Putative Molecular Aspects of Succinic Semialdehyde Dehydrogenase’s Operation in the Leaves of Wheat (Triticum aestivum L.) under Salt Stress

Elevation of the enzyme activity in the leaves of soft wheat (Triticum aestivum L.) observed under salt stress was related to the maintenance of the rate of tricarboxylic acid cycle at the expense of arrival of extra substrates. Activation of succinic semialdehyde dehydrogenase (SSADH) in the leaves of wheat exposed to salt stress induced by sodium chloride (NaCl) reaches its peak in 6 h and amounts to 12.2 E/g fr wt. Activation of the examined enzyme ensures maintenance of necessary ATP level owing to arrival of additional respiratory substrate in the TCA cycle under the effect of stress agent. It was shown that SSADH is genetically predetermined. On the basis of mRNA of homoeologous SSADH genes, specific primers were designed for quantification of their transcripts. Under the effect of salt stress, the content of transcripts of the genes encoding SSADH in the leaves of wheat changes. Comparison of changes in SSADH activity and expression of the examined genes in the leaves of wheat exposed to salt stress has shown that this enzyme is regulated by changes in their transcriptional activity. The main contribution to alteration of the content of SSADH transcripts is made by the gene SSADH belonging to subgenome A. A specific binding site for salt-dependent transcription factor WRKY was detected within promoter of gene SSADHA. Elevation of the content of WRKY transcripts may regulate expression of the gene SSADHA upon plant adaptation to stress impact via interaction with a specific binding site located in the transcription initiation region of its promoter.