The Effect Of Drought Stress On Physiological Characteristics And Antioxidant Enzyme Gene Expression Of Rapeseed At Germination And Vegetative Stage

Rapeseed belongs to genus Brassica, one of the most important oilseed crops in the world. Drought is becoming one of the most common environmental stresses that limit plant yield and survival. In China, arid and semi-arid area accounts for one-third of the total area. Under limited water resource conditions, the selection of crops with high yield and high stress tolerance is important for breeders. In our study,3 offspring lines (W134, W140, W146) derived from intergeneric somatic hybrids between Brassica napus and Sinapis alba and B. napus cv. ’Yangyou 6’(Y6) were studied during germination and vegetative stage under drought stress. The morphological, physiological and biochemical characteristics and the expression of antioxidant enzyme genes were tested and analyzed. And membership function was used to assess the drought tolerance of rapeseed at vegetative stage comprehensively. The results were as follows:(1) Under drought stress simulated by 15% PEG, the root length and plant height of 4 rapeseed materials reduced significantly than control at germination stage. The relative values of root length, plant height and total fresh weight were all less than 1, which demonstrated that the growth of root length, plant height and total fresh weight was inhibited. Based on the drought resistance coefficients of root length, plant height and total fresh weight, it showed that W134, W140, W146 were more drought tolerant than Y6 at germination stage. Under PEG stress, the MDA, proline content and the activities of SOD. POD increased significantly. And the MDA content of Y6 was higher than the other 3 rapeseed materials, but the proline content of W134 was lower than the other 3 materials. W140 maintained the highest POD activity and Y6 had the highest SOD activity. The ROS accumulation was detected by NBT staining and DAB staining under PEG stress. After and before PEG treatment, no significant differences of H2O2 content were detected in 4 rapeseed materials and the accumulation of O2- dramatically increased. However, the level of ROS in the leaves of Y6 and W134 was higher than that in W146 and W140. Under PEG stress, the expression of most antioxidant enzyme genes was up-regulated. Especially the expression of DHAR was remarkably up-regulated by drought, which was up-regulated approximately 7.05 fold in line W140.(2) Under drought stress, the leaves of 4 rapeseed materials withered seriously with increased drought stress degree and at the 12 d stress, W146 behaved better than the other 3 materials. Under drought stress, the RWC and Pn of 4 rapeseed materials decreased significantly, while the REC and MDA content, the activities of SOD and POD, the proline, soluble sugar and soluble protein content increased significantly. W146 maintained more water content, higher photosynthesis, proline content and SOD, POD activity, lower REC and MDA content. According to the comprehensive evaluation of drought resistance for four rapeseed materials at vegetative stage, the results showed that, under drought stress, the range of drought tolerance from strong to weak could be:W146>W140>Y6>W134.(3) Under drought stress, the level of ROS in the leaves of 4 rapeseed materials was determined by NBT staining and DAB staining. And darker color was witnessed in the leaves of 4 materials with the increased drought stress level. However, the H2O2 and O2- content in the leaves of W146 and W140 were lower than that in Y6 and W134. According to the expression of antioxidant enzyme genes, most of the genes were up-regulated with increased drought stress degree. And the expression of APX、Cu/Zn SOD、GPX、GR genes in W146 was up-regulated more than that in the other 3 materials. Furthermore, the expression of Cu/Zn SOD gene was up-regulated 79.77 fold in line W146 at the 7 d drought stress.This study will help establishing reliable methods for screening rape materials with improved drought tolerance for genetic breeding. Meanwhile a more drought resistance rapeseed material was selected, which was one offspring line of intergeneric somatic hybrids between B. napus and S. alba. The results revealed that the offspring line W146 might obtain drought tolerance traits from S. alba and provide enhanced drought tolerance to rapeseed.