Study On The Phase Responses And Mechanisms Of Different Winter Wheat Varieties To Drought

The dryness is one of world difficult problem. The response of crops to drought stress involves not only the research of highly effective water resources use, but also the grain production. Plants respond to drought stress by altering their cellular metabolism and invoking various defense mechanisms. Much study had showed that there existed a phase response to water deficit, and also classified different stages, such as acclimation, damage, repair and compensation. Now there are few studies about this, so it is very necessary to probe the changes of different physiological indicators under drought, which will helpful to provide theoretical basis for different phase response.In the paper, two winter wheat varieties, shaan 253 and changwu134, were used in the experiments. Water culture in artificial growth shelter and potted were designed to investigate response of physiological characteristics and growth, and also the effect of altered water condition on photosynthetic characteristic and water utilization efficiency. Some physiological indicators of osmotic adjustment and antioxidant defense systems and chlorophyll fluorescence parameters were analyzed, at the same time, the relationship of active oxygen species production and chlorophyll fluorescence quenching was discussed. The major results are as follows:1. In the course of osmotic stress, the relative water content, water potential, leaf area, osmotic potential at full tugor showed the trend of drop, however osmotic adjustment capacity showed the trend of increase. They have not displayed the stage response. However, root length, root area, R/S, proline, soluble sugar, K⁺, free amino acid, SOD, CAT, Vc showed first increase then drop, which indicated that these indicators exists the process of adaptation - injury. The initial increase is one kind of positive response for drought resistance, following reduction was thought the performance of injury.2. The content of O₂^- and H₂O₂ showed the trend of derease-increase-derease. Water stress induced generation of reactive oxygen species accumulation and then up-regulated the activities of antioxidant enzymes in wheat leaves. Therefore, the content of O₂^- and H₂O₂ reduced. When the production of reactive oxygen species excess the capability of scavenging system, ROS content then increased. The content of MDA showed the same trend with O₂^- and H₂O₂, indicated that the production of ROS was related to the membrane lipid peroxidation during the osmotic stress course.3. During the osmotic stress, there was difference in the accumulation of osmotic adjustment matters, SOD, CAT, POD activities and anti-oxide matters such as Vc, Car, GSH for two wheat varieties. The accumulation of the soluble sugar, free amino acid, Vc and Car in Shaan 253 after forces 18h is obviously higher than that of Changwu 134 after stress 18h, but on the contrary of osmotic adjustment, K⁺ content, SOD, POD, CAT activity, GSH. The production of O_<sup>2- and H₂O₂, also MDA content in Changwu 134 is lower than Shaan253, moreover, ROS was eliminated by anti-oxide matters in Shaan 253 and by protected enzyme system in Changwu 134. Above all indicated that the different varieties suffered same stress had the different drought resistance mechanisms, which provided the theory basis for breeding resistant varities.4. The activity of SOD isoenzymes such as MnSC^ CuZnSOD and FeSOD changed with increase of drought among the different isoenzymes, the region of FeSOD has the most changement, followed the CuZnSOD, MnSOD only showed little changement.5. The chlorophyll fluorescence parameters were significantly affected with the increase of osmotic stress. Fv/Fm showed first increased and then decreased, and Fv/Fo showed the trend of derease-increase-derease, which indicated that photoinhibition had not happened at the first stage of osmotic stress, however, with the increase of osmotic stress, decreased Fv/Fm showed that photoinhibition happened in wheat seedlings and resulted in the decrease of OPS II and ETR. During the course of osmotic stress, qP and qNP showed first decreased and then increased, which were helpful to enhance the open ratio of PS II reaction center and made more photosynthetic energy to use the photosynthetic electron transport in order to electron transport capacity. Meanwhile, the increase of non-photochemical quenching coefficient could helpful to dissipation of excess light energy, which protected the photosynthetic tissue and mitigated the effect of environment on photosynthesis. Above indicated that the wheat seedlings had its protection mechanism. Compared to winter wheat varieties, Changwul34 has more drought-resistance capacity thanShaan253.6. The relationship of 0² , H2O2 and qNP was negative exponential, and positive relation with qP during osmotic stress 18 h. The results showed that the production and elimination of 0 2 and H2O2 was helpful to photosynthetic electron transport when winter wheat seedlings suffered slight and moderate stress.7. Fo and qNP increased, but Fv,Fm> Fv/Fm ^ Fv/Fo > qP % ETR reduced under the water stress. However, the result was contrary under the altered water condition. It indicated that PSII reaction center was destroyed by drought stress. When water was supplied at the jointing stage and grain-filling stage, or drought at two different stages but water supplied at other stages, qP was increased, which are helpful to enhance the open ratio of PS II reaction center and make more photosynthetic energy to use the in order to electron transport capacity. Meanwhile, the increase of non-photochemical quenching coefficient can helpful to dissipation of excess light energy, which protected the photosynthetic tissue and mitigated the effect of environment on photosynthesis.8. Moderate drought was helpful to enhancement of WUE, showed the better drought adaptation. Rewatering at jointing and grain filling stage induced the high yield and WUE under moderate drought, especially more efficient for yield improvement at grain filling. Water deficit at jointing stage significantly reduced the biomass and yield. Rewatering at grainfilling stage was more efficient for yield improvement and WUE, and achieved the effect of both water-saving and high yield.