| Water stress is one of the most common stress which can lead to physiological and biochemical changes of wheat and even reduction of output. Therefore, the study about the responses of wheat to water stress can provide the theoretical foundation for the identification of drought resistance and the breeding of cultivars with drought resistance. The present study is divided into two parts. The first part compared drought resistance of seven different wheat varieties. The second part further compared the photosynthetic characteristics and the antioxidant system in two wheat cultivars.First of all, we compared the changes of the drought resistance indexes in seven different wheat cultivars (Chuanmai 42, Mianyang 15, Mianyang 11, Chuannong 19, Aikang 58, Zhoumai 21, Sy95-71) at germination and seedling stage under water stress. The method of subordinate function analysis was used to calculate membership value of each index at germination and seedling stage. Then, the drought resistance was determined by comparing the average membership value. The results indicated that relative germination rate, shoot length and root length presented the negative correlation with water stress at germination stage. Chuanmai 42 had the highest relative germination rate and relative shoot length. However, Sy95-71 presented the lowest relative germination rate, shoot length and root length. By subordinate function comprehensive analysis, we found that the drought resistance at germination was following:Chuanmai 42> Chuannong 19> Aikang 58> Mianyang 11> Zhoumai 21> Mianyang 15> Sy95-71. In addition, the relative water content (RWC) was negatively correlation with the stressed degree at seedling stage. However, malonadehyde (MDA), superoxide anion (O2·-), hydrogen peroxide (H2O2), superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) presented positive correlation with the stressed degree at seedling stage. By comprehensive analysis of the subordinate function value under water stress for 3 d, the drought resistance at seedling stage was following:Chuanmai 42> Aikang 58> Chuannong 19> Zhoumai 21> Mianyang 11> Mianyang 15> Sy95-71. Using subordinate function analysis at germination and seedling stage, the present study found that Chuanmai 42 and Sy95-71 had the strongest and lowest drought resistance, respectively.Based on above results, we further compared the photosynthetic characteristics and the antioxidant enzyme system of two wheat cultivars (Chuanmai 42 and Sy95-71, as the stronger and weaker drought resistant cultivar, respectively) under water stress. We evaluated the antioxidant system between two wheat cultivars with different drought resistance by determinating the specific enzyme activities (SOD, CAT, POD, APX, DHAR, and GR), the antioxidants (AsA and DHA), and the level of reactive oxygen species (ROS). We studies the damage of membrane by measuring the RWC, relative electric conductivity, MDA, total protein, soluble sugar, and proline content. We investigated the influence of water stress on the photochemical efficiency of photosystem Ⅱ (PSⅡ) by measuring the maximum efficiency of PSⅡ photochemistry (Fv/Fm), the quantum yield of the PSⅡ electron transport (ΦPSⅡ), the photochemical quenching (qP), and the non-photochemical quenching coefficient (NPQ). In addition, we studied the contents of thylakoid proteins and the reversible phosphorylation of PSII proteins by western blotting. To further investigate the effects of water stress on PSII structures, the thylakoid ultrastructure was analyzed with a transmission electron microscopy. We found that the activities of the antioxidant enzymes were higher in Chuanmai 42 than in Sy95-71 after water stress. Compared with Sy95-71, Chuanmai 42 accumulated a lower level of ROS after water stress. Compared to the control, Fv/Fm, ΦPSⅡ, and qP significantly decresed after water stress, and the values of NPQ obviously increased under water stress for 1 d. Compared to the control, the content of D2 protein significantly decreased in Chuanmai 42 but not in Sy95-71 under water stress. Compared to the control, water stress resulted in the increase in phosphorylated levels of CP29, D1, D2, CP43, and LHCII in both wheat cultivars. Under all conditions, the phosphorylated levels of four proteins (D1, D2, CP43, and LHCII) in Chuanmai 42 were higher than in Sy95-71. LHCII slowly dephosphorylated in Chuanmai 42. But the significant dephosphorylation of LHCII was in Sy95-71 under water stress for 3 d. Compared to the control, D1, D2, and CP43 proteins fastly dephosphorylated in both wheat cultivars under stressed condition. Relative to the control, the strongly dephosphorylated levels of D1 and D2 were in Sy95-71 under water stress for 3 d. In Sy95-71 water stress resulted in a significant destacking of grana, and the thylakoid structure suffered to a obvious damage relatived to the control plants. However, Chuanmai 42 showed the obvious damage in the structure of thylakoid under water stress for 3 d compared to the control. All the results indicated that PSⅡ and the antioxidant enzymatic systems played important roles in response to environmental stresses in plants. |
PDF Full Text Request