Pyridine nucleotides and NAD+ kinase activity in dormant and non-dormant dry seeds of Avena sativa L.

Pyridine nucleotides and NAD(+) kinase activity (ATP:NAD(+) 2'-phosphotransferase, EC 2.7.1.23) were studied in relation to the state of dormancy of dry Avena sativa L. (cv. Noire de Moyencourt) caryopses. In both nondormant and dormant seeds, NAD(+) + NADH levels were about twice those of NADP(+) + NADPH. The values of redox charges were indicative of a normal catabolism, NADH/(NAD(+)+NADH) between 0.14 and 0.24, and of a very inactive anabolism NADPH/(NADP(+)+NADPH) from 0.28 to 0.55 during after-ripening. Embryo NAD(+) kinase was more soluble than the endosperm type. In addition, and by comparison with the endosperm enzyme, the embryo NAD(+) kinase could be activated by Ca2+-calmodulin, The ratio of Ca2+-calmodulin dependent and Ca2+-calmodulin independent NAD(+) kinase activities was higher in embryos of non-dormant than of dormant caryopses. Thus, the embryo contains a Ca2+-calmodulin dependent NAD(+) kinase, the activation factor of which was related to the state of dormancy. During after-ripening : (i) soluble NAD(+) kinase activity decreased, while membrane-bound activity increased; (ii) native electrophoresis revealed activities of soluble NAD(+) kinase (one isoform in embryo against at least three in the endosperm) only slightly decreased, while G6PDH activity declined markedly.