H₂O₂, Ca²⁺/CaM Are Involved In NO-induced Adventitious Root Development Of Cucumber（Cucumis Sativus Linn）under Drought Stress

Nitric oxide（NO） is a diatomic free radical gas. As a versatile signaling molecule, NO is involved in regulating every aspect of plant growth and developmental processes. Meanwhile, NO as an essential signaling role responses might be involved in responsing to various abiotic stresses These studies have paved the way to understand the signaling roles of NO which may affect cell metabolism, cellular redox balance and gene expression in plants. Hydrogen peroxide（H₂O₂）, as a reactive oxygen species, has been considered as an important signaling molecule that mediates various physiological and biochemical processes in plants. Also, calcium(Ca²⁺) has important functional implications to modulate transduction processes in plants. In order to further investigate the mechanism of NO induce the development of adventitious root, we have showed the relationship of signaling network among NO, H₂O₂ and Ca²⁺ during adventitious rooting under drought stress and investigated H₂O₂ and Ca²⁺ as downstreams of NO participated in inducing the development of adventitious roots. Then, we have drawed the following conclusions:1. PEG treatment significantly inhibited the adventitious root number, root length and fresh weight of cucumber. The suitable concentration of SNP and H₂O₂ could remarkable increase root number, root length and fresh weight of adventitious rooting.10 μM SNP and 800 μM H₂O₂ have the most effective under drought stress. DPI, ASA and CAT treatments significantly reduced the root index. Application of NO donor（SNP） may increase endogenous H₂O₂ content under drought stress. The treatments of cPTIO, Na3 N and Na2WO4 significantly reduce NO-induced endogenous H₂O₂ content. These results showed that H₂O₂ may play an essential role in NO-induced adventitious rooting under drought stress.H₂O₂ might be a downstream molecule of NO to participate in adventitious rooting which was induced by NO under drought stress.2. The content of TBARS and Pro and the activities of LOX, POD, PPO, IAAO were measured in order to investigate the effect of NO on alleviating membrane lipid peroxidation and increasing the activities of POD, PPO, IAAO during the development process of adventitious root. The treatments of DPI、ASA、CAT indicated that H₂O₂ could be the downstream molecule of NO to mediate NO-regulated lipid peroxidation and prompt relative enzymatic activities to protect membrane stability and induce adventitious root development under drought stress.3. The suitable concentration of CaCl₂ could significantly increase root number, root length and fresh weight of adventitious rooting. The treatments of CaCl₂ inhibitors significantly reduced the root index.4. Application of NO and CaCl₂ could significantly enhance photosynthesis of cucumber leaves and increase the avtivities of antioxidant enzymes under drought stress. The treatments of CaCl₂ inhibitors significantly reduce these indexes which indicated endogenous Ca²⁺/CaM may be involved in NO-induced the development of adventitious root of cucumber under drought stress.5. We utiliazed H₂O₂ and Ca²⁺-specific fluorescent probe to investigate the H₂O₂ as upstream of Ca²⁺/CaM involved in the process of NO-induced adventitious root of cucumber under drought stress.