| Drought stress is a major limiting factor among environment stresses that limit plant growth the most, affecting almost all stages of plant growth and development. Wheat(Triticum aestivum L.) is one of the major staple cereal crops in China. Wheat frequently suffers drought stress in its life cycle which ultimately results in prominent loss in the yield. In this study, Longjian 19(for short LJ19, drought-tolerant) and Q9086(drought-sensitive) were used as the experimental materials and the effects of PEG-6000- simulated drought stress on these two wheat cultivars were studied. These studies may provide theoretical and experimental guidance for wheat drought resistance breeding. The main results are as follows:1. We treated wheat seeds with different PEG6000 concentrations including 0%, 5%, 10%, 15% and 20% to examine seed germination. The results showed that wheat seed germination was significantly delayed. Germination rate and germination potential of LJ19 at 20% PEG was 13.59% and 10.79% higher than that of Q9086, respectively. Germination index and vigor index was 22.36% and 68.93% higher than that of Q9086, respectively, under 15% PEG treatment. Seed α-amylase activity in LJ19 was 44.41% higher than that of Q9086. The reason why LJ19 germination rate is higher than Q9086 may be because LJ19 has higher α- amylase activity.2. After 7 days of treatment of seeds with different PEG6000 concentrations, we found that drought inhibited the wheat growth. Q9086 was more sensitive to drought stress than LJ19. Under 20% PEG treatment, the MDA content in Q9086 was 21.99% and 13.10% higher than that of LJ19 in shoot and root, respectively. The H2O2 content in Q9086 shoot and root under 15% PEG treatment was 16.04% and 53.78% higher than that of LJ19, respectively, indicating that Q9086 suffers more serious oxidative stress than LJ19. Furthermore, although the POD activity exhibited apparent fluctuations in both shoot and root, the activity of SOD, CAT, and APX in LJ19 was higher than that Q9086 in both shoot and root, indicating that LJ19 has stronger ability of scavenging ROS than Q9086. The higher antioxidant activities in LJ19 may be the main reason that it is more resistant to drought stress than Q9086.3. 4-day-old wheat seedlings grown under normal conditions were transferred to new bottles containing 20% PEG for further growth. The shoot height of LJ19 was 17.21% higher than that of Q9086; however, the Q9086 primary root length was 37.87% longer than that of LJ19. The relative water content dropped in both cultivars under drought stress, but the relative water content in the shoot and root of LJ19 was 2.34% and 4.00% higher than that of the Q9086, respectively. H2O2 contents in the shoot of LJ19 and Q9086 induced by 20% PEG were increased by 8.19% and 53.45% compared to the respective controls. H2O2 contents in the root of LJ19 and Q9086 were increased by 66.04% and 62.14% compared to the respective controls. The relative ion leakages in the shoot of LJ19 and Q9086 were increased by 3.08% and 88.64% compared to the respective controls, while the relative ion leakages in the root of LJ19 and Q9086 were increased by 26.41% and 35.94% compared to the respective controls under 20% PEG treatment. The contents of proline and soluble sugars showed similar changing patterns. The content of proline and soluble sugars in LJ19 roots was 52.12% and 22.10% higher than that of Q9086, respectively, suggesting that LJ19 has stronger osmotic adjustment ability. The increase of antioxidant enzyme activities in LJ19 was more pronounced than that in Q9086 under drought stress in both shoot and root, indicating LJ19 has higher ability of scavenging reactive oxygen species than Q9086. In addition, the G6 PDH activities in shoot of LJ19 and Q9086 were increased by 45.62% and 103.00% compared to the respective controls, whereas in the root of LJ19 and Q9086 the G6 PDH activities were increased by 2.00% and 9.98% compared to the respective controls under 20% PEG treatment. The G6 PDH activity in LJ19 was higher than that of Q9086, but Q9086 could produce more reactive oxygen species than LJ19. Quantitative real-time PCR analysis of the relative transcription abundance of genes indicated that the expression of Cu-Zn SOD, APX and CAT genes in LJ19 were 1.7, 2.2 and 1.1 times of that in Q9086. The expression of G6PDH2 in Q9086 was 7.1 times of that in LJ19. Moreover, chlorophyll content, light system II maximum quantum yield(Fv/Fm), and photochemical fluorescence quenching efficiency(q P) showed that drought did not considerably affect these photosynthetic parameters changes in LJ19, but Q9086 is more sensitive to drought stress than LJ19. The respiration rates in shoot and root of LJ19 was 25.57% and 25.07% higher than that of Q9086, respectively, under drought stress.In summary, drought stress noticeably affected the germination and seedling growth in two wheat cultivars. LJ19 showed a high tolerance to drought stress. These results suggested that α-amylase activities play predominant roles during seed germination. Proline contents, soluble sugar contents together with relative antioxidant enzyme gene expression and activities play essential roles in the responses to drought stress during wheat seedling growth. |
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