Does the C4 plant Trianthema portulacastrum (Aizoaceae) exhibit weakly expressed crassulacean acid metabolism (CAM)?

We examined whether crassulacean acid metabolism (CAM) is present in Trianthema portulacastrum L. (Aizoaceae), a pantropical, salt-tolerant C 4 annual herb with atriplicoid-type Kranz anatomy in leaves but not in stems. The leaves of T. portulacastrum are slightly succulent and the stems are fleshy, similar to some species of Portulaca, the only genus known in which C 4 and CAM co-occur. Low- level nocturnal acidification typical of weakly expressed, predominantly constitutive CAM was measured in plants grown for their entire life-cycle in an outdoor raised garden box. Acidification was greater in stems than in leaves. Plants showed net CO 2 uptake only during the light irrespective of soil water availability. However, nocturnal traces of CO 2 exchange exhibited curved kinetics of reduced CO 2 loss during the middle of the night consistent with low-level CAM. Trianthema becomes the second genus of vascular land plants in which C 4 and features of CAM have been demonstrated to co-occur in the same plant and the first C 4 plant with CAM-type acidification described for the Aizoaceae. Traditionally the stems of herbs are not sampled in screening studies. Small herbs with mildly succulent leaves and fleshy stems might be a numerically significant component of CAM biodiversity

Operating at the very low end of the crassulacean acid metabolism spectrum: Sesuvium portulacastrum (Aizoaceae)

Demonstration of crassulacean acid metabolism (CAM) in species with low usage of this system relative to C₃-photosynthetic CO₂ assimilation can be challenging experimentally but provides crucial information on the early steps of CAM evolution. Here, weakly expressed CAM was detected in the well-known pantropical coastal, leaf-succulent herb Sesuvium portulacastrum, demonstrating that CAM is present in the Sesuvioideae, the only sub-family of the Aizoaceae in which it had not yet been shown conclusively. In outdoor plots in Panama, leaves and stems of S. portulacastrum consistently exhibited a small degree of nocturnal acidification which, in leaves, increased during the dry season. In potted plants, nocturnal acidification was mainly facultative, as levels of acidification increased in a reversible manner following the imposition of short-term water-stress. In drought-stressed plants, nocturnal net CO₂ exchange approached the CO₂-compensation point, consistent with low rates of CO₂ dark fixation sufficient to eliminate respiratory carbon loss. Detection of low-level CAM in S. portulacastrum adds to the growing number of species that cannot be considered C₃ plants sensu stricto, although they obtain CO₂ principally via the C₃ pathway. Knowledge about the presence/absence of low-level CAM is critical when assessing trajectories of CAM evolution in lineages. The genus Sesuvium is of particular interest because it also contains C₄ species

Constitutive and facultative crassulacean acid metabolism (CAM) in Cuban oregano, Coleus amboinicus (Lamiaceae)

© 2020 CSIRO. Plants exhibiting the water-conserving crassulacean acid metabolism (CAM) photosynthetic pathway provide some of the most intriguing examples of photosynthetic diversity and plasticity. Here, a largely unnoticed facet of CAM-plant photosynthesis is highlighted: the co-occurrence of ontogenetically controlled constitutive and environmentally controlled facultative CAM in a species. Both forms of CAM are displayed in leaves of Coleus amboinicus Lour. (Lamiaceae), a semi-succulent perennial plant with oregano-like flavour that is native to southern and eastern Africa and naturalised elsewhere in the tropics. Under well-watered conditions, leaves assimilate CO2 predominantly by the C3 pathway. They also display low levels of CO2 uptake at night accompanied by small nocturnal increases in leaf tissue acidity. This indicates the presence of weakly expressed constitutive CAM. CAM expression is strongly enhanced in response to drought stress. The drought-enhanced component of CAM is reversible upon rewatering and thus considered to be facultative. In contrast to C. amboinicus, the thin-leaved closely related Coleus scutellarioides (L.) Benth. exhibits net CO2 fixation solely in the light via the C3 pathway, both under well-watered and drought conditions. However, low levels of nocturnal acidification detected in leaves and stems indicate that the CAM cycle is present. The highly speciose mint family, which contains few known CAM-exhibiting species and is composed predominantly of C3 species, appears to be an excellent group of plants for studying the evolutionary origins of CAM and for determining the position of facultative CAM along the C3-full CAM trajectory

Contribution a la recherche d'haploides de Sorghum bicolor (L.) moench par gynogenese in situ apres croisement intergenetique, pollinisation avec du pollen irradie et par androgenese in vitro

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : TD 79386 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Efecto de CO 2 elevado sobre el crecimiento y la actividad del metabolismo del ácido crasuláceo de Kalanchoe pinnata en condiciones tropicales

Kalanchoë pinnata (Lam.) Pers. (Crassulaceae), a succulent-leaved crassulacean-acid-metabolism plant, was grown in open-top chambers at ambient and elevated (two times ambient) CO2 concentrations under natural conditions at the Smithsonian Tropical Research Institute, Republic of Panama. Nocturnal increase in titratable acidity and nocturnal carbon gain were linearly related, increased with leaf age, and were unaffected by CO2 treatments. However, under elevated CO2, dry matter accumulation increased by 42–51%. Thus, the increased growth at elevated CO2 was attributable entirely to increased net CO2 uptake during daytime in the light. Malic acid was the major organic acid accumulated overnight. Nocturnal malate accumulation exceeded nocturnal citrate accumulation by six-to eightfold at both CO2 concentrations. Basal (predawn) starch levels were higher in leaves of plants grown at elevated CO2 but diurnal fluctuations of starch were of similar magnitude under both ambient and elevated CO2. In both treatments, nocturnal starch degradation accounted for between 78 and 89% of the nocturnal accumulation of malate and citrate. Glucose, fructose, and sucrose were not found to exhibit marked day-night fluctuations

Sudden Exposure to Solar UV-B Radiation Reduces Net CO(2) Uptake and Photosystem I Efficiency in Shade-Acclimated Tropical Tree Seedlings

Tree seedlings developing in the understory of the tropical forest have to endure short periods of high-light stress when tree-fall gaps are formed, and direct solar radiation, including substantial UV light, reaches the leaves. In experiments simulating the opening of a tree-fall gap, the response of photosynthesis in leaves of shade-acclimated seedlings (Anacardium excelsum, Virola surinamensis, and Calophyllum longifolium) to exposure to direct sunlight (for 20–50 min) was investigated in Panama (9°N). To assess the effects of solar UV-B radiation (280–320 nm), the sunlight was filtered through plastic films that selectively absorbed UV-B or transmitted the complete spectrum. The results document a strong inhibition of CO(2) assimilation by sun exposure. Light-limited and light-saturated rates of photosynthetic CO(2) uptake by the leaves were affected, which apparently occurred independently of a simultaneous inhibition of potential photosystem (PS) II efficiency. The ambient UV-B light substantially contributed to these effects. The photochemical capacity of PSI, measured as absorbance change at 810 nm in saturating far-red light, was not significantly affected by sun exposure of the seedlings. However, a decrease in the efficiency of P700 photooxidation by far-red light was observed, which was strongly promoted by solar UV-B radiation. The decrease in PSI efficiency may result from enhanced charge recombination in the reaction center, which might represent an incipient inactivation of PSI, but contributes to thermal dissipation of excessive light energy and thereby to photoprotection

Does the C4 plant Trianthema portulacastrum (Aizoaceae) exhibit weakly expressed crassulacean acid metabolism (CAM)?

We examined whether crassulacean acid metabolism (CAM) is present in Trianthema portulacastrum L. (Aizoaceae), a pantropical, salt-tolerant C 4 annual herb with atriplicoid-type Kranz anatomy in leaves but not in stems. The leaves of T. portulacastrum are slightly succulent and the stems are fleshy, similar to some species of Portulaca, the only genus known in which C 4 and CAM co-occur. Low- level nocturnal acidification typical of weakly expressed, predominantly constitutive CAM was measured in plants grown for their entire life-cycle in an outdoor raised garden box. Acidification was greater in stems than in leaves. Plants showed net CO 2 uptake only during the light irrespective of soil water availability. However, nocturnal traces of CO 2 exchange exhibited curved kinetics of reduced CO 2 loss during the middle of the night consistent with low-level CAM. Trianthema becomes the second genus of vascular land plants in which C 4 and features of CAM have been demonstrated to co-occur in the same plant and the first C 4 plant with CAM-type acidification described for the Aizoaceae. Traditionally the stems of herbs are not sampled in screening studies. Small herbs with mildly succulent leaves and fleshy stems might be a numerically significant component of CAM biodiversity

Thermal tolerance, net CO2 exchange and growth of a tropical tree species, Ficus insipida, cultivated at elevated daytime and nighttime temperatures

Global warming and associated increases in the frequency and amplitude of extreme weather events, such as heat waves, may adversely affect tropical rainforest plants via significantly increased tissue temperatures. In this study, the response to two temperature regimes was assessed in seedlings of the neotropical pioneer tree species, Ficus insipida. Plants were cultivated in growth chambers at strongly elevated daytime temperature (39°C), combined with either close to natural (22°C) or elevated (32°C) nighttime temperatures. Under both growth regimes, the critical temperature for irreversible leaf damage, determined by changes in chlorophyll a fluorescence, was approximately 51°C. This is comparable to values found in F. insipida growing under natural ambient conditions and indicates a limited potential for heat tolerance acclimation of this tropical forest tree species. Yet, under high nighttime temperature, growth was strongly enhanced, accompanied by increased rates of net photosynthetic CO2 uptake and diminished temperature dependence of leaf-level dark respiration, consistent with thermal acclimation of these key physiological parameters

Facultative crassulacean acid metabolism in a C-3-C-4 intermediate

The Portulacaceae enable the study of the evolutionary relationship between C-4 and crassulacean acid metabolism (CAM) photosynthesis. Shoots of well-watered plants of the C-3-C-4 intermediate species Portulaca cryptopetala Speg. exhibit net uptake of CO2 solely during the light. CO2 fixation is primarily via the C-3 pathway as indicated by a strong stimulation of CO2 uptake when shoots were provided with air containing 2% O-2. When plants were subjected to water stress, daytime CO2 uptake was reduced and CAM-type net CO2 uptake in the dark occurred. This was accompanied by nocturnal accumulation of acid in both leaves and stems, also a defining characteristic of CAM. Following rewatering, net CO2 uptake in the dark ceased in shoots, as did nocturnal acidification of the leaves and stems. With this unequivocal demonstration of stress-related reversible, i.e. facultative, induction of CAM, P. cryptopetala becomes the first C-3-C-4 intermediate species reported to exhibit CAM. Portulaca molokiniensis Hobdy, a C-4 species, also exhibited CAM only when subjected to water stress. Facultative CAM has now been demonstrated in all investigated species of Portulaca, which are well sampled from across the phylogeny. This strongly suggests that in Portulaca, a lineage in which species engage predominately in C-4 photosynthesis, facultative CAM is ancestral to C-4. In a broader context, it has now been demonstrated that CAM can co-exist in leaves that exhibit any of the other types of photosynthesis known in terrestrial plants: C-3, C-4 and C-3-C-4 intermediate