Comparative Effect of Exogenously Applied and Endogenously Synthesized Salicylic Acid in Wheat Under Cadmium Stress

Abstract

Wheat is one of the most vital cereal crops, considered as an essential food source around the globe and backbone of agriculture in Pakistan. When wheat is grown on soil contaminated with the cadmium coming from natural and anthropogenic source then the growth of wheat is affected. Cadmium can also accumulate within wheat grains and can enter in food chain to effect humans directly. Salicylic acid is phytohormone that can reduce the toxicity caused by cadmium on different plants by decreasing cadmium uptake as well as translocation and by affecting various metabolic process that make the plant tolerant against cadmium stress. To analyze the significance of salicylic acid for developing a tolerance in wheat against cadmium stress present experiment was conducted. Three levels of cadmium stress (0, 20 and 40ppm), salicylic acid in three different levels (0, 0.25, 0.5mM) and two wheat genotypes (cv. FSD-08 and cv. MH-97) were used. Priming, foliar and rooting mode of application were used for each level of salicylic acid. Cadmium retarded the growth of plants, but this effect was more prominent when 40 ppm cadmium stress was applied in both genotypes. Uptake of two monovalent Potassium (K) and Sodium (Na) and one divalent cation Calcium (Ca) was observed to decreased by the cadmium stress in both wheat genotypes. Cadmium caused increase in the lipid peroxidation and raised the proline, peroxidase and hydrogen peroxide concentrations and whereas concentrations of chlorophyll, carotenoid, catalase, superoxide dismutase, phenolics, flavonoids, total soluble sugar, ascorbic acid, protein and glycine betaine was decreased. Different gas exchange parameter, water and solute potential decreased with an increase in cadmium concentration within both genotypes. Yield parameters also decreased in cadmium stressed wheat genotypes. Salicylic acid in all its modes of application were effective. Maximum increase in ascorbic acid, Gs (stomatal conductance), K in leave and root, chlorophyll a/b ratio, Ci (internal carbon dioxide concentration) and glycine betaine was found in cv. MH-97 presoaked with 0.5mM salicylic acid alone while cations (Na and Ca) in root, some morphological characteristics, total soluble protein, phenolics and flavonoid were highest in cv. FSD-08 pretreated with salicylic acid (0.5mM) under unstressed condition. The foliar application of 0.5mM SA gave the highest carotenoid concentrations, total soluble sugar, spikelet’s per spike, A, Na in root and 100 grain weight in cv. FSD-08 whereas maximum increase was in anthocyanin content in cv. MH-97. Catalase (CAT), total soluble sugar, total chlorophyll, xxii

superoxide dismutase (SOD), Ca in leave, peroxidase (POD), the proline content and fresh/dry weight of root were found to be greater in cv. FSD-08 and Na in leaves and proline content was highest in cv. MH-97 when 0.5mM salicylic acid was given through roots. Some phenolics like Salicylic acid were determined through HPLC and result showed that maximum amount of these phenolics were observed when 0.5mM salicylic acid primed cv. FSD-08 was grown in unstressed condition. Cadmium was found in higher quantity in roots as compared to leaves. All methods of application found to be effective in decreasing cadmium uptake from root to leave. Priming with salicylic acid improved most of morphological attributes while in rooting and foliar application the yield attributes effected more. Moreover, cv. FSD-08 is tolerant genotype that can be grown in cadmium contaminated soil and 0.5mM is most effective concentration that can be used as a treatment against cadmium stress.