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The present study was conducted to evaluate the effect of salinity stress on growth of Cassia italica and role of gamma amminobutyric acid (GABA) in mitigating the salt stress induced damaging effects. Antioxidant activity, level of endogenous growth hormones and other biochemical parameters were evaluated. Salt stress enhanced the production of reactive oxygen species (ROS) resulting in the enhanced lipid peroxidation which was however reduced by application of GABA. Increased lipid peroxidation in salt stressed plants caused an obvious reduction in the total lipid content as compared to GABA treated plants. The antioxidant enzymes were higher in GABA treated plants which indicated a reduction of oxidative damage. The concentrations of growth hormones like indole acetic acid (IAA), indole butyric acid (IBA), gibberellic acid-1 (GA1), and gibberellic acid-4 (GA4) were reduced by salt stress, while enhanced by GABA treatment. In addition GABA treated plants maintained lower levels of sodium and chloride ions as compared to salt stressed plants. It could be concluded that toxic effects of salt stress on growth, antioxidant system, hormones and mineral nutrients in Cassia italica could be alleviated by exogenous application of GABA. [ABSTRACT FROM AUTHOR]

Two cultivars contrasting in NaCl tolerance were used to investigate the possible involvement of polyamines in salt tolerant mechanisms in roots of vegetable soybean. 'Tianfeng', the salt tolerant cultivar exhibited overall higher contents of free, soluble conjugated and insoluble bound forms of polyamines (putrescine, spermidine and spermine) except for free spermidine over the salt sensitive line during the course of NaCl treatment for 15 days. Consistent with this observation, arginine decarboxylase, the essential enzyme of polyamines biosynthesis and two enzymes catalyzing breakdown of polyamines were differentially regulated between the two cultivars. Antioxidant enzymes downstream to the polyamines signaling globally showed higher activity in 'Tianfeng', resulting in lower contents of reactive oxygen species and malondialdehyde subsequently. These results taken together indicate that higher levels of polyamines may be important in conferring enhanced salt tolerance in roots of vegetable soybean by activating antioxidant enzymes and, therefore, attenuating oxidative damage. [ABSTRACT FROM AUTHOR]