Understanding the regulation of aspartate metabolism using a model based on measured kinetic parameters

The aspartate-derived amino-acid pathway from plants is well suited for analysing the function of the allosteric network of interactions in branched pathways. For this purpose, a detailed kinetic model of the system in the plant model Arabidopsis was constructed on the basis of in vitro kinetic measurements. The data, assembled into a mathematical model, reproduce in vivo measurements and also provide non-intuitive predictions. A crucial result is the identification of allosteric interactions whose function is not to couple demand and supply but to maintain a high independence between fluxes in competing pathways. In addition, the model shows that enzyme isoforms are not functionally redundant, because they contribute unequally to the flux and its regulation. Another result is the identification of the threonine concentration as the most sensitive variable in the system, suggesting a regulatory role for threonine at a higher level of integration

Two cases of lymphoepithelial cyst of the pancreas

A 35-year-old man was found to have a cystic mass in the pancreatic body on a routine health examination ; high serum CA19-9 was also detected. The enucleated cyst was diagnosed as a lymphoepithelial cyst (LEC). A 74-year-old man found to have a cystic mass in the pancreatic head by computer tomography as well as high serum CA19-9 was suspected of a cystic neoplasm of the pancreas (IPMN), and pylorus-preserving pancreaticoduodenectomy (PPPD) was performed. Pathologically, the cyst was found to be LEC. It is often difficult to diagnose pancreatic cyst as LEC preoperatively. Care should be taken not to do over-surgery for benign disease LEC

A Rice Plastidial Nucleotide Sugar Epimerase Is Involved in Galactolipid Biosynthesis and Improves Photosynthetic Efficiency

Photosynthesis is the final determinator for crop yield. To gain insight into genes controlling photosynthetic capacity, we selected from our large T-DNA mutant population a rice stunted growth mutant with decreased carbon assimilate and yield production named photoassimilate defective1 (phd1). Molecular and biochemical analyses revealed that PHD1 encodes a novel chloroplast-localized UDP-glucose epimerase (UGE), which is conserved in the plant kingdom. The chloroplast localization of PHD1 was confirmed by immunoblots, immunocytochemistry, and UGE activity in isolated chloroplasts, which was approximately 50% lower in the phd1-1 mutant than in the wild type. In addition, the amounts of UDP-glucose and UDP-galactose substrates in chloroplasts were significantly higher and lower, respectively, indicating that PHD1 was responsible for a major part of UGE activity in plastids. The relative amount of monogalactosyldiacylglycerol (MGDG), a major chloroplast membrane galactolipid, was decreased in the mutant, while the digalactosyldiacylglycerol (DGDG) amount was not significantly altered, suggesting that PHD1 participates mainly in UDP-galactose supply for MGDG biosynthesis in chloroplasts. The phd1 mutant showed decreased chlorophyll content, photosynthetic activity, and altered chloroplast ultrastructure, suggesting that a correct amount of galactoglycerolipids and the ratio of glycolipids versus phospholipids are necessary for proper chloroplast function. Downregulated expression of starch biosynthesis genes and upregulated expression of sucrose cleavage genes might be a result of reduced photosynthetic activity and account for the decreased starch and sucrose levels seen in phd1 leaves. PHD1 overexpression increased photosynthetic efficiency, biomass, and grain production, suggesting that PHD1 plays an important role in supplying sufficient galactolipids to thylakoid membranes for proper chloroplast biogenesis and photosynthetic activity. These findings will be useful for improving crop yields and for bioenergy crop engineering

High temperature effects on light sensitivity in the two high mountain plant species Soldanella alpina (L.) and Rannunculus glacialis (L.)

International audienceThe susceptibility to high temperature-induced photoinhibition was investigated in leaves of two high mountain plant species, S. alpina and R. glacialis. In both species, PSII was similarly photoinactivated at 38degreesC in the light. However, recovery from damage was much faster in S. alpina and depended on protein synthesis. In contrast, recovery was independent from protein synthesis in R. glacialis. Heat-induced photoinactivation in both species was accompanied by: (1) a decrease in relative photosynthetic electron transport rates, (2) an increase in non-photochemical chlorophyll fluorescence quenching, (3) a strong accumulation of zeaxanthin, (4) a marked decrease in soluble carbon metabolites and (5) an increase in lipid metabolism products, which was more pronounced in R. glacialis than in S. alpina. These results indicate that carbon assimilation was inhibited and that membranes were affected. Lipid peroxidation and possible membrane disintegration might limit the repair of damaged PSII in R. glacialis, while S. alpina appears to be protected by carotenoids and antioxidants. A marked decrease in alpha-tocopherol content and an increase in reduced ascorbate indicated lipid peroxide scavenging activity in S. alpina. When zeaxanthin synthesis was impaired by DTT, photoinhibition increased And (x-tocopherol accumulated in R. glacialis. The increased susceptibility of R. glacialis leaves to light-induced photoinhibition after growth at mode rate temperature (Streb et al., 2003a) and the inability to repair heat-induced damage might limit the distribution of R. glacialis to lower altitudes in the Alps

Exploration de la cellule végétale par spectroscopie RMN

On rappelle d’abord quelle est la nature des informations biologiques significatives qui peuvent être obtenues avec la spectroscopie de rmn haute résolution 31P, 13C et 1H, et comment sont réalisées les mesures avec les systèmes végétaux. On présente ensuite l’apport original de la rmn dans plusieurs domaines-clés de la physiologie cellulaire végétale touchant le métabolisme énergétique (glycolyse et respiration cellulaire, photosynthèse, rôle de l’appareil vacuolaire) la régulation du pH cytoplasmique, les cinétiques et flux enzymatiques, les phénomènes de transport