The Role Of ROS In Heavy Metal Stressed Wheat Seed Germination

This study describes involvement of superoxide anion and hydrogen peroxide in the germination and early development of cadmium/copper stressed wheat seeds. The following indexes were determined: germination rate, early growth, NADPH oxidase activity (NOX), superoxide anion (O₂⁾ and hydrogen peroxide (H₂O₂) content and distribution, MDA content (peroxidative decomposition product malondialdehyde), total calcium content, cytosolic calcium concentration.The results showed that, the seeds germination and early growth were inhibited by Cd/Cu-stress, the latter was more sensitive to heavy metals than the former.When wheat seeds were exposed to 0.2 mM CdCl2 for 6 days, significant decrease of O₂ and H₂O₂ content were observed, seedlings growth were inhibited by almost 50% compared with control. The activity of NOX diminished significantly. MDA content reduced as well. Exogenous O₂ produced by generating system significant reversed the early growth of Cd-stressed seedlings, but exogenous H₂O₂ has a little effect. N-acetylcysteine (NAC) present protective effects on Cd-stressed wheat seeds germination and development, through increaseing the O₂ and H₂O₂ content of whea seeds. The wheat seedlings were inhibited by 0.5 mM CuSO4 treatment, the NOX activity, O₂ and MDA content were significant reduced. Exogenous O₂ produced by generating system could significant reverse the early growth of Cu-stressed seedlings. The H₂O₂ content increased in Cu-stressed wheat seedlings, and the number of roots was increased.Results of in-situ staining indicated that O₂ mainly distribute in the meristem zone, like root tip, zone of root elongation, tip of root hair, indicating that O₂ could promote root elongation; H₂O₂ mainly distributed in maturation zone, like ripening root and coleorhiza, H₂O₂ could increase the amount of roots.The total Ca content decreased and the cytosolic calcium concentration ([Ca²⁺]_c) increased in Cd/Cu-stressed seedlings, the high concentration of [Ca²⁺]_c could produce toxicity to wheat seedlings. Exogenous O₂ decreased [Ca²⁺]_c indicated that the O₂ was involved in the [Ca²⁺]_c releases. Exogenous Ca²⁺ could reserved the early growth of Cd-stressed seedlings through increased O₂ content and inhibited the produce of [Ca²⁺]_c, reduce the toxicity of [Ca²⁺]_c. However, exogenous Ca²⁺ could not reserved the O₂ content in Cu-stressed seedlings, so could not reserved the [Ca²⁺]_c and early growth.