Effects of exogenous salicylic acid and sodium nitroprusside on α-tocopherol and phytochelatin biosynthesis in zinc-stressed safflower plants

Abstract

The interactive effect of exogenous application of salicylic acid (SA) and sodium nitroprusside (SNP), a donor of nitric oxide,on zinc (Zn) toxicity was assessed in Zn-stressed safflower (Carthamus tinctorius L.) seedlings. Exposure to 500 µM $ZnSO_4;.7H_2O$ for 10days caused an increment in the levels of malondialdehyde (MDA), $H_2O_2$, α-tocopherol, phytochelatins (PCs), and proline. Applicationof SA or SNP, and especially their combination, resulted in remarkable decrease in MDA, $H_2O_2$, and proline content while chlorophyllcontent and the activity of catalase, ascorbate peroxidase, and guaiacol peroxidase exhibited a significant induction in comparison withplants subjected to Zn treatment alone. In Zn-treated plants, addition of SA and SA + SNP caused a progressive increase in α-tocopherollevels in comparison with plants treated with Zn alone. In plants subjected to Zn excess, no significant association was found betweenPC levels and the supplementation of SA, while application of SNP and SA + SNP caused a significant increase in PC contents. Thesedata imply that SA and SNP, and especially in combination, play a significant role in the amelioration of deleterious effects of Zn toxicity,probably due to stimulation of antioxidative defense mechanisms and PC biosynthesis.