The Alleviative Effects of Salicylic Acid on Physiological Indices and Defense Mechanisms of Maize (Zea Mays L. Giza 2) Stressed with Cadmium

Abstract

The present study evaluated the physiological and biochemical mechanisms through which exogenous salicylic acid (SA) mitigates cadmium (Cd) stress in maize. The different concentrations of Cd included 0, 5, 10 µM CdCl2.3H2O. Half of plants received salicylic acid as a soil drench. Results showed that Cd exposure reduced chlorophyll contents, chlorophyll fluorescence, photosynthetic rate and activity of catalase (CAT). However, Cd stress enhanced non-photochemical quenching (NPQ), the production of malondialdehyde (MDA) and activities of key antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (POD). The increased activities of antioxidant enzymes and concentration of MDA were reduced by exogenous application of SA as a soil drench. Our research proves that SA, as a novel endogenous plant hormone exerts beneficial physiological effects on plants as it has a dual role in scavenging active oxygen species (AOS) and modulating redox balance to enhance photosynthetic performance in cadmium-stressed maize plants. It was concluded that SA improved plant tolerance under Cd contamination and may have alleviated the inhibitory effect of Cd on photosynthesis by protecting maize plants against oxidative damage as indicated by the marked decline in net photosynthetic rates, quantum yield and chlorophyll content as well as alteration of antioxidants activity and accumulation of MDA. Collectively, results of the present study provide an insight into the alleviative role of SA in Cd-stressed maize and propose SA as a potential candidate in mitigating Cd toxicity.