Physiological And Biochemical Effects Of Exogenous Nitric Oxide On Seedlings Of Maize (Zea Mays L.) Under Copper Stress

Copper is particularly important for plant life activities. However, excessive copper is harmful for the growth of the plants. NO is an important redox signaling molecule in organisms, and also a reactive nitrogen species. Research results showed that, NO involved in many physiological processes. But so far, it was still not many research reports of the effect of NO on excessive copper stress plant especially on crops, such as maize.In this experiment, solution cultured maize seedlings of’Zhengdan-958’were employed to study the effects of exogenous nitric oxide on physiological processes of maize seedlings under excessive copper stress. We want to show the roles of NO in the copper stress plants. The following results got from the study in the effects of NO on biomass, photosynthesis, ionic homeostasis and the ROS metabolism of maize seedlings subjected to excessive copper stress.1Low concentrations of copper is less harmful for maize seedlings. At low concentrations of copper, the plant height, chlorophyll content, net photosynthetic rate (Pn), soluble sugar of maize seedlings cultured were increased. At high concentrations of copper, those were decreased. With the increase of the concentration of copper, the root length, fresh and dry weight, stomatal conductance (Cs) and transpiration rate (Tr), soluble protein of maize seedlings cultured with excessive copper solutions were decreased, while the intercellular carbon dioxide concentration (Ci) and soluble protein was increased. After the treatment with100μmol L-1sodium nitro prusside (SNP), a nitric oxide donor, the shoot and root length, fresh and dry weight, Pn, Cs, Tr and photosynthetic product such as stach, soluble sugar and soluble protein were increased, while the Ci was decreased.2The root activity was reduced under excessive copper stress. The distribution of nitrogen in maize seedlings was interfered under excessive copper stress. The contents of inorganic ions such as Mg2+, Zn2+, Mn2+in leaves of maize were first increased at low concentrations of copper. And then those were decreased at high concentrations of copper. But K+, Fe3+were decreased with the increase of the concentration of copper, while those of Ca2+, Cu2+increased. Mg2+, Ca2+, K+content in root of maize seedlings was decreased under copper stress condition, but the contents of Zn2+, Cu2+, Fe3+and Mn2+were increased. In comparison with copper stress, the root activity was increased due to SNP treatment. The distribution and partition of N was rationalized in shoot and root. The contents of Mg2+, Ca2+, Fe3+and K+in leaves were increased and Cu2+, Zn2+and Mn2+in leaves were decreased due to SNP treatment. Whereas the contents of Mg2+,Ca2+,Cu2+,Zn2+in roots were decreased and K+,Fe3+,Mn2+decreased under SNP treatment condition.3With the increase of the concentration of copper ions, the leaves of maize seedlings became yellowing. The content of carotenoid were first increased then decreased. The content of superoxide, hydroperoxide and malondiadehyde (MDA) increased simultaneously. The leakage of ion in leaves under copper stress increased, either. The activities of antioxidative enzymes such as dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD) and catalase (CAT) were increased. The contents of small molecular antioxidants such as ascorbate acid (AsA) and proline (Pro) were improved. Adding100μmol L-1SNP improved the content of chlorophyll and caroteinoid and the leaves becomes green than those of copper stress. The content of H2O2, O2·-and MDA was reduced and the leakage of ion in leave was impressed. The activities of SOD, POD, CAT, APX were elevated, but the content of AsA and Pro in leaves was improved.From these results, we can conclude that with the increase of the concentration of copper ions, the ROS is overproduced, thus leads to cell membrane system injury, the decreased content of chlorophyll. These certainly impress the photosynthesis rate. The content of MDA, accumulate, the ionic leakage rate increase and the ionic homeostasis imbalance. Then the growth of maize seedling is impressed due to excessive cooper stress. NO reduce the ROS content in leaf of magnesium deficient maize seedling by eliminating ROS directly, by regulating the activities of antioxidative enzymes or by elevating the contents of small molecular antioxidant such as AsA. Then NO increases chlorophyll content, eliminates the yellowing syndrome, improves photosynthesis. The damage of cell membrane is decreased, the ion leakage of leaf is lowered and the imbalanced ionic homeostasis is regulated to normal by NO treatment. So NO can protect maize seedling from excessive copper stress.