Responses of Glutamine Synthetase-Glutamate Synthase Cycle Enzymes in Tomato Leaves under Salinity Stress.

Reduction in leaf CO2 assimilation rate is a common effect of salinity stress. In present study, 30 days old tomato plants were exposed to 0, 60 and 120 mM NaCl for 7 days. The results showed that stomatal conductance, CO2 assimilation rate, NO3- content and NO3 - metabolizing enzymes (NR & NiR) activities decreased in salinity stressed tomato leaves, which indicated that C-N crisis is dominant during salinity stress. Interestingly, some C-N rich compounds (glutamate, proline, glycine & serine) accumulated excessively in the leaves of salinity stressed plants. Results also showed that important C and N providing enzymes such as NADP-ICDH, protease and NADH-GDH activities were enhanced during salinity stress. In salinity stressed tomato leaves, GS/GOGAT cycle enzymes (GS, NADH-GOGAT & Fd-GOGAT) activities were also increased significantly. Finally, it is concluded that GS/GOGAT cycle plays an important role for proline synthesis in tomato leaves during salinity stress. [ABSTRACT FROM AUTHOR]