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.
Published Version
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