Effects of cold on NAD+ kinase activity in winter rape plants

Low temperature (2°C) caused an increase in the activity of NAD⁺ kinase (EC 2.7.1.23) in leaves of winter rape plants ( Brassica napus L. var. oleifera L. cv. Górezański). The enzyme activity markedly increased between day 4 and 11 of plant exposure to cold, then tended to decrease. Changes in activity of NAD⁺ kinase coincided with the previously observed changes in the levels of pyridine nucleotides, NADP(H) (U. Maciejewska and A. Kacperska, Physiol. Plant. 69: 687–691, 1987). As a result of cold treatment, Ca²⁺–calmodulin–dependent and Ca²⁺–calmodulin–independent NAD⁺ kinase activities increased to almost the same extent. It seems therefore, that the cold–induced activation of NAD⁺ kinase does not depend on the Ca²⁺–calmodulin complex.