The Investigation Of Physiological Mechanisms Of Modulation Characteristics Regulated By NO-mediated Ca²⁺ Signaling In Response To Drought Stress In Alfalfa

Much attention has been paid to nitric oxide research since its discovery as a single mediator of plant defense responses. Here, in order to investigate the mechanism of Ca²⁺ signaling mediated by NO in Medicago sativa seeds under drought stress, sodium nitroprusside（SNP）, Ca Cl2, methylene blue and La Cl3 solution were used in this study. The results varied as following:1. Under the stress of 15% PEG alfalfa seed germination was inhibited, but the exogenous SNP, Ca Cl2 or SNP+Ca²⁺ can relax this condition. The exogenous No or Ca²⁺ can relax the inhibited under drought, especially 0.1 mmol/L SNP and 10 mmol/L Ca Cl2 treatment are significantly. Germination energy, germination percentage,starch content, amylase activity, soluble sugar, soluble protein and the root activity was significantly increased when SNP+Ca²⁺ treatment under drought stress. The germination rate is increased by 8.96% than SNP treatment, and 19.67 than Ca Cl2 treatment. The changes of this index was slower under both NO and Ca²⁺ treatment than SNP or Ca Cl2 alone.2. The exogenous SNP, Ca Cl2 and SNP+Ca²⁺ can improve the ability of seed and seeding under drought in alfalfa, meanwhile SNP+Ca²⁺ treatment changed significantly than single SNP or Ca Cl2. Both SNP and Ca Cl2 treatment increased the levels of proline content, activities of SOD, POD and CAT, whereas contents of MDA are decreased compared to SNP or Ca Cl2 treatment alone. In the germination of alfalfa, the proline content, activities of SOD, POD and CAT rises to 79.79%,29.00%,30.57% and 64.19%, the MDA content and the O2-rate was reduced to 29.39% and 34.48% than 15% PEG treatment. In the seedling stage of alfalfa, exogenous SNP and Ca Cl2 treatment improved the soluble protein, soluble sugar proline content and the antioxidant enzyme activities. The root activity rises to 29.10%; MDA content and the O2-· rate was reduced under the drought stress. The bands of POD isozyme changes significantly when the SNP+Ca²⁺ treatment the alfalfa under drought stress. This result showed that the small molecular enzyme content was increased and POD activity was improved.3. Under drought stress, exogenous SNP, Ca Cl2, and SNP+Ca²⁺ treatment can improve the ability of photosynthesis in alfalfa seedlings. SNP+Ca²⁺ treatment significantly increased chlorophyll content under drought stress. The chlorophyll a and chlorophyll b improves 63.11% and 15.36% than 15% PEG treatment. SNP+Ca²⁺ and SNP/Ca Cl2 treatment significant differences. Exogenous application of SNP, Ca Cl2, and SNP+Ca²⁺ have eased the photosynthesis rate, stomatal conductance, stomatal limitation value decline and intercellular CO2 rise.4. Methylene blue and La Cl3 inhibit the ability of exogenous SNP and Ca Cl2. When added the exogenous Ca²⁺ and MB, a NO blockers, the promoting effect of Ca²⁺ was inhibited. Otherwise, the promoting effect of NO could be inhibited by La3+, a Ca²⁺ channel blockers. It indicated that NO mediated the proteins modifications in alfalfa seeds under drought stress through Ca²⁺ signaling pathway.