Mechanism Of Nitric Oxide Donor Sodium Nitroprusside Confering Drought Tolerance To Wheat (Triticum Aestivum L.) Seedlings Under Drought Stress

Triticum aestivum is the second most important crop in China and its production and quality are directly linked with both international and domestic affairs. Drought is the one of the most important factor to limit the agricultural production are complicated and the study of anti-drought physiology, biochemistry, and molecular biology of T. aestivum will play an important role in providing powerful theoretical guidelines for coping with this problem. The mechanism study is a research focus in enhancing the drought resistance of wheat by exogenous substance. When the wheat seedling (with three fully expanded leaves) were treated with 15% PEG-6000 in combination with different concentrations (0.1, 0.5 and 1.0 mmol?L-1) of exogenous nitric oxide donor sodium nitroprusside (SNP), are studied the drought-resistance and its transduction mechanism to provide a theoretical basis and technical support in food safety production on arid and semi-arid areas. The main research results are as follows:1. The 15% PEG-6000 treatment apparently enhanced the H+-ATPase and Ca2+-ATPase activities before period of deterioration, accelerated the accumulation of malondialdehyde (MDA) and membrane permeability, lowered height, fresh weight dry weight and relative water content (RWC) in wheat seedling leaves under drought stress. 0.1 mmol?L-1 SNP and 0.5 mmol?L-1 SNP could enhance the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), lower O2-.production rate, H2O2 content and membrane lipid peroxidation, stabilize the structure and function of biomembranes, increase the activities H+-ATPase and Ca2+-ATPase. But it is the negative effects to decrease the membranaceous peroxide by 1.0 mmol?L-1 SNP.2. The 15% PEG-6000 could apparently enhance NOS activity in wheat seedling, NO was quickly produced by cNOS, and the proportion of iNOS in NOS was increased slowly after 6 h treatments. NO was also induced by NR, which was a little part of total NR activity. The 0.1 mmol?L-1 SNP treatment could apparently alleviate the drought-induced membrane lipid peroxidation, which consistent with the up-regulation of NOS, NR and NO. With increasing SNP concentration, it had less effect on NO content by 0.5 mmol?L-1 SNP and 1.0 mmol?L-1 SNP. The effect of SNP was decreased after treatment of blocker of plasma membrane Ca2+ channels LaCl3. The above results indicated that exogenous nitric oxide donor (SNP) could apparently increase nitric oxide-synthesis enzyme activities and NO content, and Ca2+ was involved in regulation of NO level in wheat seedling leaves by SNP under drought stress.3. The content of photosynthetic pigment increased, the photosynthetic rate (Pn) decreased with the time under drought stress, While intercellular CO2 concentration (Ci) decreased first with stomatal conductance (Gs) reducing, then slow increased after 12h treatment. Stomatal limitation is the main reason for the decline in Pn at the early stress, the latter are mainly non-stomatal limitation.is the one at the late stress. 0.1 mmol?L-1 SNP could help to increase chlorophyll a, chlorophyll b and Pn, decrease Gs to induced stomatal closure and transpiration rate (E) to relieve evaporation under drought stress. Furthermore, 0.1 mmol?L-1 SNP increased the proportion of opened PSⅡreaction centers (indicated by qp), leading to transference of the more excited light-energy to PSⅡfunction center, decreased the dissipation of excited energy in antenna pigments(NPQ), which increased the more absorbed light to participate in photochemical reaction(ΦPSⅡ). In addition, the effects of NO on the gas exchanges and chlorophyll fluorescence parameters were concentration dependent. At low concentrations (0.1 mmol?L-1 and 0.5 mmol?L-1) SNP significantly increased the Pn and decreased the Gs of the leaves so that they accumulated more osmotic substances (TFA, Pro and SS), and increased their water potential and osmotic potential.4. The stress-induced protein content was increased significantly in wheat seedling leaves under drought stress. The 26 kD protein was induced at the 3h treatment under drought stress. 0.1 mmol?L-1 SNP could not only increase the protein content (such as 26kD, 31kD and 37kD, etc.), but also advance the process of protein induced, such as the 26 kD protein increased significantly at the 1h treatment. Hemoglobin, a specific scavenger of NO, partly reversed the inductive effect. At the same time, LaC13 inhibited significantly the protein synthesis in wheat seedling leaves and postponed the process of protein induction, Ca2+ was involved in regulation of stress-induced protein in wheat seedling leaves by SNP under drought stress.The results suggest that 0.1 mmol?L-1 SNP could significantly alleviate the oxidative damage caused by drought stress. With the increased concentration, 0.5 mmol?L-1 SNP, decreased mitigation role, NO synthesis is inhibited, then Gs increased and stomatal closure blocked to impact of other regulatory mechanism.1.0 mmol?L-1 SNP was aggravated the physiological metabolic disorder of wheat seedlings under drought stress. Therefore, SNP significantly promoted the growth and regulated the physiology of wheat seedlings at 0.1 mmol?L-1 SNP.