Oecologia (1989) 81 : 138-144 Oecologia 9 Springer-Verlag1989 Effects of temperature and CO2 enrichment on kinetic properties of NADP § dehydrogenase in two ecotypes of Barnyard grass (Echinochlon crus-gallI" (L.) Beauv.) from contrasting climates Jean-Pierre Simon 1, Catherine Potvin 2,., and Boyd R. Strain 2 1 D~partement de Sciences Biologiques, C.P. 6128, Succursale A, Montreal Quebec, Canada H3C 3J7 2 Department of Botany and Duke Phytotron, Duke University, Durham, NC 27706, USA Summary. The apparent energy of activation (Ea), Michae- lis-Menten constant (K,, for oxaloacetate), Vmax/Km ratios and specific activities of NADP§ dehydrogenase (NADP+-MDH; EC 1.1.1.82) were analyzed in plants of Barnyard grass from Qu6bec (QUE) and Mississippi (MISS) acclimated to two thermoperiods 28/22~ 21/15 ~ C, and grown under two CO2 concentrations, 350 btl 1-1 and 675 btl 1-1. E, values of NADP+-MDH extracted from QUE plants were significantly lower than those of MISS plants. Km values and Vmax/K~ ratios of the enzyme from both ecotypes were similar over the range of 10-30 ~ C but reduced Vm,x/Km ratios 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 accli- mated to 22/28 ~ C. CO2 enrichment did not modify appre- ciably the catalytic properties of NADP§ 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 CO2 assimilation and these two parameters were significantly correlated. The enhanced photosynthetic performance of QUE plants under cold tem- perature conditions, as compared to that of MISS plants, cannot be attributed to kinetic differences of NADP +-ma- late dehydrogenase among these ecotypes. Key words: Echinochloa crus-galli- Ecotypes - Temperature - CO2 enrichment - C4 metabolism - NADP § de- hydrogenase - Energy of activation - Kin, Vm~x/Km Most C~ species are confined to tropical or sub-tropical regions and are usually inhibited by low temperatures (Long 1983; Pearcy and Ehleringer 1984). Only a few of these species have distributions covering several climatic regions (Teeri and Stowe 1976; Caldwell et al. 1977; Teeri 1979). The C4 weed Echinochloa crus-galli (L.)Beauv., Offprint requests to ." J.-P. Simon * Present address: Department of Biology, McGill University, 1205 Avenue du Dr. Penfield, Montreal, Quebec, Canada H3A 1B1 (Barnyard grass), is such a widely distributed species with populations colonizing disturbed and agricultural habitats from tropical to cold-temperature regions (Gould et al. 1972; Maun and Barrett 1986). Previous studies of this se- ries have compared various aspects of the C4 metabolism of populations of Echinochloa erus-galli collected from sites with contrasting climates (e.g. Robert et al. 1983; Simon et al. 1984a, b; Potvin et al. 1986; Simon 1987; Potvin 1986, 1988a, 1988b). Reciprocal transplant experiments with plants from Quebec (QUE), North Carolina (NC) and Mis- sissippi (MISS) have shown clear ecotypic differentiation as a function of climate (Potvin 1986). Under controlled conditions, analyses of photosynthetic parameters (Potvin 1985a, b; Potvin and Strain 1985a, b; Potvin 1987, 1988 b), carbon translocation (Potvin et al. 1985; Potvin 1988a), growth and resource allocation (Potvin 1985a; Potvin and Strain 1985a, b) as well as activity and kinetic properties of C4 enzymes (Simon et al. 1984a, b; Potvin et al. 1986; Simon 1987) have demonstrated that warm-adapted MISS plants are more affected by low temperatures than cold- adapted QUE plants. A recent analysis of chilling effects on the activity of the C4 enzymes of QUE and MISS plants, suggests that two steps of the C4 pathway exert regulatory control on photosynthesis:Pyruvate Pi dikinase (PPDK) and NADP+-malate dehydrogenase (NADP+-MDH). The former acts through its low, rate-limiting, activity and the latter through its great cold-sensitivity. Among the four C4 enzymes, NADP§ is the most cold-labile and shows a highly significant reduction of activity in MISS plants compared to QUE plants following cold treatments (Potvin et al. 1986; Simon 1987). The main objective of this particular study is to analyze possible differences in the kinetic properties of NADP +- MDH extracted from the two Echinochloa populations which may contribute to the enhanced photosynthetic per- formance of QUE plants under cold temperature condi- tions. As a correlated objective, we document the effect of CO2 enrichment on kinetic properties of NADP § Recent reports indicate the existence of strong interactions between CO2 enrichment and temperature effects on growth and photosynthesis of chilled plants (Sionit et al. 1981 ; Pot- vin and Strain 1985a, b). Previous studies of this series have shown that high levels of CO2 may buffer Barnyard grass against the detrimental effect of cold temperatures