PEPCase Activity Research Articles

Weak-light stress at different grain filling stages affects yield by reducing leaf carbon and nitrogen metabolism in fresh waxy maize

Insufficient light radiation is one of the main factors limiting maize yield in southern China. The plum rainy season overlaps with grain filling stage, and intermittent cloudy and rainy weather results in weak-light stress restricting the yield improvement of fresh waxy maize. This study was to assess the impact of weak-light stress at different grain filling stages on yield and leaf carbon (C) and nitrogen (N) metabolism in fresh waxy maize. Suyunuo5 (SYN5) and Jingkenuo2000 (JKN2000) were used to investigate the effects of weak-light at different stages after pollination (1–7, 8–14, 15–21 and 1–21 days, recorded as Z1, Z2, Z3 and Z4) on yield, dry matter and nitrogen (N) accumulation, C and N metabolism in leaf of fresh waxy maize from 2021 to 2022. Compared with CK (natural light treatment), weak-light decreased the fresh ear and grain yield, post-silking dry matter and N accumulation, and the decrease was maximum in Z4, followed by Z1. The decrease in JKN2000 was greater than SYN5. RUBPCase and PEPCase activities, net photosynthetic rate, transpiration rate and stomatal conductance of ear leaves decreased under weak-light, and those were lowest in Z4, followed by Z1. Furthermore, weak-light stress significantly decreased the activities of nitrate reductase, glutamine synthetase, glutamate synthase, and post-silking N accumulation. The highest decrease was found in Z4, followed by Z1. Weak-light stress also downregulated the activities of superoxide dismutase, catalase, peroxidase and raised MDA content in ear leaves during grain filling stage, which accelerated leaf senescence process. Weak-light stress after pollination decreased maize yield by affecting leaf C and N metabolism and antioxidant system, and the stress occurred in first week after pollination had a more severe impact than those in middle and later stages, and JKN2000 was more sensitive to weak-light than SYN5. Our results contributed to understanding how weak-light stress could reduce the yield of fresh waxy maize by affecting leaf C and N metabolism, and offered theoretical support for implementing measures to alleviate weak-light conditions in the planting areas of fresh waxy maize.

The effects of high temperature, drought, and their combined stresses on the photosynthesis and senescence of summer maize

Global climate change has significantly increased the frequency and intensity of high temperature and drought stresses. Additionally, the high temperature and drought are often concurred, which make the situation of maize production tougher. However, the influence of the combined stresses of high temperature and drought on summer maize production remains uncertain. The study aimed to investigate the effects of high temperature, drought, and their combined stress at different growth stages on photosynthetic and senescence characteristics of summer maize. Denghai 605 (DH605) was used as the experimental material. High temperature (T), drought (D), and their combined stress (T-D) for 6 days were set at the 3rd leaf stage, 12th leaf stage, and tasseling stage, respectively. The natural temperature and normal water management were used as the control (CK). The results showed that high temperature, drought, and their combined stress at different growth stages decreased the activities of antioxidant enzymes and soluble protein content in leaves, leading to increases in MDA content and damage to cell membranes, which accelerated the senescence of the plant. Accordingly, the activities of RuBPcase and PEPCase were decreased, indicating the abilities of plants to harvest and utilize light energy declined due to high temperature, drought, and combined stresses at different growth stages. As a result, the Pn and thus, the dry matter accumulation rate were decreased by these stresses. In addition, the translocation of dry matter to ears was impeded by stresses, especially by the high temperature at the VT stage. While, high temperatures concurred with drought aggravated the adverse effects on summer maize, compared with single stresses. Significantly, high temperature, drought, and their combined stresses at the VT stage decreased the yield mostly, followed by stresses at the V12 stage, and then by stresses at the V3 stage. Compared with CK, the yield of VT-T-D, V12-T-D, and V3-T-D were decreased by 61.6 %, 13.7 %, and 10.4 %, respectively. As global climate change is unstoppable, the superimposed changes of various meteorological factors make the growth conditions for crop production extreme. Studies to explore the combined effects of two or even more meteorological factors on crop growth are becoming more and more important. This study fulfilled the current knowledge gap of the combined stresses on maize production, however, the underlying mechanisms should be dug out in the future.

Spraying exogenous hormones alleviate impact of weak-light on yield by improving leaf carbon and nitrogen metabolism in fresh waxy maize.

Insufficient light during the growth periods has become one of the main factors restricting maize yield with global climate change. Exogenous hormones application is a feasible measure to alleviate abiotic stresses on crop productivity. In this study, a field trial was conducted to investigate the effects of spraying exogenous hormones on yield, dry matter (DM) and nitrogen (N) accumulation, leaf carbon and N metabolism of fresh waxy maize under weak-light stress in 2021 and 2022. Five treatments including natural light (CK), weak-light after pollination (Z), spraying water (ZP1), exogenous Phytase Q9 (ZP2) and 6-benzyladenine (ZP3) under weak-light after pollination were set up using two hybrids suyunuo5 (SYN5) and jingkenuo2000 (JKN2000). Results showed that weak-light stress significantly reduced the average fresh ear yield (49.8%), fresh grain yield (47.9%), DM (53.3%) and N accumulation (59.9%), and increased grain moisture content. The net photosynthetic rate (Pn), transpiration rate (Tr) of ear leaf after pollination decreased under Z. Furthermore, weak-light decreased the activities of RuBPCase and PEPCase, nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in ear leaves, and increased malondialdehyde (MDA) accumulation. And the decrease was greater on JKN2000. While ZP2 and ZP3 treatments increased the fresh ear yield (17.8%, 25.3%), fresh grain yield (17.2%, 29.5%), DM (35.8%, 44.6%) and N (42.5%, 52.4%) accumulation, and decreased grain moisture content compared with Z. The Pn, Tr increased under ZP2 and ZP3. Moreover, the ZP2 and ZP3 treatments improved the activities of RuBPCase, PEPCase; NR, GS, GOGAT; SOD, CAT, POD in ear leaves, and decreased MDA content during grain filling stage. The results also showed the mitigative effect of ZP3 was greater than ZP2, and the improvement effect was more significant on JKN2000.

The carbonate concentration mechanism of Pyropia yezoensis (Rhodophyta): evidence from transcriptomics and biochemical data

BackgroundPyropia yezoensis (Rhodophyta) is widely cultivated in East Asia and plays important economic, ecological and research roles. Although inorganic carbon utilization of P. yezoensis has been investigated from a physiological aspect, the carbon concentration mechanism (CCM) of P. yezoensis remains unclear. To explore the CCM of P. yezoensis, especially during its different life stages, we tracked changes in the transcriptome, photosynthetic efficiency and in key enzyme activities under different inorganic carbon concentrations.ResultsPhotosynthetic efficiency demonstrated that sporophytes were more sensitive to low carbon (LC) than gametophytes, with increased photosynthesis rate during both life stages under high carbon (HC) compared to normal carbon (NC) conditions. The amount of starch and number of plastoglobuli in cells corresponded with the growth reaction to different inorganic carbon (Ci) concentrations. We constructed 18 cDNA libraries from 18 samples (three biological replicates per Ci treatment at two life cycles stages) and sequenced these using the Illumina platform. De novo assembly generated 182,564 unigenes, including approximately 275 unigenes related to CCM. Most genes encoding internal carbonic anhydrase (CA) and bicarbonate transporters involved in the biophysical CCM pathway were induced under LC in comparison with NC, with transcript abundance of some PyCAs in gametophytes typically higher than that in sporophytes. We identified all key genes participating in the C4 pathway and showed that their RNA abundances changed with varying Ci conditions. High decarboxylating activity of PEPCKase and low PEPCase activity were observed in P. yezoensis. Activities of other key enzymes involved in the C4-like pathway were higher under HC than under the other two conditions. Pyruvate carboxylase (PYC) showed higher carboxylation activity than PEPC under these Ci conditions. Isocitrate lyase (ICL) showed high activity, but the activity of malate synthase (MS) was very low.ConclusionWe elucidated the CCM of P. yezoensis from transcriptome and enzyme activity levels. All results indicated at least two types of CCM in P. yezoensis, one involving CA and an anion exchanger (transporter), and a second, C4-like pathway belonging to the PEPCK subtype. PYC may play the main carboxylation role in this C4-like pathway, which functions in both the sporophyte and gametophyte life cycles.

RNA interference of GhPEPC2 enhanced seed oil accumulation and salt tolerance in Upland cotton

Phosphoenolpyruvate carboxylase (PEPCase) mainly produces oxaloacetic acid for tricarboxylic acid (TCA) cycle. Here we reported that GhPEPC2 silencing with PEPC2-RNAi vector could regulate oil and protein accumulation in cottonseeds. In GhPEPC2 transgenic plants, PEPCase activities in immature embryos were significantly reduced, and the oil content in seed kernel was increased 7.3 percentages, whereas total proteins decreased 5.65 percentages. Compared to wild type, agronomical traits of transgenic plant were obviously unaffected. Furthermore, gene expression profile of GhPEPC2 transgenic seeds were investigated using RNA-seq, most lipid synthesis related genes were up-regulated, but amino acid metabolic related genes were down-regulated. In addition, the GhPEPC2 transgenic cotton seedlings were stressed using sodium salts at seedling stage, and the salt tolerance was significantly enhanced. Our observations of GhPEPC2 in cotton would shade light on understanding the regulation of oil content, protein accumulation and salt tolerance enhancement in other plants.

Exogenous 6‐benzyladenine improves antioxidative system and carbon metabolism of summer maize waterlogged in the field

AbstractA field experiment was performed to study the effects of spraying exogenous 6‐benzyladenine (6‐BA) after waterlogging for 6 days at the third leaf stage and the sixth leaf stage on the activities of key enzymes in carbon metabolism, leaf gas exchange parameters, fluorescent characteristic, antioxidant enzymes activities and MDA content of summer maize hybrids Denghai605 (DH605) and Zhengdan958 (ZD958), in order to illuminate the regulations of exogenous spraying 6‐BA to antioxidative system and carbon metabolism of waterlogged summer maize. Results showed that exogenous application of 6‐BA effectively alleviated the adverse effects of waterlogging on carbon metabolism by improving photosynthetic characteristics and the activities of RuBPCase (in the range of 48%–81%) and PEPCase (in the range of 14%–46%). Treatments with spraying exogenous 6‐BA resulted in significant and substantial increases in net photosynthetic rate (around 49%) and ΦPSII (around 16%) compared to those of waterlogging treatments. In addition, spraying 6‐BA effectively alleviated waterlogging damages on antioxidative enzyme activity and decreased MDA content, delaying leaf senescence, resulted in significant and substantial (around 19%) increases in grain yield. Visibly, spraying exogenous 6‐BA effectively alleviated waterlogging damages on antioxidative system and carbon metabolism of summer maize, resulting in yield increase in waterlogged maize.

Salinity promotes opposite patterns of carbonylation and nitrosylation of C4 phosphoenolpyruvate carboxylase in sorghum leaves.

Carbonylation inactivates sorghum C 4 PEPCase while nitrosylation has little impact on its activity but holds back carbonylation. This interplay could be important to preserve photosynthetic C4 PEPCase activity in salinity. Previous work had shown that nitric acid (NO) increased phosphoenolpyruvate carboxylase kinase (PEPCase-k) activity, promoting the phosphorylation of phosphoenolpyruvate carboxylase (PEPCase) in sorghum leaves (Monreal et al. in Planta 238:859-869, 2013b). The present work investigates the effect of NO on C4 PEPCase in sorghum leaves and its interplay with carbonylation, an oxidative modification frequently observed under salt stress. The PEPCase of sorghum leaves could be carbonylated in vitro and in vivo, and this post-translational modification (PTM) was accompanied by a loss of its activity. Similarly, PEPCase could be S-nitrosylated in vitro and in vivo, and this PTM had little impact on its activity. The S-nitrosylated PEPCase showed increased resistance towards subsequent carbonylation, both in vitro and in vivo. Under salt shock, carbonylation of PEPCase increased in parallel with decreased S-nitrosylation of the enzyme. Subsequent increase of S-nitrosylation was accompanied by decreased carbonylation. Taken together, the results suggest that S-nitrosylation could contribute to maintain C4 PEPCase activity in stressed sorghum plants. Thus, salt-induced NO synthesis would be protecting photosynthetic PEPCase activity from oxidative inactivation while promoting its phosphorylation, which will guarantee its optimal functioning in suboptimal conditions.

Characterization and expression patterns of key C4 photosynthetic pathway genes in bread wheat (Triticum aestivum L.) under field conditions

Wheat is a C3 plant with relatively low photosynthetic efficiency and is a potential target for C4 photosynthetic pathway engineering. Here we reported the characterization of four key C4 pathway genes and assessed their expression patterns and enzymatic activities at three growth stages in flag leaves of 59 bread wheat genotypes. The C4-like genes homologous to PEPC, NADP-ME, MDH, and PPDK in maize were identified in the A, B, and D sub-genomes of bread wheat, located on the long arms of chromosomes 3 and 5 (TaPEPC), short arms of chromosomes 1 and 3 (TaNADP-ME), long arms of chromosomes 1 and 7 (TaMDH), and long arms of chromosome 1 (TaPPDK), respectively. All the four C4-like genes were expressed in the flag leaves at the three growth stages with considerable variations among the 59 bread wheat genotypes. Significant differences were observed between the photosynthesis rates (A) of wheat genotypes with higher expressions of TaPEPC_5, TaNADP-ME_1, and TaMDH_7 at heading and middle grain-filling stages and those with intermediate and low expressions. Our results also indicated that the four C4 enzymes showed activity in the flag leaves and were obviously different among the 59 wheat genotypes. The activities of PEPcase and PPDK decreased at anthesis and slightly increased at grain-filling stage, while NADP-ME and MDH exhibited a decreasing trend at the three stages. The results of the current study could be very valuable and useful for wheat researchers in improving photosynthetic capacity of wheat.

The Ameliorative Effects of Silicon on Salt-Stressed Sorghum Seedlings and Its Influence on the Activities of Sucrose Synthase and PEP Carboxylase

The Ameliorative Effects of Silicon on Salt-Stressed Sorghum Seedlings and Its Influence on the Activities of Sucrose Synthase and PEP Carboxylase Under salt stress, Silicon is considered a beneficial element for the growth of higher plants as it alleviates the harmful effects caused by salt. In the present study, Sorghum bicolor L. seedlings were grown hydroponically in growth units, filled with continuously aerated half strength of Hoagland-nutrient solution. Different treatments were manipulated to examine the negative effects of NaCl and the combined effect of NaCl with Si on seedlings growth, chlorophyll content, soluble protein content, ion accumulation, phosphoenolpyruvate carboxylase (PEPCase) and sucrose synthase (SS) activities. The salt induced decrease in seedling growth was relieved upon treatment with Si. Meanwhile, the sucrose and glucose levels were significantly increased and there was a reduction in sodium concentrations in the salt-stressed plants treated with silicon. The PEPCase activity in sorghum seedlings subjected to salt-stress was higher in the treatment with Si than that without Si, but did not significantly differ from that of control.

Photosynthetic responses to chilling in a chilling-tolerant and chilling-sensitive Miscanthus hybrid.

Miscanthus is a C4 perennial grass being developed for bioenergy production in temperate regions where chilling events are common. To evaluate chilling effects on Miscanthus, we assessed the processes controlling net CO2 assimilation rate (A) in Miscanthus x giganteus (M161) and a chilling-sensitive Miscanthus hybrid (M115) before and after a chilling treatment of 12/5 °C. The temperature response of A and maximum Rubisco activity in vitro were identical below 20 °C in chilled and unchilled M161, demonstrating Rubisco capacity limits or co-limits A at cooler temperatures. By contrast, A in M115 decreased at all measurement temperatures after growth at 12/5 °C. Rubisco activity in vitro declined in proportion to the reduction in A in chilled M115 plants, indicating Rubisco capacity is responsible in part for the decline in A. Pyruvate orthophosphate dikinase activities were also reduced by the chilling treatment when assayed at 28 °C, indicating this enzyme may also contribute to the reduction in A in M115. The maximum extractable activities of PEPCase and NADP-ME remained largely unchanged after chilling. The carboxylation efficiency of the C4 cycle was depressed in both genotypes to a similar extent after chilling. ΦP :ΦCO2 remained unchanged in both genotypes indicating the C3 and C4 cycles decline equivalently upon chilling.

Physiological and transcriptional analyses of developmental stages along sugarcane leaf.

BackgroundSugarcane is one of the major crops worldwide. It is cultivated in over 100 countries on 22 million ha. The complex genetic architecture and the lack of a complete genomic sequence in sugarcane hamper the adoption of molecular approaches to study its physiology and to develop new varieties. Investments on the development of new sugarcane varieties have been made to maximize sucrose yield, a trait dependent on photosynthetic capacity. However, detailed studies on sugarcane leaves are scarce. In this work, we report the first molecular and physiological characterization of events taking place along a leaf developmental gradient in sugarcane.ResultsPhotosynthetic response to CO2 indicated divergence in photosynthetic capacity based on PEPcase activity, corroborated by activity quantification (both in vivo and in vitro) and distinct levels of carbon discrimination on different segments along leaf length. Additionally, leaf segments had contrasting amount of chlorophyll, nitrogen and sugars. RNA-Seq data indicated a plethora of biochemical pathways differentially expressed along the leaf. Some transcription factors families were enriched on each segment and their putative functions corroborate with the distinct developmental stages. Several genes with higher expression in the middle segment, the one with the highest photosynthetic rates, were identified and their role in sugarcane productivity is discussed. Interestingly, sugarcane leaf segments had a different transcriptional behavior compared to previously published data from maize.ConclusionThis is the first report of leaf developmental analysis in sugarcane. Our data on sugarcane is another source of information for further studies aiming to understand and/or improve C4 photosynthesis. The segments used in this work were distinct in their physiological status allowing deeper molecular analysis. Although limited in some aspects, the comparison to maize indicates that all data acquired on one C4 species cannot always be easily extrapolated to other species. However, our data indicates that some transcriptional factors were segment-specific and the sugarcane leaf undergoes through the process of suberizarion, photosynthesis establishment and senescence.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0694-z) contains supplementary material, which is available to authorized users.

Overexpression of maize SDD1 (ZmSDD1) improves drought resistance in Zea mays L. by reducing stomatal density

Drought is one of major factors limiting the high and stable yields of maize, and thus, improvement of water use efficiency (WUE) and cultivation of drought-resistant maize cultivars have become very urgent. Previous research shows that SDD1 from Arabidopsis thaliana, a key gene during stomatal development, negatively regulates stomatal density, reduces transpiration, and improves WUE and drought resistance without reducing biomass. In this study, maize SDD1 (ZmSDD1) containing intron was cloned, and the phylogenetic tree was constructed, revealing a close genetic relationship with the SDD1 of Oryza sativa. ZmSDD1 was expressed in the leaves, shoots, and roots of maize. Under drought, cold, and salt stress conditions, the expression of ZmSDD1 in B73 maize leaves is reduced. To reveal the functions of ZmSDD1, we built a plant expression vector pGM626-Ubi-SDD1-ABt containing ZmSDD1 which was driven by the maize Ubiquitin promoter. Transgenic plants were obtained via shoot-tip transformation. The stomata number on leaf surfaces of the plants within Ubiquitin::ZmSDD1 overexpression plants was 30 % lower than that in the wildtype ones. After repeated drought treatments the transgenic maizes demonstrated a much higher survival rate with 6.68-fold ZmSDD1 overexpression, which indicated the expression of the gene negatively regulating stomata density and caused the reduction of stomatal conductance and transpiration rate after drought-treatment. In addition, ZmSDD1 enhanced the drought resistance in the transgenic maizes through improving WUE and photosynthetic rate which was considered as the result of the higher PEPCase activity, CO2 utilization rate and the lower CO2 compensation point.

Exogenous sucrose supply changes sugar metabolism and reduces photosynthesis of sugarcane through the down-regulation of Rubisco abundance and activity

Photosynthetic modulation by sugars has been known for many years, but the biochemical and molecular comprehension of this process is lacking. We studied how the exogenous sucrose supplied to leaves could affect sugar metabolism in leaf, sheath and stalk and inhibit photosynthesis in four-month old sugarcane plants. Exogenous sucrose 50mM sprayed on attached leaves strongly impaired the net CO2 assimilation (PN) and decreased the instantaneous carboxylation efficiency (PN/Ci), suggesting that the impairment in photosynthesis was caused by biochemical restrictions. The photosystem II activity was also affected by excess sucrose as indicated by the reduction in the apparent electron transport rate, effective quantum yield and increase in non-photochemical quenching. In leaf segments, sucrose accumulation was related to increases in the activities of soluble acid and neutral invertases, sucrose synthase and sucrose phosphate synthase, whereas the contents of fructose increased and glucose slightly decreased. Changes in the activities of sucrose hydrolyzing and synthesizing enzymes in leaf, sheath and stalk and sugar profile in intact plants were not enough to identify which sugar(s) or enzyme(s) were directly involved in photosynthesis modulation. However, exogenous sucrose was able to trigger down-regulation in the Rubisco abundance, activation state and enzymatic activity. Despite the fact that PN/Ci had been notably decreased by sucrose, in vitro activity and abundance of PEPCase did not change, suggesting an in vivo modulation of this enzyme. The data reveal that sucrose and/or other derivative sugars in leaves inhibited sugarcane photosynthesis by down-regulation of Rubisco synthesis and activity. Our data also suggest that sugar modulation was not exerted by a feedback mechanism induced by the accumulation of sugars in immature sugarcane stalk.

English

UV exclusion studies can provide the realistic assessments of sensitivity of plant to current level of UV radiation. Perusal of relevant literature reveals that UV exclusion causes enormous increase in the growth of aerial parts along with below ground parts of the plants. Exclusion of UV-B (280-315 nm) and UV-A+B (280-400 nm) enhanced the photosynthetic pigments, net photosynthetic rate and stomatal conductance along with remarkable increase in the activity of Carbonic anhydrase, Rubisco and PEPCase. UV excluded plants have higher PS II efficiency, reducing power, CO2 fixation and decreased UV-B absorbing compounds, channeling the additional fixation of carbon to improvement of yield. UV exclusion studies indicate that dicot plants are more sensitive than the monocot plants to current level of UV-B.

Regulation of pepc gene expression in Anabaena sp. PCC 7120 and its effects on cyclic electron flow around photosystem I and tolerances to environmental stresses.

Since pepc gene encoding phosphoenolpyruvate carboxylase (PEPCase) has been cloned from Anabaena sp. PCC 7120 and other cyanobacteria, the effects of pepc gene expression on photosynthesis have not been reported yet. In this study, we constructed mutants containing either upregulated (forward) or downregulated (reverse) pepc gene in Anabaena sp. PCC 7120. Results from real-time quantitative polymerase chain reaction (RT-qPCR), Western blot and enzymatic analysis showed that PEPCase activity was significantly reduced in the reverse mutant compared with the wild type, and that of the forward mutant was obviously increased. Interestingly, the net photosynthesis in both the reverse mutant and the forward mutant were higher than that of the wild type, but dark respiration was decreased only in the reverse mutant. The absorbance changes of P700 upon saturation pulse showed the photosystem I (PSI) activity was inhibited, as reflected by Y(I), and Y(NA) was elevated, and dark reduction of P700(+) was stimulated, indicating enhanced cyclic electron flow (CEF) around PSI in the reverse mutant. Additionally, the reverse mutant photosynthesis was higher than that of the wild type in low temperature, low and high pH, and high salinity, and this implies increased tolerance in the reverse mutant through downregulated pepc gene.

Improvement of the phosphoenolpyruvate carboxylase activity of Phaeodactylum tricornutum PEPCase 1 through protein engineering

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 500mL of E. coli culture was greatest for cPtPEPCase 1 (1.99mg), followed by mPtPEPCase 1 (0.82mg) and PtPEPCase 1 (0.61mg). 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.

Mineral content and biochemical variables of Aloe vera L. under salt stress.

Despite the proven economic importance of Aloe vera, studies of saline stress and its effects on the biochemistry and mineral content in tissues of this plant are scarce. The objective of this study was to grow Aloe under NaCl stress of 0, 30, 60, 90 and 120 mM and compare: (1) proline, total protein, and enzyme phosphoenolpyruvate carboxylase (PEP-case) in chlorenchyma and parenchyma tissues, and (2) ion content (Na, K, Ca, Mg, Cl, Fe, P. N, Zn, B, Mn, and Cu) in roots, stems, leaves and sprouts. Proline and PEP-case increased as salinity increased in both parenchyma and chlorenchyma, while total protein increased in parenchyma and decreased in chlorenchyma, although at similar salt concentrations total protein was always higher in chlorenchyma. As salinity increased Na and Cl ions increased in roots, stems, leaves, while K decreased only significantly in sprouts. Salinity increases typically caused mineral content in tissue to decrease, or not change significantly. In roots, as salinity increased Mg decreased, while all other minerals failed to show a specific trend. In stems, the mineral concentrations that changed were Fe and P which increased with salinity while Cu decreased. In leaves, Mg, Mn, N, and B decreased with salinity, while Cu increased. In sprouts, the minerals that decreased with increasing salinity were Mg, Mn, and Cu. Zinc did not exhibit a trend in any of the tissues. The increase in protein, proline and PEP-case activity, as well as the absorption and accumulation of cations under moderate NaCl stress caused osmotic adjustment which kept the plant healthy. These results suggest that Aloe may be a viable crop for soil irrigated with hard water or affected by salinity at least at concentrations used in the present study.

Concomitant Increases of the Developing Seed Phosph<i>oenol</i>pyruvate Carboxylase Ac-tivity and the Seed Protein Content of Field-Grown Wheat with Nitrogen Supply

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.

Photosynthetic limitations imposed by self-shading in field-grown sugarcane varieties

As a result of self-shading, a large fraction of a plant's leaf area is exposed to low light levels, causing photosynthesis to occur under limiting light conditions. The aim of this study was to evaluate photosynthesis in the canopy of two sugarcane varieties grown under field conditions in view of the effects of self-shading on photosynthetic metabolism. Photosynthesis response curves to increases in CO2 partial pressure (A/Ci) and light intensity (A/Q) were obtained for leaves from the upper (leaf +2) and lower (leaf +5) canopy layers, and the leaf nitrogen and chlorophyll content was also evaluated. The IACSP93-2060 genotype, which shows higher self-shading, did not exhibit differences in photosynthetic capacity between canopy layers, presenting similarities in C4 maximum RubisCO capacity (Vmax) and A/Q-derived parameters when the canopy layers were compared. This pattern was most likely the result of light acclimation, with IACSP93-2060 showing increased photosynthetic nitrogen use efficiency in the lower canopy layer. Despite higher light availability due to a lower level of self-shading, the IACSP95-3028 genotype showed a decrease in photosynthetic capacity in the lower layer. This response was related to a decrease in Vmax, indicating a biochemical limitation of photosynthesis due to self-shading. Our data on stomatal conductance did not show any differences in the stomatal limitation of photosynthesis in both canopy layers of both varieties. In general, self-shading reduced the chlorophyll a and b and leaf N concentrations without significant changes in the PEPCase activity (given by the initial slope of the A/Ci curve) in the lower canopy layer. In addition to presenting a higher photosynthetic capacity, IACSP95-3028 also received more light in the lower canopy layer, supporting its higher biomass production compared with IACSP93-2060.

Regulation of N2 fixation and NO3−/NH4+ assimilation in nodulated and N-fertilized Phaseolus vulgaris L. exposed to high temperature stress

Legumes need large amounts of N to grow satisfactorily. Under low NO3− availability in the soil, many legumes meet their N requirements by N2 fixation in association with rhizobia. Both NO3− uptake and N2 fixation decrease as temperature exceeds optimal growth conditions, but the mechanisms of regulation of N2 fixation and NO3−/NH4+ assimilation under high temperature stress are not completely understood. We describe an experiment in which physiological mechanisms regulating N metabolism of common bean (Phaseolus vulgaris L.) are investigated in plants submitted to daily maximum temperatures of 28, 34 and 39°C. Common bean was grown in symbiosis with each of six rhizobial strains—belonging to four different species and varying in N2 fixation effectiveness—or fertilized with NO3− until flowering. Harvest measurements included the activities of shoot, stem and root NO3− reductase (NR), nodule glutamine synthetase (GS), NADH-dependent glutamate synthase (GOGAT), nitrogenase, phosphoenol pyruvate carboxylase (PEPcase), N-export rates by nodules and concentration of N compounds in the xylem sap. Higher temperatures inhibited N2 fixation resulting in lower proportion of ureide-N in nodules and xylem sap of nodulated plants in relation to amide-N and α-amino-N. Higher temperatures consistently reduced the activity of NR in leaves of N-fertilized plants. Higher temperatures also decreased N exported from nodules and activities of nitrogenase, GS, GOGAT and PEPcase. The rate of decreases varied in plants with different strains. Furthermore, the activities of GS and GOGAT were more strongly affected by high temperatures than the activity of nitrogenase. There was a remarkable increase in the concentration of NH4+-N and ureide-N in the nodules when GS and GOGAT activities decreased. Therefore, the results provide evidence that N2 fixation in common bean submitted to heat stress is limited by NH4+ assimilation via GS-GOGAT rather than by decreased activity of nitrogenase. Rhizobial effectiveness determined the degree of down-regulation of GS-GOGAT activity in nodule tissues.