Arabidopsis GDH1 and GDH2 genes double knock-out results in a stay-green phenotype during dark-induced senescence

Yellowing is the first visually observable sign of plant leaf senescence. We found that Arabidopsis double knockout mutant gdh1gdh2 for genes of NAD(H)-dependent glutamate dehydrogenase retains green color of the leaves (stay-green phenotype) during a dark-induced senescence, in contrast to wild-type plants, whose leaves turn yellow. When the gdh1gdh2 plants are exposed to the dark more than four days, they demonstrate slower chlorophyll degradation than in the wild-type plants under the same conditions, as well as dysregulation of chlorophyll breakdown genes encoding chlorophyll b reductase, Mg-dechelatase, pheophytinase and pheophorbide a oxygenase. The slowed degradation of chlorophyll b in gdh1gdh2 plants significantly alters the chlorophyll a/b ratio. Ion leakage in the mutant plants increases significantly from four to eight days in the darkness, correlating with their premature death during this period. The discovered facts suggest a functional connection between activity of NAD(H)-dependent glutamate dehydrogenase and dark-induced senescence progress in Arabidopsis.