| As the acid rain causes much wider and more serious damages to the ecological system, the acid soil caused by acid rain is becoming one of the serious environmental problems in the world. Seed germination is the beginning of productivity. The acid rain and soil have influences on crops'germination, morphological structure, growth and development, physiology and biochemistry,etc. The rare earth(RE) has been extensively used as micro-fertilizers for many years in China. Appropriate dosage of RE could enhance crops'metabolism, and also induce plants'resistance to stress, such as UV-B radiation, heavy metals. These results indicate that RE can alleviate the damage to plants contaminated by environment. Therefore, rice seeds(Oryza sativa L.) of"Ningjing 1"and sorghum seeds(Sorghum vulare) of"Xiongza 9", were utilized as our experimental objects, which were soaked with LaCl3 solution of appropriate dosage and germinate in culture container kept in simulated acid rain. In this study, the effect of lanthanum on POD during seed germination was investigated under different level of acid rain stress. The aim was to provide macroscopically physiological and ecological references for elaborating the mechanism of RE inducing plants'resistance to acid rain stress; it also offered another new ecological defense strategy of preventing crops from acid rain stress. The major experiment results are shown as follows:1. The study reflected the stimulative and inhibitive action of Hormesis effect. Our results show that LaCl3 solution with the dose of 0 to 20 mg·L-1 could increase the germination and the activities of POD of rice and sorghum seeds, decrease MDA content, improve antioxidative metabolism and promote growth and development of two crops'seeds. The optimal spraying dosage of LaCl3 solution is 1 mg·L-1 for rice seed, and 12 mg·L-1 for sorghum seed.2. The optimal spraying dosage of LaCl3 solution could increase the germination, POD activity and soluble protein contents of rice and sorghum seeds. It also strengthen parts of peroxidase isozymes, decrease plasmolemma permeability, MDA and H2O2 content. A change in the proportion of membrane lipid fatty acids could improve the harmfulness of acid rain and the mitigatory effect of La(Ⅲ) on high pH was better than that on low one. Although acid rain stress can increase POD activity and soluble protein contents, the mechanism was different. The former one was advanced on its own initiative, while the latter one was stimulated passively.3. Under the high pH of acid rain(pH5.0 to pH3.0), POD activity increased and strengthen their capacities to scavenge reactive oxygen species(ROS). Under low pH of acid rain (pH2.5 to pH2.0), POD activity and soluble protein contents were inhibited. The ability of removing the excessive free-radicals was also weakened. However, La(Ⅲ) can effectively adjust the stability of POD and eliminate ROS, so that it alleviated the harm to seeds by acid rain stress.4. The regulative effect of La(Ⅲ) on antioxidant enzymes such as POD could strengthen their capacities to scavenge reactive oxygen species, improve the metabolism of ROS and decrease H2O2 contents. At the same time, it improved the proportion of membrane lipid fatty acids, decrease MDA contents and plasmolemma permeability. Consequently, membrane lipid peroxidation was abated.5. The response to acid rain between rice and sorghum were different. It suggested that the resistance to rice rain of rice was better than sorghum, and the alleviation of La(Ⅲ) on sorghum was better than on rice. |
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