Abstract
SALT stress is a main factor limiting plant growth and productivity. Salicylic acid (SA) has been shown to alleviate the adverse effects of different environmental stresses on plants. To investigate the protective role of salicylic acid (SA) in alleviating salt stress on Rosmarinus officinalis L. (rosemary) plant, a pot experiment was conducted to measure the growth parameters such as plant height and branch number. An antioxidant defense system, represented by catalase (CAT), superoxide dismutase (SOD) and peroxidase (PDX), was evaluated at both biochemical and transcriptional levels. NaCI was applied at 0, 25, 50 and 100mM and 0, 0.2 and 0.4mM of SA were used. The exposure of rosemary plant to salt conditions resulted in significant reduction of plant height, branches number and increases in the three measured antioxidant enzyme activities, compared to control. The foliar application of SA effectively increased growth rates and enhanced the activities of CAT, SOD and PDX enzymes. The PCR (RT-PCR) analysis revealed that the relative transcript levels of SOD, CAT, and PDX genes were changed and up-regulated compared to the control due to NaCl stress and SA treatments, reached the highest expression level by applying 25mM NaCl and 0 SA treatments. The results implied that SA regulated the transcript levels of the antioxidant genes, resulting in the increased contents of antioxidant enzymes and enhanced salt tolerance.