1989). More typical values for DMSP-producing
algae are 50–400 mM. In these algae, DMSPsulphur can comprise 50 to almost 100% of the
total cellular organic sulphur (Matrai and Keller,
1994; Keller et al., 1999a).
Knowledge of the biosynthesis of DMSP has
emerged only recently and there are now indications
that it may proceed through at least three different
pathways in different organisms (James et al., 1995;
Gage et al., 1997; Kocsis et al., 1998). The function of
DMSP in algal physiology is still unclear and the
same is true for the enzymatic cleavage of DMSP
into dimethylsulphide (DMS) and acrylate. The most
likely function of DMSP is related to the osmotic
protection of the cell (see below). There is some
limited evidence for a function as methyl donor
(Ishida, 1968) and as precursor of the phospholipid
phosphatidylsulphocholine (Kates and Volcani,
1996). The cleavage by algal DMSP lyase may be
an effective chemical defence against grazing
(Wolfe et al., 1997); the proposed anti-bacterial function of the cleavage product acrylate is unlikely
(Noordkamp et al., 2000).
It is the objective of this overview to obtain a better
understanding of the regulatory mechanisms involved
in the production and conversion of DMSP. A brief
discussion is therefore given of the pathways involved
in the biosynthesis of DMSP. This is followed by an
overview of the factors that affect DMSP biosynthesis
in relation to its physiological functions. A new
hypothesis is presented in which DMSP production
is described as an overflow mechanism for excess
reduced compounds and for energy excess. Finally,
the possible functionality of the enzymatic cleavage
185
of DMSP is discussed in the context of an overflow
mechanism.
2. DMSP biosynthesis
Much of our knowledge about processes involved
in the assimilation of sulphate up to the incorporation
of sulphur into DMSP has been derived from experiments with higher plants, but may be applicable to
algae as well.
The uptake and reduction of sulphate to sulphide is
an energy-requiring process (Brunold, 1990; Leustek
and Saito, 1999) (Fig. 1). Firstly, after being taken up
in the cytoplasm and subsequently in the chloroplast,
sulphate is activated by ATP-sulphurylase to form
adenosine 5 0 -phosphosulphate (APS). APS can subsequently be activated to form adenosine 3 0 -phosphate
5 0 -phosphosulphate (PAPS), a precursor for sulpholipids and sulphate esters of polysaccharides. This
non-reductive incorporation of sulphate in plant metabolites occurs in the cytoplasm. Sulphate esters of
polysaccharides are commonly produced by diatoms,
and form the primary component of extracellular
polymeric substances (EPS) (Hoagland et al., 1993).
They may also constitute a substantial fraction of the
colonial mucus of the phytoplankton species Phaeocystis sp. (Van Boekel, 1992).
The exact course of the subsequent reductive pathway is still under debate, but it is now accepted that
glutathione (GSH) plays a crucial role (Brunold,
1990; Leustek and Saito, 1999). Activated sulphate
in APS is transferred to GSH by APS sulphotransferase, which results in S-sulphoglutathione (Fig. 1). The
pathway then most likely proceeds towards free
sulphite after reduction with GSH, but a carrierbound pathway cannot be excluded. The reduction
of the sulpho group of PAPS may produce free
sulphite in a similar way. There are indications that
GSH may act as both the reductant and the carrier in
all these reactions. It is currently thought that the pathway through APS dominates in higher plants and
algae, whereas it may proceed through PAPS in
bacteria, yeasts and certain cyanobacteria.
In the next step, the carrier-bound or free sulphite is
reduced to carrier-bound or free sulphide. Both reactions require six electrons, which are usually provided
by reduced ferredoxin. In many organisms, however,
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J. Stefels / Journal of Sea Research 43 (2000) 183–197
NH3+
AdoMet
S
COO
Methionine
AdoHcy
NH3+
S
+
-
transamination
O
methylation
S
decarboxylation?
SMM
COO
MTOB
COO-
S
transamination/
decarboxylation
-
NADPH
NH3+
reduction
NADP
+
OH
S
DMSP-amine
COO
MTHB
oxidation?
-
AdoMet
methylation
S
+
CHO
AdoHcy
OH
DMSP-ald
S
oxidation
S
COO
+
-
+
COO
-
DMSHB
oxidative
decarboxylation
DMSP
1. COMPOSITAE
2. GRAMINEAE
3. MARINE ALGAE
Fig. 2. Schematic representation of the three pathways of DMSP biosynthesis from methionine (after Hanson and Gage, 1996; Gage et al., 1997;
Kocsis et al., 1998; Summers et al., 1998).
reduced pyridine nucleotides can also be used in the
reaction with free sulphite. Free sulphide is then
incorporated in O-acetylserine to form cysteine and
acetate. Whereas the reduction of sulphate to sulphide
occurs in the chloroplasts, enzymes for the production
of cysteine also have been found in the cytoplasm and
mitochondria. In total, one ATP, 6 electrons and the
oxidation of two thiol groups, or one ATP and 8 electrons, are needed to reduce sulphate to sulphide.
Apart from being the precursor of GSH, cysteine is
involved in two important metabolic pathways: the
synthesis of protein and the de novo production of
methionine (Fig. 1). For the latter process, the thiol
group of cysteine is transferred to O-phosphohomoserine to form homocysteine, which is subsequently
methylated to methionine (Giovanelli, 1990). Methionine is partly incorporated into protein, but the major
pathway for methionine metabolism is the utilisation
of its methyl group in transmethylation reactions via
S-adenosylmethionine (AdoMet). In this pathway,
methionine essentially acts as a catalyst, accompanied
by a recycling system in which methionine is regenerated (Giovanelli, 1987); it is thus not a true sink for
methionine. Besides its incorporation into protein, the
larger part of methionine may be consumed—albeit
not in all plants—by the production of DMSP.
Currently, there is strong evidence that the
biochemical pathway from methionine to DMSP has
evolved at least three times independently through
different intermediates (Fig. 2). The best studied
DMSP-containing plant is Wollastonia biflora
(Compositae), a common Indo-Pacific strand plant.
In W. biflora, S-methylation is the first step in the
sequence, which results in the production of S-methylmethionine (SMM). This methylation reaction is
dependent on AdoMet. After this step, the pathway
towards DMSP proceeds through the production of
DMSP-aldehyde. This involves a transamination and
J. Stefels / Journal of Sea Research 43 (2000) 183–197
decarboxylation, but no intermediates have been
identified (Hanson et al., 1994; James et al., 1995;
Hanson and Gage, 1996). Most higher plants—also
non-DMSP-containing plants—have the enzymes to
mediate the methylation of methionine and the oxidation of DMSP-ald, but it is the conversion of SMM to
DMSP-ald that is specific for DMSP synthesis. In W.
biflora, the methylation reaction occurs in the cytosol.
Then, SMM is transported to the chloroplast, where
the conversion into DMSP-ald and DMSP takes place.
The oxidation reaction is catalysed by a dehydrogenase that uses NAD as a cofactor and which has
strong similarities with betaine aldehyde dehydrogenase (Trossat et al., 1996).
A second pathway has been identified in Spartina
alterniflora (Gramineae) (Kocsis et al., 1998). In this
sea grass DMSP-amine was identified as an intermediate between SMM and DMSP-ald (Fig. 2). The
enzymes that catalyse the production and conversion
of DMSP-amine are still to be identified, but a decarboxylase and oxidase are suggested, respectively. The
specific production of DMSP-amine in grasses led the
authors to conclude that the DMSP-specific pathway
from SMM to DMSP-ald had evolved independently
in the Compositae and Gramineae.
A third and entirely different pathway (Fig. 2) was
identified in the green macroalga Enteromorpha
intestinalis (Gage et al., 1997; Summers et al.,
1998). The first step is a transamination of methionine
to form 4-methylthio-2-oxobutyrate (MTOB), which
is followed by an NADPH-linked reduction to 4methylthio-2-hydroxybutyrate (MTHB). Then an
AdoMet-dependent methylation occurs which yields
the novel sulphonium compound 4-dimethylsulphonio-2-hydroxybutyrate (DMSHB), followed by an
oxidative decarboxylation to DMSP. The first two
steps appeared reversible; they are widespread
among a variety of higher and lower plants, though
much higher activities are found in DMSP-containing
algae. The conversion of MTHB to DMSHB seems to
be specific for DMSP synthesis. DMSHB was also
found in three planktonic species: Emiliania huxleyi
(a prymnesiophyte), Melosira nummuloides (a
diatom) and Tetraselmis sp. (a prasinophyte) (Gage
et al., 1997). All three converted the supplied
DMSHB to DMSP and it was therefore suggested
that they have the same pathway as E. intestinalis.
In studies with thalli of the macroalga Ulva lactuca
187
and the heterotrophic dinoflagellate Crypthecodinium
cohnii a slightly different pathway was proposed
(Greene, 1962; Uchida et al., 1996). These authors
also did not observe SMM as an intermediate and
suggested a sequence of steps involving a decarboxylation, deamination, oxidation and methylation. This
would then involve the intermediate formation of
methylmercaptopropionate (MMPA). Their experiments are, however, not conclusive and the results
are not inconsistent with the sequence proposed by
Gage et al. (1997). Moreover, Summers et al. (1998)
measured activities of putative enzymes of the third
DMSP pathway in two other Ulva species.
3. Factors affecting DMSP synthesis
3.1. Light
Because sulphate reduction is an energy- and
reductant-consuming process, reduction is coupled
to cell metabolism, and may, in parallel with increasing metabolic rates, be stimulated by light. This
should not be confused with light dependency, as is
the case for carbon uptake. Indeed, a light stimulation
of sulphate uptake and incorporation has been
observed (Cuhel et al., 1984; Cuhel and Lean,
1987a), but dark uptake of exogenous sulphate,
when available at high concentrations, is also a
common phenomenon in plants and algae (Bates,
1981; Cuhel et al., 1984; Cuhel and Lean, 1987a,b;
Brunold, 1993). Dark uptake indicates that reducing
power does not necessarily need to be derived from
photosynthesis directly. It may continue at a rate
comparable to that under illumination, depending on
the physiological state of the cell and its light history.
Because of the high sulphate concentrations in marine
environments (approximately 28 mM), there is no
need to store sulphate in algal cells; it is taken up
when required (Cuhel et al., 1984; Cuhel and Lean,
1987a). Essential cell constituents like protein and
amino acids are important sulphur-containing
compounds, and the uptake of sulphate therefore
parallels their production. In growing cells the dark
production of protein and lipid occurs at the expense
of low molecular weight and polymeric carbohydrates
(Morris, 1981). These compounds, when respired,
provide the carbon skeletons as well as the energy
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J. Stefels / Journal of Sea Research 43 (2000) 183–197
for dark metabolism. Part of the energy can be used
for the assimilation of sulphate.
Whether the production of DMSP from methionine
is related to the light regime may differ for each
pathway. In isolated chloroplasts of the higher plant
W. biflora—which exhibits the first pathway—the
conversion of SMM to DMSP was promoted by
photosynthesis, but could also proceed in the dark at
approximately 40% of the light rates (Trossat et al.,
1996). Other experiments on the effects of light on
DMSP production are mainly done with marine
algae, which most likely display the third pathway.
In experiments with macroalgae, the stimulation of
DMSP production by light was observed after several
weeks of incubation (Karsten et al., 1990, 1991,
1992). Day length, however, appeared to be a complicating factor, by having a significant effect on DMSP
content (Karsten et al., 1990). During short-day incubations of 6 h light and 18 h dark, no effect of light
intensities was observed for Urospora penicilliformis,
whereas a long-day incubation of 18 h light and 6 h
dark resulted in a doubling of the DMSP content
between 2 and 30 mmol photons m ⫺2 s ⫺1. This indicates that DMSP production is not directly stimulated
by light but that the light history, and thus the physiological state of the cell, should be taken into consideration. Dark DMSP production was observed in Ulva
lactuca under fluctuating salinity regimes (Dickson et
al., 1982) and during 24-h measurements in a temperate strain of the planktonic species Phaeocystis
(Stefels et al., 1996), indicating that DMSP production was not directly dependent on light.
3.2. Salinity
Many unicellular algae are wall-less cells or have a
cell wall with a low elastic modulus (coefficient of
elasticity), which implies that they are not able to
build up high turgor pressures inside the cell. Upon
changes in external water potential, these cells will
first exhibit an adjustment of their cell volume as
water flows in or out of the cell. In microalgae, this
is a rapid process, completed within seconds. It results
in a dilution or concentration of the solutes inside the
cell, which changes the osmotic potential accordingly.
In order to maintain optimal growth, however, cellular
conditions like ionic composition, metabolite pools
and pH need to be kept within relatively narrow
ranges (Bisson and Kirst, 1995). Cells will therefore
try to recover their original volume. This is achieved
by adjusting the osmotic potential of the cell by means
of osmotically active compounds not directly
involved in growth. Adjustment is established by
active transportation of ions in or out of the cell and
by the accumulation or degradation of low molecular
weight organic solutes. The former process may be
completed within 20–60 min at relatively low energy
costs, whereas the latter proceeds at a slower rate and
has higher energy needs (Kirst, 1989). The adjustment
of ions and organic solutes is metabolically regulated.
It often involves the compartmentation of solutes in
order to prevent metabolic inhibition, with highest ion
concentrations found in vacuoles, and organic solutes
confined to the cytoplasm.
Marine pelagic organisms live in an environment of
low-water potential. Open ocean salinities may vary
between 33 and 37 PSU, which is equivalent to 970–
1060 mosmol kg ⫺1 or ⫺2.5 to ⫺2.73 MPa at atmospheric pressure (Kirst, 1989). In such environments,
it is important for the cell to produce organic solutes at
concentrations that are high enough to be osmotically
active and which are compatible with metabolism.
These so-called compatible solutes are non-inhibitory
low molecular weight organic solutes which accumulate in the cytoplasm of cells at low water potential.
Contrary to isosmol concentrations of ions, these
solutes have little or no inhibitory effects on metabolic
functions, protecting proteins and stabilising
membranes under conditions of high ionic strength.
Many of these compounds are direct products of
photosynthesis, like sugars (e.g. sucrose, trehalose),
polyols (e.g. glycerol, mannitol, sorbitol) and heterosides (e.g. floridoside, isofloridoside), but compounds
not directly derived from photosynthesis are also
used. These are quaternary ammonium compounds
(e.g. the betaines and especially glycine betaine),
amino acids (especially proline), and tertiary sulphonium compounds (especially DMSP) (Blunden and
Gordon, 1986; Bisson and Kirst, 1995). Not all
compounds are produced within one organism.
Rather, taxonomic differences in solute combinations
can be observed. Although isosmol concentrations of
these solutes have comparable osmotic potentials, the
energy costs and the amounts of carbon and nitrogen
required for the various solutes may differ considerably. Consequently, the physiological condition of the
J. Stefels / Journal of Sea Research 43 (2000) 183–197
Fig. 3. DMSP content of Phaeocystis sp. cells growing exponentially in batch cultures. Cells were adapted to the salinities for at
least five generations. Values are means of duplicate cultures; range
is indicated.
cell may affect the production of solutes, which results
in changes in their relative concentrations.
Subcellular compartmentation of solutes is also an
important aspect in osmotic acclimation. In vacuoles,
high concentrations of Na ⫹, Cl ⫺, to a lesser extent K ⫹
and in some cases sucrose can build up, whereas in the
cytoplasm osmotic potential is mainly controlled by
organic solutes and K ⫹. In macroalgae, intracellular
DMSP content appears to be linked to the relative
proportion of the cytoplasm, supporting a cytoplasmic
location (Reed, 1983). The cytoplasm of microalgae
makes up 25–80% of total cell volume, a relatively
high percentage compared with macroalgae and
higher plants. Consequently, the contribution of
organic solutes to total osmotic potential is also relatively high (Kirst, 1985). In W. biflora, about one-half
of the DMSP is chloroplastic (Trossat et al., 1998).
Not all organic solutes have equal protective properties. Based on a comparison of general properties of
compatible solutes and in vitro enzyme assays, Kirst
(1996) concluded that DMSP may be less effective as
compatible solute than e.g. betaine, proline or
glycerol. For instance, the property of being rapidly
synthesised or degraded upon changes in water potential seems not to be applicable to DMSP. There are
only limited data on the relatively rapid adaptation of
intracellular DMSP content after a hyperosmotic
189
shock (Dickson et al., 1982; Vairavamurthy et al.,
1985). Most observations indicate that under such
conditions DMSP is only slowly produced, if at all
(Reed, 1983; Dickson and Kirst, 1986; Edwards et
al., 1987; Stefels et al., 1996). After hypoosmotic
shocks, DMSP was rapidly released from Tetraselmis
subcordiformis cells (Dickson and Kirst, 1986),
whereas intracellular DMSP content hardly changed
in Phaeocystis sp. cells (Stefels et al., 1996).
When cultured for a prolonged period of time,
DMSP has been found to increase with salinity in
several micro- and macroalgal species (Vairavamurthy et al., 1985; Dickson and Kirst,
1986,1987a,b; Karsten et al., 1992). A typical example is provided by cultures of Phaeocystis sp. (Fig. 3).
In other cases, intracellular DMSP levels remained
unchanged (Van Diggelen et al., 1986; Edwards et
al., 1987; Colmer et al., 1996). Due to its usually
high intracellular concentrations, DMSP may thus
be considered as a constitutive compatible solute,
but not an osmoticum in the strict sense of being
responsible for osmotic balance (Reed, 1984). Kirst
(1996) suggested that DMSP may act as a buffer
during the initial period after hyperosmotic shocks,
when immediate cell volume changes result in concomitant changes of intracellular solute concentrations;
an effect which takes place without active production
or degradation of the solute.
3.3. Temperature
Besides a role in the osmotic acclimation of the
cell, there are indications that DMSP may act as cryoprotectant. Nishiguchi and Somero (1992) observed
that the compatibility of DMSP with protein structure
increased at low temperatures, and suggested that
DMSP may function as an effective cryoprotectant.
This was confirmed by experiments with extracts
from the polar macroalga Acrosiphonia arcta
(Karsten et al., 1996). At low temperatures, DMSP
appeared to stabilise the activity of malate dehydrogenase in these extracts. In fact, increased enzyme
activity was observed when high DMSP concentrations were applied. A stabilising effect was also
observed in the cold-labile enzyme lactate dehydrogenase, when DMSP was added prior to freezing and
thawing of the enzyme preparation (Karsten et al.,
1996). Stabilising effects increased with concentration
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J. Stefels / Journal of Sea Research 43 (2000) 183–197
and became increasingly stronger than those of
proline and sucrose.
A possible role of DMSP in cryoprotection was also
confirmed by observations of high intracellular
concentrations in strains of polar macroalgae cultured
at 0⬚C as compared to strains cultured at 10⬚C
(Karsten et al., 1992, 1996). These concentrations
were high enough to protect enzymes in macroalgal
tissue after periods of freezing, as are often encountered in polar regions. The same trend was observed in
the prasinophyte Tetraselmis subcordiformis cultured
at four different temperatures ranging from 5 to 23⬚C
(Sheets and Rhodes, 1996). In these cultures, the
DMSP content per cell increased 8-fold as growth
temperature decreased.
3.4. Nitrogen limitation
Already during the early days of DMSP research,
the similarity in structure and properties between
DMSP and its nitrogen analogue glycine betaine
(GBT) was noted (Challenger, 1951). This led to the
suggestion that DMSP could act as an osmolyte in
algal cells and even replace GBT (and other nitrogen-containing osmolytes such as proline, trigonelline, homarine but also free amino acids) under
conditions of nitrogen limitation. Especially in higher
plants, in which the last step in DMSP biosynthesis is
similar to the one in betaine synthesis, both mediated
by a similar enzyme (Trossat et al., 1996), one might
expect interactive production. In several studies,
indeed a positive correlation was observed between
nitrogen and GBT (Van Diggelen et al., 1986; Colmer
et al., 1996) and a negative correlation between nitrogen and DMSP (Dacey et al., 1987; Hanson et al.,
1994; Colmer et al., 1996), but a reciprocal relationship between DMSP and GBT is not always established (Mulholland and Otte, 2000).
Data on the GBT content of marine phytoplankton
are still limited. Its production appears to be species
specific, but these species are not necessarily DMSP
producers (Keller et al., 1999a). From the limited data
available, it appears that the response of GBT quota
on nitrogen availability was much more straightforward than the response of DMSP, with highest levels
under N-replete conditions (Keller et al., 1999a,b). In
several studies, DMSP production was shown to
increase with N-limitation (Turner et al., 1988;
Gröne and Kirst, 1992; Keller and Korjeff-Bellows,
1996), but this is in contrast to recent findings in batch
cultures and continuous cultures of the same species
(Keller et al., 1999a,b). The experiments in batch
cultures by Keller et al. (1999a) differed from
previous studies in that they applied 24 h light, in
stead of a dark:light cycle. In all species examined,
DMSP production continued regardless of N availability; if anything, cellular DMSP content decreased
over the growth cycle rather than increased, as was
expected. In some species this was at least partly due
to increased levels of dissolved DMSP. In continuous
cultures, the intracellular DMSP concentration was
inversely related with N-limited growth rates in Thallassiosira pseudonana, to some extent also in Emiliania huxleyi, but not in Amphidinium carterae (Keller
et al., 1999b). Additions of nitrate to N-limited
cultures resulted in reduced cellular DMSP content
in T. pseudonana and A. carterae, but not in E.
huxleyi.
In batch cultures of an Antarctic Phaeocystis strain
cultured under various iron and light conditions, intracellular DMSP concentrations increased under highlight conditions and iron depletion, but not under lowlight conditions and iron depletion (Stefels and Van
Leeuwe, 1996). Although this was not observed in the
DMSP quota on a per-cell basis, it was argued that the
intracellular concentrations are the only relevant data
to discuss from a physiological point of view. It was
inferred that under high-light and low-iron conditions
the cells were experiencing reduced nitrogen assimilation induced by iron limitation, whereas under
conditions of low light and low iron, cells were
severely energy-limited, which resulted in overall
suppressed metabolic rates. As was argued before by
Keller (1988/1989), these experiments stressed the
importance of cell volume measurements, in order
to allow calculations of intracellular concentrations.
4. DMSP production as an overflow mechanism for
excess reduced sulphur and as a means of
dissipating energy excess
From studies of higher plants it is known that the
concentrations of cysteine and methionine are kept at
a low equilibrium level in the order of 10 mM. It is
therefore important for a cell to have a buffering
J. Stefels / Journal of Sea Research 43 (2000) 183–197
NO32-
191
SO42-
amino acids
?
+
APS
serine
–
S 2-
O-acetylserine
cysteine
–
glutathione
–
protein
methionine
NH3
S-adenosyl-
tra n smeth yla ti on s methionine
algae
S-methylmethionine
NH3
higher plants
DMSP
DMS
Fig. 4. Regulatory coupling between the assimilatory nitrate and sulphate reduction pathways. Solid lines represent reaction pathways. Dotted
arrows indicate negative (⫺) or positive (⫹) regulatory effects.
mechanism to regulate cysteine and methionine
levels, when the influx of sulphur exceeds the cell’s
conversion capacity into amino acids, proteins and
other sulphur-containing components, or when
protein degradation increases the cellular concentration of these compounds (Rennenberg, 1989; Brunold,
1990; Giovanelli, 1990). In higher plants, cysteine
concentrations may be regulated by the synthesis of
glutathione with subsequent excretion into the
medium. The methionine concentration appears to
be regulated through a strong negative feedback
mechanism of its own de novo synthesis (Fig. 4)
(Giovanelli, 1990). It has been suggested that SMM
may also be involved in the methionine regulation,
by acting as a storage of methyl groups via a
small cycle in which SMM is formed from
methionine, and in which two molecules of
methionine can be regenerated when SMM
donates a methyl group to homocysteine (Fig. 1)
(Giovanelli, 1987; Mazelis, 1993). In W. biflora,
however, the flux through the SMM cycle
appeared to be small compared with the flux
through DMSP (Hanson et al., 1994).
In higher plants, it is well known that a reciprocal
regulatory coupling exists between the pathways of
assimilatory sulphate and nitrate reduction (Fig. 4)
(Giovanelli, 1990; Brunold, 1993). This mechanism
ensures the appropriate proportions of sulphurcontaining and other amino acids for protein synthesis. The availability of O-acetylserine presumably
plays a key role in this regulation. High concentrations enhance the activity of APS sulphotransferase
192
J. Stefels / Journal of Sea Research 43 (2000) 183–197
and cysteine synthesis. On the other hand, an
increased cysteine concentration has been shown to
inhibit serine acetyltransferase activity, thereby reducing O-acetylserine production. In higher plants this
mechanism may result in inhibited sulphate reduction
under nitrogen limitation, and vice versa.
For many DMSP-producing algae and plants,
however, it has been observed that N-limitation may
result in increased DMSP production (Dacey et al.,
1987; Turner et al., 1988; Gröne and Kirst, 1992;
Hanson et al., 1994; Colmer et al., 1996), in other
words, in increased sulphur incorporation relative to
nitrogen incorporation. This may be explained if the
production of DMSP is considered as an overflow
mechanism. One may regard an overflow mechanism
as a reaction of the cell under conditions of unbalanced growth: it produces (and discards) compounds
in order to ensure the continuation of other metabolic
pathways. In this respect, the continued production of
DMSP keeps the cysteine and methionine concentrations at a low level, thereby preventing possible feedback mechanisms from coming into action (Fig. 4).
This allows continued sulphate assimilation even
under nitrogen-limited conditions. The transamination reaction in the production pathway of DMSP
redistributes nitrogen into new amino acids (Gage et
al., 1997). In addition, an increased DMSP concentration may save on the cell’s nitrogen requirement as
explained above. Increased DMSP production does
not necessarily result in increased intracellular
DMSP concentrations. This will depend on the cell’s
need for compatible solutes and will be dictated by the
sum of all osmotically active compounds; not only the
N-containing compounds, but also free carbohydrates,
amino acids, etc. Increased excretion into the medium
may be a means of dissipating both excess sulphur and
carbon.
This overflow mechanism is not necessarily
confined to nitrogen deficient conditions. It may also
play a role in protein turnover. Protein turnover is an
essential process, allowing plants to re-utilise amino
acids, to change protein content during development
and to adapt their enzyme system to new environmental conditions, especially under stress (Cooke et al.,
1979; Vierstra, 1993; Dennis et al., 1997). When
methionine is produced from the degradation of
proteins by proteases, the function of DMSP production would be one of re-allocating nitrogen from
methionine to other amino acids, thereby increasing
the cell’s ability to address the new condition. Indeed,
Gröne and Kirst (1992) observed a 3-fold increase in
cellular DMSP content within 24 h in cultures of
Tetraselmis subcordiformis to which 100 mM methionine had been added. In leaf disks of W. biflora,
DMSP production also increased with the administered dose of methionine (Hanson et al., 1994).
Experiments with protease inhibitors added to T.
subcordiformis cells experiencing an hyperosmotic
shock resulted in a significantly reduced build-up of
DMSP compared to control cultures (Gröne and Kirst,
1992). The authors argued that under stress (all conditions which reduce growth) the pool of methionine
builds up, resulting in increased DMSP production.
They concluded that methionine availability may
control DMSP synthesis, indicating a possible role
for DMSP in methionine metabolism. This is consistent with an overflow hypothesis.
In general, it is observed that the production of
protein saturates at lower light intensities than does
total carbon incorporation (Morris, 1981; Cuhel et al.,
1984; Cuhel and Lean, 1987a). This is the result of
different kinetics of nitrate reduction and carbon fixation versus light intensity: the Kmlight for nitrate reduction is significantly lower than that for photosynthetic
carbon fixation (Turpin, 1991). Consequently, at lowlight intensities, nitrate assimilation is capable of outcompeting carbon fixation for reducing power,
thereby suppressing carbohydrate formation. At high
light intensities, a larger portion of total carbon is
incorporated into carbohydrates. Once the rate of
carbon incorporation exceeds the rate of protein
synthesis and cell growth is dictated by N assimilation, it may be beneficial to dissipate excess carbon
into DMSP. This hypothesis was used to explain the
results of experiments with Phaeocystis sp. cultures
grown under different conditions of iron and light
(Stefels and Van Leeuwe, 1996) (see also Section
3.4). It could also be applicable for the light experiments carried out by Karsten et al. (1990) (see also
Section 3.1): in long-day incubations (18 h light:6 h
dark), increased intracellular DMSP concentrations
were observed with increasing light intensity; in
contrast, the short-day incubations (6 h light:18 h
dark) may not have resulted in enough carbon fixation
to sustain DMSP production on top of the central
metabolic processes necessary for growth. The
J. Stefels / Journal of Sea Research 43 (2000) 183–197
relatively high DMSP concentrations in algae cultivated at low temperatures (Karsten et al., 1992, 1996;
Sheets and Rhodes, 1996) may follow a comparable
explanation. Carbon incorporation into protein often
reduces with declining temperatures, whereas the
production of carbohydrates is relatively indifferent
to temperature (Morris, 1981; Cuhel and Lean,
1987a). Consequently, at low temperatures, when
growth is unbalanced, the supply of carbohydrates
creates a potential for DMSP production.
5. Enzymatic cleavage of DMSP
Since the onset of research on DMSP production by
algae, knowledge of the degradation of this compound
has remained scarce. Most research on the enzymatic
cleavage of DMSP has addressed bacterial degradation (e.g. Kiene, 1990, 1992; Ledyard and Dacey,
1994; Taylor and Visscher, 1996), but now there is
increasing evidence for an important role of algal
DMSP lyase activity. Lyase activity has been
observed in laboratory studies on a variety of microand macro-algal species (Ishida, 1968; Stefels and
Van Boekel, 1993; Steinke et al., 1996, 1998). In
field samples, lyase activity often appears to be associated with particular species (Stefels et al., 1995), or
with the larger size fractions, suggesting a role for
algal enzymes (Cantin et al., 1999; Scarratt et al.,
2000; Steinke et al., 2000).
Little is known about the function of DMSP lyase in
algae. Experiments with crude extracts give little
information on the in vivo activity, and measurements
of DMS production in axenic cultures are limited
(Vairavamurthy et al., 1985; Stefels and Van Boekel,
1993). If DMSP plays an active role in the osmotic
acclimation of cells, degradation by DMSP lyase
could be a valuable tool for the down-regulation of
its concentration. Evidence for this is limited. Vairavamurthy et al. (1985) observed the production of
DMS in cultures of Pleurochrysis carterae ( ˆ
Hymenomonas carterae) following hypo-osmotic
shocks. However, this was observed only at large
shock ranges. Moreover, in cultures transferred to 9
and 18 PSU, output rates of DMS over a 24-h period
could only account for a 10% reduction of the original
DMSP content at 52.5 PSU. It is therefore questionable whether the conversion of DMSP into DMS in
193
this species is a relevant process in osmotic acclimation. The gradual 30% loss of specific activity of
DMSP lyase in Phaeocystis sp., when going from 20
to 45 PSU (Stefels and Dijkhuizen, 1996), also does
not support the view that cleavage of DMSP is an
accurate mechanism in osmotic acclimation.
The question therefore remains what the function of
algal DMSP lyase actually is. Volatilisation of DMSP
may be a comparable mechanism to the emission of
H2S in higher plants. The latter process has been
suggested to be of importance to the equilibration of
intracellular sulphur species, and to remove excess
reduced sulphur (Rennenberg, 1989), although this
only appears to occur under unrealistically high
sulphur concentrations. Data on the active exudation
of intracellular DMSP and its conversion into DMS
and acrylate are limited. Two studies report values of
around 1% per day of the DMSP quota (Vairavamurthy et al., 1985; Dacey and Wakeham, 1986). In
Phaeocystis sp., increasing exudation rates were
calculated over the growth phase: from 3% in the
exponential growth phase to 11% in the senescence
phase (Laroche et al., 1999). Thus, in healthy growing
cells, this would result in a release in the order of
1 mM of the internal DMSP concentration. Compared
to an equilibrium concentration of cysteine and
methionine of around 10 mM, this should be sufficient
to equilibrate large fluctuations. In stationary cells, an
increased DMSP exudation may reflect not only the
removal of excess reduced sulphur, but also the dissipation of energy excess, comparable to the exudation
of carbohydrates.
If we assume that DMSP production reflects overflow metabolism, then the equilibrium concentration
of DMSP will be regulated by its degradation rather
than by its production. As stated above, this can be
done by transporting DMSP out of the cell. Subsequent removal of DMSP by extracellular cleavage
into DMS and acrylate will facilitate this release, as
DMSP concentration gradients across the membrane
are kept maximal. This is especially relevant for the
colony-forming species Phaeocystis sp., as the mucus
layer surrounding colonial cells will increase the
diffusive boundary layer around these cells (Ploug et
al., 1999). The robustness of this boundary layer may
allow the formation of microzones around the cells in
which elevated levels of excretion products are
observed (Mitchell et al., 1985), which, in the case
194
J. Stefels / Journal of Sea Research 43 (2000) 183–197
of DMSP, would be unfavourable. In addition to the
maintenance of a DMSP gradient, the cell may simultaneously profit from the release of acrylate and
protons upon cleavage. The released protons can be
used for e.g. nutrient uptake. The build-up of acrylate
within the microzone (Noordkamp et al., 2000) may
possibly result in concentrations that are repulsive to
grazers. In this way, the otherwise wasteful release of
DMSP can be of some benefit to the cell.
6. Conclusions
Considering its generally high intracellular concentration and the fact that it is a zwitter-ion, DMSP has a
function in the osmotic protection of algal cells. It
appears to function as a compatible solute, especially
at low temperatures. The gradual shifts in DMSP
content that can usually be observed after prolonged
incubations in different salinities may, however,
reflect a changed metabolism rather than an active
regulatory mechanism. Compared to other compatible
solutes such as polyols, DMSP synthesis is an energyexpensive process. In the photic zone of the marine
environment, however, energy is usually not a
growth-limiting factor, but rather the requirement of
nutrients. In the marine environment, sulphur is a
nutrient in excess, whereas nitrogen often limits
phytoplankton growth. It is striking that the production of DMSP appears to have evolved in algae and
higher plants living in this environment. The fact that
DMSP production is confined to several algal classes
and a few families of higher plants, together with the
observation that DMSP biosynthesis may proceed
along three different pathways, may indicate that
DMSP synthesis has evolved independently several
times. Perhaps it is this relatively abundant occurrence
of sulphate that has put little pressure on the efficient
use of this compound.
It is argued here that DMSP production can be
regarded as an overflow mechanism when growth is
unbalanced and when there is a need for dissipating
excess reduced sulphur and excess energy, bringing
nitrogen back into the system. A concomitant increase
of the intracellular DMSP concentration will save on
the cell’s nitrogen requirement for osmolytes. In this
way, a continued turnover of metabolites is ascertained, without negative feedback mechanisms
coming into action, thereby providing the cell with
the means to adapt to changing environmental conditions. The enzymatic cleavage of DMSP may then
serve as regulatory mechanism to keep DMSP at an
equilibrium concentration.
Many of the arguments used in the development of
this overflow hypothesis stem from studies with
higher plants. It is a challenge to future research to
find support for this hypothesis in marine algae.
Acknowledgements
I am grateful to Luit De Kok, Maria Van Leeuwe
and Marion Van Rijssel for useful comments on the
manuscript. This is a contribution to the European
Union ELOISE Programme (Publ. no. 149) in the
framework of the ESCAPE project (contract no.
MAS3-CT96-0050).
References
Bates, S.S., 1981. Determination of the physiological state of
marine phytoplankton by use of radiosulfate incorporation. J.
Exp. Mar. Biol. Ecol. 51, 219–239.
Bates, T.S., Charlson, R.J., Gammon, R.H., 1987. Evidence for the
climatic role of marine biogenic sulphur. Nature 329, 319–321.
Bisson, M.A., Kirst, G.O., 1995. Osmotic acclimation and turgor
pressure regulation in algae. Naturwissenschaften 82, 461–471.
Blunden, G., Gordon, S.M., 1986. Betaines and their sulphonio
analogues in marine algae. In: Round, F.E., Chapman, D.J.
(Eds.). Progress in Phycological Research, Biopress, Bristol,
pp. 39–80.
Blunden, G., Smith, B.E., Irons, M.W., Yang, M., Roch, O.G., Patel,
A.V., 1992. Betaines and tertiary sulphonium compounds from
62 species of marine algae. Biochem. Syst. Ecol. 20, 373–388.
Brunold, C., 1990. Reduction of sulfate to sulfide. In: Rennenberg,
H., Brunold, C., De Kok, L.J., Stulen, I. (Eds.). Sulfur Nutrition
and Sulfur Assimilation in Higher Plants: Fundamental Environmental and Agricultural Aspects, SPB Academic Publishing,
The Hague, pp. 13–31.
Brunold, C., 1993. Regulatory interactions between sulfate and
nitrate assimilation. In: De Kok, L.J., Stulen, I., Rennenberg,
H., Brunold, C., Rauser, W.E. (Eds.). Sulfur Nutrition and
Assimilation in Higher Plants: Regulatory Agricultural and
Environmental Aspects, SPB Academic Publishing, The
Hague, pp. 61–75.
Cantin, G., Levasseur, M., Schultes, S., Michaud, S., 1999.
Dimethylsulfide (DMS) production by size-fractionated particles in the Labrador Sea. Aquat. Microb. Ecol. 19, 307–312.
Challenger, F., 1951. Biological methylation. Adv. Enzymol. 12,
429–491.
Charlson, R.J., Lovelock, J.E., Andreae, M.O., Warren, S.G., 1987.
J. Stefels / Journal of Sea Research 43 (2000) 183–197
Oceanic phytoplankton, atmospheric sulphur, cloud albedo and
climate. Nature 326, 655–661.
Colmer, T.D., Fan, T.W.-M., Läuchli, A., Higashi, R.M., 1996.
Interactive effects of salinity, nitrogen and sulphur on the
organic solutes in Spartina alterniflora leaf blades. J. Exp.
Bot. 47, 369–375.
Cooke, R.J., Oliver, J., Davies, D.D., 1979. Stress and protein turnover in Lemna minor. Plant Physiol. 64, 1109–1113.
Cuhel, R.L., Lean, D.R.S., 1987a. Influence of light intensity, light
quality, temperature, and daylength on uptake and assimilation
of carbon dioxide and sulfate by lake plankton. Can. J. Fish.
Aquat. Sci. 44, 2118–2132.
Cuhel, R.L., Lean, D.R.S., 1987b. Protein synthesis by lake plankton measured using in situ carbon dioxide and sulfate assimilation. Can. J. Fish. Aquat. Sci. 44, 2102–2117.
Cuhel, R.L., Ortner, P.B., Lean, D.R.S., 1984. Night synthesis of
protein by algae. Limnol. Oceanogr. 29, 731–744.
Dacey, J.W.H., Wakeham, S.G., 1986. Oceanic dimethylsulfide:
production during zooplankton grazing. Science 233, 1314–
1316.
Dacey, J.W.H., King, G.M., Wakeham, S.G., 1987. Factors controlling emission of dimethylsulphide from salt marshes. Nature
330, 643–645.
Dennis, D.T., Turpin, D.H., Lefebvre, D.D., Layzell, D.B. (Eds.),
1997. Plant Metabolism. Addison Wesley Longman, Essex,
England.
Dickson, D.M.J., Kirst, G.O., 1986. The role of b-dimethylsulphoniopropionate, glycine betaine and homarine in the osmoacclimation of Platymonas subcordiformis. Planta 167, 536–543.
Dickson, D.M.J., Kirst, G.O., 1987a. Osmotic adjustment in marine
eukaryotic algae: the role of inorganic ions, quaternary ammonium, tertiary sulphonium and carbohydrate solutes. I. Diatoms
and a Rhodophyte. New Phytol. 106, 645–655.
Dickson, D.M.J., Kirst, G.O., 1987b. Osmotic adjustment in marine
eukaryotic algae: the role of inorganic ions, quaternary ammonium, tertiary sulphonium and carbohydrate solutes. II. Prasinophytes and Haptophytes. New Phytol. 106, 657–666.
Dickson, D.M.J., Wyn Jones, R.G., Davenport, J., 1982. Osmotic
adaptation in Ulva lactuca under fluctuating salinity regimes.
Planta 155, 409–415.
Edwards, D.M., Reed, R.H., Chudek, J.A., Foster, R., Stewart,
W.D.P., 1987. Organic solute accumulation in osmoticallystressed Enteromorpha intestinalis. Mar. Biol. 95, 583–592.
Gage, D.A., Rhodes, D., Nolte, K.D., Hicks, W.A., Leustek, T.,
Cooper, A.J.L., Hanson, A.D., 1997. A new route for synthesis
of dimethylsulphoniopropionate in marine algae. Nature 387,
891–894.
Giovanelli, J., 1987. Sulfur amino acids of plants: an overview.
Meth. Enzymol. 143, 419–426.
Giovanelli, J., 1990. Regulatory aspects of cysteine and methionine
biosynthesis. In: Rennenberg, H., Brunold, C., De Kok, L.J.,
Stulen, I. (Eds.). Sulfur Nutrition and Sulfur Assimilation in
Higher Plants: Fundamental Environmental and Agricultural
Aspects, SPB Academic Publishing, The Hague, pp. 33–48.
Greene, R.C., 1962. Biosynthesis of dimethyl-b-propiothetin. J.
Biol. Chem. 237, 2251–2254.
Gröne, T., Kirst, G.O., 1992. The effect of nitrogen deficiency,
195
methionine and inhibitors of methionine metabolism on the
DMSP contents of Tetraselmis subcordiformis (Stein). Mar.
Biol. 112, 497–503.
Hanson, A.D., Gage, D.A., 1996. Biosynthesis of 3-dimethylsulfoniopropionate biosynthesis and the use by flowering plants. In:
Kiene, R.P., Visscher, P.T., Keller, M.D., Kirst, G.O. (Eds.).
Biological and Environmental Chemistry of DMSP and Related
Sulfonium Compounds, Plenum Press, New York, pp. 75–86.
Hanson, A.D., Rivoal, J., Paquet, L., Gage, D.A., 1994. Biosynthesis of 3-dimethylsulfoniopropionate in Wollastonia biflora (L.)
DC. Plant Physiol. 105, 103–110.
Hoagland, K.D., Rosowski, J.R., Gretz, M.R., Roemer, S.C., 1993.
Diatom extracellular polymeric substances: function, fine structure, chemistry, and physiology. J. Phycol. 29, 537–566.
Ishida, Y., 1968. Physiological studies on the evolution of dimethylsulfide. Mem. Coll. Agric. Kyoto Univ. 94, 47–82.
James, F., Paquet, L., Sparace, S.A., Gage, D.A., Hanson, A.D.,
1995. Evidence implicating dimethylsulfoniopropionaldehyde
as an intermediate in dimethylsulfoniopropionate biosynthesis.
Plant Physiol. 108, 1439–1448.
Karsten, U., Wiencke, C., Kirst, G.O., 1990. The effect of light
intensity and daylength on the b-dimethylsulphoniopropionate
(DMSP) content of marine macroalgae from Antarctica. Plant
Cell Environ. 13, 989–993.
Karsten, U., Wiencke, C., Kirst, G.O., 1991. Growth pattern and bdimethylsulphoniopropionate (DMSP) content of green macroalgae at different irradiance. Mar. Biol. 108, 151–155.
Karsten, U., Wiencke, C., Kirst, G.O., 1992. Dimethylsulphoniopropionate (DMSP) accumulation in green macroalgae from
polar to temperate regions: interactive effects of light versus
salinity and light versus temperature. Polar Biol. 12, 603–607.
Karsten, U., Kück, K., Vogt, C., Kirst, G.O., 1996. Dimethylsulfoniopropionate production in phototrophic organisms and its
physiological function as a cryoprotectant. In: Kiene, R.P.,
Visscher, P.T., Keller, M.D., Kirst, G.O. (Eds.). Biological
and Environmental Chemistry of DMSP and Related Sulfonium
Compounds, Plenum Press, New York, pp. 143–153.
Kates, M., Volcani, B.E., 1996. Biosynthetic pathways for phosphatidylsulfocholine, the sulfonium analoque of phosphatidylcholine, in diatoms. In: Kiene, R.P., Visscher, P.T., Keller,
M.D., Kirst, G.O. (Eds.). Biological and Environmental Chemistry of DMSP and Related Sulfonium Compounds, Plenum
Press, New York, pp. 109–119.
Keller, M.D., 1988/1989. Dimethyl sulfide production and marine
phytoplankton: the importance of species composition and cell
size. Biol. Oceanogr. 6, 375–382.
Keller, M.D., Korjeff-Bellows, W., 1996. Physiological aspects of
the production of dimethylsulfoniopropionate (DMSP) by
marine phytoplankton. In: Kiene, R.P., Visscher, P.T., Keller,
M.D., Kirst, G.O. (Eds.). Biological and Environmental Chemistry of DMSP and Related Sulfonium Compounds, Plenum
Press, New York, pp. 131–142.
Keller, M.D., Bellows, W.K., Guillard, R.R.L., 1989. Dimethyl
sulfide production in marine phytoplankton. In: Saltzman,
E.S., Cooper, W.J. (Eds.). Biogenic Sulfur in the Environment,
American Chemical Society, Washington, DC, pp. 167–182.
Keller, M.D., Kiene, R.P., Matrai, P.A., Bellows, W.K., 1999a.
196
J. Stefels / Journal of Sea Research 43 (2000) 183–197
Production of glycine betaine and dimethylsulfoniopropionate
in marine phytoplankton. I. Batch cultures. Mar. Biol. 135, 237–
248.
Keller, M.D., Kiene, R.P., Matrai, P.A., Bellows, W.K., 1999b.
Production of glycine betaine and dimethylsulfoniopropionate
in marine phytoplankton. II. N-limited chemostat cultures. Mar.
Biol. 135, 249–257.
Kiene, R.P., 1990. Dimethylsulfide production from dimethylsulfoniopropionate in coastal seawater samples and bacterial
cultures. Appl. Environ. Microbiol. 56, 3292–3297.
Kiene, R.P., 1992. Dynamics of dimethyl sulfide and dimethylsulfoniopropionate in oceanic water samples. Mar. Chem. 37, 29–
52.
Kiene, R.P., Visscher, P.T., Keller, M.D., Kirst, G.O. (Eds.), 1996.
Biological and Environmental Chemistry of DMSP and Related
Sulfonium Compounds. Plenum Press, New York.
Kiene, R.P., Linn, L.J., Bruton, J.A., 2000. New and important roles
for DMSP in marine microbial communities. J. Sea Res. 43 (3–
4) 209–224 (this issue).
Kirst, G.O., 1985. Osmotische adaptation bei algen. Naturwissenschaften 72, 125–132.
Kirst, G.O., 1989. Salinity tolerance of eukaryotic marine algae.
Annu. Rev. Plant Physiol. Plant Mol. Biol. 40, 21–53.
Kirst, G.O., 1996. Osmotic adjustment in phytoplankton and macroalgae: the use of dimethylsulfoniopropionate (DMSP). In:
Kiene, R.P., Visscher, P.T., Keller, M.D., Kirst, G.O. (Eds.).
Biological and Environmental Chemistry of DMSP and Related
Sulfonium Compounds, Plenum Press, New York, pp. 121–129.
Kocsis, M.G., Nolte, K.D., Rhodes, D., Shen, T.-L., Gage, D.A.,
Hanson, A.D., 1998. Dimethylsulfoniopropionate biosynthesis
in Spartina alterniflora. Evidence that S-methylmethionine and
dimethylsulfoniopropylamine are intermediates. Plant Physiol.
117, 273–281.
Laroche, D., Vezina, A.F., Levasseur, M., Gosselin, M., Stefels, J.,
Keller, M.D., Matrai, P.A., Kwint, R.L.J., 1999. DMSP synthesis and exudation in phytoplankton: a modeling approach. Mar.
Ecol. Prog. Ser. 180, 37–49.
Ledyard, K.M., Dacey, J.W.H., 1994. Dimethylsulfide production
from dimethyl-sulfoniopropionate by a marine bacterium. Mar.
Ecol. Prog. Ser. 110, 95–103.
Leustek, T., Saito, K., 1999. Sulfate transport and assimilation in
plants. Plant Physiol. 120, 637–643.
Lovelock, J.E., Maggs, R.J., Rasmussen, R.A., 1972. Atmospheric
dimethyl sulphide and the natural sulphur cycle. Nature 237,
452–453.
Matrai, P.A., Keller, M.D., 1994. Total organic sulfur and dimethylsulfoniopropionate in marine phytoplankton: intracellular variation. Mar. Biol. 119, 61–68.
Mazelis, M., 1993. Catabolism of sulfur-containing amino acids. In:
De Kok, L.J., Stulen, I., Rennenberg, H., Brunold, C., Rauser,
W.E. (Eds.). Sulfur Nutrition and Assimilation in Higher Plants:
Regulatory Agricultural and Environmental Aspects, SPB
Academic Publishing, The Hague, pp. 95–108.
Mitchell, J.G., Okubo, A., Fuhrman, J.A., 1985. Microzones
surrounding phytoplankton form the basis for a stratified marine
microbial ecosystem. Nature 316, 58–59.
Morris, I., 1981. Photosynthesis products, physiological state, and
phytoplankton growth. In: Platt, T. (Ed.), Physiological Bases of
Phytoplankton Ecology. Can. Bull. Fish. Aquat. Sci. vol. 210,
pp. 83–102.
Mulholland, M.M., Otte, M.L., 2000. Effects of varying sulphate
and nitrogen supply on DMSP and glycine betaine levels in
Spartina anglica. J. Sea Res. 43 (3–4) 199–207 (this issue).
Nishiguchi, M.K., Somero, G.N., 1992. Temperature- and concentration-dependence of compatibility of the organic osmolyte bdimethylsulfoniopropionate. Cryobiology 29, 118–124.
Noordkamp, D.J.B., Gieskes, W.W.C., Gottschal, J.C., Forney,
L.J., Van Rijssel, M., 2000. Acrylate in Phaeocystis colonies does not affect the surrounding bacteria. J. Sea Res. 43
(3–4) 287–296 (this issue).
Pakulski, J.D., Kiene, R.P., 1992. Foliar release of dimethylsulfoniopropionate from Spartina alterniflora. Mar. Ecol. Prog. Ser.
81, 277–287.
Ploug, H., Stolte, W., Epping, E.H.G., Jorgensen, B.B., 1999. Diffusive boundary layers, photosynthesis, and respiration of the
colony-forming plankton algae, Phaeocystis sp. Limnol. Oceanogr. 44, 1949–1958.
Quispel, A., Stegwee, D. (Eds.), 1983. Plantenfysiologie. Scheltema
& Holkema, Utrecht.
Reed, R.H., 1983. Measurement and osmotic significance of bdimethyl-sulfoniopropionate in marine macroalgae. Mar. Biol.
Lett. 4, 173–178.
Reed, R.H., 1984. Use and abuse of osmo-terminology. Plant Cell
Environ. 7, 165–170.
Rennenberg, H., 1989. Synthesis and emission of hydrogen sulfide
by higher plants. In: Saltzman, E.S., Cooper, W.J. (Eds.).
Biogenic Sulfur in the Environment, American Chemical
Society, Washington, DC, pp. 44–57.
Salisbury, F.B., Ross, C.W., 1992. Plant physiology, Wadsworth
Publishing Company, Belmont, CA.
Scarratt, M., Cantin, G., Levasseur, M., Michaud, S., 2000. Particle
size-fractionated kinetics of DMS production: Where does
DMSP cleavage occur at the microscale? J. Sea Res. (3–4)
245–252 (this issue).
Sheets, E.B., Rhodes, D., 1996. Determination of DMSP and other
onium compounds in Tetraselmis subcordiformis by plasma
desorption mass spectrometry. In: Kiene, R.P., Visscher, P.T.,
Keller, M.D., Kirst, G.O. (Eds.). Biological and Environmental
Chemistry of DMSP and Related Sulfonium Compounds,
Plenum Press, New York, pp. 55–63.
Stefels, J., Dijkhuizen, L., 1996. Characteristics of DMSP-lyase in
Phaeocystis sp. (Prymnesiophyceae). Mar. Ecol. Prog. Ser. 131,
307–313.
Stefels, J., Van Boekel, W.H.M., 1993. Production of DMS from
dissolved DMSP in axenic cultures of the marine phytoplankton
species Phaeocystis sp. Mar. Ecol. Prog. Ser. 97, 11–18.
Stefels, J., Van Leeuwe, M.A., 1996. Effects of iron and light stress
on the biochemical composition of Antarctic Phaeocystis sp.
(Prymnesiophyceae). I. Intracellular DMSP concentrations. J.
Phycol. 34, 486–495.
Stefels, J., Dijkhuizen, L., Gieskes, W.W.C., 1995. DMSP-lyase
activity in a spring phytoplankton bloom off the Dutch coast,
related to Phaeocystis sp. abundance. Mar. Ecol. Prog. Ser. 123,
235–243.
J. Stefels / Journal of Sea Research 43 (2000) 183–197
Stefels, J., Gieskes, W.W.C., Dijkhuizen, L., 1996. Intriguing functionality of the production and conversion of DMSP in Phaeocystis sp. In: Kiene, R.P., Visscher, P.T., Keller, M.D., Kirst,
G.O. (Eds.). Biological and Environmental Chemistry of DMSP
and Related Sulfonium Compounds, Plenum Press, New York,
pp. 305–315.
Steinke, M., Daniel, C., Kirst, G.O., 1996. DMSP lyase in marine
macro- and microalgae: intraspecific differences in cleavage
activity. In: Kiene, R.P., Visscher, P.T., Keller, M.D., Kirst,
G.O. (Eds.). Biological and Environmental Chemistry of
DMSP and Related Sulfonium Compounds, Plenum Press,
New York, pp. 317–324.
Steinke, M., Wolfe, G.V., Kirst, G.O., 1998. Partial characterisation
of dimethylsulfoniopropionate (DMSP) lyase isozymes in 6
strains of Emiliania huxleyi. Mar. Ecol. Prog. Ser. 175, 215–
225.
Steinke, M., Malin, M., Turner, S.M., Liss, P.S., 2000. Determinations of dimethylsulphoniopropionate (DMSP) lyase activity
using headspace analysis of dimethylsulfide (DMS). J. Sea
Res. 43 (3–4) 233–244 (this issue).
Summers, P.S., Nolte, K.D., Cooper, A.J.L., Borgeas, H., Leustek,
T., Rhodes, D., Hanson, A.D., 1998. Identification and stereospecificity of the first three enzymes of 3-dimethylsulfoniopropionate biosynthesis in a chlorophyte alga. Plant Physiol. 116,
369–378.
Taylor, B.F., Visscher, P.T., 1996. Metabolic pathways involved in
DMSP degradation. In: Kiene, R.P., Visscher, P.T., Keller,
M.D., Kirst, G.O. (Eds.). Biological and Environmental Chemistry of DMSP and Related Sulfonium Compounds, Plenum
Press, New York, pp. 265–276.
Trossat, C., Nolte, K.D., Hanson, A.D., 1996. Evidence that the
pathway of dimethylsulfoniopropionate biosynthesis begins in
the cytosol and ends in the chloroplast. Plant Physiol. 111, 965–
973.
197
Trossat, C., Rathinasabapathi, B., Weretilnyk, E.A., Shen, T.-L.,
Huang, Z.-H., Gage, D.A., Hanson, A.D., 1998. Salinity
promotes accumulation of 3-dimethylsulfoniopropionate and
its precursor S-methylmethionine in chloroplasts. Plant Physiol.
116, 165–171.
Turner, S.M., Malin, G., Liss, P.S., Harbour, D.S., Holligan, P.M.,
1988. The seasonal variation of dimethylsulfoniopropionate
concentrations in near-shore waters. Limnol. Oceanogr. 33,
364–375.
Turpin, D.H., 1991. Effects of inorganic N availability on algal
photosynthesis and carbon metabolism. J. Phycol. 27, 14–20.
Uchida, A., Ooguri, T., Ishida, T., Kitaguchi, H., Ishida, Y., 1996.
Biosynthesis of dimethylsulfoniopropionate in Crypthecodinium cohnii (Dinophyceae). In: Kiene, R.P., Visscher, P.T.,
Keller, M.D., Kirst, G.O. (Eds.). Biological and Environmental
Chemistry of DMSP and Related Sulfonium Compounds,
Plenum Press, New York, pp. 97–107.
Vairavamurthy, A., Andreae, M.O., Iverson, R.L., 1985. Biosynthesis of dimethyl sulfide and dimethylpropiothetin by Hymenomonas carterae in relation to sulfur source and salinity
variations. Limnol. Oceanogr. 30, 59–70.
Van Boekel, W.H.M., 1992. Phaeocystis colony mucus components
and the importance of calcium ions for colony stability. Mar.
Ecol. Prog. Ser. 87, 301–305.
Van Diggelen, J., Rozema, J., Dickson, D.M.J., Broekman, R.,
1986. b-3-dimethylsulphoniopropionate, proline and quaternary
ammonium compounds in Spartina anglica in relation to
sodium chloride, nitrogen and sulphur. New Phytol. 103, 573–
586.
Vierstra, R.D., 1993. Protein degradation in plants. Annu. Rev.
Plant Physiol. Plant Mol. Biol. 44, 385–410.
Wolfe, G.V., Steinke, M., Kirst, G.O., 1997. Grazing-activated
chemical defence in a unicellular marine alga. Nature 387,
894–897.