Abstract
ABSTRACT Lead is an important environmental pollutant, extremely toxic to plants and other living organisms. In the present study, possible ameliorating effects of salicylic acid (SA) were investigated at biochemical levels in maize exposed to lead stress. The elevation in hydrogen peroxide and malondialdehyde contents and the decline in protein thiol (PT) level were revealed under lead stress. The SA pretreatment prevented a lead-induced decrease in chlorophyll and PT contents, as well as an increase in lipid peroxidation and hydrogen peroxide levels. Lead stressed plants which are pretreated with salicylic acid accumulated more ascorbic acid, glutathione and stimulated more antioxidant enzymes activity than plants treated with lead alone. In addition, SA pretreatment of seed enhanced l-cysteine desulfhydrase activity and endogenous hydrogen sulfide content. The results indicate that SA regulates the response of plants to lead stress and suggest hydrogen sulfide as a downstream signal molecule which might be involved in SA-induced lead tolerance.
Highlights
Contamination by heavy metals is widespread as a result of human agricultural and industrial activities
Lead stressed plants which are pretreated with salicylic acid accumulated more ascorbic acid, glutathione and stimulated more antioxidant enzymes activity than plants treated with lead alone
The results indicate that salicylic acid (SA) regulates the response of plants to lead stress and suggest hydrogen sulfide as a downstream signal molecule which might be involved in SA-induced lead tolerance
Summary
Contamination by heavy metals is widespread as a result of human agricultural and industrial activities. Lead (Pb) is an element accumulated in soil and sediments. Lead is not an essential element for plants, it is absorbed and accumulated (Gobran and Huang 2011). Pb phytotoxicity involves a decrease in growth, photosynthetic pigment content, disruption of protein structure, impairment of cell division and DNA synthesis, inhibition in activities of many enzymes (by binding to the sulfhydryl groups of various proteins) and oxidative stress (Wang et al 2011; Srivastava et al 2014). Plants possess defensive mechanisms to detoxify metals for their survival. Metal ion chelation is one of the defense strategies evidenced in plants under metal stress (Hassan and Aarts 2011). Polyamines and non-protein thiols (NPT), e.g. cysteine, glutathione (GSH) and phytochelatins (PCs), are components of the chelating compounds involved in metal chelation in the cytoplasm and contribute to the amelioration of negative impacts (Hall 2002)
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