Lipoic acid mitigates oxidative stress and recovers metabolic distortions in salt-stressed wheat seedlings by modulating ion homeostasis, the osmo-regulator level and antioxidant system

BACKROUNDSoil salinity is one of the most detrimental environmental factors affecting the growth of plants and limiting their agricultural productivity. This study investigated whether exogenous lipoic acid (LA) pretreatment plays a role in promoting salt tolerance in wheat seedlings. The seedlings were treated with LA (1.75 mmol L-1) and salt (100 mmol L-1 NaCl) separately and a combination of them. RESULTSSalt stress significantly reduced relative water content, leaf surface area, ribulose bisphosphate carboxylase expression, and chlorophyll content but increased the content of osmo-regulator protein, carbohydrates and proline. In addition, salinity led to an imbalance in the inorganic composition of wheat leaves. While it elevated Na+ content compared to control, Ca content and K+/Na+ ratio were reduced. Under saline conditions, despite increases in antioxidant enzyme activity and levels of antioxidant compounds (ascorbate and glutathione), the content of reactive oxygen species (superoxide anion, hydrogen peroxide) and malondialdehyde were higher than in control seedlings. LA significantly promoted osmo-regulator level and antioxidant enzyme activities compared to stressed seedlings alone. Also, it both increased levels of ascorbate and glutathione and regenerated their oxidised forms, thus contributing to maintaining cellular redox status. Similarly, LA prevented excessive accumulation of Na+ and promoted K+/Na+ ratio and Ca content. Reactive oxygen species content was significantly reduced, and the inhibitions in the above parameters markedly recovered. CONCLUSIONLA reduced salinity-induced oxidative damage and thus contributed to the growth and development of plants in saline soils by modulating ion homeostasis between plant and soil as well as in osmo-regulator content and antioxidant system. (c) 2014 Society of Chemical Industry