Crassulacean Acid Metabolism. A Plastic Photosynthetic Adaptation to Arid Environments1
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Update on Crassulacean Acid Metabolism
Crassulacean Acid Metabolism. A Plastic Photosynthetic
Adaptation to Arid Environments1
John C. Cushman*
Department of Biochemistry, University of Nevada, Reno, Nevada 89557–0014
Crassulacean acid metabolism (CAM) is an impor- plants that inhabit extremely arid environments (e.g.
Downloaded from https://academic.oup.com/plphys/article/127/4/1439/6103653 by guest on 05 August 2021
tant elaboration of photosynthetic carbon fixation deserts), semi-arid regions with seasonal water avail-
that allows chloroplast-containing cells to fix CO2 ability (e.g. Mediterranean climates), or habitats with
initially at night using phosphoenolpyruvate carbox- intermittent water supply (e.g. tropical epiphytic
ylase (PEPC) in the cytosol. This leads to the forma- habitats). Most notable among these are commer-
tion of C4 organic acids (usually malate), which are cially or horticulturally important plants such as
stored in the vacuole. Subsequent daytime decarbox- pineapple (Ananas comosus), agave (Agave subsp.),
ylation of these organic acids behind closed stomata cacti (Cactaceae), and orchids (Orchidaceae). CAM is
creates an internal CO2 source that is reassimilated also correlated with various anatomical or morpho-
by Rubisco in the chloroplast. The refixation of this logical features that minimize water loss, including
internal CO2 generates carbohydrates via the conven- thick cuticles, low surface-to-volume ratios, large
tional photosynthetic carbon reduction cycle. Thus, cells and vacuoles with enhanced water storage ca-
CAM involves a temporal separation of carbon fixa- pacity (i.e. succulence), and reduced stomatal size
tion modes in contrast to the spatial separation found and/or frequency.
in C4 plants. The first recognition of the nocturnal The selective advantage of high WUE likely ac-
acidification process can be traced to the Romans, counts for the extensive diversification and specia-
who noted that certain succulent plants taste more tion among CAM plants principally in water-limited
bitter in the morning than in the evening (Rowley, environments. Intensive ecophysiological studies
1978). However, formal descriptions of the ability of over the last 20 years have documented that CAM is
succulent plants to conduct nocturnal CO2 fixation or present in approximately 7% of vascular plant spe-
to acidify photosynthetic tissues at night and deacid- cies, a much larger percentage than the percentage of
ify them during the day did not appear until the early C4 species (Winter and Smith, 1996a). The wide-
19th century (de Saussure, 1804; Heyne, 1815). The spread distribution of CAM among 33 taxonomically
term CAM was coined to give credit to Heyne’s diverse families (Smith and Winter, 1996) suggests
observations that were made using Bryophyllum caly- that CAM most likely evolved independently on nu-
cinum, a succulent member of the Crassulaceae. merous occasions in different families and even
Since these early descriptions, a detailed account of within individual families (Griffiths, 1989; Ehleringer
the sequence of biochemical reactions of the CAM and Monson, 1993; Pilon-Smits et al., 1996). More
recent phylogenetic reconstructions using PEPC se-
cycle (Ranson and Thomas, 1960), the complexity of
quence information have provided more convincing
the biochemical variations in the pathway among
support for the polyphyletic origins of CAM (Gehrig
different CAM species, and its regulation by the en-
et al., 1998b, 2001). It is curious that CAM is also
vironment have been achieved (Osmond, 1978; Ting,
found in aquatic vascular plants where it presumably
1985). Initial nocturnal CO2 fixation by PEPC occurs
enhances inorganic carbon acquisition in certain
when stomata are open and transpirational water
aquatic environments where CO2 availability can be-
losses are low. CO2 release during the day promotes come rate limiting for photosynthesis (Keeley, 1996,
stomatal closure and concentrates CO2 around 1998). Thus, the daytime limitation of CO2 availabil-
Rubisco, suppressing its oxygenase activity, thereby ity, brought about by water-conserving stomatal clo-
minimizing photorespiration. The net effect of this sure in arid terrestrial habitats or by competition
CO2-concentrating strategy is that CAM plants ex- from other species and the high diffusional resis-
hibit water use efficiency (WUE) rates severalfold tances limiting access to CO2 in aquatic habitats,
higher than C3 and C4 plants under comparable con- appears to be the common factor responsible for the
ditions (Drennan and Nobel, 2000). Thus, CAM is evolution of CAM.
typically, although not exclusively, associated with
1
This work was supported by the National Science Foundation A REMARKABLE PLASTICITY
(Integrative Plant Biology, Plant Genome Programs) and by the
Nevada Agricultural Experiment Station. One of most striking themes to emerge in recent
* E-mail jcushman@unr.edu; fax 775–784 –1650. years is the extent to which the phylogenetic and
www.plantphysiol.org/cgi/doi/10.1104/pp.010818. ecological diversity of CAM plants is also reflected in
Plant Physiology, December 2001, Vol. 127, pp. 1439–1448, www.plantphysiol.org © 2001 American Society of Plant Biologists 1439Cushman
a remarkable plasticity of the basic metabolic scheme phases (Table I). “Nearly-C3 ” or “CAM cycling”
described above. Genotypic, ontogenetic, and envi- species display daytime net CO2 uptake with refix-
ronmental factors such as light intensity, relative hu- ation of respiratory CO2 at night accompanied by
midity, and water availability combine to govern the only small diel C4 acid fluctuations. In plants grow-
extent to which the biochemical and physiological ing in thin soils or rock outcrops, this nocturnal
attributes of CAM are expressed (Cushman and Bor- recapture of respiratory CO2 is thought to help main-
land, 2001). The photosynthetic plasticity of CAM tain a positive carbon balance during frequent epi-
occurs within a continuum of diel gas exchange pat- sodes of drought (Martin, 1996). However, the poten-
terns that fall into four phases as defined by Osmond tial conservation of water resulting from the
(1978). The nocturnal uptake of atmospheric and re- induction of CAM cycling varies widely (5%–70%) in
spiratory CO2 via PEPC to form C4 acids (phase I) various species (Borland, 1996; Martin, 1996). In C3-
Downloaded from https://academic.oup.com/plphys/article/127/4/1439/6103653 by guest on 05 August 2021
and daytime organic acid decarboxylation to gener- CAM intermediate species, such improvements in
ate elevated Ci and stomatal closure (phase III) are WUE are not always associated with CAM induction
interspersed with transitional periods of net CO2 up- (Eller and Ferrari, 1997; Cushman and Borland, 2001).
take at the start (phase II) and end of the day (phase In “obligate” or “constitutive” CAM species, net CO2
IV) when both PEPC- and Rubisco-mediated carbox- uptake occurs almost exclusively at night (phase I),
ylation can contribute to CO2 assimilation. The pro- with some net CO2 assimilation occurring during
portion of CO2 taken up via PEPC at night or directly phases II and IV, even under well-watered condi-
during the day by Rubisco (net CO2 assimilation) is tions, accompanied by large diel C4 acid fluctuations.
dictated by the integration of stomatal behavior, fluc- Under severe drought conditions, many CAM spe-
tuations in organic acid and storage carbohydrate cies will undergo “CAM-idling” wherein stomata re-
accumulation, and the abundance and activity of pri- main closed day and night, preventing net CO2 up-
mary (PEPC) and secondary (Rubisco) carboxylating take, yet the plants will continue to conduct diel
and decarboxylating enzymes (e.g. malic enzyme or fluctuations in organic acids. Other modes of CAM
PEP carboxykinase), as well as gluconeogenic/glyco- such as latent CAM, indicated by organic acid con-
lytic enzymes responsible for the synthesis and centrations elevated above those normally present in
breakdown of C3 carbon skeletons. C3 plants but without diel fluctuation, may represent
Depending on developmental and/or environmen- a nascent C3-to-CAM progression in some species
tal influences, a variety of CO2 assimilation, acid flux, (Schuber and Kluge, 1981). A hypothetical variation
and stomatal behavior characteristics may be ob- of CAM called “rapid-cycling CAM” has also been
served outside the conventional pattern of the four proposed in which the CO2 acquisition and reduction
Table I. Plasticity of CAM modes in relationship to environmental and developmental influences
Respiratory Developmental/
Net CO2 Stomatal Behavior
CAM Variation CO2 C4 Acid Flux Environmental Proposed Functions
Uptake (Open)
Refixation? Impact
C3 Day No Day –a –/– –
CAM cycling Day Yes Day ⫹ ⫹/⫹ Maintain positive carbon
balance; improved
WUE?b; reduced photo-
respiration?
C3-CAM (faculta- Day/night Yes Day/night ⫹⫹ ⫹/⫹⫹ Maintain positive carbon
tive CAM) balance; improved
WUE?; reduced photore-
spiration
CAM (obligate Phases I, II, and IV Yes Day/night ⫹⫹⫹ ⫹/⫹⫹⫹ Improved WUE; reduced
CAM) photorespiration
Phase II CAM Phases I and II Yes Morning/night ⫹⫹⫹⫹ ⫹/⫹⫹⫹ Improved WUE; reduced
photorespiration
Phase I CAM Phase I only Yes Night only ⫹⫹⫹ ⫹/⫹⫹⫹ Improved WUE; reduced
photorespiration
CAM idling None Yes Always closed ⫹ ⫹/⫹⫹⫹⫹⫹ Protection of photosyn-
thetic apparatus from
photoinibition; maintain
a positive carbon bal-
ance
Latent CAM Day Yes Day – (elevated) ?/? C3 to CAM progression?
Rapid-cycling CAM All ? ? – (rapid) ?/? ?
(theoretical)
a b
Dashes indicate no substantial occurrence or effect. Question marks indicate that no information is available.
1440 Plant Physiol. Vol. 127, 2001Crassulacean Acid Metabolism
phases of CAM may occur over time periods shorter or abscisic acid treatment is controlled primarily by
than the normal diel cycle (Cockburn, 1998). transcriptional activation (Cushman et al., 1989,
The best examples of CAM plasticity are the C3- 2000b) initiated through a signaling cascade with
CAM intermediate species found predominantly apparent requirements for calcium and calcium-
among the Aizoaceae, Crassulaceae, Portulaceae, and dependent protein kinase activities (Taybi and Cush-
Vitaceae (Smith and Winter, 1996). These facultative man, 1999; Golldack and Dietz, 2001). In general,
or inducible CAM species use the C3 pathway to transcript and protein accumulation patterns are well
maximize growth when water is abundant, but then correlated; however, discrepancies between tran-
they undergo a gradual C3-to-CAM transition often script and protein abundance have suggested that
coincident with seasonal moisture availability (Win- changes in mRNA stability and utilization or trans-
ter et al., 1978). The C3-to-CAM transition reduces lational efficiency are also likely to govern gene ex-
Downloaded from https://academic.oup.com/plphys/article/127/4/1439/6103653 by guest on 05 August 2021
water loss and maintains photosynthetic integrity pression changes during the C3-to-CAM transition
under water-limited conditions that ultimately trans- (Cushman et al., 1990; DeRocher and Bohnert, 1993).
lates into reproductive success (Winter and Ziegler, Detailed analysis of the PEPC gene families from
1992). Among facultative CAM species, the common facultative and obligate CAM species including pine-
ice plant, Mesembryanthemum crystallinum, has been apple (Ananas comosus), K. blossfeldiana, K. daigremon-
most intensively studied (Adams et al., 1998; Bohnert tiana, common ice plant, and Vanilla planifolia has in-
and Cushman, 2001). This model species undergoes a dicated that a single member of a four- to six-member
gradual, largely irreversible, and partially develop- PEPC gene family is typically recruited to fulfill the
mentally regulated transition into CAM following primary carboxylation and carbon flux requirements
water stress (Cushman et al., 1990; Herppich et al., of CAM, as demonstrated by its enhanced expression
1992). In contrast, other inducible CAM species (e.g. in CAM-performing leaves (Cushman et al., 1989; Ge-
Clusiaceae and Bromeliaceae) display more rapid hrig et al., 1995, 1998a). Remaining isoforms, which
and reversible shifts between C3 photosynthesis and presumably fulfill anapleurotic “housekeeping” or
CAM in response to changes in water deficit, regard- tissue-specific functional roles, generally show lower
less of leaf or plant ontogeny (Schmitt et al., 1988; transcript or protein abundance and remain unaf-
Zotz and Winter, 1993; Lüttge, 1996; Borland et al., fected in their expression following CAM induction.
1998). The magnitude of CAM induction in faculta- This “gene recruitment” paradigm likely pertains to
tive CAM plants tends not only to be influenced by other gene families as well. Enhanced expression of
water deficit, but also by associated environmental
enzymes for C4 acid metabolism is accompanied by
conditions such as temperature, light intensity, and
corresponding increases in carbohydrate-forming and
humidity (Lüttge, 2000). For example, it is well es-
-degrading enzymes and transcripts (Holtum and
tablished that high light intensity or light quality can
Winter, 1982; Paul et al., 1993; Häusler et al., 2000).
enhance CAM induction in the ice plant in the pres-
Elevated organellar PEP (Kore-eda et al., 1996) and
ence or absence of salinity stress (McElwain et al.,
triose and hexose phosphate transport activities (Neu-
1992; Cockburn et al., 1996; Miszalski et al., 2001).
haus and Schulte, 1996; Kore-eda and Kanai, 1997)
associated with CAM induction in common ice plant
are matched by light-enhanced increases in transcript
MOLECULAR GENETICS OF CAM abundance and diurnal gene expression patterns of a
Since the first molecular characterization of the PEP phosphate translocator and a Glc-6-P phosphate
common ice plant Ppc1 gene encoding a CAM- translocator (Häusler et al., 2000). However, the ex-
specific isoform of PEPC more than a decade ago pression of a chloroplast Glc transporter and a triose
(Cushman et al., 1989), a large number of enzymes, phosphate transporter remain largely unchanged
transporters, and regulatory proteins required for (Häusler et al., 2000; S. Kore-eda and J.C. Cushman,
CAM have been identified and characterized (for unpublished data). Tonoplast H⫹-translocating
review, see Cushman and Bohnert, 1999, 2001; Cush- ATPase transport activity and expression of corre-
man and Borland, 2001). Most studies have been sponding tonoplast H⫹-translocating ATPase subunit
restricted to inducible C3-CAM models (e.g. common genes for energizing vacuolar malate storage is en-
ice plant and Kalanchoë sp.) because the differential hanced during the C3-CAM transition in common ice
expression of genes induced in response to water plant (Rockel et al., 1998a, 1998b; Barkla et al., 1999;
deficit serves as a convenient and reliable indicator of Golldack and Dietz, 2001). Molecular characteriza-
their potential functional role(s) in CAM. Greater tion of the vacuolar malate transporters, carriers, and
investments have been made in establishing molecu- channels for malate influx and efflux has remained a
lar genetic resources for common ice plant than other challenge (Lüttge et al., 2000). Recent measurements
CAM models because this species is also a halophyte of vacuolar malate transport activities demonstrate
and has been extensively investigated to understand an approximate 3-fold increase following CAM in-
salinity stress tolerance mechanisms (Bohnert and duction in common ice plant (Lüttge et al., 2000). A
Cushman, 2001; Bohnert et al., 2001). CAM induction strategy to analyze differences in polypeptide expres-
in response to salinity, water deficit, osmotic stress, sion patterns in C3- versus CAM-performing leaves
Plant Physiol. Vol. 127, 2001 1441Cushman
of common ice plant is being used to identify candi- land et al., 1999; Nimmo, 2000). In addition, feeding of
date vacuolar malate transporters. Antisera raised detached K. fedtschenkoi and common ice plant leaves
against affinity chromatography-purified tonoplast with various pharmacological reagents implicates the
vesicle fractions from K. daigremontiana enriched for involvement of a phosphoinositide-dependent phos-
malate transport activity has been used to identify pholipase C, inositol 1,4,5 P-gated tonoplast calcium
32- and 33-kD common ice plant polypeptides that channels, a putative Ca2⫹-dependent/calmodulin
are induced or enhanced in the CAM state (Steiger et protein kinase, and RNA and protein synthesis as
al., 1997; Lüttge et al., 2000). These low abundance possible components in the signaling cascade that reg-
polypeptides could be candidates for the vacuolar ulates PPcK activity on a circadian basis (Hartwell et
malate transporter. Amino acid sequence informa- al., 1999; Bakrim et al., 2001; Nimmo et al., 2001b).
tion from these polypeptides may facilitate the isola- However, these studies fail to address the influence of
Downloaded from https://academic.oup.com/plphys/article/127/4/1439/6103653 by guest on 05 August 2021
tion of the corresponding genes. such inhibitors on the functioning of the underlying
circadian oscillator, and so, observed changes in PEPC
activity may not reflect alterations in the PEPC kinase-
CIRCADIAN CONTROL OF CAM signaling cascade per se. One great challenge to un-
derstanding circadian regulation of CAM will be to
The circadian rhythm of CO2 fixation, primarily dissect the mechanisms responsible for controlling the
studied in K. fedtschenkoi, is one of the earliest and circadian oscillations in malate uptake and release
best documented examples of circadian rhythms in across the tonoplast membrane. In particular, it will be
higher eukaryotes (Wilkins, 1992). Diel oscillations in important to understand how tonoplast malate trans-
the activity of PEPC, controlled in part by circadian port is controlled by an underlying nuclear-controlled
changes in its phosphorylation state, play a key role circadian clock. Rapid molecular identification of
in directing carbon flux through the CAM pathway malate transport components in the tonoplast and cir-
by changing the enzyme’s sensitivity to allosteric cadian clock components from CAM species will be
inhibitors such as malate (Nimmo et al., 1987; essential for this effort.
Nimmo, 1998). PEPC phosphorylation state is con-
trolled largely by changes in the activity of PEPC
kinase (PPcK; Carter et al., 1991). In common ice A GENETIC MODEL FOR CAM?
plant, PPcK activity is induced concomitantly with a
CAM-specific isoform of PEPC (Li and Chollet, 1994). To date, ecophysiological investigations have sur-
Recent cloning of the gene for PPcK first in K. veyed a wide variety of CAM species to determine
fedtschenkoi (Hartwell et al., 1999) and then in com- which ones actually perform CAM. Alternatively,
mon ice plant (Taybi et al., 2000) demonstrated di- studies have focused on comparative analysis of spe-
rectly that this kinase is itself regulated at the level of cific aspects of CAM such as the degree of CAM
transcript abundance by a circadian oscillator. A dis- induction by water limitation (Cushman and Bor-
sociable protein inhibitor of PPcK activity has also land, 2001), intercellular localization of carboxylation
been described from K. fedtschenkoi that may function and decarboxylation processes (Borland et al., 1998),
to suppress basal kinase activity during the light or the patterns of carbohydrate partitioning within a
period and early stages of the dark period when particular family (Christopher and Holtum, 1996,
carbon flux through PEPC is not needed (Nimmo et 1998). However, unlike C3 and C4 plants, which have
al., 2001a). In contrast to C4 plants, elevations in the well-developed genetic models Arabidopsis and
cytosolic pH appear to have little (Bakrim et al., 2001) maize (Zea mays), respectively, there has been, until
or no influence (Paterson and Nimmo, 2000) on PPcK recently, no investment in the development of a ge-
activity in common ice plant or K. fedtschenkoi, re- netic model for CAM. This deficiency has hindered
spectively. However, circadian control of PPcK tran- our understanding of many of the molecular mecha-
script abundance may be merely a secondary re- nisms that regulate CAM. In the past, CAM models
sponse to other factors such as the cytosolic malate were selected for their physiological characteristics.
concentration, which has been hypothesized to reg- For example, certain obligate CAM species such as K.
ulate the transcript abundance and activity of PPcK daigremontiana are often favored for gas exchange
(Borland et al., 1999; Nimmo, 2000). Cytosolic malate and biochemical studies due to their reproducible
concentrations are likely to be controlled by transport behavior. Other CAM models such as common ice
of malate across the tonoplast, a view that is well plant can show hyperplastic stress responsiveness to
supported by temperature effects on tonoplast func- slight changes in growth conditions, which can be a
tion and modeling studies (Rascher et al., 1998; problem for reproducible physiological studies.
Lüttge, 2000). Thus, response to environmental fac- Kalanchoë species, however, lack potential for devel-
tors that alter organic acid content or malate parti- opment as a genetic system as well as any significant
tioning between the vacuole and cytosol may be able molecular genetic resources.
to override circadian rhythms of PPcK activity, pro- A comparison of the attributes of well-studied or
viding a possible mechanism for the rapid alterations commercially important CAM models from diverse
in PEPC activity observed in some CAM species (Bor- families indicates that common ice plant has many
1442 Plant Physiol. Vol. 127, 2001Crassulacean Acid Metabolism
desirable features that make it an attractive genetic sativa; Li et al., 2001). Facile screening procedures have
model (Table II). This fast-growing annual produces been developed for the isolation of CAM-defective
large quantities of small seeds (typically 10,000–15,000 mutants (Cushman et al., 2000b). Identification of
plant⫺1) under standard greenhouse or growth cham- CAM-defective mutants is based on a simple pH assay
ber conditions in 1-L pots. The plant is self-fertile, yet that detects a failure in nocturnal C4 acid accumula-
outcrossing is possible. In contrast, the perennial or tion. Mutant collections are not currently available in
semi-perennial pineapple, Kalanchoë, and Clusia spe- other CAM models. A useful by-product of such mu-
cies grow more slowly and are poor seed producers. tant screens is the identification of mutants with mor-
Although the common ice plant grows more slowly phological (e.g. dwarfism and absence of epidermal
than models such as Arabidopsis, compared with bladder cells) or physiological defects (e.g. salt sensi-
other CAM models, the common ice plant life cycle is tivity; J.C. Cushman, unpublished data).
Downloaded from https://academic.oup.com/plphys/article/127/4/1439/6103653 by guest on 05 August 2021
quite rapid. Furthermore, it is possible to accelerate Another desirable feature of the ideal CAM model
the normal life cycle of common ice plant from 4 to 5 is the availability of an efficient transformation sys-
mo under natural conditions (Winter et al., 1978) to tem, preferably one that employs a non-tissue
approximately 7 weeks under growth chamber condi-
culture-based methodology such as vacuum infiltra-
tions under continuous light or extended photoperi-
tion or floral dipping in Agrobacterium tumefaciens
ods and limited rooting volumes (Cheng and Ed-
suspensions (Bechtold et al., 1993; Clough and Bent,
wards, 1991). Acceleration of the life cycle is
conveniently accompanied by a miniaturization of the 1998). A transformation system with adequate effi-
plant. This is an important consideration when con- ciency would allow systematic functional genomic
ducting genetic screening because growth chamber or investigations to be performed involving reverse ge-
greenhouse space is often a limiting factor. Alterna- netic screens for T-DNA insertion/activation-tagged
tively, genetic screens could be conducted in a recently gene knockouts, suppression or overexpression stud-
identified dwarf mutant background that displays ies, and ultimately targeted gene replacement of reg-
CAM (see below). Finally, mutant collections have ulatory or structural genes of interest with key roles
been established in common ice plant from fast in CAM. Of the possible candidate model CAM spe-
neutron- or gamma-irradiated (Cushman et al., 2000b) cies, several are amenable to genetic manipulation
or ethylmethane sulfonate-treated seeds (Adams et al., using an A. tumefaciens-mediated transformation sys-
1998). Expansion of existing fast neutron collections tem (Truesdale et al., 1999). However, given the ice
would create a useful resource for a fast neutron plant’s susceptibility to A. tumefaciens transformation
mutagenesis-based reverse genetic screening system in tissue culture (Andolfatto et al., 1994; Ishimaru,
in the common ice plant, similar to related resources 1999) and the availability of a high efficiency regen-
recently developed in Arabidopsis and rice (Oryza eration system (Cushman et al., 2000b), an experi-
Table II. Comparison of desirable attributes of well-studied CAM models
Mother-of-Thousands
Common Ice Plant (K. daigremontiana, K. Balsam Apple (Clusia minor, Pineapple
Attribute
(M. crystallinum) blossfeldiana, K. C. major, C. rosea) (A. comosus)
fedtschenchoi)
Family Aizoaceae (dicot) Crassulaceae (dicot) Clusiaceae (dicot) Bromeliaceae (monocot)
Growth habit Annual Perennial Perennial Semiperennial
Commercial/horticultural Ornamental, ground Ornamental ($$) Ornamental (⫺) Edible crop ($$$$)
importance (relative value) cover, and fire break ($)
Mode of CAM C3-CAM and stress inducible Obligate and C3-CAM, rapid and Obligate and
developmentally reversible developmentally
regulated regulated
Propagation mode Seed Clonal Clonal Clonal
Seed production 10,000 –15,000 plant⫺1a Poor to none None Poor to none
Growth rate (to adulthood) Rapid (6 weeks) Intermediate Intermediate Slow (18 –24 mo)
(2–3 mo) (2–3 mo)
Mutant collections? Ethylmethane sulfonate, No No No
fast neutron, and gamma
irradiated
Transgenic plants? No (callus, yes) Yes No Yes
Transformable? Yes Yes ?b Yes
Genome size (Mb) 390 790 –1,500 ? 526
No. of expressed sequence ⬎15,000 0 0 0
tags (ESTs) available
Microarray availability? Yes No No No
a b
Soil-grown plants under standard laboratory conditions in 1-L pots. Question marks indicate that no information is available.
Plant Physiol. Vol. 127, 2001 1443Cushman
mental platform for future transgenic analysis in Abundant molecular genetic resources will facili-
common ice plant appears highly feasible. tate integrative approaches to phenomena ranging
The other major limitation for CAM research has from gene expression to gas exchange characteristics.
been the lack a genetic model with a wealth of avail- Such integration is required to identify and distin-
able molecular genetic information, such as the com- guish the functional contribution and regulation of
plete nucleotide sequence of the genome or at the specific gene products, especially among circadianly
very least, sizeable collections of ESTs. The common regulated genes. Large EST collections and associ-
ice plant genome is approximately 390 Mb, as esti- ated databases provide the foundation of nucleotide
mated by flow cytometry (DeRocher et al., 1990) in sequence information on which to build anticipated
nine chromosomes (2n ⫽ 18; Adams et al., 1998) or genome sequencing efforts (see below), as well as
approximately 2.5 times larger than the Arabidopsis materials with which to print cDNA-based microar-
Downloaded from https://academic.oup.com/plphys/article/127/4/1439/6103653 by guest on 05 August 2021
genome (approximately 145 Mb) and slightly smaller rays or to synthesize oligonucleotide-based Gene-
than the rice genome (approximately 420 Mb). The Chips for large-scale gene expression-profiling ex-
common ice plant genome is also smaller than all periments. Extensive or comprehensive expression
data can often provide important clues about the
other CAM models for which such data are currently
function of specific isogenes in CAM or implicate
available. For example, the pineapple genome (2n ⫽
roles in CAM for previously uncharacterized genes.
25) is somewhat larger, with a DNA content approx-
Analysis of the existing common ice plant EST data-
imately 3.7 times the size of the Arabidopsis genome base compiled from salinity-stressed, CAM-induced
(Arumuganathan and Earle, 1991; Williams and plants indicates the presence of large numbers of
Fleisch, 1993), whereas K. fedtschenkoi and K. blossfel- genes, perhaps up to several thousand, that are not
diana are two (approximately 790 Mb) and four times represented in other plant databases (Bohnert and
(approximately 1,500 Mb) the size, respectively, of Cushman, 2001). Such unknown or novel ESTs in the
the common ice plant genome (DeRocher et al., 1990). common ice plant database may arise, in part, from
Thus, the small size of the common ice plant genome the evolutionary distance between common ice plant
makes it a most attractive target for genome and the other plant models. We also expect that gene
sequencing. family expansion has occurred in the common ice
In lieu of genomic sequence information, the avail- plant, a native of the Namib Desert, to meet the
ability of information-rich sequence data from EST additional requirements of CAM for long-term sur-
collections would add strong incentives for investi- vival and reproductive success in arid environments.
gators to invest in a particular CAM model. Although Evidence for this can be seen in, for example, the
cDNA libraries are available for K. daigremontiana PEPC gene family. In Arabidopsis, this gene family is
(Bartholomew et al., 1996) and K. fedtschenkoi (Hart- comprised of four members. In the common ice plant,
well et al., 1999), the most comprehensive collection however, at least six members make up this gene
of cDNA libraries for any CAM plant is available for family, with only one specifically recruited to func-
the common ice plant. More than 30 cDNA libraries tion in CAM (Cushman and Borland, 2001).
exist from tissues that span the entire life cycle, from
seedling to adult and flowering stages, as well as
different tissues such as meristems, roots, shoots, SEQUENCING A CAM PLANT GENOME?
leaves, epidermal bladder cells, flowers and seed
capsules, and different stress treatments (Bohnert Recent technological improvements in high-
and Cushman, 2001). Furthermore, more than 15,000 throughput, automated DNA sequencing systems
and access to large capacity sequencing facilities
ESTs are now available (http://www.ncbi.nlm.nih.
make it reasonable to call for the sequencing of the
gov/dbEST/dbEST_summary.html; Bohnert and
complete genome of a CAM plant in the near future.
Cushman, 2001). In addition, a gene index has been
The common ice plant is a logical choice for such an
recently created that allows easy access to the EST undertaking because it has the smallest genome
sequence information in the form of nonredundant among well-studied CAM models and the largest
genes (singletons) and tentative consensus sequences EST collection for gene identification (Table II). This
derived from redundant cDNAs (http://www. effort will also provide important genomic informa-
tigr.org/tdb/mcgi/). However, similar investments tion for comparative genomic studies of a species
in other intensively studied models such as K. daigre- within the Caryophyllales. Most genome sequencing
montiana and Clusia spp. in which cDNA libraries are efforts target the major crop species in the Cruciferae,
also under development (T. Taybi and A.M. Borland, Poaceae, and Solanaceae. In contrast, very few
personal communication) will be needed for compar- Caryophyllales, which includes such plant families
ative analyses of the functional significance of genes as the Aizoaceae, Amaranthaceae, Cactaceae, Che-
encoding signaling and regulatory components, en- nopodiaceae, Caryophyllaceae, Phytolaccaceae, and
zymes, and transporters and to extend cross-species Portulacaceae, are targets for genomic sequencing
comparison beyond current physiological or bio- efforts because most are crop or ornamental species
chemical investigations. of relatively minor economic value. Yet, many spe-
1444 Plant Physiol. Vol. 127, 2001Crassulacean Acid Metabolism
cies in the order Caryophyllales have evolved to growth and development of Mesembryanthemum crystalli-
colonize environments characterized by water defi- num (Aizoaceae). New Phytol 138: 171–190
cit, salinity, or extreme temperatures. As such, these Andolfatto R, Bornhouser A, Bohnert HJ, Thomas JC
species can be expected to be useful sources of novel (1994) Transformed hairy roots of Mesembryanthemum
genes involved in extending unusual biochemical crystallinum: gene expression patterns upon salt stress.
pathways for plant secondary metabolites or abiotic Physiol Plant 90: 708–714
stress tolerance. For example, many species of the Arumuganathan K, Earle ED (1991) Nuclear DNA content
Caryophyllales accumulate chromogenic betacyanins of some important plant species. Plant Mol Biol Rep 9:
instead of anthocyanins and other complex substi- 208–218
tuted flavonoids. Thus, access to complete sequence Bakrim N, Brulfert J, Vidal J, Chollet R (2001) Phos-
information for the common ice plant would facili- phoenolpyruvate carboxylase kinase is controlled by a
Downloaded from https://academic.oup.com/plphys/article/127/4/1439/6103653 by guest on 05 August 2021
tate discovery of genes with CAM-specific functions similar signaling cascade in CAM and C4 plants. Bio-
or regulation (e.g. circadianly regulated genes), as chem Biophys Res Commun 286: 1158–1162
well as of new gene products for abiotic stress adap- Barkla BJ, Vera-Estrella R, Maldonaldo-Gama M, Pantoja
tation and natural product biosynthesis and chemis- O (1999) Abscisic acid induction of vacuolar H⫹-ATPase
try (Vogt et al., 1999a, 1999b). activity in Mesembryanthemum crystallinum is develop-
mentally regulated. Plant Physiol 120: 811–819
PERSPECTIVES Bartholomew DM, Rees DJG, Rambaut A, Smith JAC
(1996) Isolation and sequence analysis of a cDNA encod-
The C3 and C4 photosynthetic pathways have been ing the c subunit of a vacuolar-type H⫹-ATPase from the
extensively investigated at the molecular genetic CAM plant Kalanchoë daigremontiana. Plant Mol Biol 31:
level. Much of this research has been greatly facili-
435–442
tated by the availability of excellent and well-studied
Bechtold N, Ellis J, Pelletier G (1993) In planta
genetic models and an abundance of cDNA and
Agrobacterium-mediated gene transfer by infiltration of
genomic sequence information. In contrast, our un-
adult Arabidopsis thaliana plants. Mol Biol Genet 316:
derstanding of the complex regulation of the CAM
1194–1199
photosynthetic pathway has lagged behind these
Bohnert HJ, Ayoubi P, Borchert C, Bressan RA, Burnap
other models. However, recent advances toward the
RL, Cushman JC, Cushman MA, Deyholos M, Fischer
creation of one or more viable genetic models for
R, Galbraith DW et al. (2001) A genomics approach
CAM, coupled with increasing availability of gene
sequence and expression information, forecast a towards salt stress tolerance. Plant Physiol Biochem 39:
bright and productive future for CAM researchers. 295–311
Future development and application of genomic, Bohnert HJ, Cushman JC (2001) The ice plant cometh:
proteomic, and metabolic profiling technologies in lessons in abiotic stress tolerance. J Plant Growth Regul
selected CAM models such as the common ice plant 19: 334–346
is expected to rapidly improve our understanding of Borland AM (1996) A model for the partitioning of photo-
CAM induction by environmental and developmen- synthetically fixed carbon during the C-3-CAM transi-
tal influences and the circadian rhythms that dictate tion in Sedum telephium. New Phytol 134: 433–444
the diel patterns of CO2 fixation characteristic of Borland AM, Hartwell J, Jenkins GI, Wilkins MB,
CAM plants. Thus, the greatest challenge facing Nimmo HG (1999) Metabolite control overrides circa-
CAM researchers in the future will be to develop dian regulation of phosphoenolpyruvate carboxylase ki-
teams of interdisciplinary researchers using genomic, nase and CO2 fixation in crassulacean acid metabolism.
biochemical, and physiological research approaches Plant Physiol 121: 889–896
in selected CAM models. This approach will provide Borland AM, Tecsi LI, Leegood RC, Walker RP (1998)
an integrated view of the complex regulatory dynam- Inducibility of crassulacean acid metabolism (CAM) in
ics that allow such remarkably plastic responses to Clusia species: physiological/biochemical characteriza-
the environment that has become one of the great tion and intercellular localization of carboxylation and
hallmarks of CAM plants. decarboxylation processes in three species which exhibit
different degrees of CAM. Planta 205: 342–351
ACKNOWLEDGMENTS Carter PJ, Nimmo HG, Fewson CA, Wilkins MB (1991)
Circadian rhythms in the activity of a plant protein ki-
I would like to thank Mary Ann Cushman and James nase. EMBO J 10: 2063–2068
Hartwell for their critical reading of the manuscript. Cheng S-H, Edwards GE (1991) Influence of long photo-
Received September 7, 2001; returned for revision Septem- periods on plant development and expression of crassu-
ber 10, 2001; accepted September 16, 2001. lacean acid metabolism in Mesembryanthemum crystalli-
num. Plant Cell Environ 14: 271–278
Christopher JT, Holtum JAM (1996) Patterns of carbohy-
LITERATURE CITED
drate partitioning in the leaves of crassulacean acid me-
Adams P, Nelson DE, Yamada S, Chmara W, Jensen RG, tabolism species during deacidification. Plant Physiol
Bohnert HJ, Griffiths H (1998) Tansley Review No. 97: 112: 393–399
Plant Physiol. Vol. 127, 2001 1445Cushman
Christopher JT, Holtum JAM (1998) Carbohydrate parti- Eller BM, Ferrari S (1997) Water use efficiency of two
tioning in the leaves of Bromeliaceae performing C3 pho- succulents with contrasting CO2 fixation pathways. Plant
tosynthesis or crassulacean acid metabolism. Aust J Plant Cell Environ 20: 93–100
Physiol 25: 371–376 Gehrig H, Faist K, Kluge M (1998a) Identification of phos-
Clough SJ, Bent AF (1998) Floral dip: a simplified method phoenolpyruvate carboxylase isoforms in leaf, stem, and
for Agrobacterium-mediated transformation of Arabidopsis roots of the obligate CAM plant Vanilla planifolia SALIB.
thaliana. Plant J 16: 735–743 (Orchidaceae): a physiological and molecular approach.
Cockburn W (1998) Rapid-cycling CAM: an hypothetical Plant Mol Biol 38: 1215–1223
variant of photosynthetic metabolism. Plant Cell Environ Gehrig H, Heute V, Kluge M (1998b) Towards a better
21: 845–851 knowledge of the molecular evolution of phosphoenol-
Cockburn W, Whitelam GC, Broad A, Smith J (1996) The pyruvate carboxylase by comparison of partial cDNA
Downloaded from https://academic.oup.com/plphys/article/127/4/1439/6103653 by guest on 05 August 2021
participation of phytochrome in the signal transduction sequences. J Mol Evol 46: 107–114
pathway of salt stress responses in Mesembryanthemum Gehrig H, Heute V, Kluge M (2001) New partial sequences
crystallinum L. J Exp Bot 47: 647–653 of phosphoenolpyruvate carboxylase as molecular phy-
Cushman JC, Bohnert HJ (1999) Crassulacean acid metab- logenetic markers. Mol Phylogenet Evol 20: 262–274
olism: molecular genetics. Annu Rev Plant Physiol Plant Gehrig H, Taybi T, Kluge M, Brulfert J (1995) Identifica-
Mol Biol 50: 305–332 tion of multiple PEPC isogenes in leaves of the faculta-
Cushman JC, Bohnert HJ (2001) Induction of crassulacean tive crassulacean acid metabolism (CAM) plant Kalanchoë
acid metabolism by salinity molecular aspects. In A blossfeldiana Poelln. cv. Tom Thumb. FEBS Lett 377:
Läuchli, U Lüttge, eds, Salinity: Environment, Plants, 399–402
Molecules. Kluwer Academic Publishers, Dordrecht, The Golldack D, Dietz K-J (2001) Salt-induced expression of
Netherlands (in press) the vacuolar H⫹-ATPase in the common ice plant is
Cushman JC, Borland AM (2001) Induction of crassu- developmentally controlled and tissue specific. Plant
lacean acid metabolism by water limitation. Plant Cell Physiol 125: 1643–1654
Griffiths H (1989) Carbon dioxide concentrating mecha-
Environ (in press)
nisms and the evolution of CAM in vascular epiphytes.
Cushman JC, Meyer G, Michalowski CB, Schmitt JM,
In U Lüttge, ed, Vascular Plants as Epiphytes: Evolution
Bohnert HJ (1989) Salt stress leads to the differential
and Ecophysiology. Springer-Verlag, Berlin, pp 42–86
expression of two isogenes of phosphoenolpyruvate car-
Hartwell J, Gill A, Nimmo GA, Wilkins MB, Jenkins GI,
boxylase during crassulacean acid metabolism induction
Nimmo HG (1999) Phosphoenolpyruvate carboxylase ki-
in the common ice plant. Plant Cell 1: 715–725
nase is novel protein kinase regulated at the level of
Cushman JC, Michalowski CB, Bohnert HJ (1990) Devel-
expression. Plant J 20: 333–342
opmental control of crassulacean acid metabolism induc-
Häusler RE, Baur B, Scharte J, Teichmann T, Eicks M,
ibility by salt stress in the common ice plant. Plant
Fischer KL, Flügge U-I, Schuber S, Weber A, Fischer K
Physiol 94: 1137–1142
(2000) Plastidic metabolite transporters and their physi-
Cushman JC, Taybi T, Bohnert HJ (2000a) Induction of
ological functions in the inducible crassulacean acid me-
crassulacean acid metabolism: molecular aspects. In RC tabolism plant Mesembryanthemum crystallinum. Plant J
Leegood, TD Sharkey, S von Caemmerer, eds, Photosyn- 24: 285–296
thesis: Physiology and Metabolism. Kluwer Academic Herppich W, Herppich M, von Willert DJ (1992) The
Publishers, Dordrecht, The Netherlands, pp 551–582 irreversible C3 to CAM shift in well-watered and salt-
Cushman JC, Wulan T, Kuscuoglu N, Spatz MD (2000b) stressed plants of Mesembryanthemum crystallinum is un-
Efficient plant regeneration of Mesembryanthemum crys- der strict ontogenetic control. Bot Acta 105: 34–40
tallinum via somatic embryogenesis. Plant Cell Rep 19: Heyne B (1815) On the deoxidation of the leaves of Coltyle-
459–463 don calycina. Trans Linn Soc Lond 11: 213–215
DeRocher EJ, Bohnert HJ (1993) Developmental and envi- Holtum JAM, Winter K (1982) Activities of enzymes of
ronmental stress employ different mechanisms in the carbon metabolism during the induction of crassulacean
expression of a plant gene family. Plant Cell 5: 1611–1625 acid metabolism in Mesembryanthemum crystallinum.
DeRocher EJ, Harkins KR, Galbraith DW, Bohnert HJ Planta 155: 8–16
(1990) Developmentally regulated systemic en- Ishimaru K (1999) Transformation of a CAM plant, the
dopolyploidy in succulents with small genomes. Science facultative halophyte Mesembryanthemum crystallinum by
250: 99–101 Agrobacterium tumefaciens. Plant Cell Tiss Org Cult 57:
de Saussure T (1804) Recherches chimiques sur la végéta- 61–63
tion. Chez la V.e Nyon, Paris Keeley JE (1996) Aquatic CAM photosynthesis. In K Win-
Drennan PM, Nobel PS (2000) Responses of CAM species ter, JAC Smith, eds, Crassulacean Acid Metabolism: Bio-
to increasing atmospheric CO2 concentrations. Plant Cell chemistry, Ecophysiology and Evolution, Vol 114.
Environ 23: 767–781 Springer-Verlag, Berlin, pp 281–295
Ehleringer JR, Monson RK (1993) Evolutionary and eco- Keeley JE (1998) CAM photosynthesis in submerged
logical aspects of photosynthetic pathway variation. aquatic plants. Bot Rev 64: 121–175
Annu Rev Ecol Syst 24: 411–439 Kore-eda S, Kanai R (1997) Induction of glucose
1446 Plant Physiol. Vol. 127, 2001Crassulacean Acid Metabolism
6-phosphate transport activity in chloroplasts of Mesem- Nimmo HG (2000) The regulation of phosphoenolpyruvate
bryanthemum crystallinum by the C3-CAM transition. carboxylase in CAM plants. Trends Plant Sci 5: 75–80
Plant Cell Physiol 38: 895–901 Nimmo HG, Fontaine V, Hartwell J, Jenkins GI, Nimmo
Kore-eda S, Yamashita T, Kanai R (1996) Induction of GA, Wilkins MB (2001b) PEP carboxylase kinase is a
light-dependent pyruvate transport into chloroplasts of novel protein kinase controlled at the level of expression.
Mesembryanthemum crystallinum by salt stress. Plant Cell New Phytol 151: 91–97
Physiol 37: 257–262 Osmond CB (1978) Crassulacean acid metabolism: a curi-
Li B, Chollet R (1994) Salt induction and the partial puri- osity in context. Annu Rev Plant Physiol 29: 379–414
fication/characterization of phosphoenolpyruvate car- Paterson KM, Nimmo HG (2000) Effects of pH on the
boxylase protein-serine kinase from an inducible crassu- induction of phosphoenolpyruvate carboxylase kinase in
lacean acid metabolism (CAM) plant, Mesembryanthemum Kalanchoë fedtschenkoi. Plant Sci 154: 135–141
Downloaded from https://academic.oup.com/plphys/article/127/4/1439/6103653 by guest on 05 August 2021
crystallinum L. Arch Biochem Biophys 314: 247–254 Paul MJ, Loos K, Stitt M, Ziegler P (1993) Starch-
Li X, Song Y, Century K, Straight S, Ronald P, Dong X, degrading enzymes during the induction of CAM in
Lassner M, Zhang Y (2001) A fast neutron deletion Mesembryanthemum crystallinum. Plant Cell Environ 16:
mutagenesis-based reverse genetics system for plants. 531–538
Plant J 27: 235–242 Pilon-Smits EAH, Hart H’t, van Brederode J (1996) Evo-
Lüttge U (1996) Clusia: plasticity and diversity in a genus lutionary aspects of crassulacean acid metabolism in the
of C3/CAM intermediate tropical trees. In K Winter, JAC Crassulaceae. In K Winter, JAC Smith, eds, Crassulacean
Smith, eds, Crassulacean Acid Metabolism: Biochemis- Acid Metabolism: Biochemistry, Ecophysiology and Evo-
try, Ecophysiology and Evolution, Vol 114. Springer- lution, Vol 114. Springer-Verlag, Berlin, pp 349–359
Verlag, Berlin, pp 296–311 Ranson SL, Thomas M (1960) Crassulacean acid metabo-
Lüttge U (2000) Light-stress and crassulacean acid metab- lism. Annu Rev Plant Physiol 11: 81–110
olism. Phyton (Horn) 40: 65–82 Rascher U, Blasius B, Beck F, Lüttge U (1998) Temperature
Lüttge U, Pfeifer T, Fischer-Schliebs E, Ratajczak R (2000) profiles for the expression of endogenous rhythmicity
and arrhythmicity of CO2 exchange in the CAM plant
The role of vacuolar malate-transport capacity in crassu-
Kalanchoë daigremontiana can be shifted by slow temper-
lacean acid metabolism and nitrate nutrition: higher
ature changes. Planta 207: 76–82
malate-transport capacity in ice plant after crassulacean
Rockel B, Jia C, Ratajczak R, Lüttge U (1998a) Day-night
acid metabolism induction and in tobacco under nitrate
changes of the amount of subunit-c transcript of the
nutrition. Plant Physiol 124: 1335–1347
V-ATPase in suspension cells of Mesembryanthemum crys-
Martin CE (1996) Putative causes and consequences of
tallinum. J Plant Physiol 152: 189–193
recycling CO2 via crassulacean acid metabolism. In K
Rockel B, Lüttge U, Ratajczak R (1998b) Changes in mes-
Winter, JAC Smith, eds, Crassulacean Acid Metabolism:
sage amount of V-ATPase subunits during salt-stress
Biochemistry, Ecophysiology and Evolution, Vol 114.
induced C3-CAM transition in Mesembryanthemum crys-
Springer-Verlag, Berlin, pp 192–203
tallinum. Plant Physiol Biochem 36: 567–573
McElwain EF, Bohnert HJ, Thomas JC (1992) Light mod-
Rowley G (1978) The Illustrated Encyclopedia of Succu-
erates the induction of phosphoenolpyruvate carboxylase lents. Salamander, London
by NaCl and abscisic acid in Mesembryanthemum crystalli- Schuber M, Kluge M (1981) In situ studies on crassulacean
num. Plant Physiol 99: 1261–1264 acid metabolism in Sedum acre L. and Sedum mite Gil.
Miszalski Z, Niewiadomska E, Slesak I, Lüttge U, Kluge Oecologia 50: 82–87
M, Ratajczak R (2001) The effect of irradiance on car- Schmitt AK, Lee HSJ, Lüttge U (1988) The response of the
boxylating/decarboxylating enzymes and fumarase ac- C3-CAM trees, Clusia rosea, to light and water stress: I.
tivities in Mesembryanthemum crystallinum L. exposed to Gas exchange characteristics. J Exp Bot 39: 1581–1590
salinity stress. Plant Biol 3: 17–23 Smith JAC, Winter K (1996) Taxonomic distribution of
Neuhaus E, Schulte N (1996) Starch degradation in chloro- crassulacean acid metabolism. In K Winter, JAC Smith,
plasts isolated from C3 or CAM (crassulacean acid eds, Crassulacean Acid Metabolism: Biochemistry, Eco-
metabolism)-induced Mesembryanthemum crystallinum L. physiology and Evolution, Vol 114. Springer-Verlag, Ber-
Biochem J 318: 945–953 lin, pp 427–436
Nimmo GA, Wilkins MB, Fewson CA, Nimmo HG (1987) Steiger S, Ratajczak R, Martinoia E, Lüttge U (1997) The
Persistent circadian rhythms in the phosphorylation vacuolar malate transporter of Kalanchoë diagremontiana:
state of phosphoenolpyruvate carboxylase from Bryophyl- a 32-kDa polypeptide? J Plant Physiol 151: 137–141
lum fedtschenkoi leaves and in its sensitivity to inhibition Taybi T, Cushman JC (1999) Signaling events leading to
by malate. Planta 170: 408–415 crassulacean acid metabolism induction in the common
Nimmo GA, Wilkins MB, Nimmo HG (2001a) Partial pu- ice plant. Plant Physiol 121: 545–555
rification and characterization of a protein inhibitor of Taybi T, Patil S, Chollet R, Cushman JC (2000) A minimal
phosphoenolpyruvate carboxylase kinase. Planta 213: serine/threonine protein kinase circadianly regulates
250–257 phosphoenolpyruvate carboxylase activity in crassu-
Nimmo HG (1998) Circadian regulation of a plant protein lacean acid metabolism-induced leaves of the common
kinase. Cronobiol Int 15: 109–118 ice plant. Plant Physiol 123: 1471–1481
Plant Physiol. Vol. 127, 2001 1447Cushman
Ting IP (1985) Crassulacean acid metabolism. Annu Rev Wilkins MB (1992) Circadian rhythms: their origin and
Plant Physiol 36: 595–622 control. New Phytol 121: 347–375
Truesdale MR, Toldi O, Scott P (1999) The effect of ele- Winter K, Lüttge U, Winter E, Troughton JH (1978) Sea-
vated concentrations of fructose 2,6-bisphosphate on car- sonal shift from C3 photosynthesis to crassulacean acid
bon metabolism during deacidification in the crassu- metabolism in Mesembryanthemum crystallinum growing
lacean acid metabolism plant Kalanchoë daigremontiana. in its natural environment. Oecologia 34: 225–237
Plant Physiol 121: 957–964 Winter K, Smith JAC (1996a) An introduction to crassu-
Vogt T, Grimm R, Strack D (1999a) Cloning and expression lacean acid metabolism. In K Winter, JAC Smith, eds,
of a cDNA encoding betanidin 5-O-glucosyltransferase, a Crassulacean Acid Metabolism: Biochemistry, Ecophysi-
betanidin- and flavonoid-specific enzyme with high ho- ology and Evolution, Vol 114. Springer-Verlag, Berlin, pp
mology to inducible glucosyltransferases from the So- 1–13
Downloaded from https://academic.oup.com/plphys/article/127/4/1439/6103653 by guest on 05 August 2021
lanaceae. Plant J 19: 509–516 Winter K, Ziegler H (1992) Induction of crassulacean acid
Vogt T, Ibdah M, Schmidt J, Wray V, Nimtz M, Strack D metabolism in Mesembryanthemum crystallinum increases
(1999b) Light-induced betacyanin and flavonol accumu- reproductive success under conditions of drought and
lation in bladder cells of Mesembryanthemum crystallinum. salinity stress. Oecologia 92: 475–479
Phytochemistry 52: 83–92 Zotz G, Winter K (1993) Short-term regulation of crassu-
Williams DDF, Fleisch H (1993) Historical review of pine- lacean acid metabolism activity in a tropical hemiepi-
apple breeding in Hawaii. Acta Hortic 334: 67–76 phyte, Clusia uvitana. Plant Physiol 102: 835–841
1448 Plant Physiol. Vol. 127, 2001You can also read
