| The gaseous hormone ethylene plays a key role in regulation of diverse developmental and physiological processes throughout entire life cycle of plants. Ethylene is also a key signal in plant responses to biotic stress. Drought is one of the most significant abiotic stresses for crops and how to enhance the drought dolerance becomes one of the most important problems to be solved. The effects and function of ethylene signal will on the response to drought still be further studied. And in this dissertation, we used the mutants of key factors in ethylene signal transduction pathway, and demonstrate the mechanism of ethylene signal participate in the response to drought. This investigation could offer evidence to the upgrade crops. The main contents and results are as followed:The morphological observation and measurement showed the rosette growth, shoot biomass and leaf area under PEG stress were restrained more significant in ethylene insensitive mutants ein2-5 and ein3-1 than in Col-0 and ctrl-1. The ethylene signal magnitudes expressed in the 4 plants were:ctr1-1> Col-0> ein3-1> ein2-5, while the values of relative growth depress rate in the plants under PEG stress were:ein2-5> ein3-1> Col-0> ctrl-1, which is reversed to the ethylene signal. The results of root length showed that PEG stress could promote the elongation of Col-0 and ctrl-1 root; in the ethylene insensitive mutant ein2-5 and ein3-1, the root lengths were showed higher than the root length of control, but they were decreased with the PEG concentration increased. Though the root length of ethylene insensitive mutants ein2-5 and ein3-1 increased under PEG stress, the high concentration of PEG could depress the elongation of root. From these results, we can conclude that ethylene signal plays a positive role in regulating Arabidopsis growth and morphology under PEG stress.We also determined the physiological status in Arabidopsis under PEG stress. The water potential in Col-0 and ctrl-1 leaves were decreased with PEG concentration heightened, while the water potential in ethylene insensitive mutants ein2-5 and ein3-1 did not change significantly. The RWC values in ein2-5 and ein3-1 decreased more sharply than Col-0 and ctr1-1. And the ability of water retaining was higher in Col-0 and ctr1-1. In ethylene insensitive mutants ein2-5 and ein3-1, the MDA content increased levels were higher than Col-0 and ctr1-1 under PEG stress. It was indicated that ethylene signal could regulate the plant reduce the water potential to keep the osmotic potential, resulting in retaining water and enhance the drought tolerance. In the response of ethylene signal to drought, there was more osmotic modulatory substance, such as soluble sugar, amino acid and proteins. And these substances synthesized to a high level in fine ethylene signal pathway plants under PEG stress. We can concluded that ethylene signal can positive mediate the plant to adapt drought. In this study, we measured the ROS and antioxidative enzymes in plants leaves under PEG stress. The ROS level in ethylene insensitive mutants ein2-5 and ein3-1 was higher than that in Col-0 and ctr1-1, and SOD, POD, CAT, APX and GR played a essential role to eliminate ROS. It was indicated that ethylene signal regulated the redox state in plants, Col-0 and ctr1-1 mutant showed a high tolerance to oxidative stress and drought.
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