Accepted_test

Senescence of plant leaves is an organized, genetically programmed and strictly regulated redistribution of resources from the senescing leaf to reproductive, storage, or simply the youngest organs. Plant senescence can be induced artificially. All this makes plants an interesting model for studying genetically programmed mechanisms of senescence.

Our group found that in the double knockout mutant plants gdh1gdh2 of Arabidopsis thaliana L. (Heyn) carrying mutations in two glutamate dehydrogenase genes, when exposed to darkness for more than four days (conditions that induce senescence in Arabidopsiss), leaves do not turn yellow, which is normally the first visible sign of plant senescence. After exposure of the plants to the dark, we found dramatic differences between the mutant and wild-type plants in content and composition of chlorophylls, ionic permeability of cell membranes, as well as expression of various groups of genes associated with plant senescence (transcription factors that initiate senescence; genes controlling of chlorophyll degradation; genes providing nitrogen remobilization). The above parameters were also assessed against the background of treating plants with abscisic acid (the main hormonal regulator of plants senescence).

The discovered facts suggest the existence of a functional connection between expression of the NAD(H)-dependent glutamate dehydrogenase genes and regulation of senescence processes in plants. The lack of glutamate dehydrogenase activity during prolonged dark exposition is probably the reason of disrupted senescence in gdh1gdh2 plants. It may lead to metabolic switches followed by some toxic metabolites appearance. Thus, glutamate dehydrogenase is one of essential senescence regulators in Arabidopsis.