chlorophyll-a and malic-acid

Topics: Ananas; Antioxidants; Carbon Dioxide; Chlorophyll; Glutathione; Peroxides; Photosynthesis; Plant Leaves

We studied the effects of three organic acids (citric acid, tartaric acid and malic acid) on the biomass, photosynthetic pigment content and photosynthetic parameters of Salix variegata under Cd stress and observed the ultrastructure of mesophyll cells in each treatment. Cd stress significantly reduced photosynthesis by reducing the content of pigments and disrupting chloroplast structure, which consequently decreased the biomass. However, respective addition of three organic acids greatly increased the biomass of S. variegata under Cd stress. Among them, the effect of malic acid or tartaric acid on shoot and total biomass accumulation was greater than that of citric acid. The alleviation of biomass probably related with the photosynthetic process. Results revealed that treatment with each organic acid enhanced the net photosynthesis rate under Cd stress. Malic acid promoted plant growth and biomass by increasing the chlorophyll content and mitigating damage to the photosynthetic apparatus resulting from Cd stress. Tartaric acid had little impact on the photosynthetic pigment content, but it was important in mitigating the ultrastructural damage of plants caused by Cd. Addition of citric acid significantly increased the carotenoid as well as the number and volume of chloroplasts in mesophyll cells, while the mitigation of structural damage in the photosynthetic apparatus was weaker than that in tartaric acid or malic acid treatment. It is concluded that application of tartaric acid or malic acid is effective in increasing the growth potential of S. variegata under Cd stress and thus can be a promising approach for the phytoremediation of Cd-contaminated soil.

Topics: Biodegradation, Environmental; Biological Availability; Biomass; Cadmium; Chlorophyll; Chloroplasts; Malates; Photosynthesis; Salix; Soil Pollutants; Tartrates

Barley is described to mostly use sucrose for night carbon requirements. To understand how the transient carbon is accumulated and utilized in response to cold, barley plants were grown in a combination of cold days and/or nights. Both daytime and night cold reduced growth. Sucrose was the main carbohydrate supplying growth at night, representing 50-60% of the carbon consumed. Under warm days and nights, starch was the second contributor with 26% and malate the third with 15%. Under cold nights, the contribution of starch was severely reduced, due to an inhibition of its synthesis, including under warm days, and malate was the second contributor to C requirements with 24-28% of the total amount of carbon consumed. We propose that malate plays a critical role as an alternative carbon source to sucrose and starch in barley. Hexoses, malate, and sucrose mobilization and starch accumulation were affected in barley elf3 clock mutants, suggesting a clock regulation of their metabolism, without affecting growth and photosynthesis however. Altogether, our data suggest that the mobilization of sucrose and malate and/or barley growth machinery are sensitive to cold.

Topics: Carbon; Carbon Dioxide; Chlorophyll; Circadian Rhythm; Cold Temperature; Darkness; Fluorescence; Fructans; Hordeum; Malates; Metabolome; Photosynthesis; Plant Proteins; Plant Stomata; Plant Transpiration; Solubility; Starch; Sucrose; Sugars

The accumulation of iron (Fe) in the apical meristem is considered as a critical factor involved in limiting the elongation of roots under low phosphate (Pi) conditions. Furthermore, the antagonism between Fe and Pi largely affects the effective utilization of Fe. Although the lack of Pi serves to increase the effectiveness of Fe in rice under both Fe-sufficient and Fe-deficient conditions, the underlying physiological mechanism governing this phenomenon is still unclear. In this study, we found that low Pi alleviated the Fe-deficiency phenotype in apples. Additionally, low Pi treatments increased ferric-chelated reductase (FCR) activity in the rhizosphere, promoted proton exocytosis, and enhanced the Fe concentration in both the roots and shoots. In contrast, high Pi treatments inhibited this process. Under conditions of low Pi, malate and citrate exudation from apple roots occurred under both Fe-sufficient and Fe-deficient conditions. In addition, treatment with 0.5 mM malate and citrate effectively alleviated the Fe and Pi deficiencies. Taken together, these data support the conclusion that a low Pi supply promotes organic acids exudation and enhances Fe absorption during Fe deficiency in apples.

Topics: Anthocyanins; Chlorophyll; Citric Acid; Gene Expression Profiling; Iron; Iron Deficiencies; Malates; Malus; Phosphates; Plant Roots; Real-Time Polymerase Chain Reaction; Rhizosphere; Transcriptome

Malate exudation through wheat (Triticum aestivum L) aluminium-activated malate transporter 1 (TaALMT1) confers Al

Topics: Animals; Animals, Genetically Modified; Chlorophyll; GABA Plasma Membrane Transport Proteins; gamma-Aminobutyric Acid; Hordeum; Hydrogen-Ion Concentration; Malates; Oocytes; Organic Anion Transporters; Plant Leaves; Plant Proteins; Plant Roots; Plants, Genetically Modified; Rhizosphere; Seedlings; Stress, Physiological; Triticum; Xenopus

Rhodobacter sphaeroides is a purple non-sulfur bacterium which photoheterotrophically produces hydrogen from organic acids under anaerobic conditions. A gene coding for putative chlorophyll a synthase (chlG) from cyanobacterium Prochlorococcus marinus was amplified by nested polymerase chain reaction and cloned into an inducible-expression plasmid which was subsequently transferred to R. sphaeroides for heterologous expression. Induced expression of chlG in R. sphaeroides led to changes in light absorption spectrum within 400-700 nm. The hydrogen production capacity of the mutant strain was evaluated on hydrogen production medium with 15 mM malate and 2 mM glutamate. Hydrogen yield and productivity were increased by 13.6 and 22.6%, respectively, compared to the wild type strain. The results demonstrated the feasibility of genetic engineering to combine chlorophyll and bacteriochlorophyll biosynthetic pathways which utilize common intermediates. Heterologous expression of key enzymes from biosynthetic pathways of various pigments is proposed here as a general strategy to improve absorption spectra and yield of photosynthesis and hydrogen gas production in bacteria.

Topics: Bacteriochlorophylls; Carbon-Oxygen Ligases; Chlorophyll; Chlorophyll A; Cloning, Molecular; Gene Expression; Genes, Bacterial; Genetic Engineering; Glutamic Acid; Hydrogen; Malates; Mutation; Photosynthesis; Plasmids; Polymerase Chain Reaction; Prochlorococcus; Recombinant Proteins; Rhodobacter sphaeroides

In this study, the metabolic and physiological impacts of an altered microclimate on quality-associated primary and secondary metabolites in grape (Vitis vinifera) 'Sauvignon Blanc' berries was determined in a high-altitude vineyard. The leaf and lateral shoot removal in the bunch zones altered the microclimate by increasing the exposure of the berries. The physical parameters (berry diameter and weight), primary metabolites (sugars and organic acids), as well as bunch temperature and leaf water potential were predominantly not affected by the treatment. The increased exposure led to higher levels of specific carotenoids and volatile terpenoids in the exposed berries, with earlier berry stages reacting distinctly from the later developmental stages. Plastic/nonplastic metabolite responses could be further classified to identify metabolites that were developmentally controlled and/or responded to the treatment in a predictable fashion (assessed over two consecutive vintages). The study demonstrates that grapevine berries exhibit a degree of plasticity within their secondary metabolites and respond physiologically to the increased exposure by increasing metabolites with potential antioxidant activity. Taken together, the data provide evidence that the underlying physiological responses relate to the maintenance of stress pathways by modulating antioxidant molecules in the berries.

Topics: Carbohydrate Metabolism; Carotenoids; Chlorophyll; Fruit; Genes, Plant; Malates; Metabolic Networks and Pathways; Microclimate; Models, Biological; Plant Leaves; Tartrates; Terpenes; Vitis; Wine; Xanthophylls

Phosphorus (P) availability in alkaline soils of arid and semi-arid regions is a major constraint for decreased crop productivity. Use of plant growth promoting rhizobacteria (PGPR) may enhance plant growth through the increased plant antioxidation activity. Additionally, PGPR may increase nutrient uptake by plants as a result of induced root exudation and rhizosphere acidification. The current study was aimed to investigate combined effects of P and Pesudomonas putida (PGPR) on chickpea growth with reference to antioxidative enzymatic activity and root exudation mediated plant nutrient uptake, particularly P. Half of the seeds were soaked in PGPR solution, whereas others in sterile water and latter sown in soils. Plants were harvested 8 weeks after onset of experiment and analyzed for leaf nutrient contents, antioxidant enzymes activities and organic acids concentrations. Without PGPR, P application (+P) increased various plant growth attributes, plant uptake of P and Ca, soil pH, citric acid and oxalic acid concentrations, whereas decreased the leaf POD enzymatic activity as compared to the P-deficiency. PGPR supply both under -P and +P improved the plant growth, plant uptake of N, P, and K, antioxidative activity of SOD and POD enzymes and concentrations of organic acids, whereas reduced the rhizosphere soil pH. Growth enhancement by PGPR supply was related to higher plant antioxidation activity as well as nutrient uptake of chickpea including P as a result of root exudation mediated rhizosphere acidification.

Topics: Antioxidants; Biological Availability; Chlorophyll; Cicer; Citric Acid; Enzymes; Hydrogen-Ion Concentration; Malates; Oxalic Acid; Phosphorus; Plant Exudates; Plant Leaves; Pseudomonas putida; Rhizosphere; Seeds; Soil

Global DNA methylation changes caused by in vitro conditions are associated with the subculturing and phenotypic variation in Agave angustifolia Haw. While the relationship between the development of albinism and in vitro culture is well documented, the role of epigenetic processes in this development leaves some important questions unanswered. During the micropropagation of Agave angustifolia Haw., we found three different phenotypes, green (G), variegated (V) and albino (A). To understand the physiological and epigenetic differences among the somaclones, we analyzed several morphophysiological parameters and changes in the DNA methylation patterns in the three phenotypes during their in vitro development. We found that under in vitro conditions, the V plantlets maintained their CAM photosynthetic capacity, while the A variant showed no pigments and lost its CAM photosynthetic ability. Epigenetic analysis revealed that global DNA methylation increased in the G phenotype during the first two subcultures. However, after that time, DNA methylation levels declined. This hypomethylation correlated with the appearance of V shoots in the G plantlets. A similar correlation occurred in the V phenotype, where an increase of 2 % in the global DNA methylation levels was correlated with the generation of A shoots in the V plantlets. This suggests that an "epigenetic stress memory" during in vitro conditions causes a chromatin shift that favors the generation of variegated and albino shoots.

Topics: Agave; Carotenoids; Chlorophyll; Chromosome Segregation; Clone Cells; DNA Methylation; Malates; Phenotype; Photoperiod; Plant Stomata; Tissue Culture Techniques

As plants are sessile, they often face high light (HL) stress that causes damage of the photosynthetic machinery leading to decreased photosynthesis. The importance of alternative oxidase (AOX) in optimizing photosynthesis is well documented. In the present study, the role of AOX in sustaining photosynthesis under HL was studied using AOX1a knockout mutants (aox1a) of Arabidopsis thaliana. Under growth light (GL; 50 μmol photons m(-2) s(-1)) conditions, aox1a plants did not show any changes in photosynthetic parameters, NAD(P)/H redox ratios, or respiratory O2 uptake when compared to wild-type (WT). Upon exposure to HL (700 μmol photons m(-2) s(-1)), respiratory rates did not vary between WT and aox1a. But, photosynthetic parameters related to photosystem II (PSII) and NaHCO3 dependent O2 evolution decreased, while the P700 reduction state increased in aox1a compared to WT. Further, under HL, the redox state of cellular NAD(P)/H pools increased with concomitant rise in reactive oxygen species (ROS) and malondialdehyde (MDA) content in aox1a compared to WT. In presence of HL, the transcript levels of several genes related to antioxidant, malate-oxaloacetate (malate-OAA) shuttle, photorespiratory and respiratory enzymes was higher in aox1a compared to WT. Taken together, these results demonstrate that under HL, in spite of significant increase in transcript levels of several genes mentioned above to maintain cellular redox homeostasis and minimize ROS production, Arabidopsis plants deficient in AOX1a were unable to sustain photosynthesis as is the case in WT plants.

Topics: Antioxidants; Arabidopsis; Arabidopsis Proteins; Cell Respiration; Chlorophyll; Gene Expression Regulation, Plant; Homeostasis; Light; Lipid Peroxidation; Malates; Malondialdehyde; Mitochondrial Proteins; Oxaloacetic Acid; Oxidation-Reduction; Oxidoreductases; Oxygen; Photosynthesis; Photosystem II Protein Complex; Plant Leaves; Plant Proteins; Reactive Oxygen Species; Stress, Physiological

Demand for broccoli has increased due to its high content of bioactive compounds. However, broccoli is a perishable commodity with a short shelf life mainly due to dehydration, yellowing and losses of bioactive compounds. Thus, efficient treatments to preserve broccoli quality are needed.. The effect of heat treatment on senescence and antioxidant compounds evolution during storage at 20 °C was evaluated in organic and conventionally grown broccoli. Senescence evolved quickly as manifested by floral head yellowing, which was higher in conventional than in organic broccolis, but senescence was significantly delayed by heat treatment. All organic acids, including ascorbic acid, were found at higher concentrations in organic than in conventional broccoli at harvest but decreased during storage in all broccolis. Phenolic concentration and antioxidant activity (in both hydrophilic and lipophilic fractions) also decreased during storage, although these decreases were higher in conventional than in organic broccolis, and no differences were found attributable to heat treatment.. Heat treatment was effective in delaying broccoli senescence, manifested by chlorophyll retention. In addition, organic broccoli maintained higher concentrations of bioactive compounds (ascorbic acid and phenolics) and antioxidant potential during storage than conventional broccoli, with higher potential health beneficial effects.

Topics: Antioxidants; Ascorbic Acid; Brassica; Chlorophyll; Flowering Tops; Food Preservation; Food Quality; Food Storage; Food, Organic; Hot Temperature; Hydrophobic and Hydrophilic Interactions; Malates; Phenols; Pigments, Biological; Plant Stems; Spain; Tartrates; Time Factors

Many plant species grown under in vitro controlled conditions can be used as models for the study of physiological processes. Adult pineapple can display CAM physiology while in vitro it functions as a C3 plant. Ex vitro Ananas comosus has plastic morphology and physiology, both easy to modify from C3 to CAM by changing the environmental conditions. The yield of survival for a rentable propagation protocol of pineapple is closely related with the C3/CAM shift and the associated physiological characteristics. In the present work, ex vitro pineapple plants were divided in two sets and subjected to C3 and CAM-inducing environmental conditions, determined by light intensity and relative humidity, respectively, 40 μmol m(-2) s(-1)/85% and 260 μmol m(-2) s(-1)/50%. The results demonstrated that the stress imposed by the environmental conditions switched pineapple plants from C3 to CAM behavior. Comparing to CAM induced, C3-induced pineapple plants showed substandard growth parameters and morphological leaf characteristics but a better rooting process and a higher ABA production, a phenotype closer to adult plants, which are expected to produce fruits in a normal production cycle. We conclude that the upholding of these characteristics is conditioned by low light intensity plus high relative humidity, especially during the first 8 weeks of ex vitro growth. It is expected that the better understanding of pineapple acclimatization will contribute to the design of a protocol to apply as a rentable tool in the pineapple agronomic industry.

Topics: Abscisic Acid; Acclimatization; Agricultural Irrigation; Ananas; Biomass; Carbon; Chlorophyll; Chlorophyll A; Environment; Fluorescence; Humidity; Light; Malates; Oxidative Stress; Photosynthesis; Plant Leaves; Temperature; Waxes

Transport of dicarboxylates across the chloroplast envelope plays an important role in transferring carbon skeletons to the nitrogen assimilation pathway and exporting reducing equivalent to the cytosol to prevent photo-inhibition (the malate valve). It was previously shown that the Arabidopsis plastidic 2-oxoglutarate/malate transporter (AtpOMT1) and the general dicarboxylate transporter (AtpDCT1) play crucial roles at the interface between carbon and nitrogen metabolism. However, based on the in vitro transport properties of the recombinant transporters, it was hypothesized that AtpOMT1 might play a dual role, also functioning as an oxaloacetate/malate transporter, which is a crucial but currently unidentified component of the chloroplast malate valve. Here, we test this hypothesis using Arabidopsis T-DNA insertional mutants of AtpOMT1. Transport studies revealed a dramatically reduced rate of oxaloacetate uptake into chloroplasts isolated from the knockout plant. CO(2) -dependent O(2) evolution assays showed that cytosolic oxaloacetate is efficiently transported into chloroplasts mainly by AtpOMT1, and supported the absence of additional oxaloacetate transporters. These findings strongly indicate that the high-affinity oxaloacetate transporter in Arabidopsis chloroplasts is AtpOMT1. Further, the knockout plants showed enhanced photo-inhibition under high light due to greater accumulation of reducing equivalents in the stroma, indicating malfunction of the malate valve in the knockout plants. The knockout mutant showed a phenotype consistent with reductions in 2-oxoglutarate transport, glutamine synthetase/glutamate synthase activity, subsequent amino acid biosynthesis and photorespiration. Our results demonstrate that AtpOMT1 acts bi-functionally as an oxaloacetate/malate transporter in the malate valve and as a 2-oxoglutarate/malate transporter mediating carbon/nitrogen metabolism.

Topics: Arabidopsis; Arabidopsis Proteins; Carbon; Chlorophyll; Chloroplasts; Dicarboxylic Acid Transporters; Malates; Nitrogen; Plants, Genetically Modified; Reverse Transcriptase Polymerase Chain Reaction

In this study some aspects of organic and amino acid metabolism in cherry endocarp and seed were investigated during their development. The abundance and location of a number of enzymes involved in these processes were investigated. These enzymes were aspartate aminotransferase (AspAT; EC:2.6.1.1), glutamine synthetase (GS; EC:6.3.1.2), phosphoenolpyruvate carboxylase (PEPC; EC:4.1.1.31), phosphoenolpyruvate carboxykinase (PEPCK; EC:4.1.1.49), and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC:4.1.1.39). There was a transient and massive accumulation of vegetative storage proteins in the endocarp. These proteins were remobilised as the endocarp lignified and at the same time that proteins were accumulated in the seed. This raised the possibility that a proportion of imported amino acids were temporarily stored in the endocarp as protein, and that these were later utilised by the seed when it started to accumulate storage proteins. Rubisco was present in the embryo and integuments of the seed although no chlorophyll was present. This is the first time that Rubisco has been detected in non-green seeds. The maximum abundance of Rubisco in the seed coincided with the deposition of seed storage proteins. A possible function for Rubisco in cherry seed is discussed. PEPCK was located in the integuments and appeared when seed storage proteins were being accumulated. In the integuments and embryo AspAT, GS, PEPC and Rubisco also appeared, or greatly increased in abundance, when seed storage proteins were being deposited.

Topics: Aspartate Aminotransferases; Carbohydrate Metabolism; Chlorophyll; Electrophoresis, Polyacrylamide Gel; Glutamate-Ammonia Ligase; Malates; Phosphoenolpyruvate Carboxykinase (ATP); Plant Extracts; Plant Proteins; Prunus; Ribulose-Bisphosphate Carboxylase; Seed Storage Proteins; Seeds

We systematically analyzed a developmental gradient of the third maize (Zea mays) leaf from the point of emergence into the light to the tip in 10 continuous leaf slices to study organ development and physiological and biochemical functions. Transcriptome analysis, oxygen sensitivity of photosynthesis, and photosynthetic rate measurements showed that the maize leaf undergoes a sink-to-source transition without an intermediate phase of C(3) photosynthesis or operation of a photorespiratory carbon pump. Metabolome and transcriptome analysis, chlorophyll and protein measurements, as well as dry weight determination, showed continuous gradients for all analyzed items. The absence of binary on-off switches and regulons pointed to a morphogradient along the leaf as the determining factor of developmental stage. Analysis of transcription factors for differential expression along the leaf gradient defined a list of putative regulators orchestrating the sink-to-source transition and establishment of C(4) photosynthesis. Finally, transcriptome and metabolome analysis, as well as enzyme activity measurements, and absolute quantification of selected metabolites revised the current model of maize C(4) photosynthesis. All data sets are included within the publication to serve as a resource for maize leaf systems biology.

Topics: Chlorophyll; Cluster Analysis; Enzyme Activation; Gene Expression Regulation, Plant; Genes, Plant; Light; Malates; Metabolome; Oxygen; Photosynthesis; Plant Leaves; Plant Proteins; Pyruvic Acid; Transcription Factors; Transcription, Genetic; Transcriptome; Zea mays

While malate and fumarate participate in a multiplicity of pathways in plant metabolism, the function of these organic acids as carbon stores in C(3) plants has not been deeply addressed. Here, Arabidopsis (Arabidopsis thaliana) plants overexpressing a maize (Zea mays) plastidic NADP-malic enzyme (MEm plants) were used to analyze the consequences of sustained low malate and fumarate levels on the physiology of this C(3) plant. When grown in short days (sd), MEm plants developed a pale-green phenotype with decreased biomass and increased specific leaf area, with thin leaves having lower photosynthetic performance. These features were absent in plants growing in long days. The analysis of metabolite levels of rosettes from transgenic plants indicated similar disturbances in both sd and long days, with very low levels of malate and fumarate. Determinations of the respiratory quotient by the end of the night indicated a shift from carbohydrates to organic acids as the main substrates for respiration in the wild type, while MEm plants use more reduced compounds, like fatty acids and proteins, to fuel respiration. It is concluded that the alterations observed in sd MEm plants are a consequence of impairment in the supply of carbon skeletons during a long dark period. This carbon starvation phenotype observed at the end of the night demonstrates a physiological role of the C(4) acids, which may be a constitutive function in plants.

Topics: Arabidopsis; Carbon; Carbon Dioxide; Chlorophyll; Chloroplasts; Fluorescence; Fumarates; Gas Chromatography-Mass Spectrometry; Malates; Microscopy, Electron, Transmission; Phenotype; Plants, Genetically Modified

The effect of salt stress on nitrogen fixation, in relation to sucrose transport towards nodules and other sink organs and the potential of sucrose breakdown by nodules, was investigated in two lines of Medicago ciliaris. Under salt stress conditions, the two lines showed a decrease of total biomass production, but TNC 1.8 was less affected by salt than TNC 11.9. The chlorophyll content was not changed in TNC 1.8, in contrast to TNC 11.9. Shoot, root, and nodule biomass were also affected in the two lines, but TNC 1.8 exhibited the higher potentialities of biomass production of these organs. Nitrogen fixation also decreased in the two lines, and was more sensitive to salt than growth parameters. TNC 1.8 consistently exhibited the higher values of nitrogen fixation. Unlike nodules, leaves of both lines were well supplied in nutrients with some exceptions. Specifically, the calcium content decreased in the sensitive line leaves, and the nodule magnesium content was not changed in either line. The tolerant line accumulated more sodium in its leaves. The two lines did not show any differences in the nodule sodium content. Sucrose allocation towards nodules was affected by salt in the two lines, but this constraint did not seem to affect the repartition of sucrose between sink organs. Salt stress induced perturbations in nodule sucrolytic activities in the two lines. It inhibited sucrose synthase, but the inhibition was more marked in TNC 11.9; alkaline/neutral activity was not altered in TNC 1.8, whereas it decreased more than half in TNC 11.9. Thus, the relative tolerance of TNC 1.8 to salt stress could be attributed to a better use of these photoassimilates by nodules and a better supply of bacteroids in malate. The hypothesis of a competition for sucrose between nodules and other sink organs under salt stress could not be verified.

Topics: Biological Transport; Carbohydrate Metabolism; Chlorophyll; Ions; Malates; Medicago; Nitrogen Fixation; Plant Leaves; Root Nodules, Plant; Sodium Chloride; Stress, Physiological; Sucrose

In the Crassulacean acid metabolism (CAM) plants Clusia alata Triana and Planch., decarboxylation of citrate during phase III of CAM took place later than malate decarboxylation. The interdependence of these two CO(2) and NADPH sources is discussed. High light accelerated malate decarboxylation during the day and lowered citrate levels. Strong light stress also activated mechanisms that can protect the plant against oxidative stress. Upon transfer from low light (200micromol m(-2)s(-1)) to high light (650-740micromol m(-2)s(-1)), after 2 days, there was a transient increase of non-photochemical quenching (NPQ) of fluorescence of chlorophyll a of photosystem II. This indicated acute photoinhibition, which declined again after 7 days of exposure. Conversely, after 1 week exposure to high light, the mechanisms of interconversion of violaxanthin (V), antheraxanthin (A), zeaxanthin (Z) (epoxydation/de-epoxydation) were activated. This was accompanied by an increase in pigment levels at dawn and dusk.

Topics: Adaptation, Physiological; Chlorophyll; Chlorophyll A; Citric Acid; Clusia; Decarboxylation; Fluorescence; Light; Malates; Photosynthesis; Photosystem II Protein Complex; Stress, Physiological; Xanthophylls; Zeaxanthins

Mesembryanthemum crystallinum L. (Aizoaceae) is a facultative annual halophyte and a C(3)-photosynthesis/crassulacean acid metabolism intermediate species currently used as a model plant in stress physiology. Both salinity and high light irradiance stress are known to induce CAM in this species. The present study was performed to provide a diagnosis of alterations at the photosystem II level during salinity and irradiance stress. Plants were subjected for up to 13 days to either 0.4M NaCl salinity or high irradiance of 1000 micromol m(-2)s(-1), as well as to both stress factors combined (LLSA=low light plus salt; HLCO=high light of 1000 micromol m(-2)s(-1), no salt; HLSA=high light plus salt). A control of LLCO=low light of 200 micromol m(-2)s(-1), no salt was used. Parameters of chlorophyll a fluorescence of photosystem II (PSII) were measured with a pulse amplitude modulated fluorometer. HLCO and LLSA conditions induced a weak degree of CAM with day/night changes of malate levels (Deltamalate) of approximately 12mM in the course of the experiment, while HLSA induced stronger CAM of Deltamalate approximately 20 mM. Effective quantum yield of PSII, DeltaF/F'(m), was only slightly affected by LLSA, somewhat reduced during the course of the experiment by HLCO and clearly reduced by HLSA. Potential quantum efficiency of PSII, F(v)/F(m), at predawn times was not affected by any of the conditions, always remaining at 0.8, showing that there was no acute photoinhibition. During the course of the days HL alone (HLCO) also did not elicit photoinhibition; salt alone (LLSA) caused acute photoinhibition which was amplified by the combination of the two stresses (HLSA). Non-photochemical, NPQ, quenching remained low (<0.5) under LLCO, LLSA and HLCO and increased during the course of the experiment under HLSA to 1-2. Maximum apparent photosynthetic electron transport rates, ETR(max), declined during the daily courses and were reduced by LLSA and to a similar extent by HLSA. It is concluded that M. crystallinum expresses effective stress tolerance mechanisms but photosynthetic capacity is reduced by the synergistic effects of salinity and light irradiance stress combined.

Topics: Chlorophyll; Fluorescence; Light; Malates; Mesembryanthemum; Photosynthesis; Photosystem II Protein Complex; Sodium Chloride

In an effort to understand the mechanisms that sustain rootless atmospheric plants, the modulation of Crassulacean acid metabolism (CAM) in response to variations in irradiance and water supply was investigated in the epiphyte Tillandsia usneoides. Plants were acclimated to three light regimes, i.e. high, intermediate and low, with integrated photon flux densities (PFD) of 14.40, 8.64 and 4.32 mol m-2 d-1 equivalent to an instantaneous PFD of 200, 100, and 50 mumol m-2 s-1, respectively. Daily watering was then withdrawn from half of the plants at each PFD for 7 d prior to sampling. In response to the three PFD treatments, chlorophyll content increased in plants acclimated to lower irradiances. Light response curves using non-invasive measurements of chlorophyll fluorescence demonstrated that photosystem II efficiency (phi PSII) was maintained in high PFD acclimated plants, as they exhibited a larger capacity for non-photochemical dissipation (NPQ) of excess light energy than low PFD acclimated plants. Net CO2 uptake increased in response to higher PFD, reflecting enhanced carboxylation capacity in terms of phosphoenolpyruvate carboxylase (PEPc) and ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities. After water was withdrawn, nocturnal net CO2 uptake and accumulated levels of acidity declined in all PFD treatments, concomitant with increased respiratory recycling of malate. Examining the strategies employed by epiphytes such as T. usneodies to tolerate extreme light and water regimes has demonstrated the importance of physiological mechanisms that allow flexible carboxylation capacity and continued carbon cycling to maintain photosynthetic integrity.

Topics: Acclimatization; Carbon Dioxide; Chlorophyll; Light; Malates; Phosphoenolpyruvate Carboxylase; Photosynthesis; Photosynthetic Reaction Center Complex Proteins; Ribulose-Bisphosphate Carboxylase; Tillandsia; Water

Water is a principal limitation to agricultural production during drought and in arid regions of the world. Mechanisms that plants use to cope with drought can be grouped into two different strategies: drought tolerance and drought avoidance. Previous efforts toward engineering plants for improved performance during drought have focused on drought tolerance, the ability to adjust to dry conditions. This report addresses the engineering of a drought-avoidance phenotype, which allows for the conservation of water during plant growth. The majority of water lost from plants occurs through stomata. When stomata are open, potassium, chloride and/or malate are present at high concentrations in guard cells. The accumulation of large numbers of ions during stomatal opening increases the turgor pressure of the guard cells, which results in increased pore size. Expression of a single gene from maize, NADP-malic enzyme (ME), which converts malate and NADP to pyruvate, NADPH, and CO(2), resulted in altered stomatal behaviour and water relations in tobacco. The ME-transformed plants had decreased stomatal conductance and gained more fresh mass per unit water consumed than did the wild type, but they were similar to the wild type in their growth and rate of development. Providing chloride via the transpiration stream partially reversed the effects of ME expression on stomatal aperture size, which is consistent with the interpretation that expression of ME altered malate metabolism in guard cells. These results suggest a role for malic enzyme in the mechanism of stomatal closure, as well as a potential mechanism for genetically altering plant water use.

Topics: Acclimatization; Biological Transport, Active; Carbon Dioxide; Chlorides; Chlorophyll; Disasters; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Malate Dehydrogenase; Malates; Nicotiana; Phenotype; Plant Structures; Plants, Genetically Modified; Potassium; Water; Zea mays

Experiments have been carried out with field-grown pear trees to investigate the effect of iron chlorosis on the composition of the leaf apoplast. Iron deficiency was associated with an increase in the leaf apoplastic pH from the control values of 5.5-5.9 to 6.5-6.6, as judged from direct pH measurements in apoplastic fluid obtained by centrifugation and fluorescence of leaves incubated with 5-CF. The major organic acids found in leaf apoplastic fluid of iron-deficient and iron-sufficient pear leaves were malate, citrate and ascorbate. The total concentration of organic acids was 2.9 mM in the controls and increased to 5.5 mM in Fe-deficient leaves. The total apoplastic concentration of inorganic cations (Ca, K and Mg) increased with Fe deficiency from 15 to 20 mM. The total apoplastic concentration of inorganic anions (Cl-, NO3-, SO4(2-) and HPO4(2-)) did not change with Fe deficiency. Iron concentrations decreased from 4 to 1.6 microM with Fe deficiency. The major Fe species predicted to exist in the apoplast was [FeCitOH](-1) in both Fe-sufficient and deficient leaves. Organic acids in whole leaf homogenates increased from 20 to 40 nmol x m(-2) with Fe deficiency. The accumulation of organic anions in the Fe-deficient leaves does not appear to be associated to an increased C fixation in leaves, but rather it seems to be a consequence of C transport via xylem.

Topics: Anions; Ascorbic Acid; Biological Transport; Carbohydrates; Cations; Chlorophyll; Citric Acid; Enzymes; Fruit; Hydrogen-Ion Concentration; Iron; Iron Chelating Agents; Malates; Nucleotides; Plant Diseases; Plant Leaves; Rosales; Trees