title: Effects of temperature and CO2enrichment on kinetic properties of NADP+-malate dehydrogenase in two ecotypes of Barnyard grass (Echinochloa crus-galli (L.) Beauv.) from contrasting climates.
abstract: The apparent energy of activation (Ea), Michaelis-Menten constant (Kmfor oxaloacetate), Vmax/Kmratios and specific activities of NADP+-malate dehydrogenase (NADP+-MDH; EC 1.1.1.82) were analyzed in plants of Barnyard grass from Québec (QUE) and Mississippi (MISS) acclimated to two thermoperiods 28/22°C, 21/15°C, and grown under two CO2concentrations, 350 μl l-1and 675 μl l-1. Eavalues of NADP+-MDH extracted from QUE plants were significantly lower than those of MISS plants. Kmvalues and Vmax/Kmratios of the enzyme from both ecotypes were similar over the range of 10-30°C but reduced Vmax/Kmratios were found for the enzyme of QUE plants at 30 and 40°C assays. MISS plants had higher enzyme activities when measured on a chlorophyll basis but this trend was reversed when activities were expressed per fresh weight leaf or per leaf surface area. Activities were significantly higher in plants of both populations acclimated to 22/28°C. CO2enrichment did not modify appreciably the catalytic properties of NADP+-MDH and did not have a compensatory effect upon catalysis or enzyme activity under cool acclimatory conditions. NADP+-MDH activities were always in excess of the amount required to support observed rates of CO2assimilation and these two parameters were significantly correlated. The enhanced photosynthetic performance of QUE plants under cold temperature conditions, as compared to that of MISS plants, cannot be attributed to kinetic differences of NADP+-malate dehydrogenase among these ecotypes.
authors.affiliation: Département de Sciences Biologiques, Succursale A, C.P. 6128, H3C 3J7, Montréal, Québec, Canada.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Simon
authors.affiliation: Department of Botany and Duke Phytotron, Duke University, 27706, Durham, NC, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Potvin
authors.affiliation: Department of Botany and Duke Phytotron, Duke University, 27706, Durham, NC, USA.
authors.forename: Boyd R
authors.initials: BR
authors.lastname: Strain
keywords: C4 metabolism; CO2 enrichment; Echinochloa crus-galli; Ecotypes; Energy of activation; K m, V max/K m; NADP+-malate dehydrogenase; Temperature