Changes in NAD+ kinase activity during germination of Phaseolus vulgaris and P. acutifolius, and effects of drought stress

In embryonic bean axes during germination, it can be seen that there is a decrease of ADH activity, an increase of NAD+ kinase activity, and then an emergence of G6PDH activity. Ethanol and hydrogen peroxide, which are shown to enhance the efficiency of P. vulgaris germination, accumulate to a significant degree during germination, hydrogen peroxide being much more concentrated than ethanol at the radicleprotrusion stage. Five forms of NAD+ kinase can be distinguished: a soluble Ca2+ sensitive form; two Ca-CaM independent forms; one soluble, one membranal; and two Ca-CaM dependent forms, one soluble and one membranal. In dry seeds, the membranal Ca-CaM dependent form is represented more in P. vulgaris (100% of the total pelletable activity) than in P. acutifolius (30%). This membranal Ca-CaM dependent NAD+ kinase, prevalent after radicle protrusion, might be important for early growth metabolism, since an ethanol treatment applied until radicle protrusion reduces membranal NAD+ kinase and G6PDH activities as well as growth, while an H2O2 treatment slightly reinforces G6PDH and membranal NAD+ kinase activities. Except for drought-stressed P. vulgaris at the stage of radicle protrusion in which NAD+ kinase activities are not perturbed, in both P. vulgaris and P. acutifolius NAD+ kinase activities temporarily decrease in response to drought stress, these being restored after subsequent rehydration.