Download Desiccation-tolerant plants in dry environments

Rev Environ Sci Biotechnol (2006) 5:269–279
DOI 10.1007/s11157-006-0015-y
REVIEW PAPER
Desiccation-tolerant plants in dry environments
T.-N. Le Æ S. J. McQueen-Mason
Received: 24 February 2006 / Accepted: 13 June 2006 / Published online: 14 July 2006
Springer Science+Business Media B.V. 2006
Abstract The majority of terrestrial plants are
unable to survive in very dry environments.
However, a small group of plants, called ‘resurrection’ plants, are extremely desiccation-tolerant
and are capable of losing more than 90% of the
cellular water in vegetative tissues. Resurrection
plants can remain dried in an anabiotic state for
several years and, upon rehydration, are able to
resume normal growth and metabolism within
24 h. Vegetative desiccation tolerance is thought
to have evolved independently several times
within the plant kingdom from mechanisms that
allow reproductive organs to survive air-dryness.
Resurrection plants synthesise a range of compounds, either constitutively or in response to
dehydration, that protect various components of
the cell wall from damage during desiccation and/
or rehydration. These include sugars and late
embryogenesis abundant (LEA) proteins that are
thought to act as osmoprotectants, and free radical-scavenging enzymes that limit the oxidative
damage during dehydration. Changes in the cell
wall composition during drying reduce the
mechanical damage caused by the loss of water
and the subsequent shrinking of the vacuole.
These include an increase in expansin or cell
T.-N. Le (&) Æ S. J. McQueen-Mason
CNAP, Department of Biology, University of York,
P.O. Box 373, York, YO10 5YW, UK
e-mail: [email protected]
wall-loosening activity during desiccation that
enhances wall flexibility and promotes folding.
Keywords Cell wall Æ Desiccation tolerance Æ
Drought stress Æ Dry environments Æ Expansins Æ
Resurrection plants Æ Water deficit
Introduction
Plants exhibit several strategies to deal with life in
extremely dry environments; namely avoidance,
resistance, or tolerance to desiccation (Levitt
1980). Some plants (e.g. annuals) complete their
life cycles during the part of the year when water
is plentiful and growth conditions are favourable,
and avoid times during which desiccation is frequent (e.g. summer). Desiccation avoidance may
enable plants to achieve maximal growth and
productivity, but it also confines them to areas or
periods with favourable conditions. Other plants,
for example perennials such as cacti, have modified morphological structures that allow them to
retain most of their cellular water and resist
equilibration with the air. These adaptations allow desiccation-resistant plants to extend the
range of conditions and habitats in which they can
remain metabolically active throughout the year.
The main drawback for plants with a desiccation
survival strategy geared towards resistance is that
growth often proceeds very slowly. A small group
123
270
of plants, the so-called ‘resurrection plants’ (Gaff
1971), are extremely desiccation-tolerant, and can
survive almost complete desiccation, usually
considered as drying to < 0.1 g H2O g–1 dry
mass or to 10% absolute water content or less
(Alpert 2005).
Desiccation tolerance has been defined as the
ability of an organism to equilibrate its internal
water potential with that of moderately dry air,
and then resume normal function after rehydration (Alpert 2000). Air-dryness at a relative
humidity of 50% at 28C would equate to a water
potential of – 100 MPa (Gaff 1997), a water
deficit that would be lethal to the majority of
modern day flowering plants. However, a few
resurrection plants possess vegetative tissues that
can tolerate loss of greater than 90% of their
cellular water, and some can tolerate drying to
water potentials as low as – 650 MPa without
injury (Gaff 1997). Resurrection plants are usually found in habitats of sporadic rainfall,
including rocky outcrops, and arid zones within
tropical and subtropical areas (Rascio and La
Rocca 2005). It is estimated that there are about
300 angiosperms which possess vegetative desiccation tolerance (Porembski and Barthlott 2000).
Desiccation-tolerant plants have been found in all
continents except Antarctica (Alpert 2000), and
in all groups of seed plants except for the gymnosperms (Oliver 1996). Resurrection plants, like
their desiccation-tolerant animal counterparts,
are generally small in size. The absence of vegetative desiccation tolerance within the gymnosperms, or within any vascular plant more than
3 m in height, is thought to be due to the physical
constraint of re-establishing water flow in the
xylem during rehydration after it has been interrupted during desiccation due to cavitation
(Alpert 2005).
This review will focus on the ability of vegetative tissues of resurrection plants to survive
extreme desiccation. First we examine how desiccation tolerance of vegetative tissues evolved in
vascular plants. Then we investigate the different
mechanisms used by resurrection plants to protect
cell membranes and organelles during desiccation, and to repair dehydration-induced damage
upon rehydration. This includes examining the
roles of key proteins (e.g. LEAs and transcription
123
Rev Environ Sci Biotechnol (2006) 5:269–279
factors), sugars and other compatible solutes in
the protection and maintenance of cellular
integrity. We also review some adaptations of
resurrection plants for surviving desiccation
including changes in the cell wall and lipid composition, and the establishment of anti-oxidant
systems.
Evolution of desiccation tolerance
In order to colonize the land, the earliest terrestrial plants must have been desiccation-tolerant at
every stage of the life cycle (Oliver et al. 2005).
With the evolution of more complex vascular
plants, desiccation tolerance was lost in vegetative
tissues but was retained in reproductive tissues
(Oliver et al. 2000). The acquisition of desiccation
tolerance is part of a maturation program during
normal seed development. The majority of
terrestrial plants today are capable of producing
desiccation-tolerant structures such as spores,
seeds and pollen which can remain viable in the
desiccated state for decades, or centuries, in the
case of the ancient Nelumbo nucifera (sacred
lotus) seed from China (Shen-Miller et al. 1995).
The structural genes required for desiccation
tolerance are not unique to resurrection plants,
but are also present in the genomes of desiccation-sensitive plants (Bartels and Salamini 2001).
However, resurrection plants may have enlisted
genes normally expressed in seed tissue for
expression in vegetative tissue to allow these
plants to withstand desiccation (Illing et al. 2005).
For example, genes encoding late embryogenesis
abundant (LEA) proteins (see below) that are
normally expressed in the seeds of desiccationsensitive plants during embryo maturation (Close
1996) have been isolated from drought-stressed
vegetative tissues of resurrection plants such as
Sporobolus stapfianus (Neale et al. 2000) and
Craterostigma plantagineum (Bartels 2005).
Recent phylogenetic evidence suggests that these
vascular plants gained the ability to withstand
desiccation of their vegetative tissues from a
mechanism present first in spores, and that this
evolution (or re-evolution) has occurred on at
least ten independent occasions within the
angiosperms (Oliver et al. 2005).
Rev Environ Sci Biotechnol (2006) 5:269–279
Plant strategies to survive desiccation
Several different strategies are utilised by resurrection plants to survive desiccation. Some plants
have evolved mechanisms that protect cellular
membranes and organelles during desiccation.
Other plants employ a constitutive repair system
which allows them to rapidly mobilize repair
mechanisms in the damaged cell upon rehydration. In general, both the protection and repair
mechanisms are used by resurrection plants, with
mosses generally utilizing a repair mechanism and
vascular plants using a protective mechanism
(Oliver 1996). Regardless of the strategy used by
a particular resurrection plant, three factors have
been identified as being crucial for surviving
desiccation: maintaining life in the dried state,
limiting the extent of damage to existing tissues so
that repair is unnecessary or manageable, and
mobilizing repair systems upon rehydration
(Bewley 1979).
Tolerance to near-complete desiccation of
vegetative organs is a widespread capability in
bryophytes (Rascio and La Rocca 2005), a group
that includes mosses and liverworts. The desiccation-tolerant moss Tortula ruralis is a cosmopolitan species that is found in many parts of the
world (Oliver 1996). T. ruralis, whose natural
habitat includes fallen trees and rocks, has
evolved tolerance mechanisms that allow the
plant to survive rapid drying rates. These mechanisms include a constitutive cellular protection
component, and a rehydration-inducible recovery
process designed to repair cellular damage experienced during rapid desiccation and subsequent
rehydration (Oliver et al. 2000). This strategy allows for frequent and rapid desiccation to be
tolerated; often desiccation can occur within 1 h
(Bohnert 2000). The main drawbacks of the constitutive repair strategy for desiccation survival
are low metabolic rates, possibly due to the cost
associated with constitutive expression of repair
genes, that (at least in vascular plants) result in
slow growth and a limit in size (Bohnert 2000).
The capacity of T. ruralis to repair damaged
membranes and organelles can be found in ribonucleoprotein particles which contain a complex
of proteins and mRNAs that can be rapidly
translated into repair enzymes upon imbibition
271
(Wood and Oliver 1999). Proteins whose synthesis is initiated or increased during rehydration
after a desiccation event are termed rehydrins
(Scott and Oliver 1994). A recent investigation of
a T. ruralis rehydration cDNA library has found
that many of the 10,368 expressed sequence tags
(ESTs) encode gene products that are involved in
protein synthesis, ion and metabolite transport,
oxidative stress metabolism, and membrane
biosynthesis and repair (Oliver et al. 2004).
Desiccation-tolerant angiosperms such as the
dicot C. plantagineum and the monocot S. stapfianus utilise a protection-based strategy for surviving desiccation. These plants can persist in the
air-dried state for months, and revive from the
desiccated state even after several years. Desiccation tolerance in C. plantagineum is induced in
vegetative tissues upon slow drying of the whole
plant, and plants do not survive if dehydration
occurs too rapidly (Bartels and Salamini 2001).
Similarly, the desiccation-tolerant C. wilmsii also
exhibits substantial ultrastructural damage upon
rapid drying (Cooper and Farrant 2002). This
suggests that desiccation-tolerant flowering plants
requires a slow drying time in order for mechanisms that protect membranes and organelles
during desiccation to be established.
Effects of hormones on desiccation tolerance
Abscisic acid (ABA) is known to be involved in
embryo maturation and germination, and in the
response of vegetative tissues to osmotic stress.
ABA has been proposed to be an essential
mediator in triggering plant responses to various
adverse environmental conditions such as
drought, high salinity, and cold. Endogenous
ABA levels have been reported to increase as a
result of water stress, and ABA induces stomatal
closure in guard cells by activating Ca2+, potassium (K+), and anion channels (Leung and Giraudat 1998). ABA has also been shown to play a
role in the desiccation tolerance of C. plantagineum vegetative tissues. Undifferentiated callus
tissue from C. plantagineum, although intrinsically not desiccation-tolerant, acquires tolerance
after it has been cultured on medium containing
ABA (Bartels and Salamini 2001). Treatment of
C. plantagineum callus with ABA also induces the
123
272
expression of a similar set of genes to that
activated in vegetative tissues upon drying. In S.
stapfianus, ABA level increases 6-fold during
strong drought stress, and reaches a maximum
during severe desiccation (20–10% relative water
content). However, studies with S. stapfianus
protoplasts showed that exogenously applied
ABA only promotes protoplasmic drought tolerance (PDT) to a degree that is very much less
than is required for desiccation tolerance (Ghasempour et al. 2001). Brassinosteroids, methyl
jasmonate, and ethylene promoted PDT in S.
stapfianus to a higher degree than ABA, but not
to a sufficient level to allow the plant to survive
desiccation. Of the hormones normally associated
with cell differentiation and growth, auxins had
no effect, while cytokinins had a deleterious effect
on PDT (Ghasempour et al. 2001).
Molecular approaches to the study of water
deficit
Apart from T. ruralis (Oliver et al. 2005), S. stapfianus (Neale et al. 2000) and C. plantagineum
(Bartels 2005), the molecular basis of desiccation
tolerance has been studied in relatively few resurrection plants. Recently, the mechanisms of
desiccation tolerance have been studied in several
other resurrection plants including the ferns
Polypodium virginianum (Reynolds and Bewley
1993) and P. polypodioides (Helseth and Fischer
2005), and desiccation-tolerant monocots such as
Xerophyta viscosa (Sherwin and Farrant 1998)
and X. umilis (Collett et al. 2004). Genes that are
expressed in response to drought stress are
classified into two main types: those that encode
for products with putative protective functions,
and those that encode for regulatory proteins
such as transcription factors.
Compatible solutes
Upon dehydration, many plants accumulate nontoxic or ‘compatible’ solutes such as proline,
mannitol, and glycine betaine (Chen and Murata
2002). The net result of compatible solute accumulation is an increase in cellular osmolarity
which, in turn, leads to an influx of water into, or
at least a reduced efflux from, cells (Hare et al.
123
Rev Environ Sci Biotechnol (2006) 5:269–279
1998). Compatible solutes have been proposed to
protect cells during drying through the stabilisation of cytoplasmic constituents, ion sequestration, and increased water retention. Transgenic
non-resurrection plants over-producing various
types of compatible solutes, either individually or
in combination, show improved tolerance to
drought as well as other osmotic stresses [for a
review, see Chen and Murata (2002)].
Sugar contents
Water deficit results in a reduction of photosynthesis and starch content in leaf tissues. There is a
rapid conversion of starch into sugars, the most
common of which are sucrose and trehalose
(Crowe et al. 1998). Conversion of starch, which
is usually stored in plastids, into sucrose is
attributed primarily to activation of sucrose
phosphate synthase by reversible protein phosphorylation upon perception of osmotic stress.
The activation of sucrose synthesis may also be
associated with a concurrent inhibition of starch
synthesis. Sucrose biosynthetic genes have been
shown to be induced by both desiccation and
ABA in the resurrection plant C. plantagineum
(Kleines et al. 1999).
Sucrose and trehalose have been proposed to
contribute towards the maintenance of turgor
during stress, and the prevention of protein
denaturation and membrane fusions in the cell
(Crowe et al. 1998). Both sugars are capable of
forming biological glasses (a process called vitrification) within the dried cell. Vitrification of the
cytoplasm may not be due to the effects of sugars
only, but probably results from the interaction of
sugars with other molecules, most likely proteins
(Hoekstra 2005). The formation of an intracellular glass phase is believed to be indispensable to
survival during desiccation, and cells of many
desiccation-tolerant plants and animals undergo
vitrification upon drying to protect organelles
from damage (Buitink and Leprince 2004).
Vitrification is thought to limit the production of
free radicals through the slowing down of chemical reaction rates and molecular diffusion in the
cytoplasm (Hoekstra 2005). It may also help to
preserve protein structure. Thus, vitrification
may be an important protective mechanism for
Rev Environ Sci Biotechnol (2006) 5:269–279
resurrection plants against oxidative damage
during desiccation.
In fully hydrated S. stapfianus leaves, glucose,
fructose, and galactose are present in large
amounts. During dehydration, sucrose increases
to high levels in air-dry leaves to become the
predominant sugar (Ghasempour et al. 1998).
Other sugars such as raffinose and trehalose are
also detected, and they may supplement the role
of sucrose as osmotic protectants during drying.
The sugar changes observed in S. stapfianus
leaves were quantitatively similar to those reported for other resurrection plants where the
common trend was the conversion of monosaccharides present in fresh leaves into sucrose in
dried leaves, and vice versa in rehydrated leaves
(Murelli et al. 1996). In C. plantagineum, the
unusual eight-carbon sugar, 2-octulose, is the
predominant sugar in fully-hydrated leaves.
During dehydration, 2-octulose is converted to
sucrose, with the reverse process being observed
during rehydration (Bartels and Salamini 2001).
Sucrose also accumulates in the roots of drying C.
plantagineum plants, suggesting that it may play a
protective role within the root systems of resurrection plants during desiccation (Norwood et al.
2003). The importance of sugars in desiccation
tolerance has been implicated in several studies.
Transgenic rice plants expressing two genes
encoding trehalose biosynthetic enzymes from
Escherichia coli showed high levels of tolerance
to drought stress, as well as salt and cold stress
(Garg et al. 2002).
LEA proteins
The ability of a plant to survive desiccation
appears to depend upon the accumulation of a
large set of proteins with putative protective
functions. These proteins include the late
embryogenesis abundant (LEA) proteins which,
as their name suggests, increase markedly in
abundance during the latter stages of embryo
development as the seed dries (Dure 1993). Some
LEA genes are also induced in vegetative tissues
in response to various abiotic stresses, including
drought, cold, and salt, as well as to ABA. LEA
transcripts are also abundant in T. ruralis during
rehydration, suggesting that LEAs may also play a
273
role in recovery from desiccation when water is
reintroduced into dried tissues (Oliver et al. 2004).
LEA proteins have been classified into eighteen different groups based on sequence homology (Dure 1993). A common feature of LEA
proteins is that they are extremely hydrophilic,
and are soluble at high (80C) temperatures. LEA
proteins do not possess any apparent catalytic
activity or structural domains, and most of them
lack cysteine and tryptophan residues (Close
1996). The predicted functions of LEA proteins
include the unwinding or repair of DNA, forming
cytoskeletal filaments to counteract the physical
stresses imposed by desiccation, and acting as
molecular chaperones (Wise and Tunnacliffe
2004). It has also been suggested that LEA proteins, possibly in combination with compatible
solutes, could replace water and thus maintain the
hydration shell of proteins and other molecules
during desiccation (Bartels 2005). In rehydrating
T. ruralis gametophytes, LEA proteins may
function in stabilizing membranes, or perhaps in
the transport of lipids for reconstitution of damaged membranes (Oliver et al. 2005). Although
many LEA genes have been isolated, a functional
role in desiccation tolerance has been demonstrated for only few. The expression of the barley
LEA gene, HVA1, increased drought tolerance in
transgenic wheat plants (Sivamani et al. 2000). In
rice, over-expression of HVA1 enhances tolerance to high-salt as well as drought stress (Rohila
et al. 2002). Recently, it has been shown that two
LEAs of distinct phylogenetic origins (one from
wheat and the other from a nematode) can prevent protein aggregation during desiccation, and
this protective effect is synergistically enhanced
when trehalose is added (Goyal et al. 2005).
Transcription factors
Many genes that are responsive to cold and
drought stress in the desiccation-sensitive model
plant Arabidopsis thaliana contain DRE/CRT
(dehydration-responsive element/C-repeat) elements within their 5¢ regulatory regions, and are
regulated by DREB/CBF (DRE-binding protein/
C-repeat binding factor) transcription factors
(Stockinger et al. 1997; Liu et al. 1998). The
DREB/CBF proteins belong to the AP2/EREBP
123
274
(ethylene responsive-element binding protein)
family of transcription factors which are important regulators of flower development and plant
responses to abiotic stresses (Riechmann and
Meyerowitz 1998; Shigyo et al. 2006). Homologues of the Arabidopsis DREB/CBF genes have
also been isolated from other non-resurrection
plants where they have been shown to function in
both the drought and cold response pathways
(Jaglo et al. 2001). However, only one such AP2/
EREBP transcription factor has been reported as
a regulator of the drought response pathway in a
resurrection plant (Le 2005).
Nearly all of the drought-induced transcription
factors isolated thus far from resurrection plants
have come from C. plantagineum and they belong
to either the Myb or the homeodomain-leucine
zipper (HD-Zip) family (Iturriaga et al. 1996;
Frank et al. 1998). Two Myb-related genes,
cpm10 and cpm7, show differential expression
and regulation in response to desiccation and
ABA in C. plantagineum (Iturriaga et al., 1996).
Cpm10 is expressed only in undifferentiated callus tissue, and is up-regulated by ABA, while
cpm7 is induced only by dehydration in the roots.
Transgenic Arabidopsis plants over-expressing
cpm10 displayed increased tolerance to drought
and salt stress (Villalobos et al. 2004). Interestingly, these plants also showed ABA hypersensitivity and glucose-insensitivity, suggesting that
cpm10 is involved in mediating ABA and glucose
signaling responses in Arabidopsis as well as the
response to drought stress. Two HD-Zip genes,
CPHB-1 and CPHB-2, are induced by dehydration in leaves and roots of C. plantagineum, but
show different responses to exogenously applied
ABA (Frank et al. 1998). ABA treatment induces
the transcription of CPHB-2, but not that of
CPHB-1. Five other HD-Zip genes have been
isolated from C. plantagineum, two of which were
induced by ABA in undifferentiated callus, while
the other three were not (Deng et al. 2002). This
suggests that these HD-Zip genes act in different
pathways of the dehydration response; some
mediated by ABA, while others are independent
of ABA (Bartels and Salamini 2001). Many
studies have shown that the expression of
drought-responsive genes in both resurrection
and non-resurrection plants is mediated by ABA-
123
Rev Environ Sci Biotechnol (2006) 5:269–279
independent as well as ABA-dependent signal
transduction pathways (Bartels 2005).
Morphological adaptations
Water deficit induces many morphological
changes in desiccation-tolerant vascular plants,
the most obvious of which is leaf folding. The
folding of leaves during drying is not unique to
resurrection plants and also occurs in desiccationsensitive plants. Leaves of the desiccation-tolerant
dicot C. wilmsii, which are fully expanded when
watered, progressively curl inward during drying
and become tightly folded so that only the abaxial
surfaces of the older leaves in the outer whorl are
exposed to the sun (Sherwin and Farrant 1998).
Leaf folding is thought to limit oxidative stress
damage from UV radiation, and is an important
morphological adaptation for surviving desiccation. Indeed, C. wilmsii plants do not survive
desiccation in sunlight if the leaves are mechanically prevented from folding (Farrant et al. 2003).
The leaf blades of the desiccation-tolerant
monocot X. humilis fold in half along the midrib
upon dehydration, leaving only the abaxial surfaced exposed to the light (Sherwin and Farrant
1998). In the desiccation-tolerant grass S. stapfianus, the leaf adaxial side, which is most exposed
to sun radiation, is very rich in epicuticular waxes,
whose main function is probably to reflect light,
and to limit irradiation and heating of leaf tissues
(Dalla Vecchia et al. 1998). During dehydration,
this cuticular wax covering, together with the
closure of stomata, helps to decrease the rate of
water loss. This may also be an important protective mechanism for the thylakoid membranes,
which are maintained in the chloroplasts and are
particularly sensitive to light damage in water
stress (Dalla Vecchia et al. 1998).
Cell wall changes during desiccation
When water availability to roots decreases, plants
tend to limit water loss from transpiration by
closing the stomata, and thereby reducing the
water flux through the plant, and by reducing leaf
growth, which results in a smaller transpiring leaf
area (Tardieu 2005). The reduction of growth
under water deficit is accomplished by a reduction
Rev Environ Sci Biotechnol (2006) 5:269–279
in cell division rate and an increase in cell wall
stiffening, which inhibits cell wall expansion
(Cosgrove 2000). This stiffening of the cell wall
poses a problem for drying cells. In order to tolerate desiccation, any cell with a large, water-filled vacuole must overcome or limit the
mechanical stress caused by its shrinking during
drying. The cell walls of some resurrection plants
have special adaptations that promote folding to
reduce the mechanical stress caused by desiccation. In C. wilmsii, a significant increase in xyloglucans and unesterified pectins is observed in the
cell wall during drying (Vicre et al. 1999). Dehydration also induces a considerable reduction of
glucose in the hemicellulosic fraction of C. wilmsii
cell walls (Vicre et al. 2004). These changes are
thought to enhance the tensile strength of the C.
wilmsii cell wall, allowing it to contract and to
fold without collapsing in the dried tissue. Thus,
cell wall flexibility is an important factor in tolerance to injury caused by desiccation. In C.
plantagineum, an increase in expansin activity
during desiccation is associated with a rise in cell
wall flexibility and folding (Jones and McQueenMason 2004). Similarly, desiccation-sensitive
maize plants adapted to low water potentials are
able to maintain root growth by increasing the
extensibility of their cell walls (Wu et al. 1996).
This increase in cell wall flexibility is correlated
with an increase in expansin activity and transcript accumulation (Wu et al. 2001). Expansins
were first identified as cell wall-loosening factors in acid-induced cell expansion (McQueenMason et al. 1992). They are thought to act by
disrupting the hydrogen bonds between cellulose
and hemicellulose polymers in the cell wall
(McQueen-Mason and Cosgrove 1995).
Lipid composition of cellular membranes
In the desiccation-tolerant mosses T. ruralis and
Selaginella lepidophylla, the shrinking of cells
caused by dehydration results in cells with highly
convoluted walls and membranes that are similar
in appearance to cells in dry seeds (Platt et al.
1994). The plasma membrane during desiccation
contains numerous tightly associated lipid droplets and shows a normal lipid bilayer organization.
In desiccation-tolerant vascular plants, dehydra-
275
tion generally causes a general decrease in total
lipids as well the unsaturation level of individual
phospholipids (Quartacci et al. 2002). However,
the opposite trend is observed in the resurrection
plant Boea hygroscopica where increased unsaturation of fatty acids was observed in all lipid
classes upon dehydration regardless of whether it
was slow or rapid (Navari-Izzo et al. 1995). It is
generally known that a high degree of poly-unsaturation in phospholipids results in greater
membrane fluidity. As discussed earlier, increased
cell wall and membrane fluidity may be an
important protective mechanism for the survival
of resurrection plants during desiccation. In S.
stapfianus during desiccation, phospholipid content increased in leaves dried attached to the
parent, but decreased in leaves that have been
dried detached (Quartacci et al. 1997). The fact
that attached dried leaves develop desiccation
tolerance, while detached dried leaves do not
(Neale et al. 2000), may in part be due to the level
of polyunsaturated lipids within the plasma
membrane. Upon rehydration in S. stapfianus,
leaves desiccated on the plant regained almost all
of the lipid content, whereas detached dried
leaves suffered a complete lipid degradation with
the loss of polyunsaturated fatty acids (Quartacci
et al. 1997).
Anti-oxidant systems
Recovery of a resurrection plant correlates with
its capacity to establish a number of anti-oxidant
protective mechanisms during dehydration, and
to maintain these systems upon rehydration
(Kranner et al. 2002). Desiccation results in the
production of reactive oxygen species (ROS) that
can damage membrane lipids and proteins. An
important protective mechanism in S. stapfianus is
the induction of free radical-scavenging enzymes
such as glutathione reductase, ascorbate peroxidase, and dehydroascorbate reductase to remove
the ROS (Sgherri et al. 1994a). Antioxidant
activity also increases in other resurrection plants
during desiccation (Sgherri et al. 1994b; Sherwin
and Farrant 1998). It has been shown that more
damage occurs during rehydration than during
desiccation because of intensified oxidative stress
during the recovery phase (Sgherri et al. 1994a).
123
276
In desiccation-sensitive S. stapfianus leaves dried
detached, however, ascorbate peroxidase activity
decreased during desiccation, resulting in reduced
antioxidant capacity (Sgherri et al. 1994a).
This may be another reason for the failure of
detached dried leaves of S. stapfianus to recover
from desiccation.
Anti-oxidant enzymes such as superoxide
dismutase, glutathione reductase, and ascorbate
peroxidase are induced in response to various
abiotic stresses in both desiccation-tolerant as well
as desiccation-sensitive organisms, and are considered as general ‘housekeeping’ protectants (Illing
et al. 2005). However, only in desiccation-tolerant
tissues can the activities of these enzymes remain
elevated during dehydration. This may be a consequence of mechanisms that protect and maintain
the anti-oxidant enzymes in their native states,
which results in increased activity and/or half-life
of the proteins, rather than a unique desiccation
tolerance mechanism (Illing et al. 2005).
Resurrection plants can persist in the desiccated state for several years. However, they cannot remain indefinitely in this anabiotic state
because, in part, oxidative damage increases with
duration of desiccation and results in the gradual
loss of viability. Failure of the anti-oxidant system
during long-term desiccation triggers programmed cell death, causing ageing and eventual
death of the plant (Illing et al. 2005). The acyl
chains of the membrane polar lipids, which may
contain unsaturated double bonds, are particularly sensitive to free radical attack. The leaves of
resurrection plants contain a relatively high
number of double bonds in their polar lipids,
which is a general characteristic of chloroplasts
(Hoekstra, 2005). Hoekstra (2005) has shown that
there is a negative correlation between the longevity of desiccation-tolerant tissues and the
number of double bonds in the polar lipids of
membranes, and that the lifespan of resurrection
plants during prolonged desiccation is generally
limited to several years maximally.
Photosynthesis and photosystem (PS)II
activity
Some homoiochlorophyllous resurrection plants
retain all of their chlorophyll during desicca-
123
Rev Environ Sci Biotechnol (2006) 5:269–279
tion, whereas others lose their chlorophyll and
are thus termed poikilochlorophyllous (Oliver
et al. 2000). It has been hypothesised that
certain desiccation-tolerant monocots evolved
the strategy of poikilochlorophylly to survive
and compete in marginal habitats where light
availability is variable (Oliver et al. 2000). In
contrast, the photosynthetic machinery in
desiccation-tolerant bryophytes appears to be
constitutively protected during drying such that
photosynthetic activity recovers quickly following rehydration (Oliver et al. 2005). The desiccation-tolerant grass S. stapfianus is partially
poikilochlorophyllous, and retains most of its
chlorophyll content during desiccation (Quartacci et al. 1997). After a cycle of dehydration
to air-dryness and rehydration to full turgor, S.
stapfianus regained all of its photosynthetic
capability within 24 h. Like all other plants, S.
stapfianus lowered its PSII during dehydration.
In general, water deficit causes a reduction in
the photosynthesis rate, resulting in the decline
in the photochemical efficiency of PSII and
electron transport rate in desiccation-tolerant as
well as desiccation-sensitive plants (Ekmekci
et al. 2005). The decline in PSII activity could
represent a protective mechanism from toxic
oxygen production in order to maintain membrane integrity and to ensure protoplast survival (Di Blasi et al. 1998). However, only
proteins within the thylakoid membranes of
resurrection plants remain stable during desiccation and rehydration, whereas those of desiccation-sensitive
plants
are
completely
destroyed after a short-term desiccation event
(Deng et al. 2003).
Conclusion
The ability of vegetative tissues to survive near
complete desiccation is shared by about 400
species of resurrection plants, and appears to have
evolved from reproductive tissues at least 10 times
independently during the evolution of vascular
plants. Genes involved in desiccation tolerance
may be constitutively expressed, as in mosses, or
induced during dehydration stress, as in most
resurrection angiosperms, a process that may or
Rev Environ Sci Biotechnol (2006) 5:269–279
may not involve abscisic acid as a signal. In order
to survive in dry environments, plants must limit
damage from desiccation and/or rehydration to a
minimum, maintain cellular integrity in the dried
state, and activate repair mechanisms upon rehydration. This is accomplished by the synthesis of
compatible solutes including sugars (sucrose in
most plants), and proteins with putative protective
functions such as LEAs. Sugars such as sucrose
and trehalose are particularly important in vitrification of the cell cytoplasm during desiccation,
which may decrease chemical reaction rates and
molecular diffusion, and limit oxidative damage.
Oxidative stress damage is further reduced by the
induction of anti-oxidant enzymes such as glutathione reductase, and the inhibition of photosynthesis, with some resurrection plants losing all of
their chlorophyll during desiccation altogether.
Dehydrating plant cells must also prevent or
minimize mechanical damage to the cell wall and
membranes due to the shrinking of the vacuole.
The increase in cell wall flexibility that promotes
wall folding may be due to the increase in activity
and transcript accumulation of cell wall-loosening
proteins such as expansins. Thus, the ability of
resurrection plants to survive in extremely dry
environments is a multigenic trait that relies on
systems of cellular protection during dehydration,
and recovery and repair upon rehydration (Rascio
and La Rocca 2005).
References
Alpert P (2000) The discovery, scope, and puzzle of desiccation tolerance in plants. Plant Ecol 151:5–17
Alpert P (2005) The limits and frontiers of desiccationtolerant life. Integr Comp Biol 45:685–695
Bartels D (2005) Desiccation tolerance studied in the
resurrection plant Craterostigma plantagineum.
Integrative and Comparative Biology 45:696–701
Bartels D, Salamini F (2001) Desiccation tolerance in the
resurrection plant Craterostigma plantagineum. A
contribution to the study of drought tolerance at the
molecular level. Plant Physiol 127:1346–1353
Bewley JD (1979) Physiological aspects of desiccation
tolerance. Ann Rev Plant Physiol 30:195–238
Bohnert H (2000) What makes desiccation tolerable?
Genome Biol 1:1010.1011–1010.1014
Buitink J, Leprince O (2004) Glass formation in plant
anhydrobiotes: survival in the dry state. Cryobiology
48:215–228
277
Chen THH, Murata N (2002) Enhancement of tolerance of
abiotic stress by metabolic engineering of betaines
and other compatible solutes. Curr Opin Plant Biol
5:250–257
Close TJ (1996) Dehydrins—emergence of a biochemical
role of a family of plant dehydration proteins. Physiol
Plantarum 97:795–803
Collett H, Shen A, Gardner M, Farrant JM, Denby KJ,
Illing N (2004) Towards transcript profiling of desiccation tolerance in Xerophyta humilis: construction of
a normalized 11 k X. humilis cDNA set and microarray expression analysis of 424 cDNAs in response to
dehydration. Physiol Plantarum 122:39–53
Cooper K, Farrant JM (2002) Recovery of the resurrection
plant Craterostigma wilmsii from desiccation: protection versus repair. J Exp Bot 53:1805–1813
Cosgrove DJ (2000) Expansive growth of plant cell walls.
Plant Physiol Biochem 38:109–124
Crowe JH, Carpenter JF, Crowe LM (1998) The role of
vitrification in anhydrobiosis. Annu Rev Physiol
60:73–103
Dalla Vecchia F, Elasmar T, Calamassi R, Rascio N,
Vazzana C (1998) Morphological and ultrastructural
aspects of dehydration and rehydration in leaves
of Sporobolus stapfianus. Plant Growth Regul
24:219–228
Deng X, Phillips J, Meijer AH, Salamini F, Bartels D
(2002) Characterization of five novel dehydrationresponsive homeodomain leucine zipper genes from
the resurrection plant Craterostigma plantagineum.
Plant Mol Biol 49:601–610
Deng X, Hu Z-A, Wang H-X, Wen X-G, Kuang T-Y
(2003) A comparison of photosynthetic apparatus of
the detached leaves of the resurrection plant Boea
hygrometrica with its non-tolerant relative Chirita
heterotrichia in response to dehydration and
rehydration. Plant Sci 165:851–861
Di Blasi S, Puliga S, Losi L, Vazzana C (1998) S. stapfianus
and E. curvula cv. Consol in vivo photosynthesis, PSII
activity and ABA content during dehydration. Plant
Growth Regul 25:97–104
Dure L (1993) Structural motifs of LEA proteins in higher
plants. In: Close TJ, Bray EA (eds) Responses of
plants to cellular dehydration during environmental
stress. American Society for Plant Physiology,
Rockville, pp 104–118
Ekmekci Y, Bohms A, Thomson JA, Mundree SG (2005)
Photochemical and antioxidant responses in the
leaves of Xerophyta viscosa Baker and Digitaria sanguinalis L. under water deficit. Z Naturforschung C-A
J Biosci 60:435–443
Farrant JM, van der Willigen C, Loffell DA, Bartsch
S, Whittaker A (2003) An investigation into the
role of light during desiccation of three angiosperm resurrection plants. Plant Cell Environ
26:1275–1286
Frank W, Phillips J, Salamini F, Bartels D (1998) Two
dehydration-inducible transcripts from the resurrection plant Craterostigma plantagineum encode interacting homeodomain-leucine zipper proteins. Plant J
15:413–421
123
278
Gaff DF (1971) Desiccation tolerant plants in southern
Africa. Science 174:1033–1034
Gaff DF (1997) Mechanisms of desiccation tolerance in
resurrection vascular plants. In: Basra AS, Basra
RK (eds) Mechanisms of environmental stress
resistance in plants. Harwood Academic Publishers,
Amsterdam, pp 43–58
Garg AK, Kim J-K, Owens TG, Ranwala AP, Choi YD,
Kochian LV, Wu RJ (2002) Trehalose accumulation
in rice plants confers high tolerance levels to different
abiotic stresses. PNAS 99:15898–15903
Ghasempour HR, Anderson EM, Gaff DF (2001) Effects
of growth substances on the protoplasmic drought
tolerance of leaf cells of the resurrection grass,
Sporobolus stapfianus. Aust J Plant Physiol 28:1115–
1120
Ghasempour HR, Gaff DF, Williams RPW, Gianello RD
(1998) Contents of sugars in leaves of drying desiccation tolerant flowering plants, particularly grasses.
Plant Growth Regul 24:185–191
Goyal K, Walton LJ, Tunnacliffe A (2005) LEA proteins
prevent protein aggregation due to water stress.
Biochem J 388:151–157
Hare PD, Cress WA, van Staden J (1998) Dissecting the
roles of osmolyte accumulation during stress. Plant
Cell Environ 21:535–553
Helseth LE, Fischer TM (2005) Physical mechanisms of
rehydration in Polypodium polypodioides, a resurrection plant. Phys Rev E 71(6):061903
Hoekstra FA (2005) Differential longevities in desiccated
anhydrobiotic plant systems. Integr Comp Biol
45:725–733
Illing N, Denby KJ, Collett H, Shen A, Farrant JM (2005)
The signature of seeds in resurrection plants: a
molecular and physiological comparison of desiccation tolerance in seeds and vegetative tissues. Integr
Comp Biol 45:771–787
Iturriaga G, Leyns L, Villegas A, Gharaibeh R, Salamini
F, Bartels D (1996) A family of novel myb-related
genes from the resurrection plant Craterostigma
plantagineum are specifically expressed in callus and
roots in response to ABA or desiccation. Plant Mol
Biol 32:707–716
Jaglo KR, Kleff S, Amundsen KL, Zhang X, Haake V,
Zhang JZ, Deits T, Thomashow MF (2001) Components of the ArabidopsisC-repeat/dehydrationresponsive element binding factor cold-response
pathway are conserved in Brassica napus and other
plant species. Plant Physiol 127:910–917
Jones L, McQueen-Mason S (2004) A role for expansins
in dehydration and rehydration of the resurrection
plant Craterostigma plantagineum. FEBS Lett
559:61–65
Kleines M, Elster RC, Rodrigo MJ, Blervacq AS, Salamini
F, Bartels D (1999) Isolation and expression analysis
of two stress-responsive sucrose-synthase genes from
the resurrection plant Craterostigma plantagineum
(Hochst.). Planta 209:13–24
Kranner I, Beckett RP, Wornik S, Zorn M, Pfeihofer HW
(2002) Revival of a resurrection plant correlates with
its antioxidant status. Plant J 31:13–24
123
Rev Environ Sci Biotechnol (2006) 5:269–279
Le T-N (2005) Genetics of desiccation tolerance in the
resurrection plant Sporobolus stapfianus. PhD thesis.
Monash University, Melbourne, Australia
Leung J, Giraudat J (1998) Abscisic acid signal transduction. Ann Rev Plant Physiol Plant Mol Biol
49:199–222
Levitt J (1980) Responses of plants to environmental
stresses, 2nd edn. Academic Press, New York
Liu Q, Kasuga M, Sakuma Y, Abe H, Miura S, Yamaguchi-Shinozaki K, Shinozaki K (1998) Two transcription factors, DREB1 and DREB2, with an EREBP/
AP2 DNA-binding domain separate two cellular signal transduction pathways in drought- and low-temperature-responsive gene expression, respectively, in
Arabidopsis. Plant Cell 10:1391–1406
McQueen-Mason SJ, Cosgrove DJ (1995) Expansin
mode of action on cell walls—analysis of wall
hydrolysis, stress-relaxation, and binding. Plant
Physiol 107:87–100
McQueen-Mason SJ, Durachko DM, Cosgrove DJ (1992)
Two endogenous proteins that induce cell wall
expansion in plants. Plant Cell 4:1425–1433
Murelli C, Adamo V, Finzi PV, Albini FM, Bochicchio A,
Picco AM (1996) Sugar biotransformations by fungi
on leaves of the resurrection plant Sporobolus
stapfianus. Phytochemistry 43:741–745
Navari-Izzo F, Ricci F, Vazzana C, Quartacci MF (1995)
Unusual composition of thylakoid membranes of the
resurrection plant Boea hygroscopica—changes in
lipids upon dehydration and rehydration. Physiol
Plantarum 94:135–142
Neale AD, Blomstedt CK, Bronson P, Le T-N, Guthridge
K, Evans J, Gaff DF, Hamill JD (2000) The isolation
of genes from the resurrection grass Sporobolus
stapfianus which are induced during severe drought
stress. Plant Cell Environ 23:265–277
Norwood M, Toldi O, Richter A, Scott P (2003) Investigation into the ability of roots of the poikilohydric
plant Craterostigma plantagineum to survive
dehydration stress. J Exp Bot 54:2313–2321
Oliver M, Dowd S, Zaragoza J, Mauget S, Payton P (2004)
The rehydration transcriptome of the desiccationtolerant bryophyte Tortula ruralis: transcript classification and analysis. BMC Genomics 5:89
Oliver MJ (1996) Desiccation tolerance in vegetative plant
cells. Physiol Plantarum 97:779–787
Oliver MJ, Tuba Z, Mishler BD (2000) The evolution of
vegetative desiccation tolerance in land plants. Plant
Ecol 151:85–100
Oliver MJ, Velten J, Mishler BD (2005) Desiccation tolerance in bryophytes: a reflection of the primitive
strategy for plant survival in dehydrating habitats?
Integr Comp Biol 45:788–799
Platt KA, Oliver MJ, Thomson WW (1994) Membranes
and organelles of dehydrated Selaginella and Tortula
retain their normal configuration and structural
integrity—freeze fracture evidence. Protoplasma
178:57–65
Porembski S, Barthlott W (2000) Granitic and gneissic
outcrops (inselbergs) as centers of diversity for desiccation-tolerant vascular plants. Plant Ecol 151:19–28
Rev Environ Sci Biotechnol (2006) 5:269–279
Quartacci MF, Forli M, Rascio N, Dallavecchia F,
Bochicchio A, Navari-Izzo F (1997) Desiccation-tolerant Sporobolus stapfianus: lipid composition and
cellular ultrastructure during dehydration and rehydration. J Exp Bot 48:1269–1279
Quartacci MF, Glisic O, Stevanovic B, Navari-Izzo F
(2002) Plasma membrane lipids in the resurrection
plant Ramonda serbica following dehydration and
rehydration. Journal of Experimental Botany
53:2159–2166
Rascio N, La Rocca N (2005) Resurrection plants: the
puzzle of surviving extreme vegetative desiccation.
Crit Rev Plant Sci 24:209–225
Reynolds T, Bewley J (1993) Characterisation of protein
synthetic changes in a desiccation tolerant fern
Polypodium virginianum: comparison of the effects of
drying, rehydration and abscisic acid. J Exp Bot
44:921–928
Riechmann JL, Meyerowitz EM (1998) The AP2/EREBP
family of plant transcription factors. Biol Chem
379:633–646
Rohila JS, Jain RK, Wu R (2002) Genetic improvement of
Basmati rice for salt and drought tolerance by regulated expression of a barley Hva1 cDNA. Plant Sci
163:525–532
Scott HB, Oliver MJ (1994) Accumulation and polysomal
recruitment of transcripts in response to desiccation
and rehydration of the moss Tortula ruralis. J Exp Bot
45:577–583
Sgherri CLM, Loggini B, Puliga S, Navari-Izzo F
(1994a) Antioxidant system in Sporobolus stapfianus—changes in response to desiccation and
rehydration. Phytochemistry 35:561–565
Sgherri CLM, Loggini B, Bochicchio A, Navari-Izzo F
(1994b) Antioxidant system in Boea hygroscopica:
changes in response to desiccation and rehydration.
Phytochemistry 37:377–381
Shen-Miller J, Mudgett MB, Schopf JW, Clarke S, Berger
R (1995) Exceptional seed longevity and robust
growth—ancient sacred lotus from China. Am J Bot
82:1367–1380
Sherwin HW, Farrant JM (1998) Protection mechanisms
against excess light in the resurrection plants Craterostigma wilmsii and Xerophyta viscosa. Plant
Growth Regul 24:203–210
279
Shigyo M, Hasebe M, Ito M (2006) Molecular evolution of
the AP2 subfamily. Gene 366:256–265
Sivamani E, Bahieldin A, Wraith JM, Al-Niemi T, Dyer
WE, Ho DT-H, Qu R (2000) Improved biomass
productivity and water use efficiency under water
deficit conditions in transgenic wheat constitutively
expressing the barley HVA1 gene. Plant Sci 155:1–9
Stockinger EJ, Gilmour SJ, Thomashow MF (1997) Arabidopsis thaliana CBF1 encodes an AP2 domaincontaining transcriptional activator that binds to the
C-repeat/DRE, a cis-acting DNA regulatory element
that stimulates transcription in response to low temperature and water deficit. PNAS 94:1035–1040
Tardieu F (2005) Plant tolerance to water deficit: physical
limits and possibilities for progress. C R Geosci
337:57–67
Vicre M, Lerouxel O, Farrant J, Lerouge P, Driouich
A (2004) Composition and desiccation-induced
alterations of the cell wall in the resurrection
plant Craterostigma wilmsii. Physiol Plantarum
120:229–239
Vicre M, Sherwin HW, Driouich A, Jaffer MA, Farrant
JM (1999) Cell wall characteristics and structure of
hydrated and dry leaves of the resurrection plant
Craterostigma wilmsii, a microscopical study. J Plant
Physiol 155:719–726
Villalobos MA, Bartels D, Iturriaga G (2004) Stress
tolerance and glucose insensitive phenotypes in
Arabidopsis overexpressing the CpMYB10 transcription factor gene. Plant Physiol 135:309–324
Wise MJ, Tunnacliffe A (2004) POPP the question: what
do LEA proteins do? Trends Plant Sci 9:13–17
Wood AJ, Oliver MJ (1999) Translational control in plant
stress: the formation of messenger ribonucleoprotein
particles (mRNPs) in response to desiccation of
Tortula ruralis gametophytes. Plant J 18:359–370
Wu YJ, Sharp RE, Durachko DM, Cosgrove DJ (1996)
Growth maintenance of the maize primary root at
low water potentials involves increases in cell-wall
extension properties, expansin activity, and wall
susceptibility to expansins. Plant Physiol 111:765–772
Wu YJ, Thorne ET, Sharp RE, Cosgrove DJ (2001)
Modification of expansin transcript levels in the maize
primary root at low water potentials. Plant Physiol
126:1471–1479
123