NAD- and NADP-isocitrate dehydrogenases and glutamate decarboxylase of peaseedlings as affected by salinity stress

Activities of NAD- and NADP-isocitrate dehydrogenases (NAD-IDH and NADP-IDH ) and glutamate decarboxylase (GDC) were followed for 24 h in leaves and ro ots of pea (Pisum sativum L,) seedlings grown on 0.5-strong Knop solution a nd treated with 3% NaCl. NAD-IDH and NADP-IDH activities fluctuated, with a maximum after l-h exposure to saline and a second, somewhat lower, peak of activity observed after 14-h exposure. In the presence of 100 mu M cyclohe ximide, the enzyme activities declined, starting from the very beginning of exposure, and were behind the level of the untreated plants in the course of the whole experiment. GDC activity in the roots and leaves gradually inc reased in the presence of NaCl in the course of 24-h exposure. Adding cyclo heximide to the nutrient medium reduced GDC activation but did not abolish it completely. NaCl-dependent regulation of enzyme activities in pea leaves and roots is probably related to enhanced enzyme synthesis, providing for better coordination and integration of carbon and nitrogen metabolism under salinity stress.