Crassulacean Acid Metabolism Photosynthesis Research Articles

Multiple origins of crassulacean acid metabolism and the epiphytic habit in the Neotropical family Bromeliaceae.

The large Neotropical family Bromeliaceae presents an outstanding example of adaptive radiation in plants, containing a wide range of terrestrial and epiphytic life-forms occupying many distinct habitats. Diversification in bromeliads has been linked to several key innovations, including water- and nutrient-impounding phytotelmata, absorptive epidermal trichomes, and the water-conserving mode of photosynthesis known as crassulacean acid metabolism (CAM). To clarify the origins of CAM and the epiphytic habit, we conducted a phylogenetic analysis of nucleotide sequences for 51 bromeliad taxa by using the plastid loci matK and the rps16 intron, combined with a survey of photosynthetic pathway determined by carbon-isotope ratios for 1,873 species representing 65% of the family. Optimization of character-states onto the strict consensus tree indicated that the last common ancestor of Bromeliaceae was a terrestrial C(3) mesophyte, probably adapted to moist, exposed, nutrient-poor habitats. Both CAM photosynthesis and the epiphytic habit evolved a minimum of three times in the family, most likely in response to geological and climatic changes in the late Tertiary. The great majority of epiphytic forms are now found in two lineages: in subfamily Tillandsioideae, in which C(3) photosynthesis was the ancestral state and CAM developed later in the most extreme epiphytes, and in subfamily Bromelioideae, in which CAM photosynthesis predated the appearance of epiphytism. Subsequent radiation of the bromelioid line into less xeric habitats has led to reversion to C(3) photosynthesis in some taxa, showing that both gain and loss of CAM have occurred in the complex evolutionary history of this family.

Changes in photosynthetic pigment composition and absorbed energy allocation during salt stress and CAM induction in Mesembryanthemum crystallinum.

Mesembryanthemum crystallinum L. undergoes a transition from the C3 photosynthetic pathway to crassulacean acid metabolism (CAM) in response to increasing salinity. As a consequence, growth is greatly reduced and less light energy is utilised in carbon fixation, leading to an increase in dissipation of thermal energy to remove potentially dangerous excess excitation energy. The pigment composition of plants grown for 4 weeks at 20 mm (low) and 400 mm (high) NaCl was sampled, and photochemical performance, tissue acidity and growth were sampled at 2 and 4 weeks. High-salt-grown plants, which switched to CAM, accumulated only 25% of the fresh weight of low-salt-grown plants, which maintained C3 photosynthesis. Predawn Fv / Fm and de-epoxidation of violaxanthin [(A + Z) / (V + A + Z)] was similar between plants after 2 and 4 weeks, revealing no sustained depression in PSII efficiency under the high-salt treatment. However, at midday under high photosynthetic photon flux densities (PPFD) high-salt plants displayed lower PSII efficiency, higher (A + Z) / (V + A + Z) and greater allocation of energy to thermal dissipation over photochemistry than low-salt plants. Pigment contents were similar between treatments for the first 3 weeks, but after 4 weeks high-salt plants had accumulated significantly less chlorophyll and lutein than low-salt plants. However, V + A + Z content did not differ. High-salt treatment, leading to CAM photosynthesis and substantial reduction in growth, was associated with increased allocation of energy to xanthophyll cycle-dependent energy dissipation at high light and adjustment of thylakoid pigment composition.

Crassulacean acid metabolism photosynthesis: ;working the night shift'.

Crassulacean acid metabolism (CAM) can be traced from Roman times through persons who noted a morning acid taste of some common house plants. From India in 1815, Benjamin-Heyne described a 'daily acid taste cycle' with some succulent garden plants. Recent work has shown that the nocturnally formed acid is decarboxylated during the day to become the CO(2) for photosynthesis. Thus, CAM photosynthesis extends over a 24-hour day using several daily interlocking cycles. To understand CAM photosynthesis, several landmark discoveries were made at the following times: daily reciprocal acid and carbohydrate cycles were found during 1870 to 1887; their precise identification, as malic acid and starch, and accurate quantification occurred from 1940 to 1954; diffusive gas resistance methods were introduced in the early 1960s that led to understanding the powerful stomatal control of daily gas exchanges; C(4) photosynthesis in two different types of cells was discovered from 1965 to approximately 1974 and the resultant information was used to elucidate the day and night portions of CAM photosynthesis in one cell; and exceptionally high internal green tissue CO(2) levels, 0.2 to 2.5%, upon the daytime decarboxylation of malic acid, were discovered in 1979. These discoveries then were combined with related information from C(3) and C(4) photosynthesis, carbon biochemistry, cellular anatomy, and ecological physiology. Therefore by approximately 1980, CAM photosynthesis finally was rigorously outlined. In a nutshell, 24-hour CAM occurs by phosphoenol pyruvate (PEP) carboxylase fixing CO(2)(HCO(3) (-)) over the night to form malic acid that is stored in plant cell vacuoles. While stomata are tightly closed the following day, malic acid is decarboxylated releasing CO(2) for C(3) photosynthesis via ribulose bisphosphate carboxylase oxygenase (Rubisco). The CO(2) acceptor, PEP, is formed via glycolysis at night from starch or other stored carbohydrates and after decarboxylation the three carbons are restored each day. In mid to late afternoon the stomata can open and mostly C(3) photosynthesis occurs until darkness. CAM photo-synthesis can be both inducible and constitutive and is known in 33 families with an estimated 15 to 20 000 species. CAM plants express the most plastic and tenacious photosynthesis known in that they can switch photosynthesis pathways and they can live and conduct photosynthesis for years even in the virtual absence of external H(2)O and CO(2), i.e., CAM tenaciously protects its photosynthesis from both H(2)O and CO(2) stresses.

Are crassulacean acid metabolism and C4 photosynthesis incompatible?

This paper originates from a presentation at the IIIrd International Congress on Crassulacean Acid Metabolism, Cape Tribulation, Queensland, Australia, August 2001. Despite sharing a similar metabolism, crassulacean acid metabolism (CAM) and C4 photosynthesis are not known to occur in identical species, with the exception of Portulaca spp. In Portulaca, C4 and weak CAM photosynthesis occur in distinct regions of the leaf, rather than in the same cells. This is in marked contrast to the situation in most CAM species where C3 and CAM photosynthesis are active in the same cell over the course of a day and growing season. The lack of CAM and C4 photosynthesis in identical cells of a plant indicates these photosynthetic pathways are incompatible. Incompatibilities between CAM and C4 photosynthesis could have a number of biochemical, anatomical and evolutionary explanations. Biochemical incompatibilities could result from the requirement for spatial separation of C3 and C4 phases in C4 plants versus temporal separation in CAM plants. In C4 plants, regulatory systems coordinate mesophyll and bundle sheath metabolism, with light intensity being the major environmental signal. In CAM plants, a circadian oscillator coordinates day and night phases of CAM. The requirement for rapid intercellular transport in C4 plants may be incompatible with the intracellular transport and storage needs of CAM. For example, the large vacuole required for malate storage in CAM could impede metabolite diffusion between mesophyll and bundle sheath cells in C4 plants. Anatomical barriers could also exist because both CAM and the C4 pathway require distinct leaf anatomies for efficient function. Efficient function of the C4 pathway generally requires an outer layer of cells specialized for phosphoenolpyruvate (PEP) carboxylation and regeneration and an inner layer for CO2 accumulation and refixation, while CAM species require enlarged vacuoles and tight cell packing. In evolutionary terms, barriers preventing CAM and C4 photosynthesis in the same species may be the initial steps in the respective evolutionary pathways from C3 ancestors. The first steps in C4 photosynthesis are related to scavenging photorespiratory CO2 via localization of glycine decarboxylase in the bundle sheath cells. The initial steps in CAM evolution are associated with the scavenging of respiratory CO2 at night by PEP carboxylation. In each, simplified versions of the specialized anatomy may need to be present for the evolutionary sequence to begin. For C4 evolution, enhanced bundle sheath size may be required in C3 ancestors; for CAM evolution, succulence may be required. Thus, before CAM or C4 photosynthesis began to evolve, the outcome of the evolutionary experiment may have been predetermined.

Phosphoenolpyruvate Carboxylase Kinase Is Controlled by a Similar Signaling Cascade in CAM and C4 Plants

In Crassulacean acid metabolism (CAM) plants, phosphoenolpyruvate carboxylase (PEPC) is subject to day-night regulatory phosphorylation of a conserved serine residue in the plant enzyme's N-terminal domain. The dark increase in PEPC-kinase (PEPC-k) activity is under control of a circadian oscillator, via the enhanced expression of the corresponding gene (1). The signaling cascade leading to PEPC-k up-regulation was investigated in leaves and mesophyll cell protoplasts of the facultative, salt-inducible CAM species, Mesembryanthemum crystallinum. Mesophyll cell protoplasts had the same PEPC-k activity as leaves from which they were prepared (i.e., high at night, low during the day). However, unlike C4 protoplasts (2), CAM protoplasts did not show marked PEPC-k up-regulation when isolated during the day and treated with a weak base such as NH4Cl. Investigations using various pharmacological reagents established the operation, in the darkened CAM leaf, of a PEPC-k cascade including the following components: a phosphoinositide-dependent phospholipase C (PI-PLC), inositol 1,4,5 P (IP3)-gated tonoplast calcium channels, and a putative Ca2+/calmodulin protein kinase. These results suggest that a similar signaling machinery is involved in both C4 (2, 3) and CAM plants to regulate PEPC-k activity, the phosphorylation state of PEPC, and, thus, carbon flux through this enzyme during CAM photosynthesis.

The Evolution of Plant Ecophysiological Traits: Recent Advances and Future Directions

functional diversity, which underlies variation in growth rates, productivity, population and community dynamics, and ecosystem function. The broad congruence of these variations with climatic and environmental conditions on local, regional, and global scales has fostered the concept that plant ecophysiological characteristics are well adapted to their local circumstances. For example, the repeated occurrence of plants with CAM (Crassulacean Acid Metabolism) photosynthesis and succulent leaves or stems in severely water-limited environments, and the independent evolution of these traits in numerous plant lineages, provides compelling evidence of the physiological evolution of these water-conserving traits under the influence of natural selection (Ehleringer and Monson 1993). Similarly, studies of the evolution of heavy metal tolerance confirm that natural selection may cause rapid ecophysiological evolution in just a few generations, leading to local adaptation in populations just a few meters apart (Antonovics et al. 1971). Many ecophysiological traits—considered here as all aspects of resource uptake and utilization, including biochemistry, metabolism, gas exchange, leaf structure and function, nutrient and biomass allocation, canopy structure, and growth—are likely to influence fitness and undergo adaptive evolution. Traits affecting the assimilation and use of resources such as carbon, water, and nutrients directly influence plant growth. Patterns of resource allocation to growth, reproduction, defense, and stress tolerance are also likely to be under strong selection. Phenotypic plasticity, the expression of different phenotypes by

Extrapolating feedback processes from the present to the past

Extant terrestrial vegetation alters its physical environment via its albedo, and its influence on immediate temperature via stomatal and boundary–layer influences of energy dissipation as sensible and latent heat; aquatic vegetation also controls albedo (e.g. coccolithophorids) and, by competing with water for electromagnetic energy absorption, the depth of the mixed layer and hence the quantity of nutrients trapped for the spring bloom. Both aquatic and terrestrial vegetation have had, together with microbial and geological processes, an influence on O2and CO2levels, and hence on the availability and biological functioning of Fe, Mn, Cu, Zn, Se and P, and the relative competitive advantage of C3versus C4, crassulacean acid metabolism (CAM) and carbon concentration mechanism (CCM) organisms. Less directly, changes in primary productivity impact on the production of CH4and N2O which, like CO2, are greenhouse gases, while some (marine) primary producers yield dimethyl sulphide (and hence cloud condensation nuclei, with effects on cloudiness) and halocarbons (via, in part, O2–dependent processes), partly negating the O3attenuation of UV–B radiation. These effects can be related to the terrestrial embryophytic vegetation back to ca. 450 Ma, and to eukaryotic marine vegetation back to at least 1.7, and probably 2.1 Ga, with implications for inter alia C3versus C4, CAM and CCM photosynthesis, and Fe acquisition mechanisms. Even earlier (3.8 Ga onwards) prokaryotes may have influenced CO2levels and hence controlled (as they did later) surface temperature. By producing O2, they led to decreasing availability of Fe, Mn and P (and utility of Se?), and increasing availability of Cu (and Zn?) that shaped the biochemistry on which later biogeochemistry was based.

CAM photosynthesis in submerged aquatic plants

Crassulacean acid metabolism (CAM) is a CO2-concentrating mechanism selected in response to aridity in terrestrial habitats, and, in aquatic environments, to ambient limitations of carbon. Evidence is reviewed for its presence in five genera of aquatic vascular plants, includingIsoetes, Sagittaria, Vallisneria, Crassula, andLittorella. Initially, aquatic CAM was considered by some to be an oxymoron, but some aquatic species have been studied in sufficient detail to say definitively that they possess CAM photosynthesis. CO2-concentrating mechanisms in photosynthetic organs require a barrier to leakage; e.g., terrestrial C4 plants have suberized bundle sheath cells and terrestrial CAM plants high stomatal resistance. In aquatic CAM plants the primary barrier to CO2 leakage is the extremely high difrusional resistance of water. This, coupled with the sink provided by extensive intercellular gas space, generates daytime CO2(pi) comparable to terrestrial CAM plants. CAM contributes to the carbon budget by both net carbon gain and carbon recycling, and the magnitude of each is environmentally influenced. Aquatic CAM plants inhabit sites where photosynthesis is potentially limited by carbon. Many occupy moderately fertile shallow temporary pools that experience extreme diel fluctuations in carbon availability. CAM plants are able to take advantage of elevated nighttime CO2 levels in these habitats. This gives them a competitive advantage over non-CAM species that are carbon starved during the day and an advantage over species that expend energy in membrane transport of bicarbonate. Some aquatic CAM plants are distributed in highly infertile lakes, where extreme carbon limitation and light are important selective factors.

Evidence that the induction of crassulacean acid metabolism by water stress in Mesembryanthemum crystallinum (L.) involves root signalling

ABSTRACTThe aim of this study was to investigate whether the root system of Mesembryanthemum crystallinum (L.) plays a role in triggering the induction of crassulacean acid metabolism (CAM) during water stress. Depriving well‐irrigated plants of water, by allowing the soil surrounding the roots to dry, caused increased daily losses in leaf relative water content (RVVC) and mesophyll cell turgor pressure. The RWC of the roots also declined. Subsequently plants exhibited physiological characteristics of CAM photosynthesis (i.e. diurnal fluctuations in leaf titratable acidity and nocturnal net CO2 fixation). When the root system of plants was divided equally between two soil compartments and one half deprived of water, plants exhibited physiological characteristics of CAM without prior changes in leaf RWC content or mesophyll cell turgor pressure. Only the RWC of the water‐stressed portion of the roots was reduced. These data suggest that in water‐stressed plants daily changes in leaf water relations greater than those observed in well‐irrigated plants, are not essential to trigger CAM expression. It is probable that a reduction in soil water availability can be perceived by the roots of M. crystallinum and that this information is conveyed to the leaves triggering the transition from C3 to CAM photosynthesis.

A salinity-induced gene from the halophyte M. crystallinum encodes a glycolytic enzyme, cofactor-independent phosphoglyceromutase

In the facultative halophyte Mesembryanthemum crystallinum (ice plant), salinity stress triggers significant changes in gene expression, including increased expression of mRNAs encoding enzymes involved with osmotic adaptation to water stress and the crassulacean acid metabolism (CAM) photosynthetic pathway. To investigate adaptive stress responses in the ice plant at the molecular level, we generated a subtracted cDNA library from stressed plants and identified mRNAs that increase in expression upon salt stress. One full-length cDNA clone was found to encode cofactor-independent phosphoglyceromutase (PGM), an enzyme involved in glycolysis and gluconeogenesis. Pgm1 expression increased in leaves of plants exposed to either saline or drought conditions, whereas levels of the mRNA remained unchanged in roots of hydroponically grown plants. Pgm1 mRNA was also induced in response to treatment with either abscisic acid or cytokinin. Transcription run-on experiments confirmed that Pgm1 mRNA accumulation in leaves was due primarily to increased transcription rates. Immunoblot analysis indicated that Pgm1 mRNA accumulation was accompanied by a modest but reproductible increase in the level of PGM protein. The isolation of a salinity-induced gene encoding a basic enzyme of glycolysis and gluconeogenesis indicates that adaptation to salt stress in the ice plant involves adjustments in fundamental pathways of carbon metabolism and that these adjustments are controlled at the level of gene expression. We propose that the leaf-specific expression of Pgm1 contributes to the maintenance of efficient carbon flux through glycolysis/gluconeogenesis in conjunction with the stress-induced shift to CAM photosynthesis.

Effects of Different Nitrogen Sources and Concentrations on CAM Photosynthesis in Kalanchoe blossfeldiana

When Kalanchoe blossfeldiana Poelln. cv. Hikan plants were cultured in solutions containing 0-2, 1-0, 5-0 or 10 mM of nitrate or ammonium under a long-day photoperiod, some criteria of CAM (Crassulacean acid metabolism) photosynthesis (diurnal changes of C02 uptake, titratable acidity and malate content in leaves) were examined. The plants absorbed 90 to 100% of C02 during the light phase regardless of the supplied nitrogen. Nitrate-grown plants absorbed about 10% of C02 during the dark phase regardless of the supplied concentration, whereas in ammonium-grown plants the nocturnal C02 uptake occurred at 0 2 mM, at which the plants depleted nitrogen and no uptake was observed at the higher concentrations. Changes of nocturnal increase in titratable acidity and malate content almost corresponded with the changes in the amount of nocturnal C02 uptake. Also K. daigremontiana plants supplied with 10 mM of ammonium had a less CAM-like pattern of diurnal C02 uptake than the plants supplied with 10 mM of nitrate. These results suggest that a sufficient supply of ammonium depresses CAM photosynthesis.

ファレノプシスにおけるＣＡＭ型光合成への葉齢・花序・水分・温度・光条件の影響

Effects of some factors on CAM (Crassulacean acid metabolism) photosynthesis in Phalaenopsis were investigated by measuring diurnal CO2 exchange patterns. Following results were obtained.1. The diurnal CO2 uptake pattern of Phalaenopsis leaves is nearly typical of CAM photosynthesis. Leaf age had no influence on CAM photosynthesis; the youngest leaf absorbed slightly more CO2 during the day and less at the night than did mature leaves. Although the third and forth leaves were shaded by the upper leaves, they fixed CO2 via CAM photosynthesis at rates similar to the upper two leaves fully exposed to light.2. Formation of inflorescence did not influence the diurnal pattern of CO2 uptake of CAM photosynthesis. But the plants without inflorescence had lower activities in CO2 uptake via CAM photosynthesis than those with inflorescence.3. When the day and night temperature were kept constant, 20°C was the optimum for the night time CO2 uptake. Although the day time CO2 uptake decreased as temperature increased, total CO2 uptake during 24 hr was maximized at 20°C. Higher day and lower night temperatures (25°15°C) were more favorable than a constant 20°C with respect to CO2 assimilation of CAM photosynthesis at night or during the entire day. Low day time temperature of 10°C depressed CO2 uptake rates at night and promotes during the day so that the Phalaenopsis leaves approximated those of plants with C3-photosynthetic system.4. The day and night time CO2 uptake increased with higher light intensity up to 130μE/m2/sec. Above 130μE/m2/sec the capacity of leaves to assimilate CO2 at night was saturated and that during the day became lower. Therefore, CAM photosynthesis in Phalaenopsis has a lower light saturating point than other plants.5. Under our growing conditions, withholding water for 10 days resulted in a severe water stress which significantly depressed CO2 uptake both day and night.

Seasonal Shifts of Photosynthesis in Portulacaria afra (L.) Jacq.

Portulacaria afra (L.) Jacq., a perennial facultative Crassulacean acid metabolism (CAM) species, was studied under natural photoperiods and temperatures in San Diego, California. The plants were irrigated every fourth day throughout the study period. Measurements of (14)CO(2) uptake, stomatal resistance, and titratable acidity were made periodically from July 1981 through May 1982. P. afra maintained C(3) photosynthesis during the winter and the spring. Diurnal acid fluctuations were low and maximal (14)CO(2) uptake occurred during the day. The day/night ratio of carbon uptake varied from 5 to 10 and indicated little nocturnal CO(2) uptake. CAM photosynthesis occurred during the summer and a mixture of both C(3) and CAM during the fall. Large acid fluctuations of 100 to 200 microequivalents per gram fresh weight were observed and maximal (14)CO(2) uptake shifted to the late night and early morning hours. Daytime stomatal closure was evident. A reduction in the day/night ratio of carbon uptake to 2 indicated a significant contribution of nocturnal CO(2) uptake to the overall carbon gain of the plant. The seasonal shift from C(3) to CAM was facilitated by increasing daytime temperature and accompanied by reduced daytime CO(2) uptake despite irrigation.

Inorganic carbon assimilation in the Isoetids, Isoetes lacustris L. and Lobelia dortmanna L.

The inorganic carbon fixation patterns of Isoetes lacustris and Lobelia dortmanna from an oligotrophic Scottish loch have been examined by following titratable acidity changes in plant sap and light/dark 14CO2 incorporation by roots and shoots. The diurnal pattern of titratable acidity changes in I. lacustris suggests crassulacean acid metabolism (CAM) while the lack of any change in titratable acidity in L. dortmanna suggests C3 metabolism. Of the carbon fixed by L. dortmanna, 99.9% was taken up through the roots and fixation occurred primarily during the day. In Isoetes, CO2 was taken up by both roots and shoots and during both day and night. Regardless of the site of CO2 uptake, fixation occurred only in the shoots of both plants. Analysis of carbon isotope ratios of plant organic material was used to further investigate the photosynthetic mechanisms of these Isoetids. Considering the absence of a nighttime peak in titratable acidity in L. dortmanna, the Δ13C (Δ=δ13C plant-δ13C source) value of the shoots of L. dortmanna (-14.2‰) is indicative of C3 photosynthesis limited by the rate of CO2 diffusion. The less negative Δ of I. lacustris (-6.0‰) is consistent with both dark acidification of CAM and CO2 limited C3 photosynthesis. This is in contrast to the terrestrial Isoetes durieui which is shown to have a Δ value which is similar to a terrestrial C3 plant. The carbon fixation patterns of these Isoetids suggest that the CO2 concentration in the loch may be growth limiting, and that root uptake and/or dark acidification are means of optimising CO2 supply. However, in view of the relatively high levels of CO2 in sediment and bulk water, it is suggested that low levels of nutrients may also limit growth in these plants.

Aspects of carbon metabolism in Welwitschia

Under glasshouse and growth chamber conditions, Welwitschia mirabilis showed a typical C 3 type of gas exchange with 14CO 2 uptake occurring largely during the day. Total titratable acidity was high, in the range typical of Crassulacean acid metabolism (CAM) plants, and in the case of the growth chamber experimental conditions, a definite diurnal fluctuation of acidity was observed. The carbon isotope composition expressed as δ 13C for the plants used in the growth chamber experiments was −25.8%, and in the greenhouse it was about −24.4%. We conclude that Welwitschia shows cycling of organic acids, a phenomenon now known to occur in succulent plants, rather than CAM photosynthesis.

Enzyme Regulation in Crassulacean Acid Metabolism Photosynthesis

Cell-free preparations of the Crassulacean acid metabolism (CAM) plant, Kalanchoë daigremontiana, were analyzed for thioredoxins and ferredoxin-thioredoxin reductase. Three distinct forms of thioredoxin were identified in Kalanchoë leaves, two of which specifically activated fructose 1,6-bisphosphatase (designated f(1) and f(2)) and a third which activated NADP-malate dehydrogenase (thioredoxin m). The apparent molecular weight of both forms of thioredoxin f was 11,000 and that of thioredoxin m was 10,000. In parallel studies, ferredoxin and ferredoxin-thioredoxin reductase were purified from Kalanchoë leaf preparations. Kalanchoë ferredoxin-thioredoxin reductase was similar to that of C(3) and C(4) plants in molecular weight (31,000) and immunological cross-reactivity. Kalanchoë ferredoxin-thioredoxin reductase exhibited an affinity for ferredoxin as demonstrated by its binding to an immobilized ferredoxin affinity column. The purified components of the Kalanchoë ferredoxin-thioredoxin system could be recombined to function in the photoregulation of chloroplast enzymes. The data suggest that the ferredoxin/thioredoxin system plays a role in enzyme regulation of all higher plants irrespective of whether they show C(3), C(4), or CAM photosynthesis.

Shifts in the Carbon Metabolism of Xerosicyos danguyi H. Humb. (Cucurbitaceae) Brought About by Water Stress

Xerosicyos danguyi Humbert (Cucurbitaceae) is a leaf succulent endemic to Madagascar. Under well-watered conditions, the plant exhibited Crassulacean acid metabolism (CAM) but shifted to a dampened form of CAM, CAM-idling, when subjected to water stress. The purpose of this investigation was to examine the effects of a shift in carbon metabolism on phosphoenolpyruvate carboxylase and on NADP-malic enzyme in X. danguyi. Experiments were conducted to determine the diurnal patterns of enzyme activity and pH optima of both enzymes, as well as the approximate molecular mass, kinetic patterns, malate inhibition, and glucose-6-phosphate stimulation of phosphoenolpyruvate carboxylase. The two enzymes extracted from well-watered and water-stressed plants were similar in most parameters investigated; thus, CAM-idling appeared to be only a dampened form of CAM photosynthesis.

Effects of Light Quantity and Quality on the Decarboxylation of Malic Acid in Crassulacean Acid Metabolism Photosynthesis

The rate of malic acid consumption in the Crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perrier was found to be more rapid than the rate of photosynthetic oxygen evolution under all levels of irradiation by white light. This accounts for the accumulation of carbon dioxide in CAM tissues in the light.Action spectra of malate consumption and photosynthetic oxygen evolution in Kalanchoë were similar. Experiments using monochromatic photosynthetically active light in addition to a range of narrow waveband irradiations demonstrated that malic acid consumption in the experiments from which the action spectrum of acid consumption was constructed was not limited by the rate of photosynthesis. These data indicate that light involved in the promotion of malate consumption in CAM is absorbed by the same pigments that absorb the light which powers photosynthesis.