Influence of plant growth regulators on carbon/nitrogen metabolism of cucumber under salt stress

This study was designed with the objective of comparing three different plant growth regulators, putrescine (Put), meta-topolin (mT), and 24-epibrassinolide (EBL), in affecting cucumber plants under salt stress. The pilot assessment revealed that all treatments had a significant effect (P < 0.05) on vegetative traits, seedling vigor, total chlorophyll content, and root activity compared to control. The treatment T5 showed the greatest numbers in regard to the above–mentioned traits compared with other combinations. The salt stress study reported that T2 increased superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) activities in leaves by 31%, 4.4%, 22.4%, and 35.2%, respectively, in comparison with the control.  On the other hand, S3 markedly increased antioxidant enzyme activities, and the activity level was significantly higher than the control and salt treatment. Exogenous S3 had a highly significant effect on glutamine synthetase (GS), glutamate synthase (GOGAT), and (GDH), glutamate dehydrogenase activities in leaves and roots compared with T2. Application of S3 had a highly significant effect on sucrose synthase (SS) and sucrose phosphate synthase (SPS) under salinity stress in leaves and roots compared with other salt stress treatments. The results showed that (5 mM Put + 0.002 ppm mT + 0.001 ppm EBR) treatment alleviated the growth inhibition caused by salt stress by regulating the C-N enzyme activities in cucumber plants.