Drought Induced By Pretreatment Of Corn Seedlings Cross-adaptation And Its Mechanism

We use maize seedlings (Zea mays L.) and tobacco (Nicotiana plumbagin~folia L.) as material. In the first section, we have tried to probe into that drought harden can enhance resistance of drought stress, chilling stress, heat stress and salt stress in plants by studying on maize seedlings. In the second section, we have tried to establish a transgenic tobacco system expression CaMICaMBP genes, so that the others can use it to investigate the process of physiology and biochemistry which endonuclear and intracytoplasma calmodulin have take part in. For the first part, we used maize (DaHuang, Qing No.3) seedlings as experimental material. First, we have studied effects of drought, chilling, heat and salt stress on the survival percentage (%) of two varieties of maize seedlings after drought hardened. It has been confirmed that the phenomenon of cross adaptation exists in maize seedlings. Afterwards, we measured the electrolyte leakage of maize roots and the vitality maize coleoptiles, these results confirmed further that the phenomenon of cross adaptation exists in maize seedlings. Then we measured the activities of ascorbate peroxidase (APX), glutathione reductase (GR), catalase (CAT), superoxide dismutase (SOD) and guaiacol peroxidase (GPX) of drought pretreatmented maize seedlings in the course of drought, chilling, heat and salt stressing. We found that drought pretreatment enabled the seedlings to keep relatively higher activities 2~iL~ 4 of APX, OR, CAT, SOD and GPX than control. These indicate that the improvement of stress tolerance is often related to the enhancement of activity of antioxidant enzyme system in plants. At the same time, we probed into the role of hydroperoxide (1-1202), it seemed that H202 is the signal of environmental stress, or we can suggest that H2O2 initiated the process of cross adaptation. In the second section, we used two verities of transformed tobacco (Tetr3.2, H02O2.0) leaves as experimental material, which have kanamycin resistance. The gene of CaM or CaMBP was transferred into leaf disks with the help of Ti-plasmid of agrobacterium tumeinfaciens. Tobacco seeds were germinated in MS medium containing Km. Leaf disks have been rooted in MS medium contain Km and hygromycin after agroinfection, co-culture in 2-3 months. We have been established a transgenic tobacco system expressing calmodulin or calmodulin-binding protein. In the experiment, there are many influent factors: (1) Effect of agroinfection on plants in different growth period is different. (2) It is efficient when leaf disks was soaked in solution containing agro bacterium fume infaciens for 10 mm. (3) It is efficient if leaf disks was cultured with agrobacterium tumeinfaciens for 3-4 days; In the course of co-culture, it is better to weaken light intensity; The best co-culturing temperature is 22C. (4) Culture and dilution of agrobacterium tumeinfaciens could influence on transgenic efficiency. (5) Difficulty and time of transgene were affected different varieties. (6) False positive seedling is easy to be getting in the side of leaf disks, which are far from culture medium. 5 Thus, it is important for rooting of seedlings in the rooting medium. In our experiment, we established transgenic tobacco system expressing...