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Key indicators of pro-/antioxidant status were studied in leaves of Plantago media L. (C3 species) and Hylotelephium triphyllum (Haw.) Holub (facultative CAM species) grown in the unclosed floodplain meadow biogeocenosis in the middle taiga subzone of the Komi Republic (European Northeast of Russia). During the period of reproductive development, the average content of lipid peroxidation products in leaves of H. triphyllum was 400 nmol/g dry wt, which was 1.2 times higher than in P. media leaves. The content of hydrogen peroxide (Н2О2) in leaves of H. triphyllum reached the level of 90 μmol/g dry wt while it did not exceed 25 μmol/g dry wt in P. media. Activity of superoxide dismutase (SOD) in leaves of H. triphyllum ranged between 50 and 80 unit/mg protein, which was 2–3 times higher than in the leaves of P. media. The treatment of H. triphyllum leaves with an oxidative stress inducer methyl viologen (10 μM) increased SOD activity by 1.6 times but had no significant influence on H2O2 content and the accumulation of lipid peroxidation products. Thus, H. triphyllum leaves were characterized by a higher pro-/antioxidant status than the leaves of a C3 P. media plant grown under identical environmental conditions; this elevated status was due to the operation of CAM photosynthesis in H. triphyllum leaves. The transition of H. triphyllum to CAM photosynthesis during reproductive development is indicated by previously revealed regular diurnal changes in cell sap acidity, malate content, and phosphoenolpyruvate carboxylase activity. The results are consistent with the notion that an increased pro-/antioxidant status is a general feature of CAM plant metabolism, while the consistently high Н2О2 content provides evidence for the involvement of Н2О2 in regulation of crassulacean acid metabolism.

C4 plants play a key role in world agriculture. For example, C4 crops such as maize and sorghum are major contributors to food production in both developed and developing countries, and the C4 grasses sugarcane, miscanthus, and switchgrass are major plant sources of bioenergy. In the challenge to manipulate and enhance C4 photosynthesis, steady-state models of leaf photosynthesis provide an important tool for gas exchange analysis and thought experiments that can explore photosynthetic pathway changes. Here a previous C4 photosynthetic model developed by von Caemmerer and Furbank has been updated with new kinetic parameterization and temperature dependencies added. The parameterization was derived from experiments on the C4 monocot, Setaria viridis, which for the first time provides a cohesive parameterization. Mesophyll conductance and its temperature dependence have also been included, as this is an important step in the quantitative correlation between the initial slope of the CO2 response curve of CO2 assimilation and in vitro phosphoenolpyruvate carboxylase activity. Furthermore, the equations for chloroplast electron transport have been updated to include cyclic electron transport flow, and equations have been added to calculate the electron transport rate from measured CO2 assimilation rates., Update of a C4 photosynthesis model developed by von Caemmerer and Furbank to include temperature dependencies and equations to calculate the electron transport rate from measured CO2 assimilation rates.

Climate changes severely influence photosynthetic activity of plants. Studies on the combined effect of drought and heat stress on photosynthesis, pigments, and xanthophyll cycle particularly in alfalfa (Medicago sativa L.) are limited. Thus, this study investigated the combined effects of drought and heat stress in two alfalfa varieties ('Deqin' and 'Algonguin'). Results revealed that the values of the net photosynthetic rate demonstrated a significantly decreasing tendency under stresses. The effect of stresses on ribulose 1,5-bisphosphate carboxylase activity in both varieties showed a trend of first declining and then rising. Meanwhile, phosphoenolpyruvate carboxylase activity showed an increasing tendency. The intensification of stresses led to reduced photochemical efficiency and increased capability of thermal dissipation. A linear correlation was found between nonphotochemical quenching and xanthophyll cycle components. Thus, the change in carotenoids demonstrated an important role in photoprotection, the xanthophyll cycle was the main way of dissipation of excess energy under stress conditions in alfalfa.

Molasses wastewater can be utilized for microalgae cultivation, and the harvested algal biomass is suitable for biofuel production. In this study, the effects of melatonin on the metabolism and activities of three key lipid biosynthetic enzymes of Monoraphidium sp. FXY-10 cultured in molasses wastewater were evaluated. The maximal biomass (1.21 g L−1) and lipid content (68.69%) were obtained during melatonin treatment and were approximately 1.42- and 1.15-fold, respectively, of the group not treated with melatonin. The carbohydrate and protein contents of melatonin-treated cells were also increased. MT treatment upregulated the activities of malic enzyme and acetyl-CoA carboxylase but downregulated phosphoenolpyruvate carboxylase activity, which was correlated with lipid accumulation in FXY-10. MT-treated samples showed greater potentials for removing organic carbon (92.33% chemical oxygen demand removal) and nutrients (90.07% nitrogen removal, 86.04% phosphorus removal) than the non-treated samples. Additionally, the economic feasibility of melatonin treatment demonstrated that a combined strategy is ideal for molasses wastewater treatment and biofuel production.

The contents of seed storage compounds, protein and oil, determine the best use of soybean seeds, namely materials for food processing and oil production. Genetic and environmental factors could affect the chemical compositions of soybean seeds. However, the mechanisms of how the accumulation of these primary seed compounds is regulated are mostly unclear. In this chapter, we describe the different effects of nodulation on the protein and oil contents in soybean seeds and the crucial role of phosphoenolpyruvate carboxylase (PEPC) in the protein accumulation of soybean seeds. Based on our previous studies on soybean seeds, we introduce five manners deduced; (1) protein accumulation is independent of oil accumulation, (2) nitrogen fixation results in decreasing oil amount per seed and decreased seed oil content, (3) a high pseudo negative correlation between protein and oil contents in seeds is likely to be observed under less nitrogen supply from the soil, (4) nitrogen absorbed from soil during the late growth stage promote seed production, (5) plant-type PEPC, ex. Gmppc2 in soybean could play a role in amino acid biosynthesis for storage protein accumulation in seeds during the late maturation period.

Plant stress implies a series of processes and states where growth and development conditions are extremely different from optimal ones. Numerous data indicate that plant response to stress is strongly associated with changes in protein phosphorylation state under all known stress factors and extracellular signals. Self-incompatibility, initiation of mitosis, isoprenoid biosynthesis, cytoplasmic streaming, sucrose phosphate synthase activity, MSERK1 activity and phosphoenolpyruvate carboxylase activity are the examples of regulation of cellular responses that involved different protein kinases and protein phosphatases. Another feature of protein phosphatase is regulation, which underlies the mutual relationship between the type of a biotic stress factor and different regulating subunits. Here we present a brief overview of current experimental data on the role of plant phosphatases in stress, with an emphasis on tyrosine protein phosphatases (PTP1, DSPsI, MKPs) and Ser/Thr protein phosphatases of types PP1, PP2 and PP2C, especially with regard to cytoskeletal regulation.

Cassava is an important staple crop in sub‐Saharan Africa, due to its high productivity even on nutrient poor soils. The metabolic characteristics underlying this high productivity are poorly understood including the mode of photosynthesis, reasons for the high rate of photosynthesis, the extent of source/sink limitation, the impact of environment, and the extent of variation between cultivars. Six commercial African cassava cultivars were grown in a greenhouse in Erlangen, Germany, and in the field in Ibadan, Nigeria. Source leaves, sink leaves, stems and storage roots were harvested during storage root bulking and analyzed for sugars, organic acids, amino acids, phosphorylated intermediates, minerals, starch, protein, activities of enzymes in central metabolism and yield traits. High ratios of RuBisCO:phosphoenol pyruvate carboxylase activity support a C3 mode of photosynthesis. The high rate of photosynthesis is likely to be attributed to high activities of enzymes in the Calvin–Benson cycle and pathways for sucrose and starch synthesis. Nevertheless, source limitation is indicated because root yield traits correlated with metabolic traits in leaves rather than in the stem or storage roots. This situation was especially so in greenhouse‐grown plants, where irradiance will have been low. In the field, plants produced more storage roots. This was associated with higher AGPase activity and lower sucrose in the roots, indicating that feedforward loops enhanced sink capacity in the high light and low nitrogen environment in the field. Overall, these results indicated that carbon assimilation rate, the K battery, root starch synthesis, trehalose, and chlorogenic acid accumulation are potential target traits for genetic improvement., The Plant Journal, 102 (6), ISSN:0960-7412, ISSN:1365-313X

Phosphenolpyruvate carboxylase (PEPC)-catalysed fixation of bicarbonate to C4 acids is commonly believed to represent a rather small flux in illuminated leaves. In addition, its potential variation with O2 and CO2 is not documented and thus is usually neglected in gas-exchange studies. Here, we used quantitative NMR analysis of sunflower leaves labelled with 13 CO2 (99% 13 C) under controlled conditions and measured the amount of 13 C found in the four C-atom positions in malate, the major product of PEPC activity. We found that amongst malate 13 C-isotopomers present after labelling, most molecules were labelled at both C-1 and C-4, showing the incorporation of 13 C at C-4 by PEPC fixation and subsequent redistribution to C-1 by fumarase (malate-fumarate equilibrium). In addition, absolute quantification of 13 C content showed that PEPC fixation increased at low CO2 or high O2 , and represented up to 1.8 μmol m-2 s-1 , that is, 40% of net assimilation measured by gas exchange under high O2 /CO2 conditions. Our results show that PEPC fixation represents a quantitatively important CO2 -fixing activity that varies with O2 and/or CO2 mole fraction and this challenges the common interpretation of net assimilation in C3 plants, where PEPC activity is often disregarded or considered to be constant at a very low rate.

The significance of integrated nutrient management practices is well established in improving the productivity of chickpea (Cicer arietinum); however, the effects of the inoculation of cyanobacterial inoculants on nodule metabolism, microbiome and associated genes are less explored. In the present investigation, cyanobacterium Anabaena laxa (A. laxa) and biofilm developed using Anabaena torulosa, with Mesorhizobium ciceri as a partner (An-M. ciceri), were evaluated along with Mesorhizobium ciceri (M. ciceri) alone, in three chickpea cultivars. Microbial inoculation led to 40–70% enhancement in nitrogen fixation, leghaemoglobin and ureide content, and two- to threefold increment in nitrate reductase and phosphoenolpyruvate carboxylase activity of the nodules. An enhancement of 30–50% in the soil available macro- and micronutrients and plant growth attributes was also observed. A significant correlation between the soil microbiological and plant parameters was recorded, particularly in relation to the nitrogen dynamics. Increases in the leghaemoglobin content in nodules due to An-M. ciceri, A. laxa and M. ciceri ranged from 18 to 40%, particularly in chickpea cv. BG372 in which 60–80% enhancement was recorded. Whereas the nifH gene copies in the nodule tissues ranged from 5.00 × 106 to 3.35 × 107 g−1, the application of A. laxa led to higher abundances of nifH gene copies in desi chickpea cv. BG372 and kabuli BG1053 cultivars. An-M. ciceri, followed closely by A. laxa, was the top-ranking treatment, and chickpea cv. BG372 was the best performing cultivar; An-M. ciceri—chickpea cv. BG372 proved to be the superior combination for higher plant growth and soil nutrient-related traits.

Photosynthetic characteristics of ear and flag leaves of wheat species, tetraploid Triticum dicoccoides Kom and hexaploid Bima1, were studied in plants grown under well-watered (WW) and water-stressed (WS) conditions. Compared to ears, flag leaves exhibited higher photosynthetic rate (P N) at the filling stage, but more severe decrease under WS. P N in the tetraploid wheat ear remained higher than that in the hexaploid wheat during the grain-filling stage. Water stress decreased PN in both the organs; this decline was caused by a reduction in Rubisco activity, not by drought-induced stomatal limitation. Tetraploid wheat ears exhibited higher relative water content and water-use efficiency than that of hexaploid wheat, under WS. The change in phosphoenolpyruvate carboxylase activity and carbon isotope composition indicated the absence of C4 metabolism in the ears of both species under both conditions. The improved performance of the tetraploid wheat ears under WS was associated with better water relations.

The Kok and Laisk techniques can both be used to estimate light respiration Rlight . We investigated whether responses of Rlight to short- and long-term changes in leaf temperature depend on the technique used to estimate Rlight . We grew Eucalyptus tereticornis in whole-tree chambers under ambient temperature (AT) or AT + 3°C (elevated temperature, ET). We assessed dark respiration Rdark and light respiration with the Kok (RKok ) and Laisk (RLaisk ) methods at four temperatures to determine the degree of light suppression of respiration using both methods in AT and ET trees. The ET treatment had little impact on Rdark , RKok or RLaisk . Although the thermal sensitivities of RKok or RLaisk were similar, RKok was higher than RLaisk . We found negative values of RLaisk at the lowest measurement temperatures, indicating positive net CO2 uptake, which we propose may be related to phosphoenolpyruvate carboxylase activity. Light suppression of Rdark decreased with increasing leaf temperature, but the degree of suppression depended on the method used. The Kok and Laisk methods do not generate the same estimates of Rlight or light suppression of Rdark between 20 and 35°C. Negative rates of RLaisk imply that this method may become less reliable at low temperatures.

Enhancing lipid productivity and reducing oxidative damage is essential for lipid overproduction in microalgae. In this study, addition of 20 mg/L fulvic acid (FA) resulted a 34.4% increase of lipid yield in Schizochytrium sp. Furthermore, the cooperative effect of FA and EDTA on cell growth and lipid production was investigated. The combined addition of 20 mg/L FA and 1.0 g/L EDTA yielded a maximal cell dry weight of 130.7 g/L and lipid productivity of 1.16 g/L/h, representing 36.4% and threefold increase over the non-supplemented group, respectively. Moreover, compared with the non-supplemented group, the combined addition strategy exhibited overall lower levels of reactive oxygen species and malondialdehyde, which accompanied with 66.7% and 81.9% higher superoxide dismutase and catalase activity, respectively. Furthermore, a 24.1–37.1% increase of malic enzyme and 19.4–25.2% decrease of phosphoenolpyruvate carboxylase activity was observed during the entire fermentation stage (0–108 h). Results suggested that the combined addition strategy not only enhanced lipid accumulation, but also prevented the lipid peroxidation.

The petE gene transcription can be regulated by copper titer in some cyanobacteria. In order to regulate the activity of phosphoenolpyruvate carboxylase (PEPC) in Synechocystis PCC 6803, “Ω-PpetE” fragment, containing T4 transcription terminating sequence, anti-spectinomycin gene and petE promoter sequence was inserted between the native promoter and the ORF of ppc (gene encoding PEPC). After several rounds of selection, a stable and completely segregated mutant was attained. Cultured in different copper titers, the mutant presented narrow enzyme activity variance in the late exponential phase. A basal enzyme activity was observed in the culture without copper. When copper titer was increased to more than 280 nM which was the normal level of BG11 broth, the activity was stable. When PEPC activity was downregulated, the content of intracellular total carbonhydrate increased significantly and the content of intracellular total protein decreased. In central metabolic network, regulation characteristics of PEPC in Synechocystis PCC 6803 showed considerable robustness. Within the studied range of regulation, it can be regarded a pivotal node in central metabolic network which controls carbon flux distribution and decides the ratio of major biomass constituents.

Wheat seed storage protein is of great importance for human food. To increase the contents of storage proteins effectively, nitrogen fertilizer at flowering stages is commonly applied. In our previous study, rice phosphoenolpyruvate carboxylase (PEPCase) activity in developing seeds was observed in response to nitrogen application at a flowering stage and was positively correlated to the response of the protein content in seeds of six cultivars. This observation might indicate that the seeds have a biological system for accepting nitrogen in seeds by using PEPCase. To test whether this physiological event occurs in wheat, we examined the PEPCase activity and protein content in field-grown wheat seeds under different nitrogen supply conditions. With only basal dressing, seeds showed lower PEPCase activity and protein content (both 0.90-fold) compared to seeds without basal fertilizer. With ammonium sulfate application at 8.3 and 25 g/m2 at a flowering stage, seeds showed higher PEPCase activity (1.08- and 1.17-fold, respectively) and protein content (1.15- and 1.42-fold, respectively), depending on the nitrogen level. We investigated the relationship between PEPCase activity and protein content in the seeds among four conditions. The effect of the nitrogen supply on PEPCase activity during grain-filling stages was validated by the results of a hydroponic culture experiment. Together the results demonstrate that our hypothesis seems to apply to field-grown wheat.

Potassium (K) plays important roles in the metabolism of carbon (C) and nitrogen (N), but studies of K deficiency affecting C-N balance are lacking. This study explored the influence of K deficiency on C-N interaction in cotton leaves by conducting a field experiment with cotton cultivar DP0912 under two K rates (K0: 0 kg K2O ha-1 and K67: 67 kg K2O ha-1) and a controlled environment experiment with K-deficient solution (K1: 0 mM K+) and K-sufficient solution (K2: 6 mM K+). The results showed that leaf K content, leaf number, leaf area, boll number, reproductive dry weight and total dry weight were significant lower under K deficiency (K0 or K1). Lower total chlorophyll content and Chl a/b ratio, and decreased Pn along with lower Gs and higher Ci were measured under K deficiency, suggesting that the decrease in Pn was resulted from non-stomatal limitation. Leaf glucose, fructose, sucrose and starch contents were higher under K deficiency, because lower sucrose export was detected in phloem. Although leaf nitrate and ammonium contents significantly decreased, free amino acid content was increased by 40-63% under K deficiency, since lower amino acid export was also measured in phloem. K deficiency also induced lower soluble protein content in leaves. Leaf ATP level was significantly increased under K deficiency, indicating ATP utilization was lower, so that less energy was supplied to C and N metabolism. The ratio of soluble sugar to free amino acid and the C/N ratio markedly increased under K deficiency, and one reason was that the phloem export reduced more prominent for sucrose (54.6-78.0%) than amino acid (36.7-85.4%) under K deficiency. In addition, lower phosphoenolpyruvate carboxylase activity limited malate and citrate biosynthesis under K deficiency, causing a decrease of C flux into the amino acids, which was not beneficial for maintaining C-N balance. Sucrose phosphate synthase and nitrate reductase activities were lower under K deficiency, which would limit sucrose biosynthesis and nitrate assimilation. This was another factor altering soluble sugar to free amino acid ratio and C/N ratio in the K-deficient leaves.

To compare the differences in physiology and metabolism between phosphoenolpyruvate carboxylase (PEPC) transgenic rice and its control, untransformed wild rice, dry matter accumulation, soluble sugar, starch and protein contents and enzyme activities were determined in different plant parts during flowering. Results revealed that PEPC transgenic rice had higher dry weights for leaf, stem and sheath as well as panicle than the untransformed wild rice did, with the largest increase in the panicle. Soluble sugar and protein content in the grains of PEPC transgenic rice were significantly enhanced while starch content changed less. PEPC transgenic rice exhibited high levels of PEPC activity, manifesting in high net photosynthetic rates during flowering. Moreover, transgenic rice with high PEPC expression levels also had elevated levels of the enzymes such as sucrose-p-synthase and sucrose synthase, which may confer a higher capacity to assimilate CO2 into sucrose. Little increase in grain starch content was observed in transgenic plants due to the stable activities of starch synthase and Q enzyme. However, the PEPC transgenic rice plant induced the activities of nitrate reductase, glutamate oxaloacetate transaminase, glutamate pyruvate transaminase, glutamine synthetase, and asparagine synthase to high levels, as compared with the untransformed rice plant. PEPC activity was correlated with protein content in grains and the enzymes of nitrogen metabolism, suggesting that high PEPC activity in transgenic rice might be able to redirect carbon and nitrogen flow by regulating some enzymes related to carbon or nitrogen metabolisms. These results may help to understand how the C3 plants possessing a C4-like photosynthesis pathway worked by expression of PEPC.

To clarify why fruit bagging reduces sugar content at harvest, we investigated its effect on carbon dioxide assimilation by Satsuma mandarin (Citrus unshiu) fruit through photosynthesis and phosphoenolpyruvate carboxylase (PEPC; enzyme code 4.1.1.31). Seasonal changes in gross photosynthesis ranged from 70 to 400 μmol·d−2·h−1 O2 with a peak at 99 days after full bloom (DAFB) when the assimilation rate of fruit was comparable to that of leaves. However, a peak showing net photosynthesis appeared at 112 DAFB because of high fruit respiration. When fruit were bagged at 85 DAFB, the net photosynthetic peak disappeared, perhaps as a result of the decline in chlorophyll content in the rind. Sugar and organic acid content in the bagged fruit were 0.3% and 0.16% less, respectively, than controls at the mature stage (204 DAFB). PEPC activity in the rind was much higher than in leaves on a protein basis; it increased between 92 and 112 DAFB and showed a peak of 72 units. The PEPC activity peak was also 90% of control after fruit bagging. Thus, just before their color development, mandarin fruit assimilate CO2 actively through photosynthesis and PEPC. However, these activities are inhibited by bagging, likely resulting in lower sugar content at harvest. The concomitant activation of PEPC and photosynthesis between 99 and 126 DAFB indicates that CO2 fixed by PEPC might be used for photosynthesis in mandarin fruit, because photosynthesis in several fruit such as apple (Malus pumila) and pea (Pisum sativum) is considered to have an intermediate status among C3, non-autotrophic tissue, and C4/CAM photosynthesis.

With 7 figures and 2 tables Abstract Attempts have been made to transform C3 crops with C4 genes to improve the photosynthetic rate of C3 plants. In our study, a full-length cDNA for phosphoenolpyruvate carboxylase gene (pepc) was isolated from Zea mays by PCR. The pepc gene was introduced into wheat plants (Triticum aestivum) by particle bombardment transformation. The integration, transcription and expression of the pepc gene were confirmed by Southern blot, RT-PCR and Western blot analysis. Physiological studies showed that phosphoenolpyruvate carboxylase activity in the transgenic plants was 140% higher than that of the untransformed plants. The highest rate of photosynthesis in the transgenic plants was 31.95 μmol CO2/m2/s, which was 26% greater than the rate in untransformed plants. The light saturation point and carboxylation efficiency of pepc transgenic wheat were 20% and 22.57% higher, respectively, than those of untransformed wheat. As a result, the weight of seed per spike and thousand-grain weight were 0.23 g and 1.21 g higher than those of untransformed wheat. Our research will facilitate the further study of the function of the pepc gene in wheat plants.

Differences in light quality penetration within a leaf and absorption by the photosystems alter rates of CO2 assimilation in C3 plants. It is also expected that light quality will have a profound impact on C4 photosynthesis due to disrupted coordination of the C4 and C3 cycles. To test this hypothesis, we measured leaf gas exchange, 13CO2 discrimination (Δ13C), photosynthetic metabolite pools and Rubisco activation state in Zea mays and Miscanthus × giganteus under steady-state red, green, blue and white light. Photosynthetic rates, quantum yield of CO2 assimilation, and maximum phosphoenolpyruvate carboxylase activity were significantly lower under blue light than white, red and green light in both species. However, similar leakiness under all light treatments suggests the C4 and C3 cycles were coordinated to maintain the photosynthetic efficiency. Measurements of photosynthetic metabolite pools also suggest coordination of C4 and C3 cycles across light treatments. The energy limitation under blue light affected both C4 and C3 cycles, as we observed a reduction in C4 pumping of CO2 into bundle-sheath cells and a limitation in the conversion of C3 metabolite phosphoglycerate to triose phosphate. Overall, light quality affects rates of CO2 assimilation, but not the efficiency of CO2 concentrating mechanism.

Physiological measurements were used to investigate the dependence of photosynthesis on light, temperature, and intercellular carbon dioxide (CO2) levels in the C4 marsh grass Spartina alterniflora. Functional relationships between these environmental variables and S. alterniflora physiological responses were then used to improve C4-leaf photosynthesis models. Field studies were conducted in monocultures of S. alterniflora in Virginia, USA. On average, S. alterniflora exhibited lower light saturation values (~1000 μmol m−2 s−1) than observed in other C4 plants. Maximum carbon assimilation rates and stomatal conductance to water vapor diffusion were 36 μmol (CO2) m−2 s−1 and 200 mmol (H2O) m−2 s−1, respectively. Analysis of assimilation-intercellular CO2 and light response relationships were used to determine Arrhenius-type temperature functions for maximum rate of carboxylation (Vcmax), phosphoenolpyruvate carboxylase activity (Vpmax), and maximum electron transport rate (Jmax). Maximum Vcmax values of 105 μmol m−2 s−1 were observed at the leaf temperature of 311 K. Optimum Vpmax values (80.6 μmol m−2 s−1) were observed at the foliage temperature of 308 K. The observed Vpmax values were lower than those in other C4 plants, whereas Vcmax values were higher, and more representative of C3 plants. Optimum Jmax values reached 138 μmol (electrons) m−2 s−1 at the foliage temperature of 305 K. In addition, the estimated CO2 compensation points were in the range of C3 or C3–C4 intermediate plants, not those typical of C4 plants. The present results indicate the possibility of a C3–C4 intermediate or C4-like photosynthetic mechanism rather than the expected C4-biochemical pathway in S. alterniflora under field conditions. In a scenario of atmospheric warming and increased atmospheric CO2 concentrations, S. alterniflora will likely respond positively to both changes. Such responses will result in increased S. alterniflora productivity, which is uncharacteristic of C4 plants.

This study compared the specific activity of phosphoenolpyruvate carboxylase (PEPC) of Spartina densiflora Brongn., collected from four populations along its latitudinal distribution range. Spartina densiflora is a halophyte with C(4) photosynthesis that has a very wide latitudinal distribution, from Patagonia to the southwest Iberian Peninsula. The basis of intraspecific differences in PEPC activity were analysed by recording the phosphorylation state and amount of the enzyme, comparing leaf anatomy and evaluating leaf gas exchange. S. densiflora individuals from Patagonia had 60% higher PEPC specific activity than plants from the other three populations due to higher levels of PEPC protein that coincided with lower activation mediated by phosphorylation, yielding similar net photosynthesis rate (c. 29 micromol CO(2)xm(-2)xs(-1)). Patagonian plants had a higher area of photosynthetic mesophyll relative to total chlorophyll than plants from north Argentina and the southwest Iberian Peninsula. Ecotypic differentiation in PEPC activity and leaf anatomy were found, distinguishing a higher-latitude ecotype from lower-latitude populations. The higher PEPC protein levels of the Patagonian ecotype seemed to be a response to lower light activation level of the enzyme, as judged by the low PEPC phosphorylation state.

The relationship between phosphoenolpyruvate carboxylase (PEPC) activities in flag leaf blade and ear organs (glume and grain) and protein content of grain as well as grain weight after flowering were studied in different winter wheat (Triticum aestivum L.) genotypes. Results showed higher PEPC activity in the developing grain than in flag leaf blade and glume during grain development. For 16 of the genotypes studied, the mean PEPC activity in the developing grain or glume at 15 and 25 days after flowering was significantly and positively correlated with final protein content of grain. Enzyme activities in glume and flag leaf blade were positively correlated with final grain weight but the activity in developing grain was weakly and negatively correlated with grain weight. The overall data suggest that PEPC may be involved in protein biosynthesis during grain development, and it may have an important role in regulating carbon and nitrogen metabolism in the ear of wheat.

The cytosolic phosphoenolpyruvate carboxylase (PEPC) catalyses the anaplerotic synthesis of oxalacetic acid resulting in the replenishment of citric acid cycle intermediates, which are precursors for the synthesis of amino acids. Biotic stress in plants generally leads to redistributions in primary and secondary pathways and therefore to a shift in the requirement of proteins. To reveal whether and how PEPC is affected by biotic stress we analysed PEPC activity after treating cucumber (Cucumis sativus) leaves with the synthetic plant activator benzothiadiazole (BTH) and extracts of the economically important phytopathogenic fungi Cercospora beticola and Fusarium graminearum. BTH as well as fungal extracts increased PEPC activity significantly 72 and 96 hours after treatments. In addition, the extracts, but not BTH, induced the formation of necrotic lesions. Defence responses are generally associated with decreased photosynthesis rates, an enhanced respiration rate and an increased demand in proteins. Regarding our results we assume that the increase in PEPC activity by biotic stress is conducive to a compensation of these antagonistic processes. However, PEPC activity enhancements are not necessarily associated with the formation of necrotic lesions. This study indicates that PEPC is involved in biotic stress responses and we suggest that PEPC contributes to successful defence responses in plants.

The full-length of intact Zea mays gene for phosphoenolpyruvate carboxylase gene (ZmC4Ppc) is 6 781 bp. The products of PCR for this gene were not clear with poor repeatability, resulting in that it was difficult for marker-assisted selection (MAS) both in rice and maize. For selecting the markers for MAS, sequences presented only in maize rather than in rice were identified by BLAST, and used for primer design using Primer Premier 5.0. A pair of specific primer termed MRpc (Forward: 5' AAGCAGGGAAGCGAGACG 3', Reverse: 5' GATTGCCGCCAGCAGTAG 3') was used for selection of transformed rice, and ZmC4Ppc could be highly and constitutively expressed at each tested developmental stages in the transformed rice selected by using MRpc. Thus, MRpc was used for MAS of progenies carrying ZmC4Ppc gene in rice and some restorer lines with ZmC4Ppc (e.g. FPM881) derived from ZmC4Ppc-transformed Kitaake backcrossed with a restorer line Shuhui 881 were obtained. The analyses on genetic background, PEPCase activity, net photosynthetic rate, general combining ability (GCA) and specific combining ability (SCA) of FPM881 showed that similarity of genetic background reached above 95%, the PEPCase and net photosynthetic rate were higher than those of the control, and some of the progenies carrying ZmC4Ppc gene had better GCA and SCA for grain yield per plant, number of panicles per plant, and 1000-grain weight than those of the control. This suggested that the introduction of maize ZmC4Ppc gene via MAS and its stable expression could increase grain yield of rice and would likely provide a pathway for rice varietal improvement.

Lipid-derived reactive carbonyl species (RCS) possess electrophilic moieties and cause oxidative stress by reacting with cellular components. Arabidopsis (Arabidopsis thaliana) has a chloroplast-localized alkenal/one oxidoreductase (AtAOR) for the detoxification of lipid-derived RCS, especially α,β-unsaturated carbonyls. In this study, we aimed to evaluate the physiological importance of AtAOR and analyzed AtAOR (aor) mutants, including a transfer DNA knockout, aor (T-DNA), and RNA interference knockdown, aor (RNAi), lines. We found that both aor mutants showed smaller plant sizes than wild-type plants when they were grown under day/night cycle conditions. To elucidate the cause of the aor mutant phenotype, we analyzed the photosynthetic rate and the respiration rate by gas-exchange analysis. Subsequently, we found that both wild-type and aor (RNAi) plants showed similar CO2 assimilation rates; however, the respiration rate was lower in aor (RNAi) than in wild-type plants. Furthermore, we revealed that phosphoenolpyruvate carboxylase activity decreased and starch degradation during the night was suppressed in aor (RNAi). In contrast, the phenotype of aor (RNAi) was rescued when aor (RNAi) plants were grown under constant light conditions. These results indicate that the smaller plant sizes observed in aor mutants grown under day/night cycle conditions were attributable to the decrease in carbon utilization during the night. Here, we propose that the detoxification of lipid-derived RCS by AtAOR in chloroplasts contributes to the protection of dark respiration and supports plant growth during the night.

Storage protein synthesis is dependent on available nitrogen in the seed, which may be controlled by amino acid import via specific transporters. To analyze their rate-limiting role for seed protein synthesis, a Vicia faba amino acid permease, VfAAP1, has been ectopically expressed in pea (Pisum sativum) and Vicia narbonensis seeds under the control of the legumin B4 promoter. In mature seeds, starch is unchanged but total nitrogen is 10% to 25% higher, which affects mainly globulin, vicilin, and legumin, rather than albumin synthesis. Transgenic seeds in vitro take up more [14C]-glutamine, indicating increased sink strength for amino acids. In addition, more [14C] is partitioned into proteins. Levels of total free amino acids in growing seeds are unchanged but with a shift toward higher relative abundance of asparagine, aspartate, glutamine, and glutamate. Hexoses are decreased, whereas metabolites of glycolysis and the tricarboxylic acid cycle are unchanged or slightly lower. Phosphoenolpyruvate carboxylase activity and the phosphoenolpyruvate carboxylase-to-pyruvate kinase ratios are higher in seeds of one and three lines, indicating increased anaplerotic fluxes. Increases of individual seed size by 20% to 30% and of vegetative biomass indicate growth responses probably due to improved nitrogen status. However, seed yield per plant was not altered. Root application of [15N] ammonia results in significantly higher label in transgenic seeds, as well as in stems and pods, and indicates stimulation of nitrogen root uptake. In summary, VfAAP1 expression increases seed sink strength for nitrogen, improves plant nitrogen status, and leads to higher seed protein. We conclude that seed protein synthesis is nitrogen limited and that seed uptake activity for nitrogen is rate limiting for storage protein synthesis.

In order to simulate the in vivo activity of phosphoenolpyruvate carboxylase (PEPc) of Corynebacterium glutamicum 2262 during the temperature-triggered glutamate fermentation, the enzyme activity was assessed in presence of physiological concentrations of its main effectors. For this purpose, cellular volume and effectors intracellular level were measured or estimated over the process. The influence of the main effectors was checked as well. It was then shown that the PEPc activity was maximal during the glutamate production phase. Compared to the result obtained without effector, the presence of physiological concentrations of its effectors was shown to increase the enzyme affinity for phosphoenolpyruvate.

Isolated mesophyll cells from darkened leaves of the C(4) plant Digitaria sanguinalis keep functional plasmodesmata that allow the free exchange of low molecular mass compounds with the surrounding medium. This cell suspension system has been used to measure C(4) PEPC activity in situ using a spectrophotometric assay. Compared to the extracted enzyme assayed in vitro, the essentially non-phosphorylated 'in-cell' C(4) PEPC showed altered functional and regulatory properties. While the S (0.5) for PEP at pH 7.3 was only modestly changed (0.4-0.6 mM), the response to pH was shifted towards the acidic range, being close to the maximal value at pH 7.3. Using expected physiological concentrations of the metabolites, at pH 7.3, the IC(50) for malate showed a five-fold increase, from 1.5 to 8 mM, and was increased further to 22 mM in the presence of the allosteric activator glucose-6-phosphate (4 mM). Thiol compounds like DTT, mercaptoethanol and reduced glutathione weakened the in-situ sensitivity of C(4) PEPC to malate. However, none of them had any effect on this process in vitro. This was not due to thioredoxin-mediated or phoshorylation-dependent processes. Since glutathione is a physiological compound that is present mostly in the reduced state in the cell cytosol, a possible contribution of this thiol to the protection of the enzyme against malate in situ is proposed.

Spinach ( Spinacea oleracea L. “Correnta F1”) and pea ( Pisum sativum L. “Macrocarpon”) plants were grown in a hydroponic culture with nitrate (5 mM), or ammonium (5 mM) as the nitrogen source. Dry matter accumulation declined dramatically in spinach plants fed with ammonium, whereas there was no change in pea plants when compared with nitrate-fed plants. Data obtained from δ 15 N, the organic nitrogen content, N-assimilation enzyme activity, glutamine synthetase (L-glutamate:ammonia-ligase; EC 6.3.1.2), glutamate dehydrogenase (L-glutamate:NAD + -oxidoreductase; EC 1.4.1.2) and enzymes from the tricarboxylic acid cycle suggest that ammonium incorporation into organic nitrogen is localized in the roots in pea plants and in the shoots in spinach plants. Distribution of incorporated ammonium (in shoots and roots) may determine ammonium tolerance. Our results show that unlike in spinach plants, in pea plants, an ammonium-tolerant species, GDH enzyme plays an important role in ammonium detoxification by its incorporation into amino acids. Furthermore, phosphoenolpyruvate carboxylase (phosphate:oxaloacetate-carboxy-lyase; EC 4.1.1.31) and pyruvate kinase (ATP:pyruvate-2- O -phosphotransferase; EC 2.7.1.40) activities reflect a major flow of carbon for ammonium assimilation through oxalacetate in pea plants and through pyruvate in spinach plants. The differences in the sensitivity to ammonium between the species are discussed in terms of differences in the site of ammonium assimilation as well as in the nitrogen assimilation ways.

The anatomy, biochemistry and physiology of Phragmites leaves have been investigated. Biochemical and physiological measurements indicate that Phragmites australis leaves have a C 3 mechanism of carbon fixation. However, structural and ultra-structural observations of young leaves are more reminiscent of a C 4 -like anatomy. In addition, chloroplasts apparently fully competent for photochemical and biochemical reactions were in both the mesophyll and in the bundle sheath cells of young leaves. The activity of the principal enzyme involved in carbon metabolism, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), was high under ambient conditions (59.8 and 64.2 μmol m −2 s −1 , respectively in mature and young leaves). In contrast, phosphoenolpyruvate carboxylase activity was low in both mature and young leaves (7.8 and 8.1 μmol m −2 s −1 , respectively) Despite the high Rubisco activity, the rate of photosynthesis of Phragmites leaves on a leaf area basis was low. We investigated if resistances to CO 2 entry in the leaves could limit photosynthesis. However, stomatal and mesophyll resistances to CO 2 diffusion in Phragmites leaves were comparable to those of terrestrial plants and did not restrict intercellular CO 2 concentration significantly.

Root tips of Fe-deficient and Fe-sufficient sugar beet plants grown in hydroponics have been used to study the changes in the amount and activity of the cytosolic enzyme phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31). Phosphoenolpyruvate carboxylase activity in extracts of the yellow Fe-deficient root tips was, at pH 7.3, 30-fold higher (when expressed on a FW basis) and 7.1-fold higher (when expressed on a protein basis) than that found in the extracts of Fe-sufficient root tips. The amount of phosphoenolpyruvate carboxylase protein determined by immuno-blotting was, on a protein basis, 35-fold larger in the yellow zone of Fe-deficient root tips than in the Fe-sufficient root tips. The inhibition of the phosphoenolpyruvate carboxylase activity by 500 μm malate was 41 and 58% in the extracts Fe-deficient and Fe-sufficient roots. The possibility that post-translational regulation of phosphoenolpyruvate carboxylase may occur mediated through phosphorylation, was studied by immunological detection of phosphoserine residues in root tip extracts.

In order to mitigate CO2 accumulation and decrease the rate of global warming and climate change, we previously presented a strategy for the development of an efficient CO2 capture and utilization system. The system employs two recombinant enzymes, carbonic anhydrase and phosphoenolpyruvate carboxylase, which were originated from microalgae. Although utilization of this integrated system would require a large quantity of high quality PEPCase protein, such quantities could be produced by increasing the solubility of the Phaeodactylum tricornutum PEPCase 1 (PtPEPCase 1) protein in the Escherichia coli heterologous expression system. We first expressed the putative mitochondria targeting peptide- and chloroplast transit peptide-truncated proteins of PtPEPCase 1, mPtPEPCase 1 and cPtPEPCase 1, respectively, in E. coli. After affinity chromatography, the amount of purified PEPCase protein from 500 mL of E. coli culture was greatest for cPtPEPCase 1 (1.99 mg), followed by mPtPEPCase 1 (0.82 mg) and PtPEPCase 1 (0.61 mg). Furthermore, the enzymatic activity of mPtPEPCase 1 and cPtPEPCase 1 showed approximately 1.6-fold (32.19 units/mg) and 3-fold (59.48 units/mg) increases, respectively. Therefore, cPtPEPCase 1 purified using the E. coli heterogeneous expression system could be a strong candidate for a platform technology to capture CO2 and produce value-added four-carbon platform chemicals.

The effects of a humic fraction, with a high molecular weight (Hsp) extracted from a soil with a Fagus sylvatica vegetal cover were compared on ammonium (NH+ 4) and nitrate (NO− 3) uptake in two different coniferous species (Pinus pinaster and Pinus laricio). The activity of malate dehydrogenase (MDH; EC 1.1.1.37), glutamate dehydrogenase (GDH; EC 1.4.1.3) and phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) key enzymes involved in nitrogen metabolism were tested. The data obtained indicate that the humic fractions, at all concentrations, increased ammonium uptake by both species, while nitrate uptake was unaffected. In P. laricio seedlings this fraction increased only leaf malate dehydrogenase activity, while in P. pinaster seedlings an increase of glutamate dehydrogenase in leaves, and of phosphoenolpyruvate carboxylase activity in both roots and leaves was observed. These results show that humic substances stimulate only ammonium uptake and differently influence ammonium assimilation in the two spec...

The activity of 6-phosphogluconate dehydrogenase, aspartate kinase and phosphoenolpyruvate carboxylase has been studied at different dilution rates in aerobic continuous culture of Corynebacterium glutamicum. 6-Phosphogluconate dehydrogenase and aspartate kinase reached their maximum values at the lower dilution rates (0.02–0.06 h−1), when L-lysine was produced. The phosphoenolpyruvate carboxylase activity seemed to be independent of metabolite synthesis. The production of L-lysine was also studied in non-growing cells in batch cultures. In these conditions, statistical analysis revealed significant differences in L-lysine titres when glucose or gluconic acid were used as carbon sources. Higher L-lysine concentration obtained with gluconic acid was found to be associated with a high 6-phosphogluconate dehydrogenase activity.

Plant phosphoenolpyruvate carboxylase (PEPc) activity and allosteric properties are regulated by PEPc kinase (PPcK) through reversible phosphorylation of a specific serine (Ser) residue near the N terminus. We report the molecular cloning of PPcK from the facultative Crassulacean acid metabolism (CAM) common ice plant (Mesembryanthemum crystallinum), using a protein-kinase-targeted differential display reverse transcriptase-polymerase chain reaction approach. M. crystallinum PPcK encodes a minimal, Ca2+-independent Ser/threonine protein kinase that is most closely related to calcium-dependent protein kinases, yet lacks both the calmodulin-like and auto-inhibitory domains typical of plant calcium-dependent protein kinase. In the common ice plant PPcK belongs to a small gene family containing two members. McPPcK transcript accumulation is controlled by a circadian oscillator in a light-dependent manner. McPPcK encodes a 31.8-kD polypeptide (279 amino acids), making it among the smallest protein kinases characterized to date. Initial biochemical analysis of the purified, recombinant McPPcK gene product documented that this protein kinase specifically phosphorylates PEPc from CAM and C4 species at a single, N-terminal Ser (threonine) residue but fails to phosphorylate mutated forms of C4 PEPc in which this specific site has been changed to tyrosine or aspartate. McPPcK activity was specific for PEPc, Ca2+-insensitive, and displayed an alkaline pH optimum. Furthermore, recombinant McPPcK was shown to reverse the sensitivity of PEPc activity to l-malate inhibition in CAM-leaf extracts prepared during the day, but not at night, documenting that PPcK contributes to the circadian regulation of photosynthetic carbon flux in CAM plants.

The changes in the activity of glucose-6-phosphate dehydrogenase (G6PDH) (EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (6PGDH) (EC 1.1.1.44) in leaf tissues and the subcellular localisation of their isozymes in protoplasts derived from healthy and potato virus Y (PVY) infected plants of Nicotiana tabacum L. cv. Samsun were determined. The activities of G6PDH and 6PGDH were markedly increased in virus-infected leaves during the acute phase of infection both in crude homogenate and partial purificate (when compared with the values found in healthy control plants) and correlated with the multiplication curve of PVY. Intact chloroplasts and soluble cytosolic proteins were obtained from whole plants upon the culmination of the multiplication curve of PVY and upon the enhancement of the activity of both dehydrogenases by means of differential centrifugation of broken protoplasts. The chloroplastic fraction from infected protoplasts (based on chlorophyll content or NADP + -triosephosphate dehydrogenase activity) showed an enhanced activity of G6PDH (1.81 times that of healthy protoplasts), and 6PGDH (1.77 times). Cytosol from infected protoplasts (based on phosphoenolpyruvate carboxylase activity) contained only slightly enhanced activities of G6PDH and 6PGDH (only 1.26 and 1.16 times, respectively).

Maize plants of CPB2 and CPB8 hybrids were kept under water deficit for 22 d. In the CPB8 hybrid, leaf rolling initiated at the 9th d of water deficit period, while in CPB2 hybrid it was at the 15th d. Both hybrids showed leaf rolling initiation at the same leaf water potential, ΨW of -0.480±0.095 MPa. At leaf rolling initiation, the leaf osmotic potential, ΨS was -0.730±0.085 MPa in CPB8 and 0.630±0.110 MPa in CPB2. The leaf temperature and stomatal conductance were higher in CPB8 than in CPB2. Values of leaf ΨW, ribulose-1,5-bisphosphate carboxylase activity, chlorophyll content, and specific leaf area were similar in both hybrids. Phosphoenolpyruvate carboxylase activity and protein content were lower in the CPB2 hybrid than in CPB8. In both hybrids leaf rolling initiation was associated with: (1) higher leaf temperature, with leaf rolling effect related to leaf temperature reduction, and (2) lower leaf ΨS, related to osmotic adjustment as an additional component of drought-tolerance strategy.

When leaf discs of a C 4 species, Alternanthera pungens (L.) H.B. and K. or Amaranthus hypochondriacus L., were preincubated in 7.5 mM NH 4 Cl, the pH of the cell sap increased by nearly 0.3 unit, while the activity of phosphoenolpyruvate carboxylase (PEPC) about doubled compared to the cell sap from control leaf discs (preincubated in 5 mM Tricine-KOH, pH 8.5). The sensitivity of PEPC to L-malate (a feedback inhibitor) decreased marginally as a result of cytosolic alkalization. The pH of the cell sap and PEPC activity decreased by nearly 0.4 unit and 50%, respectively, when leaf discs were incubated in weak organic acids such as propionic, butyric or salicylic acid. Thus, our results demonstrate a marked modulation in vivo of cell sap pH and PEPC activity in leaf discs from C 4 plants by external alkalizing or acidifying reagents. The rise in PEPC activity due to alkalization of leaf discs was not sensitive to cycloheximide, implying that cytosolic protein synthesis was not involved in the activation of PEPC. Despite the marked increase in the PEPC activity due to the base-loading of leaf discs, the change in malate sensitivity of the enzyme was only marginal, indicating that there was no significant increase in the extent of PEPC-phosphorylation. Besides the physiological significance, the technique of acid/ base-loading may be an important tool for studying the regulation of PEPC in leaf discs of C 4 species, since the activity of PEPC could be enhanced apparently without phosphorylation of the enzyme.

The variegated leaves of the Crassulacean acid metabolism (CAM) species Agave americana have a large central longitudinal green band with narrow yellow bands on either side. The yellow bands had 97% less pigment content, 84% lower ribulose-1,5-bisphosphate carboxylase/oxygenase activity, but only 20% lower phosphoenolpyruvate carboxylase activity than the green band. The green bands exhibited gas exchange typical of CAM plants, with most CO2 uptake occurring at night, leading to a daily net CO2 uptake of 127 mmol m−2 day−1. The yellow bands had some nighttime net CO2 uptake but a larger loss during the daytime, indicating that they were sink tissues. Nocturnal citrate and malate accumulations for the yellow bands were 65 and 75%, respectively, of those of the green bands; sucrose supported 64-83% of their nocturnal acid accumulation. This is the first evidence that agaves, which are malic-enzyme-type CAM plants, use sucrose as the carbon source for nocturnal acid accumulation. About 44% of the carbon demand of the yellow bands can be supplied by sucrose diffusing via the symplast from the adjacent green band, about 25% from fructose and glucose diffusion, and some via the apoplast.

The growth rate, glucose consumption rate, and production rate of an L-lysine producing Corynebacterium glutamicum mutant were studied in batch and fed-batch cultures. In batch fermentation, higher L-lysine productivity (1.93 g l−1 h−1) and L-lysine yield of 0.70 g g−1 were obtained with lower lysine excretion (34 g l−1). A strong enhancement of L-lysine production (110.6 g l−1) was obtained in fed-batch culture, whereas the kinetic parameters remained lower than those observed in batch cultures. In both culture techniques high L-lysine productivity and L-lysine yield occurred at the lower growth rate ranging from 0.02 h−1. Enzymatic analysis revealed that the higher L-lysine production could be obtained under a higher phosphoenolpyruvate carboxylase/citrate synthase enzyme activity ratio to avoid biomass production at the expense of L-lysine. This is a direct proof of the important role of both phosphoenolpyruvate carboxylase activity and the composition of the growth medium on the L-lysine overproduction phase.

Important gas exchange characteristics of C4 plants depend on the properties of phophoenolpyruvate carboxylase (PEPC), the enzyme catalysing the primary fixation of CO2 during C4 photosynthesis. In this study, the relationship between intracellular resistance for CO2 fixation (ri) at high photosynthetically active photon flux densities (PPFD) and maximum PEPC activity in vitro (Vpm) was examined in leaves of Zea mays L. The analysis allowed the estimation of the Michaelis constant Kp of the enzyme for CO2 (or the equivalent number for bicarbonate) in vivo. At low PPFD (below 100 μmol m-2 s-1) the initial slopes of the curves describing net CO2 uptake rate A as a function of intercellular CO2 concentration ci increased with increasing PPFD. The increase (i. e. a decrease in ri) was interpreted as due to a reversible activation of PEPC by light. Including this assumption into a model of C4 photosynthesis enabled us to reproduce A(ci) response curves measured at low levels of PPFD. Fitting the model to experimental data resulted in values for KI, the PPFD at which PEPC reaches half of its full activation, of about 200 μmol m-2 s-1. Similar results were derived from the dependence of ri on PPFD. The analysis of the relationships between ri and Vpm and between ri and PPFD, as well as fitting of the model to gas exchange data all gave rise to estimates for the resistance for CO2 transfer within mesophyll cells that are comparable with those known from C3 plants.

Nia30(145) transformants with very low nitrate reductase activity provide an in vivo screen to identify processes that are regulated by nitrate. Nia30(145) resembles nitrate-limited wild-type plants with respect to growth rate and protein and amino acid content but accumulates large amounts of nitrate when it is grown on high nitrate. The transcripts for nitrate reductase (NR), nitrite reductase, cytosolic glutamine synthetase, and glutamate synthase increased; NR and nitrite reductase activity increased in leaves and roots; and glutamine synthetase activity increased in roots. The transcripts for phosphoenolpyruvate carboxylase, cytosolic pyruvate kinase, citrate synthase, and NADP-isocitrate dehydrogenase increased; phosphoenolpyruvate carboxylase activity increased; and malate, citrate, isocitrate, and [alpha]-oxoglutarate accumulated in leaves and roots. There was a decrease of the ADP-glucose pyrophosphorylase transcript and activity, and starch decreased in the leaves and roots. After adding 12 mM nitrate to nitrate-limited Nia30(145), the transcripts for NR and phosphoenolpyruvate carboxylase increased, and the transcripts for ADP-glucose pyrophosphorylase decreased within 2 and 4 hr, respectively. Starch was remobilized at almost the same rate as in wild-type plants, even though growth was not stimulated in Nia30(145). It is proposed that nitrate acts as a signal to initiate coordinated changes in carbon and nitrogen metabolism.

Previous studies have indicated that the rate of photorespiration in C4 plants is low or negligible. In this study, wild-type and mutant leaves of the C4 plant Amaranthus edulis were treated with the glutamine synthetase inhibitor, phosphinothricin and the glycine decarboxylase inhibitor, aminoacetonitrile, at different concentrations of CO2. The time course of ammonia accumulation in leaves of the wild type was compared with a mutant lacking phosphoenolpyruvate carboxylase activity (EC 4.1.1.31), and with three different mutants that accumulated glycine. The increase in the concentration of ammonia in the leaves, stimulated by the treatments was used as a measurement of the rate of photorespiration in C4 plants. The application of glutamine and glycine maintained the rate of photorespiratory ammonia production for a longer period in the wild type, and increased the rate in a mutant lacking phosphoenolpyruvate carboxylase suggesting that there was a lack of amino donors in these plants. The calculated rate of photorespiration in Amaranthus edulis wild-type leaves when the supply of amino donors was enough to maintain the photorespiratory nitrogen flow, accounted for approximately 6% of the total net photosynthetic CO2 assimilation rate. In a mutant lacking phosphoenolpyruvate carboxylase, however, this rate increased to 48%, when glutamine was fed to the leaf, a value higher than that found in some C3 plants. In mutants of Amaranthus edulis that accumulated glycine, the rate of photorespiration was reduced to 3% of the total net CO2 assimilation rate. The rate of ammonia produced during photorespiration was 60% of the total produced by all metabolic reactions in the leaves. The data suggests that photorespiration is an active process in C4 plants, which can play an important role in photosynthetic metabolism in these plants.

Bean plants (Phaseolus vulgaris L. cv. Zlota Saxa) were grown on complete (control plants) and phosphate-deficient (low-P plants) culture solutions for 17d. Phosphate deficiency markedly reduced leaf growth, but only slightly decreased the photosynthesis rate. The intensity of reactions releasing inorganic orthophosphate during photosynthesis was examined. In the leaves of low-P plants the pools of photorespiratory metabolites (glycolate and glycine + serine) were markedly increased. At the same time synthesis of soluble sugars from intermediates of glycolic acid cycle was probably enhanced. In low-P leaves the phosphoenolpyruvate carboxylase activity and malate synthesis were increased. Phosphoenolpyruvate and malate were effectively used for amino acid synthesis. Both aspartate and alanine accumulation was twice higher in low-P leaves. It was found that no enhancement in starch and sucrose synthesis rate takes place in phosphate deficient bean leaves. Modifications of photosynthetic metabolism observed under moderate phosphate deficiency facilitate plants acclimation to low-P conditions by enhancement of P i recirculation during glycolic and phosphoenolpyruvate metabolism.

Many forest tree species are dependent on their symbiotic interaction with ectomycorrhizal (ECM) fungi for phosphorus (P) uptake from forest soils where P availability is often limited. The ECM fungal association benefits the host plant under P limitation through enhanced soil exploration and increased P acquisition by mycorrhizas. To study the P starvation response (PSR) and its modification by ECM fungi in Populus tremuloides, a comparison was made between nonmycorrhizal (NM) and mycorrhizal with Laccaria bicolor (Myc) seedlings grown under different concentrations of phosphate (Pi) in sand culture. Although differences in growth between NM and Myc plants were small, Myc plants were more effective at acquiring P from low Pi treatments, with significantly lower k m values for root and leaf P accumulation. Pi limitation significantly increased the activity of catalase, ascorbate peroxidase, and guaiacol-dependent peroxidase in leaves and roots to greater extents in NM than Myc P. tremuloides. Phosphoenolpyruvate carboxylase activity also increased in NM plants under P limitation, but was unchanged in Myc plants. Formate, citrate, malonate, lactate, malate, and oxalate and total organic carbon exudation by roots was stimulated by P limitation to a greater extent in NM than Myc plants. Colonization by L. bicolor reduced the solution Pi concentration thresholds where PSR physiological changes occurred, indicating that enhanced Pi acquisition by P. tremuloides colonized by L. bicolor altered host P homeostasis and plant stress responses to P limitation. Understanding these plant-symbiont interactions facilitates the selection of more P-efficient forest trees and strategies for tree plantation production on marginal soils.

The antioxidative protection during the C3-CAM shift induced by water stress was investigated in the temperate succulent Sedum album L. The C3-CAM shift was characterized in terms of CO2 exchange, titratable acidity and phosphoenolpyruvate carboxylase activity. Well-watered plants displayed C3-like patterns of gas exchange and exhibited a mild day-night acid fluctuation indicating that those plants were performing CAM-cycling metabolism. Imposed drought highly stimulated CAM cycling, decreasing the net CO2 uptake during the day, eliminating net CO2 efflux at night and stimulating tissue acid fluctuations. As water deficit developed, chlorophyll fluorescence measurements showed a decrease in the Fv/Fm ratio, indicating that photoinhibition could follow after severe drought. Protection might be performed by the increased activity of enzymes involved in the destruction of free radicals and oxidants, but their response depended on the water status of the plant. Ascorbate peroxidase and superoxide dismutase activities increased in plants subjected to mild stress but declined during severe water stress. Catalase activity, however, was quite stable under mild water stress and was clearly inhibited under severe water stress. At this stage, glutathione reductase and monodehydroascorbate reductase seemed to be very important in the protection against oxidants, both increasing considerably their activities under severe water stress. Even if recycling has been shown to alleviate photoinhibition, our results clearly demonstrate that antioxidative enzymes play an important role in the protection of plants from oxidants during the C3-CAM shift induced by water stress.

Responses of plants seedlings to hypobaria (reduced pressure of air) exposure (up to 8 kPa) and exogenously applied ethylene (10 -4 , 10 -5 , 10 -6 kPa) was studied using a gasometric system based on CO 2 -laser photoacoustic spectrometer. The increase of O 2 -evolution (in the dark) by pea (Pisum sativum L.), wheat (Triticum aestivum L.), maize (Zea mays L.), barley (Hordeum vulgare L.) and pine seedlings (Pinus sylvestris L.) was revealed. Some differences in dynamics of CO 2 -evolution and signal magnitudes are probably stipulated by the objects specificity. The alcohol-dehydrogenase, isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, phosphoenolpyruvate carboxylase activity and contents of malate, pyruvate and lactate were studied in pea leaves. It was shown that an anaerobic metabolism increases with time and also when the air pressure is decreased. An increase of CO 2 -evolution from ethylene-treated pea seedlings and alcohol-dehydrogenase activation were observed.