Physiological And Biochemical Effects Of Exgenous Nitric Oxide On Seedlings Of Maize (Zea Mays L.) Under Magnesium Deficient Stress

In recent years, magnesium deficiency becomes more and more seriously with acid deposition due to the rapid development of industry in china, potassium fertilizer application increasing in agriculture. These lead to decrease of magnesium content in soil and reduction of crops because of magnesium deficiency stress. Nitric oxide (NO) is an important redox signaling molecule in organisms, and also a reactive nitrogen species. Research results showed that, NO involved in plant growth, development, disease resistance, stress tolerance and other physiological processes. But so far, it was still no research report of the effect of NO on magnesium deficient 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 the growth, photosynthesis, reactive oxygen metabolism, root activity and some inorganic ionic balance of maize seedlings under magnesium deficient stress. We want to show light on that if NO has effect on magnesium deficient maize and the mechanism of NO. 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 magnesium deficiency.1 The shoot and root length, fresh and dry weight, chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Cs) and transpiration rate (Tr) of maize seedlings cultured with magnesium deficient solutions were decreased, so did the content of photosynthetic product such as starch, soluble sugar and soluble protein, while the intercellular carbon dioxide concentration (Ci) was increased. After the treatment with 100μmol L-1 sodium nitroprusside (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.2 The root activity was reduced under magnesium deficiency. The distribution of nitrogen in shoot and root was interfered under magnesium deficiency stress. The contents of inorganic ions such as Mg2+, Cu2+, Fe3+and Mn2+in younger and older leaves of maize subjected to magnesium deficiency were decreased, while those of Ca2+, K+ and Zn2+increased. Magnesium content in root of maize seedlings was decreased under Mg deficient condition, but the contents of Ca2+, K+, Zn2+, Cu2+, Fe3+ and Mn2+ were increased. In comparison with magnesium deficient 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+, Cu2+, Fe3+and Mn2+ in younger leaves and those of Cu2+, Fe3+ and Mn2+ in older leaves were increased due to SNP treatment. Whereas the contents of Ca2+, K+ and Zn2+ in younger leaves and Mg2+, Ca2+, K+ and Zn2+ in older leaves were decreased under SNP treatment condition. Contents of all of the ions decreased in roots of magnesium deficient maize seedlings due to SNP treatment.3 Because of the reduction of chlorophyll content, the leaves of maize under magnesium deficiency stress became yellowing with the magnesium deficiency depleting. The content of carotenoid decreased, either. The content of superoxide, hydroperoxide and malondiadehyde (MDA) increased simultaneously. The leakage of ion inleave under magnesium deficiency stress elevated, either. The activities of antioxidative enzymes such as dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) were increased, while those of peroxidase (POD) and catalase (CAT) decreased. The contents of small molecular antioxidants such as ascorbate acid (AsA) and proline (Pro) were improved. Adding 100μmol L-1 SNP improved the content of chlorophyll and caroteinoid and the leaves becomes green than those of magnesium deficiency stressed. The content of H2O2, O2-,MDA and Pro was reduced and the leakage of ion in leave was impressed. The activities of SOD, POD, CAT were elevated, while those of APX and GR reduced, but the content of AsA in leave was improved.From these results, we can conclude that balance of the producing and the scavenging of ROS is destroyed under magnesium deficient stress. The ROS is overproduced, thus leads to the decreased content of chlorophyll and the yellowing leaves of seedling. These certainly impress the photosynthesis rate. Overproduced ROS leads to cell membrane system injury, 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 magnesium deficiency 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, the imbalanced ionic homeostasis is regulated to normal by NO treatment. So NO can protect maize seedling from magnesium deficiency stress.