Changes in soluble and membrane-bound isoforms of calcium-calmodulin-dependent and -independent NAD+ kinase, during the culture of after-ripened and dormant seeds of Avena sativa

Activities of the soluble and membrane-boundisoforms of Ca 2+ calmodulin (CaCam)-dependent and-independent NAD + kinases, were followed in theembryos during the culture of dormant (D) and after-ripened (AR) seeds ofAvena sativa L. Embryos of D and AR seeds differ mainly in the evolution ofmembrane-bound activities, the majority of which are CaCam-dependent andlinked to mitochondria. The in vivo application ofgibberellic acid, CaCl2 andH2O2, which enhanced germination,induced an enhancement of all CaCam-dependent isoforms. Trifluoperazine (TFP),a calmodulin antagonist, greatly enhanced all CaCam-dependent isoforms andabolished the differences between the NAD + kinaseactivities of the two kinds of embryo. In addition, TFP rendered embryosunable to resume axis growth, probably due to pleiotropic effects. In contrastto H2O2, the reducing agentdithiothreitol diminished the soluble CaCam-dependent enzyme and blocked thegermination of both types of seed, whereas it increased the dependentmembrane-bound activities. The results demonstrate (1) that theCaCam-dependent NAD + kinase isoforms —amongst which is the isoform bound to mitochondrial membranes — play animportant role at the end of sensu stricto germinationand during the following growth of Avena sativa; and (2)that an excess of activity of these isoforms could be markers of stress orlethal conditions.