Effect of Aluminium on Calmodulin-Dependent and Calmodulin-Independent NAD Kinase Activity in Wheat ( Triticum aestivum L.) Root Tips

Abstract

Total NAD kinase activity is twice as high in the Al tolerant wheat strain (BHG) than in the Al sensitive variety (Grana). In the former the calmodulin-dependent enzyme constitutes about 50 % of the total activity, whereas in the latter it does not exceed 30 %. Aluminium induced NAD kinase activity 2.5 fold in the sensitive variety Grana and six fold in the Al tolerant BHG upon 10 h incubation in 0.74 mM Al. The induction, abolished by cycloheximide, involves in Grana both calmodulin-dependent and calmodulin-independent enzymes, whereas in the Al tolerant genotype the induction involves only the calmodulin-independent form, and the activity of the calmodulin-dependent enzyme becomes marginal. Changes in the activity of NAD kinase are paralleled by the shift in the NADP/NAD ratio. It is suggested that the mechanism of Al tolerance is manifested in proportion to calmodulin-dependent and calmodulin-independent NAD kinases and in the ability to replace the former by the latter enzyme in the tolerant genotype under Al stress.