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

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, CaCl 2 andH 2 O 2 , 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 H 2 O 2 , 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. Keywords: Avena sativa L., calcium, calmodulin, dormancy, germination, membrane-bound and soluble enzyme, NAD + kinase. Australian Journal of Plant Physiology 27(7) 649 - 658 Full text doi:10.1071/PP00010 © CSIRO 2000