Marie-Louise Champigny

Further studies of phosphoglycerate kinase and ribulose-5-phosphate kinase of the photosynthetic carbon reduction cycle: Regulation of the enzymes by the adenine nucleotides

Abstract Phosphoglycerate (PGA) kinase was purified from spinach chloroplasts. Its activity was determined in a single enzymatic reaction without any coupling with the glyceraldehyde-3-phosphate dehydrogenase. With respect to ATP it exhibits non-Michaelis kinetics and behaves like an allosteric enzyme. The Hill coefficient is 1.35 and the calculated Km(ATP) is 2 mM. Ribulose-5-phosphate (Ru5P) kinase was purified from spinach leaves. It exhibits Michaelis kinetics with respect to ATP. The Km(ATP) is 0.42 mM. Both kinases from spinach chloroplasts are controlled by the adenylate energy charge.

Physiological Studies on two Cultivars of Pennisetum: P. americanum 23 DB, a Cultivated Species and P. mollissimum, a Wild Species I. Photosynthetic Carbon Metabolism

Summary The photosynthetic carbon metabolism and the anatomical features of the leaves of twO series of plants of Pennisetum have been studied: plants from 23 DB line from the cultivated Pearl millet P. americanum (thyphoides), plants from an ecotype of P. mollissimum , one of its related wild species originating from Mali. The activities and intracellular location of the enzymes of carbon metabolism are very similar in the two plants. These characteristics together with the leaf anatomy indicate that both Pennisetum have the C4 pathway of CO 2 assimilation and belong to the NADP-ME-type. In mesophyll cells two enzymes function to reduce oxaloacetate: the light-activated chloroplast NADP-malate dehydrogenase and the cytoplasmic NAD-malate dehydrogenase. Like malic acid, aspartic acid participates to the transport of CO 2 from the mesophyll to the bundle sheath cells. The labelling pattern of aspartic acid and malic acid during a 14 C0 2 pulse and chase experiment indicate that the turn-over rates of the carbon chains of malate and aspartate are very different and that there are two ways of decarboxylation. While malate synthesized in the mesophyll cells is rapidly decarboxylated in the presence of the bundle sheath chloroplast NADP-malic enzyme, malate originating in the bundle sheath mitochondria from the carbon chain of aspartic acid is more slowly decarboxylated in the presence of the mitochondrial NAD-malic enzyme. The two C4 acids are described as representing two different compartments and having distinct roles in the photosynthetic carbon metabolism. Malic acid is the single CO 2 donor while aspartic acid plays the role of a reservoir for C4 acids. It is assumed that the major and the minor ways of decarboxylation could at least partly be controlled by the nucleotide supply via photosynthesis (NADP) and (or) mitochondrial respiration (NAD). Except for the fact that P. mollissimum fixes more actively CO2 and accumulates more starch than P. americanum 23 DB, it is noteworthy that the two plants have developped similar metabolic adaptation.

Physiological Studies on two Cultivars of Pennisetum: P. americanum 23 DB, a Cultivated Species and P. mollissimum, a Wild Species: II. Effects of Leaf Age on Biochemical Characteristics and Activities of the Enzymes Associated with the Photosynthetic Carbon Metabolism

Summary Two genotypes of Pennisetum were studied for biochemical characteristics and enzyme activities associated with photosynthetic carbon metabolism with regard to the effect of leaf age. Research was conducted with fully just expanded 4th leaves from 12 to 35 day old plants. Growth analysis, leaf area, protein and starch content, chlorophyll content, and dry weight were investigated. All these parameters were higher for P. mollissimum compared to P. americanum . Starch content of leaves was always higher in P. mollissimum . The PEP carboxylase activity was highest in young leaves and decreased rapidly with subsequent full leaf expansion. For RuBP carboxylase, the activity increased quickly until full leaf expansion. The ratio PEP carboxylase/RuBP carboxylase activity was high in young tissue as expected for C 4 type plants. Mature leaf tissue had a ratio of 1, a value nearer to the C 3 type plant. These data indicate that there are physiological changes which occur during development of Pennisetum leaves.

Thermal sensitivity of NAD-malate dehydrogenase isoforms from various Pennisetum ecotypes

Thermal sensitivity of NAD-malate dehydrogenase (NAD-MDH) was studied in several Pennisetum ecotypes. The effect of temperature was investigated using either crude extracts from shoots or separated isoforms. In all the ecotypes tested, in vitro temperature optima were found to be near 45°C. A high heat stability of NAD-MDH was observed for all the ecotypes studied. Three isoenzymes were isolated by DEAE-cellulose chromatography and analyzed by starch gel electrophoresis. Three anodic isoenzymes were separated on the electrophoretic pattern, they are known to be associated with peroxisomes, mitochondria and soluble leaf compartments, respectively. The soluble NAD-MDH isoenzyme was found to be more affected at high temperature than the peroxisomal and mitochondrial forms.

Les différents types métaboliques végétaux et l'assimilation de CO2, leur diversité botanique

ResumeLes definitions des types metaboliques des vegetaux C3, C4 et CAM sont donnees, ainsi que leurs particularites anatomiques, cytologiques, enzymatiques, en insistant sur lagencement et le compartimentage reactionnel qui les caracterisent. Les consequences physiologiques des differents mecanismes sur la photosynthese, la photorespiration, le fractionnement isotopique 13C/12C, ainsi que leurs relations avec les migrations des photosynthetats et la vitesse de croissance des organismes sont soulignes.La diversite, a linterieur de chaque type, est decrite, ainsi que les intermediaires et les tentatives dhybridation entre plantes C3 et C4. Ladaptation a la secheresse, aux temperatures et aux eclairements eleves des especes C4, linduction des caracteres CAM, les rapports entre echanges de CO2 et deau dans les differents types metaboliques, sont egalement decrits.Lorigine des plantes C4 et CAM, plus recente que celle des especes de type C3, le probleme de la convergence morphologique et fonctionnelle,...