Adaptation and acclimation of higher plants at the enzyme level: Latitudinal variations of thermal properties of NAD malate dehydrogenase in Lathyrus japonicus Willd. (Leguminosae).

Thermal properties of NAD malate dehydrogenase were investigated in 8 clonal populations of Lathyrus japonicus Willd. collected over a 16° latitudinal gradient in eastern North America. Clones from warmer summer sites had higher activation energies (E a) and enhanced thermostability for the enzyme under three contrasting growth temperature regimes. A strong component of acclimation was associated with E a, but not with thermostability. Activity levels of the enzyme were higher in warm-adapted genotypes but cold-acclimated plants had similar low levels of specific activity. The clones were differentiated by ordination in a pattern related to climatic origin.