Crassulacean Research Articles

Total alkaloids from the seed embryo of Nelumbo nucifera Gaertn. improve cognitive impairment in APP/PS1 mice and protect Aβ-damaged PC12 cells

ABSTRACT The seed embryo of Nelumbo nucifera Gaertn. is a famous traditional Chinese medicine and food which is considered conducive to the prevention of Alzheimer's disease (AD). In this study, the effect and mechanism of TASENN (total alkaloids from the seed embryo of Nelumbo nucifera Gaertn.) on AD mice and amyloid-β (Aβ) injured PC12 cells were evaluated. HPLC-UV analysis showed that the extracted TASENN (purity = 95.6%) mainly contains Liensinine, Isoliensinine, and Neferine (purity was 23.01, 28.02, and 44.57%, respectively). In vivo, oral treatment with TASENN (50 mg/kg/day for 28 days) improved the learning and memory functions of APP/PS1 transgenic mice, ameliorated the histopathological changes of cortical and hippocampal neurons, and inhibited neuronal apoptosis. We found that TASENN reduced the phosphorylation of Tau and the formation of neurofibrillary tangles (NFTs) in APP/PS1 mouse brain. Moreover, TASENN down-regulated the expression of APP and BACE1, ameliorated Aβ deposition, and inhibited microglial proliferation and aggregation. The elevated protein expression of CaM and p-CaMKII in APP/PS1 mouse brain was also reduced by TASENN. In vitro, TASENN inhibited the apoptosis of PC12 cells injured by Aβ25–35 and increased the cell viability. Aβ25–35-induced increase of cytosolic free Ca2+ level and high expression of CaM, p-CaMKII, and p-Tau were decreased by TASENN. Our findings indicate that TASENN has a potential therapeutic effect on AD mice and a protective effect on PC12 cells. The anti-AD activity of TASENN may be closely related to its negative regulation of the CaM pathway.

Evaluation of the Effectiveness of Common Indoor Plants in Improving the Indoor Air Quality of Studio Apartments

People spend most of their time indoors, and prolonged exposure to pollution can harm their health. The degradation of indoor air quality (IAQ) has raised serious issues. Botanical biofilters are an exciting solution for lowering indoor air pollution. However, plants cultivated inside under low light intensity (10–50 μmole PAR m−2 s−1) generate CO2 in the indoor atmosphere. Combining C3 (Calvin Cycle) and Crassulacean Acid metabolism (CAM) plants may be able to address this problem by lowering CO2 emission levels and enhancing the efficiency of pollution removal by removing the primary indoor air pollutants from actual interior settings, including carbon dioxide (CO2), formaldehyde (HCHO), particulate matter (PM2.5 and PM10), and total volatile organic compounds (TVOCs). As a result, a successful botanical biofilter made of several plants was researched. Indoor plants can phytoremediate a variety of indoor contaminants. However, just a few studies have demonstrated its efficacy in practical contexts. Due to the harsh winter, apartments in South Korea are frequently closed, necessitating the measurement of interior air pollution concentration in real-time. Four apartments (APT I through APT IV) with various ventilation and indoor plant setups were selected for this investigation. Various combinations of indoor environments (ventilation, low light) and a combination of C3 and CAM indoor plants as a botanical biofilter were used to study the sites over two months. Current research indicates that combining a botanical biofilter with ventilation can reduce levels of CO2, TVOCs, HCHO, PM2.5, and PM10 by 76%, 87%, 75%, 52%, and 51%, respectively. The current study concluded that different indoor potted plants provide an effective, affordable, self-regulating, sustainable option for enhancing indoor air quality and, consequently, human well-being and productivity in small, cramped places.

Response and acclimatization of a CAM orchid, Dendrobium Sonia ‘Earsakul’ to drought, heat, and combined drought and heat stress

Response and the acclimation to abiotic stress, including drought, heat (40–45°C), and combined drought and heat stress for 30 days, have been clarified in a crassulacean acid metabolism (CAM)-orchid, Dendrobium Sonia ‘Earsakul’. The drought stress alone caused a more severe effect than the heat stress only. In the drought stress, at 30 days after stress treatments (DAT), the stomatal conductance (gs) and transpiration rate (TR) rapidly dropped after the peak time (6 pm) then the stomata were completely closed to maintain the leaf's relative water content (RWC) at 95.6%, resulting in a drop in the carbon exchange rate (CER). However, the phosphoenolpyruvate carboxylase (PEPC) activity, malondialdehyde (MDA), and antioxidant activity increased at 30 DAT. In heat stress, CER dropped significantly at 7 DAT and was retrieved to the same as the control's level during 14–30 DAT.Moreover, the gs and TR of the heat treatment were significantly increased during 14–30 DAT. In addition, we also found the presence of aerenchyma in leaf sheath in response to heat stress. The combined drought and heat stress caused the severest symptom. The significant loss of leaf RWC at the back pseudobulb was detected from 7 to 30 DAT, resulting in decreasing leaf CER, gs, and TR. However, an increase in PEPC, MDA, and antioxidant activity at 30 DAT was observed after facing both stress combinations.

Re-identification of non-facultative crassulacean acid metabolism behavior for red-fleshed pitaya (Hylocereus polyrhizus) micropropagules in vitro using an Arduino-based open system

A non-facultative crassulacean acid metabolism (CAM) profile has been documented in pitaya, in which closed flow photosynthesis systems have been used to evaluate the CAM capacity and characteristics of plants, albeit with overestimation. By contrast, open-flow systems promote measurement reliability and continuously monitor the photosynthetic profile, which has not been reported in pitaya. Therefore, this study aimed to overview the diel gas exchange capacity of Hylocereus polyrhizus ‘Da Hong’ in an open-flow system, in which the explants were incubated in vitro to prevent measurement deviations caused by microorganism activity. The experimental conditions were 80 µmol/m2/s light intensity at 25 °C under a 16/8 h (D/N) photoperiod. The Arduino-based assembled system contained three subsystems: explant growth, air supplementation, and air sampling and environmental monitoring. The growth vessel had an 83.5% light transmittance with a 3.8 mol/m2/day light intensity. Air ventilation was performed at a flow rate of 1,000 mL/min with 99.9% relative humidity through the filters, which precluded infection and provided a high moisture content environment in the growth vessel during the experiments. A real-time clock library programmed on the development board realized an accurate sampling point and period. The diel gas exchange pattern of pitaya exhibited four phases; explants had a net photosynthetic rate (Pn) of 2.63 μmol/m2/s at midnight, and the total net CO2 uptake over 24 h was 73.98 mmol/m2/day. The positive Pn observed during the daytime was noteworthy. This study successfully measured the photosynthetic profile of pitaya in vitro, providing a diel gas exchange reference. An open-flow whole-canopy system could be used in other explants to evaluate the photosynthesis profile in the era of climate change.

Weak crassulacean acid metabolism and other xerophytic adaptive traits in the genus Beaucarnea Lem. (Asparagaceae).

The genus Beaucarnea (Asparagaceae) has economic value as an ornamental plant but also has ecological importance. Nonetheless, habitat, physiological traits and growth parameters of this genus remain largely unknown. We characterized the environmental ranges of Beaucarnea inermis, B. gracilis and B. pliabilis; and screened for the presence of physiological adaptations to drought (biomass allocation, presence of crassulacean acid metabolism [CAM] and its effect on plant water use). We performed experiments in 3- and 5-year-old nursery-grown plants of the three species, measured dry mass accumulation in leaves/stems/roots and screened for CAM using gas exchange, titratable acidity and δ13 C. We performed a second experiment on the water and light use responses of B. pliabilis under drought treatment. We found that B. gracilis was limited to xerophytic scrubs (precipitation >400 mm yr-1 ), while B. pliabilis and B. inermis (precipitation >500 and 700 mm year-1 , respectively) inhabited dry forests. Beaucarnea gracilis had the lowest dry mass and allocation to leaves, while B. inermis showed the opposite pattern. Only B. pliabilis exhibited small but significant acid fluctuations, characterized as weak CAM, along with high proline content. Acid concentration contributed in 2.7% of the daily carbon during the wet season but represented most of the carbon in the dry season, under closed stomata and had an important contribution to osmolality. Thus, CAM is described for the first time in the genus Beaucarnea, but was only present in one of three species, warranting exploration of this metabolism in the remaining species of this genus.

Identification and expression analysis of pineapple sugar transporters reveal their role in the development and environmental response.

In plants, sugars are required for several essential functions, including growth, storage, signaling, defense and reproduction. Sugar transporters carry out the controlled movement of sugars from source (leaves) to sink (fruits and roots) tissues and determine the overall development of the plant. Various types of sugar transporter families have been described in plants, including sucrose transporters (SUC/SUT), monosaccharide transporter (MST) and SWEET (from "Sugar Will Eventually be Exported Transporters"). However, the information about pineapple sugar transporters is minimal. This study systematically identified and classified 45 MST and 4 SUC/SUT genes in the pineapple genome. We found that the expression patterns of sugar transporter genes have a spatiotemporal expression in reproductive and vegetative tissues indicating their pivotal role in reproductive growth and development. Besides, different families of sugar transporters have a diel expression pattern in photosynthetic and non-photosynthetic tissues displaying circadian rhythm associated participation of sugar transporters in the CAM pathway. Moreover, regulation of the stress-related sugar transporters during cold stress indicates their contribution to cold tolerance in pineapple. Heterologous expression (yeast complementation assays) of sugar transporters in a mutant yeast strain suggested that SUT1/2 have the ability to transport sucrose, and STP13, STP26, pGlcT-L2 and TMT4 are able to transport glucose, whereas SWEET11/13 transport both sucrose and fructose. The information provided here would help researchers further explore the underlying molecular mechanism involved in the sugar metabolism of pineapple.

Experimental comparison of two extensive green roof designs in Northwest Mexico

Accelerated population growth and urbanization have negative environmental impacts, such as habitat destruction, biodiversity loss, natural resource depletion, and pollution. They speed up climate change, contribute to urban heat islands, and increase energy use. Green roofs (GRs) can reduce the ecological footprint and improve the quality of life within cities but require careful design for best results. This study analyzes the thermal performance of GRs in six experimental modules differing in roof cover: concrete, reflective coating, dry soil, wet soil, traditional GR with Sedum acre, and wetland GR with Salicornia pacifica. The two plant species have different carbon assimilation metabolisms: S. pacifica is a native wetland C3 species with diurnal transpiration that grows in flooded soils, and S. acre is an exotic Crassulacean Acid Metabolism (CAM) species with night-time transpiration, commonly used in GRs. GRs were monitored during the winter of 2020 in Ensenada, Baja California, México, a city with a semi-arid Mediterranean climate. We found that vegetated covers reduced the temperature oscillation with an insulating effect. During the warmest week, they reduced the internal roof surface temperature (Ts,in) up to 12.4 °C in comparison to the concrete roof. They maintained Ts,in up to 5.8 °C warmer than concrete roof during the coldest week, indicating that GRs are efficient thermal regulators in this region, potentially reducing buildings’ thermal load as well as providing additional ecosystemic services. Since S. pacifica had higher survival and coverage, we recommend its use in GRs located in Northwest Mexico and climatically similar world regions.

Physiological and transcriptomic analysis uncovers salinity stress mechanisms in a facultative crassulacean acid metabolism plant Dendrobium officinale.

Dendrobium officinale is a precious medicinal Chinese herb that employs facultative crassulacean acid metabolism (CAM) and has a high degree of abiotic stress tolerance, but the molecular mechanism underlying the response of this orchid to abiotic stresses is poorly understood. In this study, we analyzed the root microstructure of D. officinale plantlets and verified the presence of chloroplasts by transmission electron microscopy. To obtain a more comprehensive overview of the molecular mechanism underlying their tolerance to abiotic stress, we performed whole‐transcriptome sequencing of the roots of 10-month-old plantlets exposed to salt (NaCl) treatment in a time‐course experiment (0, 4 and 12 h). The total of 7376 differentially expressed genes that were identified were grouped into three clusters (P < 0.05). Metabolic pathway analysis revealed that the expression of genes related to hormone (such as auxins, cytokinins, abscisic acid, ethylene and jasmonic acid) biosynthesis and response, as well as the expression of genes related to photosynthesis, amino acid and flavonoid metabolism, and the SOS pathway, were either up- or down-regulated after salt treatment. Additionally, we identified an up-regulated WRKY transcription factor, DoWRKY69, whose ectopic expression in Arabidopsis promoted seed germination under salt tress. Collectively, our findings provide a greater understanding of the salt stress response mechanisms in the roots of a facultative CAM plant. A number of candidate genes that were discovered may help plants to cope with salt stress when introduced via genetic engineering.

Morphological, photosynthetic, and CAM physiological responses of the submerged macrophyte Ottelia alismoides to light quality

Light quality strongly affect a great many physiological processes in terrestrial plants. Whatever, few studies have investigated how the submerged macrophytes response to different light quality. The present research aimed to understand how light quality affect morphogenesis, photosynthesis, as well as crassulacean acid metabolism (CAM) operation during the growth of Ottelia alismoides , a freshwater facultative CAM macrophyte. The plants were grown under three light qualities of white (W), red (R) and blue (B) lights with same light intensity of 100 μmol m −2 s −1 . Leaf development, leaf anatomic characteristics, photosynthetic traits, as well as CAM metabolism were determined on the newly produced leaves during light treatment. Monochromatic R stimulated leaf blade and petiole elongation, leaf area and dry weight, but reduced leaf thickness, negatively influenced chlorophyll content and Fv/Fm. On the contrary, B- grown plants were dwarf and with compact size as well as lower leaf dry weight. The content of photosynthetic product starch under B was significantly lower as compared with R, moreover, combined with the analysis of ultrastructural characteristics of epidermal and mesophyll chloroplasts, it showed that B inhibited starch to be translocated out of epidermal chloroplasts. Furthermore, both R- and B- grown plants exhibited obvious diurnal acidity fluctuation comparable to W- grown plants, and had high activity of enzymes including ribulose-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPC) and pyruvate phosphate dikinase (PPDK) that required for CAM cycle, indicating that CAM was present in both R- and B- grown plants and monochromatic R and B did not affect CAM activity. In conclusion, monochromatic red and blue light differentially played their special roles in regulating leaf growth and morphogenesis, as well as photosynthetic metabolism in O. alismoides . • O. alismoides displayed strong morphological plasticity to light quality. • Leaf elongation was promoted by red light but inhibited by blue light. • Red light favoured O. alismoides leaf development and photosynthesis. • Blue light inhibited translocation of starch out of epidermal chloroplasts. • O. alismoides exhibited comparable CAM activity under white, red and blue light.

Carbon and nitrogen metabolic regulation in freshwater plant Ottelia alismoides in response to carbon limitation: A metabolite perspective.

Carbon and nitrogen metabolism are basic, but pivotal metabolic pathways in plants and are tightly coupled. Maintaining the balance of carbon and nitrogen metabolism is critical for plant survival. Comprehensively revealing the metabolic balance of carbon–nitrogen interactions is important and helpful for understanding the adaptation of freshwater plants to CO2 limited aqueous environment. A comprehensive metabolomics analysis combined with physiological measurement was performed in the freshwater plant Ottelia alismoides acclimated to high and low CO2, respectively, for a better understanding of how the carbon and nitrogen metabolic adjustment in freshwater plants respond to carbon limitation. The present results showed that low CO2 acclimated O. alismoides exhibited significant diurnal titratable acidity and malate fluctuations, as well as an opposite diel pattern of starch change and high enzymatic activities required for crassulacean acid metabolism (CAM) photosynthesis, which indicates that CAM was induced under low CO2. Moreover, the metabolomic analysis showed that most intermediates of glycolysis, pentose phosphate pathway (PPP) and tricarboxylic acid (TCA) cycle, were increased under low CO2, indicative of active respiration in low-CO2-treated O. alismoides. Meanwhile, the majority of amino acids involved in pathways of glutamate and arginine metabolism, aspartate metabolism, and the branched-chain amino acids (BCAAs) metabolism were significantly increased under low CO2. Notably, γ-aminobutyric acid (GABA) level was significantly higher in low CO2 conditions, indicating a typical response with GABA shunt compensated for energy deprivation at low CO2. Taken together, we conclude that in low-CO2-stressed O. alismoides, CAM photosynthesis was induced, leading to higher carbon and nitrogen as well as energy requirements. Correspondingly, the respiration was greatly fueled via numerous starch degradation to ensure CO2 fixation in dark, while accompanied by linked promoted N metabolism, presumably to produce energy and alternative carbon sources and nitrogenous substances for supporting the operation of CAM and enhancing tolerance for carbon limitation. This study not only helps to elucidate the regulating interaction between C and N metabolism to adapt to different CO2 but also provides novel insights into the effects of CO2 variation on the metabolic profiling of O. alismoides.

Integrated Analysis of Transcriptome and Small RNAome Reveals the Regulatory Network for Rapid Growth in Mikania micrantha.

M. micrantha has caused huge ecological damage and economic losses worldwide due to its rapid growth and serious invasion. However, the underlying molecular mechanisms of its rapid growth and environmental adaption remain unclear. Here, we performed transcriptome and small RNA sequencing with five tissues of M. micrantha to dissect miRNA-mediated regulation in M. micrantha. WGCNA and GO enrichment analysis of transcriptome identified the gene association patterns and potential key regulatory genes for plant growth in each tissue. The genes highly correlated with leaf and stem tissues were mainly involved in the chlorophyll synthesis, response to auxin, the CAM pathway and other photosynthesis-related processes, which promoted the fast growth of M. micrantha. Importantly, we identified 350 conserved and 192 novel miRNAs, many of which displayed differential expression patterns among tissues. PsRNA target prediction analysis uncovered target genes of both conserved and novel miRNAs, including GRFs and TCPs, which were essential for plant growth and development. Further analysis revealed that miRNAs contributed to the regulation of tissue-specific gene expression in M. micrantha, such as mmi-miR396 and mmi-miR319. Taken together, our study uncovered the miRNA-mRNA regulatory networks and the potential vital roles of miRNAs in modulating the rapid growth of M. micrantha.

Predicting plant Rubisco kinetics from RbcL sequence data using machine learning.

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is responsible for the conversion of atmospheric CO2 to organic carbon during photosynthesis, and often acts as a rate limiting step in the later process. Screening the natural diversity of Rubisco kinetics is the main strategy used to find better Rubisco enzymes for crop engineering efforts. Here, we demonstrate the use of Gaussian processes (GPs), a family of Bayesian models, coupled with protein encoding schemes, for predicting Rubisco kinetics from Rubisco large subunit (RbcL) sequence data. GPs trained on published experimentally obtained Rubisco kinetic datasets were applied to over 9000 sequences encoding RbcL to predict Rubisco kinetic parameters. Notably, our predicted kinetic values were in agreement with known trends, e.g. higher carboxylation turnover rates (Kcat) for Rubisco enzymes from C4 or crassulacean acid metabolism (CAM) species, compared with those found in C3 species. This is the first study demonstrating machine learning approaches as a tool for screening and predicting Rubisco kinetics, which could be applied to other enzymes.

Genome sequencing and comparative analysis of Ficus benghalensis and Ficus religiosa species reveal evolutionary mechanisms of longevity

SummaryFicus benghalensis and Ficus religiosa are large woody trees well known for their long lifespan, ecological and traditional significance, and medicinal properties. To understand the genomic and evolutionary aspects of these characteristics, the whole genomes of these Ficus species were sequenced using 10x Genomics linked reads and Oxford Nanopore long reads. The draft genomes of F. benghalensis and F. religiosa comprised of 392.89 Mbp and 332.97 Mbp, respectively. We established the genome-wide phylogenetic positions of the two Ficus species with respect to 50 other Angiosperm species. Comparative evolutionary analyses with other phylogenetically closer Eudicot species revealed adaptive evolution in genes involved in key cellular mechanisms associated with prolonged survival including phytohormones signaling, senescence, disease resistance, and abiotic stress tolerance, which provide genomic insights into the mechanisms conferring longevity and suggest that longevity is a multifaceted phenomenon. This study also provides clues on the existence of CAM pathway in these Ficus species.

Bioclimatic controls of CO2 assimilation near range limits of the CAM succulent tree Aloidendron dichotomum.

Aloidendron dichotomum appears to be undergoing the early stages of a range shift in response to anthropogenic climate change in south-western Africa. High mortality has been recorded in warmer populations, while population expansions have been recorded in cooler poleward parts of its range. This study aimed to determine the key environmental controls on A. dichotomum photosynthesis in areas of population expansion, to inform the potential attribution of directional population expansion to anthropogenic warming. Nocturnal acid accumulation and CO2 assimilation were measured in individuals growing under a range of temperature and watering treatments in a greenhouse experiment. In addition, nocturnal acid accumulation and phosphoenolpyruvate carboxylase activity were quantified in two wild populations at the most southerly and south-easterly range extents. Multiple lines of evidence confirmed that A. dichotomum performs Crassulacean acid metabolism. Total nocturnal acid accumulation was highest at night-time temperatures of ~21.5 °C, regardless of soil water availability, and night-time CO2 assimilation rates increased with leaf temperature, suggesting a causal link to the cool southern range limit. Leaf acidity at the start of the dark period was highly predictive of nocturnal acid accumulation in all individuals, implicating light availability during the day as an important determinant of nocturnal acid accumulation.

Agave americana: Characteristics and Potential Breeding Priorities.

Agave americana L. is one of many Agave species that could be developed for the production of valuable agricultural products. Although all species in this genus use Crassulacean Acid Metabolism (CAM) and most have drought and heat tolerance, Agave americana also has the combined traits of high yield and cold tolerance. This review highlights key characteristics of Agave americana that make it an exceptional novel crop for fiber, sweeteners, bioproducts, and bioethanol with resilient traits for changing climate conditions. Then, it proposes potential directions for breeding that will support production in semi-arid climates. With selection and breeding, yields of 16 Mg ha−1 y−1 may be achieved. Current field observations, with no crop improvement, indicate ~9 Mg ha−1 is the maximum yield, and in arid regions, a yield of ~3 Mg ha−1 y−1 is observed. It may be beneficial to breed for a shorter time to flowering, as has been successful for Agave tequilana Weber var. azul, so that further breeding goals are achievable in a decadal timespan. Specific trait selection during breeding will depend on whether fiber or sugar yields are the desired products at a given location. Even without breeding, varieties of Agave americana are climate resilient alternatives for some current commodity crops.

Comparative analyses of the metabolite and ion concentrations in nectar, nectaries, and leaves of 36 bromeliads with different photosynthesis and pollinator types.

Floral nectar contains mainly sugars as well as smaller amounts of amino acids and further compounds. The nectar composition varies between different plant species and it is related to the pollination type of the plant. In addition to this, other factors can influence the composition. Nectar is produced in and secreted from nectaries. A few models exist to explain the origin of nectar for dicotyl plant species, a complete elucidation of the processes, however, has not yet been achieved. This is particularly true for monocots or plant species with CAM photosynthesis. To get closer to such an elucidation, nectar, nectaries, and leaves of 36 bromeliad species were analyzed for sugars, starch, amino acids, and inorganic ions. The species studied include different photosynthesis types (CAM/C3), different pollination types (trochilophilous/chiropterophilous), or different live forms. The main sugars in nectar and nectaries were glucose, fructose, and sucrose, the total sugar concentration was about twofold higher in nectar than in nectaries, which suggests that sugars are actively transported from the nectaries into the nectar. The composition of amino acids in nectar is already determined in the nectaries, but the concentration is much lower in nectar than in nectaries, which suggests selective retention of amino acids during nectar secretion. The same applies to inorganic ions. Statistical analyses showed that the photosynthesis type and the pollination type can explain more data variation in nectar than in nectaries and leaves. Furthermore, the pollinator type has a stronger influence on the nectar or nectary composition than the photosynthesis type. Trochilophilous C3 plants showed significant correlations between the nitrate concentration in leaves and the amino acid concentration in nectaries and nectar. It can be assumed that the more nitrate is taken up, the more amino acids are synthesized in leaves and transported to the nectaries and nectar. However, chiropterophilous C3 plants show no such correlation, which means that the secretion of amino acids into the nectar is regulated by further factors. The results help understand the physiological properties that influence nectaries and nectar as well as the manner of metabolite and ion secretion from nectaries to nectar.

Physiological ecology of Mexican CAM plants: history, progress, and opportunities

In Mexico, plants with crassulacean acid metabolism (CAM) are part of the Mexican culture, have different uses and are even emblematic. Unfortunately, only a small fraction of the Mexican CAM plants has been studied physiologically. For this review, the following questions were considered: What ecophysiological studies have been conducted with CAM species native to Mexico? What ecophysiological processes in Mexican CAM plants are the most studied? What type of ecophysiological studies with CAM plants are still needed? A database of scientific studies on CAM plant species from Mexico was documented, including field and laboratory works for species widely distributed, and those studies made outside Mexico with Mexican species. Physiological processes were grouped as germination, photosynthesis, and water relations. Most studies were done for CAM species of Cactaceae, Bromeliaceae, Asparagaceae and Orchidaceae, andmost ecophysiological studies have been done on germination of cacti. Field and laboratory studies on photosynthesis and water relations were mostly for terrestrial cacti and epiphytic bromeliads. There were few physiological studies with CAM seedlings in Mexico and few studies using stable isotopes of water and carbon of CAM plants in the field. More field and laboratory studies of physiological responses and plasticity of CAM plants to multiple stress factors are required to model plant responses to global climate change. In general, more physiological studies are essential for all CAM species and for species of the genus Clusia , with C3-CAM and CAM members, which can become ecologically important under some climate change scenarios.

Photosynthesis of Submerged and Surface Leaves of the Dwarf Water Lily (Nymphoides aquatica) Using PAM Fluorometry

Dwarf Water Lilies (Nymphoides aquatica (J.F. Gmel) Kuntze have floating and submerged leaves. Some submerged aquatic vascular plants have a form of CAM (Crassulacean Acid Metabolism) called Submerged Aquatic Macrophyte (SAM) metabolism. Blue-diode based PAM technology was used to measure the Photosynthetic Oxygen Evolution Rate (POER: 1O2 ≡ 4e– ). Optimum Irradiance (Eopt), maximum POER (POERmax) and quantum efficiency (α0) all vary on a diurnal cycle. The shape of the POER vs. E curves is different in seedling, submerged and surface leaves. Both Eopt and POERmax are very low in seedling leaves (Eopt ≈ 104 μmol photon m–2 s–1, PPFD; POERmax ≈ 4.95 µmol O2 g–1 Chl a s–1), intermediate in mature submerged leaves (Eopt ≈ 419 µmol photon m–2 s–1 PPFD, POERmax ≈ 38.1 µmol O2 g–1 Chl a s–1) and very high in surface leaves (Eopt ≈ 923 µmol photon m–2 s–1 PPFD, POERmax ≈ 76.1 µmol O2 g–1 Chl a s–1). Leaf titratable acid (C4 acid pool) is too small (≈20 to 50 mol H+ m–3) to support substantial SAM metabolism. Gross daily photosynthesis of surface leaves is ≈3.71 g C m–2 d–1 in full sun and as much as 1.4 gC m–2 d–1 in shaded submerged leaves. There is midday inhibition of photosynthesis.

Comparative genomics analysis of drought response between obligate CAM and C3 photosynthesis plants

Crassulacean acid metabolism (CAM) plants exhibit elevated drought and heat tolerance compared to C3 and C4 plants through an inverted pattern of day/night stomatal closure and opening for CO2 assimilation. However, the molecular responses to water-deficit conditions remain unclear in obligate CAM species. In this study, we presented genome-wide transcription sequencing analysis using leaf samples of an obligate CAM species Kalanchoë fedtschenkoi under moderate and severe drought treatments at two-time points of dawn (2-h before the start of light period) and dusk (2-h before the dark period). Differentially expressed genes were identified in response to environmental drought stress and a whole genome wide co-expression network was created as well. We found that the expression of CAM-related genes was not regulated by drought stimuli in K. fedtschenkoi. Our comparative analysis revealed that CAM species (K. fedtschenkoi) and C3 species (Arabidopsis thaliana, Populus deltoides ‘WV94’) share some common transcriptional changes in genes involved in multiple biological processes in response to drought stress, including ABA signaling and biosynthesis of secondary metabolites.

Spatial resolution of an integrated C4+CAM photosynthetic metabolism.

C4 and CAM photosynthesis have repeatedly evolved in plants over the past 30 million years. Because both repurpose the same set of enzymes but differ in their spatial and temporal deployment, they have long been considered as distinct and incompatible adaptations. Portulaca contains multiple C4 species that perform CAM when droughted. Spatially explicit analyses of gene expression reveal that C4 and CAM systems are completely integrated in Portulaca oleracea, with CAM and C4 carbon fixation occurring in the same cells and CAM-generated metabolites likely incorporated directly into the C4 cycle. Flux balance analysis corroborates the gene expression findings and predicts an integrated C4+CAM system under drought. This first spatially explicit description of a C4+CAM photosynthetic metabolism presents a potential new blueprint for crop improvement.