Glycine betaine-induced lead toxicity tolerance related to elevated photosynthesis, antioxidant enzymes suppressed lead uptake and oxidative stress in cotton

Anthropogenic activities contaminate soils with heavy metal concentrations including lead (Pb), cadmium (Cd), copper (Cu), and chromium (Cr). Pb has higher potential for ready accumulation, sedimentation, and poisoning of the soil than other heavy metals. The present study was conducted to induce Pb tolerance, in solution culture-grown cotton, by exogenous glycinebetaine (GB) application using 3 levels of Pb (0, 50, and 100 mu m) and 2 GB levels (0 and 1 mM). The results revealed that Pb stress decreased gas exchange characteristics (net photosynthetic rate, stomatal conductance, transpiration rate, water use efficiency, chlorophyll, carotenoids, and SPAD value) and the performance of antioxidant enzymes. Toxic effects of Pb stress were mitigated by GB application, which in turn increased the plant growth and gas exchange characteristics by reducing the performance of malondialdehyde (MDA), hydrogen peroxide (H2O2), and electrolytic leakage. An increase in the activity of antioxidant enzymes helped in mediating the adverse effect of the Pb stress as compared to plants treated with Pb alone. The results revealed that exogenous application of GB significantly alleviated the Pb toxicity by improving the growth, biomass, and photosynthetic parameters in cotton (Gossypium L.) plants. GB increased Pb tolerance by enhancing the chlorophyll synthesis, photosynthetic activities, and antioxidant enzyme activities and by lowering the electrolytic leakage, MDA, and H2O2 levels.