Download translation no. 4849

CANADIAN TRANSLATION OF FISHERIES AND AQUATIC SCIENCES
No.
4849
Photosynthesis in the marine world
by
Y. Fujita
Original Title:
From:
Umi no sekai no kogosei
Kagaku 38: 2-9, 1979.
Translated by the Translation Bureau (ELC/PS)
Multilingual Services Division
Department of the Secretary of State of Canada
Department of Fisheries and Oceans
Arctic Biological Station
Ste. Anne de Bellevue, Que.
1982
24 Pages typescript
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4
DEPARTMENT OF THE SECRETARY OF STATE
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TRANSLATED FROM - TRADUCTION DE
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Japanese
AUTHOR - AUTEUR
FUJITA Yoshihiko
TITLE IN ENGLISH - TITRE ANGLAIS
Photosynthesis in the marine world
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Kagaku
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Chemistry
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Kagaku
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38
No.
•
8, 1979 Pp2
Photobynthesis in thé marine World
(Mechanisms used in feeble light)
FUJITA Yoshihiko,
D.Sc.
Scanning elebtron microphotographof a diatom
Department of ravine biophysics, Intitute for maritime research,
University of Tokyo '
SEC 5- 25 (Rev. 6/78)
7 19tYe
2
1.
Introduction
It is no exaggeration to say that radiant energy from the sun is
311
the source of support for the activity of%ife on earth. About 70% of
the solar radiation which reaches the earth's surface is light energy in the so-calleâ
visible
wavelength range.
Plants which live on thè ground or in the oceans trans--
form this light energy by means of a chain of photosynthetic processes into
chemical energy and synthesize the components of living tissues. Organisms
which are not photosynthetic range all the way from bacteria to humanity
and they obtain the food which they need from other organisms by what is
known as he.reronomous nutrition.
When the food chain is followed back it
leads to the organic nutrients produced by photosynthesis in plants. Since
the source of supply of our life energy is the prolific growth of plants
on the earth, it can be said that the source of all organic life is the
radiant energy from the sun which is utilized by these plants. Everyone
knows that photosynthesis occurs in the green leaves of the higher plants,
the trees, shrubs and grasses. Green grana -- the chloroplasts which are the
photosynthesis organs -- are
tightly packed into the cells of green leaves and the leaves are green
because they contain chlorophyll which captures the solar energy. When
photosynthesis is mentioned, many people will therefore think of the green
colour of the green leaves of plants.
However photosynthesis is not confined to the activity of these
higher plants on the ground. Pond water becomes green in summer, water
in goldfish bowls may become green, and this greening mostly results from
a luxuriant growth of single cell green algae which are also plants in which
photosynthesis occurs.
Not only green algae but many other types of algae
are active in the waters of lakes, marshes and rivers, and the photosynthesis
which occurs in these algae in the same way
as in the higher plants
produces the life energy for other organisms in the water. 70% of the
surface of the globe is covered by
Se25.
The living activity of organisms
in this vast ocean is supported by photosynthesis, and the plants in which
this photosynthesis occurs are algae, just as they are in lakes and marshes.
Many people will probably associate the idea of marine algae with edible
seaweeds such as asakusanori
(laver, Porphyra), konbu (tangle, Laminaria)
or wakame ( Undaria). However, a major role in photosynthesis in the sea
is played by diatoms and flagellates which float or drift as single cells
or colonies in the phytoplankton.
Except in cases such as the well-known
red tide of such algae in the Inland Sea of Japan, the quantity present in
sea water is never large, and even when
drawing seawater
we cannot easily
be aware of their presence. Nevertheless, the area of the ocean is, as
already mentioned, very large, and as Table 1 shows, photosynthesis in the
sea amounts to more than half of the photosynthesis on land.
We may say that this
shows how important the photosynthesis performed in the oceans by phytoplankton is
to the support of life on land.
Table 1.
Global production of organic substances by photosynthesis
Mean quantity
per unit area
World total
(10
9
tons per year)
(g/m2 per year)
Land total
730
109
Sea
155
55
World total
320
164
4
Photosynthesis by higher plants and by algae procee^s through
a complicated chain of reactions, but the overall result can be
consolidated in the following equation
hV
H20
+
CO2
CH2O
+
02
(1)
This reaction not only produces life energy for the organisms but also
is of importance in the provision of the oxygen molecules which an
extremely large number of organisms require. For this reason, too, it
may be said that photosynthesis in the sea must not be neglected in
relation to life on earth.
p3
2.
Light on land, light in the sea
ener9Y
The ultra violet part of the solar radiation"'is greatly reduced
by scattering and absorption in the air and in the ozone layer before it
reaches the earth's surface, and as shown in Figure 1(a), the energy
distribution in the light which is incident on the surface has its maximum
energy in the visible region at about 500 nm. This visible light is the
source of energy for photosynthetic plants on land. However the phytoplankton and the marine algae in the sea live mostly in the water and the
light which is to be used for photosynthesis has passed through a medium far
more dense than the air. The phytoplankton living at depths of some tens of
metres to a hundred metres are those of most importance to photosynthesis in
the sea, and the solar light which penetrates to such depths has not only been
greatly reduced in total energy but has lost much of the visible red light
through absorption in the water and has lost the near ultraviolet by absorption
or by scattering by dissolved organic matter and by particles suspended in the
sea water.
The light is finally restricted to a narrow band centred around
5
Figure 1
The energy distribution in the solar radiation
(a)
On land
Open sea
(h)
Coastal water
(a)
1.511.5
ca l /(cm2 .m in .p )
ÉEW -‹
0.5 -
500
400
1000
500
600
700
(nm)
(nm)
Figure 2
(a)
The absorption spectrum of the green leaves of the higher plants
(b)
The photosynthesis quantum yield (moles/Einstein) (the number of
moles of oxygen evolved per Einstein)
(a)
Absorption
(%)
17,UMSLI:JV'M
4 00
SIDO
6(1)0
700
(nm)
eod
T A i) ij
0.1
C.; N
NR
inf.ornld:ion sc;:uk,ir,ent
Quantum
yield
I 0.05
400
500
600
(nm)
700
6
480 nm to 500 nm, as shown by the solid lines in Figure 1(b). Marine algae,
other than those which live in the tidal zone, must use this type of light
for photosynthesis. In the coastal waters where the algae live, there is more
plankton than
in the open sea, and
once again the near ultraviolet light is greatly diminished by the bodies
of these organisms and by the organic compounds which they produce.
light which reaches
these comparatively shallow
The
regions is
severely limited, as shown by the dotted lines in Figure 1(b).
The higher plants which are most important for photosynthesis on
land harvest light principally in chlorophyll a and b. Chlorophyll contains
magnesium linked to a distorted porphyrin, and its light absorption
properties are consequently those of a metal porphyrin with an alpha band
in the red at 650 nm to 700 nm and a gamma band in the blue at 430 nm to
450 nm, so that it takes on a green colour. Consequently its efficiency
in utilizing light energy for photosynthesis -- the photosynthesis quantum
yield -- is high in the red and the blue, and is lower in the 500 nm region
(
where the energy distribution in the sun's light has its maximum.' This
distinctive feature of photosynthesis by land plants would be quite useless
with the light energy distribution which can be used for photosynthesis in
the sea.
It is therefore to be expected that algae living in the sea will
make efficient use of the light in the sea by means quite different from
those used by land plants. This fact is considered to be one of the
distinctive features of photosynthesis in the sea.
The reaction yield per light quantum. Since the photosynthetic reaction
is given by equation (1), the quantity of oxygen evolved is a measure
of the normal reaction. Consequently it is the molar number of the
oxygen molecules evolved per light quantum.
7
3.
The principal factors in photosynthesis in the sea
Photosynthesis occurs in the sea in familiar algae such as
p4
asakusanori. (laver, Porphyra) and konbu (tangle, Laminaria) which are not
3E all,
green ^ An abnormal development of phytoplankton in which the sea water
becomes clouded with phytoplankton leads to the red tide, but the colour
developed is the well-known reddish brown and a green colour is not formed.
As these examples show, the photosynthetic organisms in the sea differ from
those on land and chlorophyll is by no means the principal photosynthetic
pigment.
Table 2 shows the answers to questions as to what types of algae
the photosynthetic organisms in the sea are, and what pigments they contain.
The principal pigments in the green algae are chlorophyll a and b, as they
Table 2
Photosynthetic organisms in the sea.
Algae and the composition of their photosynthetic pigments
Green
algae
Chlorophyll a
b
++
Diatoms
Dinofla
gellates
Red
algae
Bluegreen
algae
++
++
++
++
++
+
+
+
+
+
+
+
+
Brown
algae
+
c
P-,Carotene
+
Lutein
++
Fucoxanthin
++
++
++
++
Peridinin
Phycoerythrin
Phycocyanin
++
Principal pigment
+
Presence found
8
are in the higher plants on land but as marine algae they practically all
live in the tidal zone where the light environment does not differ from
that on land, and they are rare among the algae in the phytoplankton.
Consequently it may be said that the algae which bear the main burden of
photosynthesis in the sea differ greatly from land plants in pigment
composition. The most important phytoplankton are diatoms, dinoflagellates
and blue-gree algae, whereas the red algae and brown algae are important
algae in the sea from the tidal zones to the depths. Comparisons of the
photosynthetic pigments in these principal marine photosynthetic organisms
with those on land shows that chlorophyll a is common to all organisms
but diatoms, dinoflagellates and brown algae contain chlorophyll c instead
of chlorophyll b.
Of the carotenoids,
-carotene is present throughout,
but the principal component present in diatoms and brown algae is fucoxanthin
and in dinoflagellates it is peridinin (more than 70% of the total).
of this, these algae have a brown colour.
Because
The solid line in Figure 3 (a)
is the absorption spectrum of a live diatom cell for comparison with
Figure 2 (a). A distinctive feature of red,algae and blue-green algae is
their phycoerythrin content. The absorption band at 500 nm to 600 nm in
the absorption spectrum of Figure 3 (b) is due to this pigment and is the
source of the reddish purple colour. Thus each of the taxonomic groups
of the marine algae differs from the others in the composition of its
photosynthetic pigments, but one may say that the principal algae, at least,
contain carotenoids or phycoerythrin which enable them to absorb light in
the vicinity of 500 nm at the peak of the energy distribution of light
which has penetrated the sea. In fact, the light energy absorbed by these
pigments is used for photosynthesis with high efficiency.
The solid lines
9
Absorption
(%)
400
500 • 600
700
nm)
O. I
Quantum
yield
0.05
400
500
600
700
(nm)
Figure 3.
The absorption spectra and quantum yields
of diatoms* and red algae
(a)
Absorption spectrum of red algae
Absorption spectrum of diatoms
(b)
The quantum yield of red algae
The quantum yield of diatoms
There is an apparent discrepancy between the references to Figure 3
and the captions. I have not tried to adjust these. Translator.
10
in Figures 3(a), (h) show the effective spectrum of the quantum yield of
red algae and diatoms, and it is evident that the yields of both in the
neighbourhood of 500 nm are higher than those of land plants (Figure 2(b)).
It is particularly surprising that the quantum yield of red algae is very
greatly reduced in the absorption band of chlorophyll a.
It may be said
that the substances which work most importantly to bring light energy into
photosynthesis in the sea are not chlorophyll but phycoerythrin and the
carotenoids fuèoxanthin and peridinin. An attempt will be made, below,
to explain the nature of these pigments and how they operate in the living
body, but first some description is given of the general mechanism by which
photosynthetic pigments harvest light energy.
4.
The mechanism of light energy harvesting
Neither in the higher plants nor in algae do the photosynthetic
pigment molecules participate directly in photochemical reactions.
P5
Calculations based on the quantity of oxygen evolved by irradiation with
a single short (about 10 microseconds) but sufficiently strong flash, show
that in higher plants and algae
one unit in which the photochemical
reaction occurs is present for about 500 to 600 molecules of chlorophyll.
Thus the photosynthetic pigment is present in the chloroplasts in the form
of groups, by means of which the excitation energy of a large number of
pigment molecules is transferred collectively to the molecules in which the
photochemical reaction occurs (the reaction centres). This transfer of
excitation energy between the pigment molecules is a weak interaction between
the molecules based on a dipole-dipole interaction, and the transfer
frequency from molecule j to molecule k can be represented by
1
equation .
the following
11
•D T
n 1->k
•
9000 tc2 In 10
-
128 7r 5 n' NorIC
5"
f
—
— di)
(
2)
o
kacon
In equation 2
N
o
-113-
cs.>)
•
a coefficient representing the orientation of the dipoles
•
the refractive index of the solvent
=
Avogadro's number
•
the intrinsic lifetime of the excited state of molecule j
=
the distance between the molecules
=
the wave number
=
the molecular light absorption coefficient of the molecule k
=
the fluorescent emission spectrum distribution of the molecule j.
In short, when the overlap integral of the fluorescent emission spectrum of
molecule j on the absorption spectrum of molecule k
becomes large, n
•k
becomes large, and it is also inversely proportional to the sixth power of
the distance between the molecules.
At the present time this is thought
to be the most applicable mechanism, and using the fluorescence of the
chlorophyll a in the chloroplasts as an index, the excitation energy of
the various pigments is transferred as shown in Table 3.
Table 3
The transfer of excitation energy between the photosynthetic pigments
Efficiency (%)
Chlorophyll b
p
-
carotene
-->
a
--> chlorophyll a
Chlorophyll c
100
Type of plant
Green algae
40
a
90
Brown algae
chlorophyll a
90
Diatoms
Phycoerythrin
chlorophyll a
7 80
Phycocyanin
chlorophyll a
86
Fucoxanthin
—
›
Red algae
Blue-green algae
12
A first distinctive feature is the high transfer efficiency in
light quantum units, a second is the transfer from a molecule in a high
energy state to a lower molecule, and these are well explained by the
proposed mechanism.
In both higher plants and algae the photosynthetic
ptiotod lLhlLLi1
reaction progresses through a cooperative two-type Y process2. Consequently
each pigment group is attributed to its own reaction centres, and becomes
the source from which energy is distributed to them (Figure 4). Each
pigment group is linked to individual protein molecules4, and it is believed
that the pigment proteins are symmetrically located in the fatty double
layer of the photosynthetic membrane (thylakoid membrane) where the distance
between the pigment molecules will be sufficiently small (the transfer
frequency being inversely proportional to the sixth power of the distance
between the molecules). Even so, there is at present little progress in
understanding the circumstances, already mentioned, of fucoxanthin-peridinin
and of phycoerythrin or the detailed coordination of the pigment molecules,
but we will now try to discuss these pigments.
5.
The carotenoid-chlorophyll a protein complexes
As shown in Figure 5, the basic structures of fucoxanthin and
peridinin are the same as that of (? -carotene. The oxidized positions
on the ionone rings are the same as in the xanthophylls of the higher plants.
The differences are that in fucoxanthin C-8 is oxidized outsieie-
the
kl}a ^
ionone rings and"C-,6' and C-7' are dehydrated, whereas in peridinin C-,11'
and C-19' are oxidized and C-6 and C-7 are dehydrated. However it is not
known why, with these structural differences, the excitation energy of the
xanthophylls can be efficiently transferred to chlorophyll a and used for
p6
13
CHLOROPHYLL D
CHLOROPHYLL h
Figure 4
3)
Butler-Kitajima's three pigment zone model
The arrows show the direction of energy transfer, and their thickness
shows the magnitude of the transfer. "I" and "II" in the circles show
photochemical reaction centres.
%^.^^.•^--^
`11
' \^ ^^3 ^ \ y^ ^-'' ^y ^.
I
I
ki0)\./\OCOCH3
(b)
CI-I,CO0
The structure of
(a)
carotene
(b)
Fucoxanthin
(c)
Peridinin
14
photosynthesis. Considering the mechanism of energy transfer already
discussed it is necessary that the separation normally present between the
xanthophyll and the chlorophyll a should be sufficiently small. Both
chlorophyll a and xanthophylls are strongly lipidophile compounds which will
be disolved in the fat of the thylakoid membrane, and in this condition
there is no restriction on the conshaapproach of the two pigments. In the
50-called
higher plants, the chlorophyll is combined with the vmembrane protein and
forms r.ous
4
, and the same arrangement will apply in the case of
xanthophylls and chlorophyll a.
It is known that when the cells of
dinoflagellates which contain peridinin as the photosynthetic pigment are
destroyed, a red-orange pigment is eluted, and Haxo et al
5
have shown that
the pigment is linked to a protein and have purified it by means of ion
exchange chromatography and molecular sieve chromatography.
The pigment
protein shows the absorption spectrum of Figure 6, and the pigments it
contains are peridinin and chlorophyll a. The protein portion has an
isoelectric point of about 7.5 and is a neutral protein with a reported
composition whose distinctive feature is an amino acid structure with more
than 50% alanine. The molecular weight is 32000 daltons and it is confirmed
to consist of a single peptide chain. Nine molecules of peridinin and two
molecules of chlorophyll are linked to one protein molecule. Since the
probe.iYt
pitymeht is easily extracted froethe compound by any organic solvent it is
supposed that there is no covalent bonding to the aminoacids which comprise
the peptide chain.
As can be seen from the fluorescence excitation spectrum
of the chlorophyll a shown in Figure 6, the excitation energy of the
peridinin in this pigment protein is transferred to the chlorophyll a with
15
Figure 6
o
(VS
I
(a) The absorption spectrum of
peridinin-chlorophyll a protein
o
(15
(b)
o
(b-A)
The fluorescence excitation
spectrum
(b-B)
The fluorescence emission
spectrum
o
ocrli
o:
o
O
3(J0
400
500
600
700
.(nm )
2HD
HO
0,
fle°
\CH3
CH3 .--
f\j-)--1
913
-N/Idt-N
Kt.
/
2
CL /CH2 H
I
N-- CH3
/ Y
642
CH3
\c=cfi
016E133
0
H30.—
pmkin
Figure 7
The model with two pigments ove the
peridinin-chlorophyll a protein .
This qualitative diagram shows two types of
arrangement of a pair of peridinin molecules
at a fixed angle in relation to the molecule
of chlorophyll a.
UNEDITD
î'zr
16
L7:
.
.;
•
•
6
extremely high efficiency (100% according to Song et al) .
distance between the peridinin and chlorophyll molecules
this transfer efficiency by means of equation 2 is 5.8
The effective
e.,,pecle.d from
R
to 6.8
R.
Song
et al measured the dichroism in circularly polarized light and the polarized
light characteristics of this pigment protein, and proposed the arrangement
6
of pigments above (or inside) the protein shown in Figure 7 .
Since one
protein molecule contains nine peridinin molecules and two chlorophyll a
molecules it is thought that the arrangement shown in the Figure is present
in sets of two. Such a regular pigment molecule arrangement bonded to a
protein may be possible. No such knaNledge has yet been gathered about the
fucoxanthin of diatoms.
However when fucoxanthin in chloroplasts is
compared with that dissolved in organic solvents, the absorption band is
said to be displaced by several tens of nanometers to the long wavelength
7
si de . Since displacement of the absorption band to the long wavelength
side has been reported for the
p
-carotene protein complex extracted from
higher plants, this fact shows that fucoxanthin bonded to protein in the
same way as peridinin may be arranged so as to be close to chlorophyll a
The
protein complex containing chlorophyll a here present differs from the
carotenoids in land plants, and may increase the transfer efficiency of
excitation energy. However almost nothing
is known about the arrangement
61,e_
on the thylakoid membrane of the pigment proteins containin3 y photosynthesis
reaction centres, or about the details of the linking of the pigments to
the proteins.
For these we must await future studies.
Arguing from the presence of peridinin and chlorophyll a proteins
one can imagine the relations between the photosynthetic pigments to be
as shown in Figure 8.
They operate probably in the same way as the chlorophyll
a and b proteins in the higher plants and in the green algae.
hV
hl)
CHLOPoPHYLL C
PERICI`IN OR FUCO- ^)
XANTHiN
CHLOROPH LL
Figure 8
Photosynthetic pigment relations
in dinoflagellates and diatoms
CHzOH
HO
Figure 9
Structure of siphonoxanthin
18
I
Green algae have the same photosynthetic pigment composition as
the higher plants, and in general the efficiency of utilization of the
carotenoid excitation energy is low (see Figure 2 (b) ). However it has
recently been found that green algae living in fairly deep places (around la Yn
may be- quite different. As Figure 1 (b) shows, the light which penetrates
to deep places is restricted to a green region centred around about 510 nm.
Investigation of the pigment composition of green algae growing in such
places has shown that they contain siphonoxanthin (Figure 9). Figure 10
p8
shows measurements of the absorption spectra of such algae, and also of
the fluorescence excitation spectrum of the chlorophyll a which corresponds
to the operative photosynthesis spectrum. The absorption spectrum shows
the distinctive siphonoxanthin protein band in the neighbourhood of 530 nm,
and the same pattern is found in the utilization spectrum. Thus the
excitation energy of the siphonoxanthin is efficiently transferred to the
chlorophyll a and the photosynthetic quantum yield in green algae is
increased.
It is a very interesting fact about peridinin, fucoxanthin
and siphonoxanthin that in all three there are oxidized carbon atoms outside
the ionone rings. Although it is purely speculative, it may be that in
the peridinin , chlorophyll a arrangement this structure is geometrically
related to the chlorophyll a molecule. Alternatively, it may, for example,
easily form a hydrogen bond with the protein.
19
(a)
Figure 10
A green algae frond
(a) Absorption spectrum
(h) Fluorescence excitation spectrum
of chlorophyll a
.
•
400
500
(nm)
600
A: Living at 10 m depth
B:
v
Living at the surface
ey
. 4" ,:.e
e"
(-,'-e
0
0
H H il
H II
-HN-C-C--#----N Ç-C
CH2
CH,
S
Peiv[icle chaill
'
(5
HOOC 6=0
Figure 11
Phycoerythrin structure
and bonding to protein
H
0"N
N"0
H
H
Figure 12
The absorption spectrum in the
visible of phycoerythrin from
red algae
113'
0
450
500
550
(nm)
600
20
6.
Phycoerythrin
The characteristic photosynthetic pigment in red algae and blue-
green algae, phycoerythrin, differs from chlorophyll and carotenoids, in
that it is strongly covalently bonded to protein.
The pigment is a cleaved
tetrapyrrole porphyrin of the same Yfamily as phycocyanin and allophycocyanin
which together are called the phycobili proteins.
In light morphogenesis
of higher plants the light signal receptor pigment phytochrome is said to
belong to the same pigment protein family.
The chemical structure of phyco-
erythrobiline, in which phycoerythrin is the pigment is shown in Figure 11,
and bonds are made to the cystine SH and to the serin OH in the peptide
chain.
In the red algae, the protein part has a molecular weight of
19500 daltons and consists of two sets of peptides.
Three to four protein
8
molecules are bonded to two pigment molecules . Thus one protein molecule
is linked to five or six pigment molecules, and the absorption spectrum
shows three absorption bands at 500 nm, 540 nm and 565 . nm as shown in
Figure 12. This protein is acidic and strongly hydrophilic, and consequently
differs greatly in its properties from the chlorophyll protein in the
thylakoid membrane.
Consequently one must think of the two proteins as
present separately on the inside and the outside of the thylakoid membrane.
Nevertheless, according to equation (2) they must be sufficiently close
together. Electron microscope investigation of the chloroplasts in red
algae have shown that phycoerythrin, phycocyanin and allophycocyanin form
aggregates of high degree and assume granular structures which are found
9
arranged over the thylakoid membrane (Figure 13) .
These granular
structures are called phycobilisomes, and phycobilisomes bonded to chlorophyll a have recently been extracted from blue-green algae
10
. It was
21
(0
Y
)
Figure 13
ef -.5 % 5_55 r'S,
(...,
....)
`,....., r-- `, \...)
II,
I
'
'I'
i- - s
i .---) r -s l
The arrangement of phycobilisomes on
•
'' ;",;
\,_.1,----,2—
`,.._.' (--s,
•-_
,'--'', '\--; ■'—', ',---;
x
',....,. l' — ‘,
(s,
—
—
the thylakoid membranes of red algae
I
Y
(h)
(b
)(
Y
(a) Surface
Cross-section.
The sections - shown
are along the lines X and Y in (a)
t tt it t:
Z7fZZ:t7.12±...MtfZZ
Figure 14
Photosynthetic pigment
relations in red algae
.
' PHYCOCYANIN
1;
(
'Ail° pkycoeyahin
22
I
found that chlorophyll a is present at the points of contact between the
phycobilisomes and the thylakoid membrane, and that it receives the
excitation energy of the phycoerythrin. Consequently the pigment protein
p9
outside the thylakoid membrane. in red algae and blue-green algae may be
said to operate as an antenna in harvesting light energy. However there
is much that is unknown about the arrangement and structure of the pigment proteins
in the phycobilisomes or about the way in which the phycobilisomes combine with
and there is very little knowledge of the
the thylakoid membrane,
chlorophyll a arrangement which lies behind the high efficiency of transfer
to it of the phycoerythrin excitation energy.
Setting up an outline process diagram similar to those given in
Figure 4 and in Figure 8 for the operation of photosynthetic pigments such
as phycoerythrin results in Figure 14. Characteristic of this case is that
the phycobilisome excitation energy is transferred to only a very small
number of chlorophyll a. The remaining large number of chlorophyll a
cannot distribute this excitation energy to two types of photochemical
reaction, and consequently, as can be seen in Figure 3(b), the quantum
yield from the light absorbed by the chlorophyll a is lowered.
7.
Conclusions
This paper has discussed one of the most distinctive features of
photosynthesis in the sea by algae, the way in which the photosynthetic
pigments match the light energy which penetrates into the sea. In land
plants the strongest light energy at about 500 nm is avoided, but algae
in the sea have pigment systems which positively and preferentially
utilize it.
As compared with land plants, algae have an environment in
IV
23
ti
the sea in which the light energy is extremely low and they possess pigment
systems which through long evolutionary stages have been adapted and
developed to suit the mode of life in the sea.
In writing about photosynthesis in these marine plants, it was
originally hoped to discuss them in one or two stages in comparison with
land plants.
However research into photosynthesis in marine algae lags far
behind research on the higher plants. As has already been stated chemical
information is particularly lacking even for the photosynthesis systems
about which most is known. To some extent this may be due to the author's
incapacity but for the moment' we must wait for future studies.
This is because the photosynthetic organisms
in the sea, the algae and particularly the plankton algae, are difficult
to procure.
A normal prerequisite for studies with physiological or
biochemical objectives is the procurement of considerable quantities of
algae or of algal cells. This makE8the artificial rearing of the marine
Considering only the phenomenon of photosynthesis, the
algae necessary.
in Hie- pasb
objects usedYhave been land or land water plants, but the algae living in
the sea have quite different properties. Some as yet unknown distinctive
features such as the photosynthetic production discussed in this paper
are probably still hidden from us. In order to bring them to light,
artificial means of rearing algae have become essential, and we feel it
our duty to promote this in the planning of marine biology.
24
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L_
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