Mercury-induced Phytotoxicity and Responses in Upland Cotton (Gossypium hirsutum L.) Seedlings

Cotton is a potential and excellent candidate to balance both agricultural production and reme-diation of mercury-contained soil, as its main production fiber hardly involve into food chains. However, there is known rarely about the tolerance and response to Hg environments in cotton. In this study, The biochemical and physiological damages, in response to mercury (Hg), were investigated in upland cotton seedlings. The results on cottonseeds germination, indicated the germination rate were suppressed by high Hg levels, as the decrease of percentage was more than 10% at 1000 µM Hg. Shoots and roots’ growth were significantly inhibited above 10 µM Hg. The inhibitor rates (IR) in fresh weight were close between shoots and roots, whereas that in dry weight the root growth was more obviously influenced by Hg. In comparison of organs, the growth inhibition ranked as root > leaf > stem. The declining of translocation factor (TF) op-posed the Hg level even as low to 0.05 at 50 µM Hg. The assimilation of cotton plants was af-fected negatively by Hg toxicity, as evidenced from the performances on photosynthesis pig-ments (chlorophyll a and b) and gas exchange (Intercellular CO2 concentration (Ci), CO2 assimila-tion rate (Pn) and stomatal conductance (Gs)). Sick phenotypes on leaf surface included small white zone, shrinking and necrosis. Membrane lipid peroxidation and leakage were Hg dose-dependent as indicated by malondialdehyde (MDA) content and relative conductivity (RC) values in leaves and roots. More than 10 µM Hg damaged antioxidant enzyme system in both leaves and roots (P<0.05). Concludingly, 10 µM Hg post negative consequences to upland cotton plants in growth, physiology and biochemistry, whereas high phytotoxicity and damage ap-peared at more than 50 µM Hg concentration.