Cold stress in soybean (Glycine max L.) roots: exogenous gallic acid promotes water status and increases antioxidant activities

Gallic acid (GLA; 3,4,5- trihydroxybenzoic acid) is a strong antioxidant in plants. In order to clarify the effects of GLA as a pro-oxidant or an antioxidant on cells under stress conditions, soybean (Glycine max) was grown under normal conditions or in the presence of cold stress (5 and 10°C) in the absence or presence of gallic acid (GLA; 1 and 2 mM) for 72 h. The soybean roots exposed to stress exhibited a significant decline in growth (RGR), water content (RWC), osmotic potential (ψII) and proline content (Pro). However, GLA treatment under stress significantly improved these parameters and alleviated the stress-generated damage. Stress decreased superoxide dismutase (SOD) activity, but GLA effectively mitigated the adverse effects on enzyme activity. After stress treatment, only catalase (CAT) was induced in soybean roots, although it was not sufficient to prevent toxic hydrogen peroxide (H2O2) accumulation. Thus, the levels of lipid peroxidation (TBARS content) markedly increased. However, GLA contributed to detoxification of H2O2 and lipid peroxidation by enhancing activities of CAT and peroxidase (POX). In addition to these enzymes, SOD activity was able to scavenge superoxide anion radicals, as evidenced by decline in TBARS content. However, monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), total ascorbate (tAsA) and glutathione (GSH) showed a decline of content in roots treated with GLA (both concentrations) plus stress. Our results suggest a protective role of GLA, which may strengthen plant tolerance by ensuring efficient water use and enhancing antioxidant systems. In soybean roots, GLA successfully alleviated the toxicity of cold stress by modulating the activities of SOD, CAT and POX rather than enzymes of the ascorbate-glutathione cycle.