Comparative studies of activity and properties of ferredoxin–NADP+ reductase during cold hardening of wheat

Abstract

Activity and properties of chloroplast ferredoxin–NADP− reductase (EC 1.6.7.1) were studied during cold hardening of two varieties of wheat (Triticum aestivnm), hardy Kharkov (winter wheat) and much less hardy Rescue (spring wheat), to determine whether adaptation to low temperatures involves changes in the activity and properties of this enzyme. Specific activity of ferredoxin–NADP− reductase increased during hardening of both varieties, but the increase was much greater in the more hardy variety, Kharkov 22 MC. No changes were found in the Michaelis constants for NADPH and 2,6-dichlorophenol indophenol, activation energy values, inhibition constants for p-chloromercuriphenylsulfonate, and sensitivity toward cold and heat inactivation of the enzyme from control and cold-hardened seedlings of both varieties. The data suggest that there is a preferential synthesis of ferredoxin–NADP− reductase during hardening of wheat, but the enzyme molecule remains unchanged.