GLUCOSE-6-PHOSPHATE-DEHYDROGENASE DURING COLD-HARDENING IN LOLIUM-PERENNE

Glucose 6-phosphate dehydrogenase (G6PDH) was studied in crude and partially purified extracts from nonhardened and cold-hardened leaves of two cultivars of Lolium perenne L.: the winter hardy cv. Mondial and the less hardy cv. Yatsyn 1. The maximum catalytic activity of G6PDH increased during cold-hardening of both cultivars, and was highest in the most hardy cultivar. The temperature coefficients of G6PDH from the leaves were higher over the range 5-10 degrees C than over the range 15-25 degrees C, independently of either cultivar or treatment. No differences were found in substrate affinity of enzyme for nonhardened and cold-hardened plants of both cultivars, when assayed at 25 degrees C. Lowering the assay temperature to 4 degrees C caused a decrease in affinity for glucose 6-phosphate of enzyme from nonhardened and cold-hardened plants of both cultivars; no changes were found in the affinity for NADP. The results are discussed in relation to the accumulation of sugars and the possible role of the pentose phosphate pathway during cold-hardening.