Role of Hormonal System in the Manifestation of Growth Promoting and Antistress Action of Salicylic Acid

Abstract

Salicylic acid (SA) is an endogenous plant growth regulator. When applied to wheat plants in concentration similar to that used in case of exogenous hormones (0.05 mM), SA causes growth promoting and protective effects against an abiotic stresses. SA was shown to cause changes in hormonal system associated with transitory parallel accumulation of IAA and ABA with no change in cytokinins, which took place in case of treatment of seeds before sowing as well as seedling treatment. SA-induced accumulation of ABA lead to no detrimental effects, evidenced by clearcut stimulation of growth of root cells both by division and expansion, accumulation of raw and dry mass of seedlings and productivity of wheat treated with SA. This indicated an important role to IAA in the expression of growth stimulating action of SA. ABA is likely to be intermediator in manifestation of antistress action of SA. This is evidenced by the data showing that SA-induced accumulation of ABA was followed by enhanced expression of genes of dehydrins and accumulation of proline, i.e. substances having a relation with osmoprotection of cells. Moreover, SA causes activation of superoxide dismutase and peroxidase, including anionic peroxidase, phenylalanin-ammonia-lyase, favouring accelerated lignification of cell walls of seedlings roots. This is likely to contribute to a decline in the extent of injurious effects of salinity and water deficit on plants, pretreated with SA, evidenced by a decline in the level of lipid peroxidation and leakage of electrolytes from plant tissues as well as by more intensive growth processes as compared to control plants. It is important to underline that pretreatment with SA prevents a sharp decline in IAA and cytokinin content observed under stress and maintains a high level of ABA. Such a character of SA effect on the state of hormonal system may well contribute to protective reactions of plants and acceleration of reparative processes during a post-stress period.