The Physiological Responses Of Catharanthus Roseus Seedling To Zn Stress And The Involved Role Of Ethylene During This Process

Catharanihus roseus (L.) is widely cultivated in south, east and southwest of China. Catharanthus roseus is a kind of medicine on prevention and treatment of cancer, the anticancer ingredient of vinblastine and vincristine that extracted from stems and leaves, is currently a critical source of most anti-cancer medicine. As an essential micro element for plant, Zinc (Zn) is also a kind of heavy metal that threatens plant growth. In general, heavy metal disorders of physiological metabolism and accelerates plant senescence and death.In this paper, to investigate the primary metabolism in plants and Zn ion transformation as well as its accumulation combined with the secondary metabolism response to Zn stress in plant, Catharanthus roseus was selected as experiment material. A cultivate system that nutrient solution irrigated to perlite was sued. Moreover, exogenous ethylene was applied to Zn stressed seedlings to study the effects of ethylene in regulating Catharanihus roseus response to Zn stress.The results are as follows:1. The growth of Catharanthus roseus was promoted under low concentrations of Zn presence while it was inhibited under high levels Zn condition. The root system of Catharanthus roseus was more tolerant to excess Zn, indicating the tolerance of Catharanthus roseus to Zn was high. Under Zn stress, the chlorophyll and photosynthesis was prompted and depressed under low or high levels of Zn. respectively, suggesting that high levels of Zn results in the degradation of chlorophyll by which decreased its photosynthesis ability. Under Zn stress, application of exogenous ethylene alleviated excess Zn induced damage to plants. Excess Zn treatment increased ethylene production and the production will increased slightly. On contrary, application of exogenous ethylene under Zn stress increased ethylene production dramatically,17.8times higher than that of control at its peak value. However, as the treatment time prolonged, the production of ethylene decreased under ethylene sole treatment condition, suggesting that ethylene production will decrease as the time past.2. As the high ability in absorbing and accumulating Zn ion, the root system of Catharanthus roseus was hypersensitive to Zn stress. The ability of absorbing and accumulating of Zn ion in Catharanthus roseus root was increased under low Zn condition while depressed under high Zn condition. The accumulation of Zn ion in plant stem and root was increased as the Zn treatment concentration increased, suggesting the higher ability of Catharanthus roseus in absorbing and accumulating Zn ion. Specifically, the high transformation ability was mainly due to the transformation of Zn ion from mature tissue to younger tissue. Under Zn stress, application of exogenous ethylene decreased the accumulation of Zn ion in many tissues, and alleviated the damage induced by excess Zn ion to plant. Furthermore, its application also promotes transformation of Zn ion from mature tissue to younger tissue and inhibited its transformation between other tissues.3. Under Zn stress, cells was severe damaged by stress induced oxidative stress, however. the activities of POD. CAT and SOD was increased that was considered to be ROS scavengers and protect cell membranes from oxidative damage. Also, the concentrations of MDA and soluble sugars were also increased which then alleviated the damage induced by-excess Zn to plants. One of the important mechanisms that Zn induced damage to plants was the oxidative stress that caused by ROS. However, application of exogenous ethylene alleviated Zn stress induced damage to plants.4. Vindoline, vinblastine and catharanthine, three forms of indole alkaloids in Catharanthus roseus, combined the vinblastine in roots displayed characteristics of tissue specific. The concentrations of vindoline and vinblastine varies depends on the location of tissue, it was higher in upper younger leaves but lower in bottom mature ones. This phenomenon was consist with the classical theory that there was more secondary metabolites in younger tissue while less in mature ones, by which to guarantee the organism develop and growth ordinarily. Application of exogenous ethylene stimulates biosynthesis of indole alkaloid in Catharanthus roseus under excess Zn stress.