Effect of salicylic acid on salt tolerance of Aloe vera plants under both salt-acclimated and non-acclimated conditions

Since the role of salicylic acid (SA) in Aloe vera plants under salt stress is not yet clarified, this experiment was conducted to investigate the role of SA (100 and 500 mu;M) in photosynthesis, antioxidative capacity and ion homeostasis in salt acclimated (EC 6 dS/m) and nonacclimated Aloe plants against subsequent salt stress (EC 21 dS/m). Salinity exerted an adverse effect on the leaf dry weight, whereas foliar spray of 100 mu;M SA mitigated the saltinduced inhibitory effects on the plant growth, especially under acclimated conditions. While salt stress caused a significant increase in Na accumulation and a considerable decrease in K and Ca, higher levels of K/Na ratio was observed after SA treatment. SA application (100 mu;M) also alleviated the damage to PSII function induced by salt, contributing to the improvement of electron trapping under salinity. Furthermore, Aloe plants exposed to EC 21 dS/m exhibited an oxidative damage, determined by increased content of oxidants (hydrogen peroxide and malondialdehyde). In contrast, foliar spray of 100 mu;M SA increased CAT activity as well as carotenoids content, and reduced content of oxidants under salt stress. Consequently, under both saltacclimated and nonacclimated conditions, SA at concentration of 100 mu;M was more effective in alleviation of salt stress in Aloe plants via the enhancement of photochemical activity of photosynthesis, the activities of antioxidant enzymes and the ratio of K and Na under salinity.