Studies On The Effect Of Nitric Oxide In The Root Growth Of Pea Under The Iron Deficiency Stress

Iron is an essential mineral element for plant growth and the component of multiple enzymes which exerts great influence on the growth and development of plants. However, iron exists in the soil in the form of Fe3+ which can hardly be used by plants in a direct way, especially in alkaline soil where the solubility of Fe3+ is even lower. Therefore, plants are often in the tight corner of iron deficiency which not only causes oxidative damage to plants but also affects human health for the lack of iron intake. Nitric oxide, a new bioactive and signal molecule discovered recently, participates in the growth and development of plants and plays an important role in the defense responses of them. NO (Nitric Oxide) has a high affinity with iron, so NO is closely related to the iron metabolism in plants. Using Pisum sativum L., the influence of NO on the growth and development of the root system of Pisum sativum L. under the condition of iron deficiency had been explored in this study. Major findings are as follows:(1) NO increases the number of lateral root, but inhibits the elongation of the main root; it also shows that as a non-specific inhibitor of endogenous NO, NaN3 (Sodium azide) strongly inhibits the generation of endogenous NO. Elimination of NO strongly inhibits the generation of lateral root and the elongation of the main root. The result of root-tip stain by the specific probe of NO, DAF-2DA (4,5-Diaminofluorescein diacetate), shows that cells with active division have a higher content of NO. For example, there are more fluorescence signals of NO in cells of the root cap and lateral root primodia. NO inhibits the activity of IAAO (Indoleacetic Acid Oxidase) under the condition of iron-deficiency and increases the content of endogenous IAA(Auxin); IAA and NO interact with each other and jointly promote the root development of Pisum sativum L. seedling under iron-deficiency stress.(2) NO treatment increases NR (Nitrate Reductase) activity and endogenous NO and promotes the nitrogenous metabolism which thereby provides more materials for protein synthesis. NO treatment decreases the electric conductivity of the cell membrane in root tips and the activity of lipoxygenase; it reduces damages to the cell membrane by free radicals and provides a stable membrane structure for a variety of transport enzymes。(3) Meanwhile, NO treatment increases the activity of Fe3+ reductase activity under the condition of iron deficiency and promotes the iron intake of the root system; NO also maintain the balance of mineral elements in roots, meanwhile increases the root activity. NO inhibits the activity of ACO (Aconitase) by regulating the content of H2O2 (Hydrogen peroxide) in the root of Pisum sativum L. and converts ACO to IRPs which inhibits the transcription and translation of FER (Ferritin) mRNA. Semi-quantitative PCR detects that NO inhibits the expression of FER mRNA, thereupon reduces the storage of iron in FER and increases the content of Fe2+ for various life activities.