Salicylic acid-induced protection against cadmium toxicity in wheat plants

• SA pretreatment reduces detrimental effect of Cd stress on wheat plant growth.
• SA pretreatment diminishes hormonal changes induced by Cd stress.
• SA-induced ABA accumulation mediates protective effect of SA on wheat plants.
• SA-induced PAL activity coupled with lignin deposition inhibits Cd uptake.
• Dehydrins are involved in the protective action of SA against Cd toxicity.

We have studied the influence of pretreatment of wheat seedlings (Triticum aestivum L.) with 50 μM salicylic acid (SA) on plant resistance to subsequent action of 1 mM cadmium acetate. SA pretreatment decreased the extent of detrimental effect of cadmium on wheat plants, as judged by the decline in the level of stress-induced accumulation of MDA and electrolyte leakage. Furthermore, SA-pretreatment contributed to maintenance of growth characteristics of wheat seedlings at the level close to the control under stress conditions and to acceleration of growth recovery during post-stress period. Detected defense effect of SA may be due to a decline in the amplitude of cadmium-induced accumulation of abscisic acid (ABA) and to reduced fall of indoleacetic acid (IAA) and cytokinins (CK) in stressed plants. In the course of one day treatment, SA activated phenylalanine ammonia-lyase (PAL), the key enzyme of lignin biosynthesis, in roots of seedlings under normal growth conditions contributing to the strengthening of carrier functions of cell walls. This assumption is supported by the data showing significant decline in cadmium accumulation in SA-pretreated plants, especially in the shoots. Cd-treatment was shown to result in accumulation of dehydrins with molecular mass 22, 28, 55 and 69 kDa in wheat seedlings, although low molecular weight dehydrins (22 and 28 kDa) showed greater stress sensitivity. It is noteworthy that SA-pretreatment by itself led to 1.5-fold increase in the content of low molecular weight dehydrins. Nevertheless, SA-pretreated seedlings were characterized by significantly lower Cd-induced accumulation of all of the four dehydrins, apparently due to inhibition of cadmium flow into the plants. The obtained data suggest involvement of dehydrins in the range of defense reactions induced by SA-treatment contributing significantly to development of plant resistance to subsequent action of stress. The use of fluridone allowed us to demonstrate the key role of endogenous ABA in SA-induced changes in the level of dehydrins as well as in the protective effect of SA on wheat plants under cadmium stress resulting from development of defense responses in the course of SA-treatment.