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Plastidial carbonic anhydrase in cotton (Gossypium hirsutum L.): characterization, expression, and role in lipid biosynthesis
Recently, plastidial carbonic anhydrase (CA, EC 4.2.1.1) cDNA clones encoding functional CA enzymes were isolated from a nonphotosynthetic cotton tissue. The role of CA in photosynthetic tissues have been well characterized, however there is almost no information for the role of CA in nonphotosynthetic tissues. A survey of relative CA transcript abundance and enzyme activity in different cotton organs revealed that there was substantial CA expression in cotyledons of seedlings and embryos, both nonphotosynthetic tissues. To gain insight into the role(s) of CA, I examined CA expression in cotyledons of seedlings during post-germinative growth at different environmental conditions. CA expression in cotyledons of seedlings increased from 18 h to 72 h after germination in the dark. Seedlings exposed to light had about a 2-fold increase in CA activities when compared with seedlings kept in the dark, whereas relative CA transcript levels were essentially the same. Manipulation of external CO2 environments [zero, ambient (350 ppm), or high (1000 ppm)] modulated coordinately the relative transcript abundance of CA (and rbcS) in cotyledons, but did not affect enzyme activities. On the other hand, regardless of the external CO2 conditions seedlings exposed to light exhibited increase CA activity, concomitant with Rubisco activity and increased chlorophyll content. Our data revealed that steady-state levels of CA and rbcS transcripts are regulated at the transcriptional level in response to external CO2 conditions, while CA and Rubisco activities are modulated at the post-transcriptional level by light. Thus CA expression in cotyledons during post-germinative growth may be to “prime” cotyledons for the transition at the subcellular level for the transition from plastids to chloroplasts, where it provides CO2 for Rubisco during photosynthesis. Furthermore, CA expression increased during embryo maturation similar to oil accumulation. Specific sulfonamide inhibitors of CA activity significantly reduced the
rate of [14C]-acetate incorporation into total lipids in cotton embryos and tobacco leaves and cell suspensions in vivo and in vitro. Similar results were obtained in chloroplasts isolated from leaves of transgenic CA antisense-suppressed tobacco plants (5% of wildtype activity). Collectively, these results support the notion that CA plays several physiological roles in nonphotosynthetic tissues
Identification and expression analysis of phosphoenolpyruvate carboxylase (PEPC) and PEPC kinase genes in C3 plants
Phosphoenolpyruvate carboxylase (PEPc) is a cytosolic enzyme that plays a wide range of roles in different tissues of higher plants. A photosynthetic isoform of PEPc catalyses the primary fixation of CO2 in C4 and CAM plants. Other isoforms are thought to be responsible for different functions, including the replenishment of tricarboxylic acid cycle intermediates, pH control, and the provision of malate in guard cells, developing fruit and legume root nodules. PEPc is an allosteric enzyme, inhibited by malate and activate by glucose 6- phosphate. Superimposed on this is control by reversible phosphorylation of a single serine residue close to the N-terminus of the protein. Phosphorylation modulates the allosteric properties of the enzyme, with the phosphorylated form being less sensitive to malate inhibition. The phosphorylation state of PEPc is controlled largely at the level of expression of PEPc kinase (PPCK) genes. The aim of this work was to identify and characterise PEPC and PPCK genes in C3 plants, particularly in the leguminous plant soybean {Glycine max). In legume root nodules, PEPc plays a central role in the metabolism that allows fixation of atmospheric N2 by bacteroids. It provides the C4 dicarboxylates that are required by the bacteroids for energy generation and also the carbon skeletons that are needed for the subsequent assimilation of ammonium into amino acids. In soybean one PEPc gene (GmPEPCT) is highly and relatively specifically expressed in nodules. To test the hypothesis that PEPc kinase expression would show a similar pattern, the expression of both PPCK and PEPC genes were analysed in soybean. Soybean contains at least four PPCK genes. The genomic and cDNA sequences of these genes were determined, and the function of the gene products demonstrated by in vitro expression and enzyme assays. For two of these genes, GmPPCK2 and GmPPCKS, transcript abundance is highest in nodules and is markedly influenced by supply of photosynthate from the shoots. One gene, GmPPCK4, is under robust circadian control in leaves but not in roots. Its transcript abundance peaks in the latter stages of subjective day. This is the first report of a C3 PPCK gene that is controlled in this manner. The expression patterns of five PEPC genes, including one encoding a bacterial-type PEPc lacking the phosphorylation site of the "plant" PEPcs, were also investigated. The PEPC expression patterns do not match those of any of the PPCK genes, arguing against the existence of specific PEPc-PEPc kinase expression partners. Collectively, the results demonstrate that the PEPC and PPCK gene families in soybean are significantly more complex than previously understood. Another role of PEPc is the production of organic acids in developing fruit. Previous work had identified two PPCK genes in tomato (Lycopersicon esculentum), one of which (LePPCK2) contained a novel second intron that exhibits alternative splicing. The correctly spliced transcript encodes a functional PEPc kinase, whereas unspliced or incorrectly spliced transcripts encode a truncated, inactive protein. The relative abundance of the transcripts varies in different tissues, both in wild-type plants and in the greenflesh tomato mutant. A PPCK2 gene was identified in tobacco (Nicotiana tabacum), also exhibiting alternative splicing and producing various amounts of the transcript in different tissues. Similar sequences are also present in potato {Solanum tuberosum) and aubergine {Solarium melongena). The data suggest that the alternative splicing of PPCK2 transcripts is functionally significant. The release of the rice {Oryza sativa) genome sequence allowed the identification of three putative PPCK genes. The sequence of one of these genes (OsPPCK2) was unusual in containing three in frame methionine residues at the 5' end, potentially allowing the production of a larger PEPc kinase protein. The functionality of these genes was assessed, but the results were unable to provide unequivocal evidence demonstrating the phosphorylation of PEPc by the Tong' form ofOsPPCK2. Overall the data presented in this thesis reveal a novel picture of the transcriptional control of PEPc kinase in C3 plants
Biotin-containing enzymes from Brassica napus and Arabidopsis thaliana.
SIGLEAvailable from British Library Document Supply Centre-DSC:DXN014415 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Cinétique de la nutrition minérale et métabolisme du carbone et de l'azote dans des suspensions cellulaires hétérotrophes et photomixotrophes : aspects physiologiques et biochimiques chez Abrus precatorius L. (Leguminosae)
SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Legume Genetics and Biology
Legumes have played an important part as human food and animal feed in cropping systems since the dawn of agriculture. The legume family is arguably one of the most abundantly domesticated crop plant families. Their ability to symbiotically fix nitrogen and improve soil fertility has been rewarded since antiquity and makes them a key protein source. Pea was the original model organism used in Mendel´s discovery of the laws of inheritance, making it the foundation of modern plant genetics. This book based on Special Issue provides up-to-date information on legume biology, genetic advances, and the legacy of Mendel
Regulation of Central Carbon and Amino Acid Metabolism in Plants
Due to their lightweight and high specific strength, Mg-based alloys are considered as substitutes to their heavier counterparts in applications in which corrosion is non-relevant and weight saving is of importance. Furthermore, due to the biocompatibility of Mg, some alloys with controlled corrosion rates are used as degradable implant materials in the medical sector. The typical processing route of Mg parts incorporates a casting step and, subsequently, a thermo–mechanical treatment. In order to achieve the desired macroscopic properties and thus fulfill the service requirements, thorough knowledge of the relationship between the microstructure, the processing steps, and the resulting property profile is necessary. This Special Issue covers in situ and ex situ experimental and computational investigations of the behavior under thermo–mechanical load of Mg-based alloys utilizing modern characterization and simulation techniques. The papers cover investigations on the effect of rare earth additions on the mechanical properties of different Mg alloys, including the effect of long-period stacking-ordered (LPSO) structures, and the experimental and computational investigation of the effect of different processing route