Study On Desiccation Tolerance Of Excised Embryos In Davidia Involucrate

Seed preservation at present is the most ideal way for the long-term preservation of plant germplasm resources. The key of long-term preservation of seed is making moisture content decrease to a certain extent, so the desiccation tolerance of seeds becomes the decisive factor of long-term preservation, especially for non-orthodox seeds which are not resistant to dehydration.Dove tree(Davidia involucrata Baill) is one of endangered plants in China,with high value both in academic and ornamental horticulture fields. In this study, the excised embryos of Dove tree seeds were at first dehydrated for different time period, and then tissue culture of excised embryos, the determination of relative conductivity and the enzyme activity of antioxidant defense system, and microscopic observation of subcellular structure were conducted, in order to figure out the mechanism for desiccation tolerance and desiccation damage. The experimental results are as follows:1. The percent seedling emergence of excised embryo of Davidia involucrata gradually decreased with the dehydration process, whereas, the relative electric conductivity and malondialdehyde(MDA) content gradually increased, indicating that the cell membrane permeability and the degree of membrane lipid peroxidation increased gradually, and the cell membrane damage aggravated gradually with dehydration.2. With the dehydration process, activity of superoxide dismutase(SOD),catalase(CAT), ascorbate peroxidase(APX) and dehydroascorbate reductase(DHAR)at first increased, and when the water content decreased to 18.45±1.02%,activity of four kinds of antioxidase reached up the highest value, and then with further decrease in water content, activity of four kinds of antioxidase decreased.The results showed that a mild dehydration could activate the antioxidae in Davidia involucrata embryos itself, and consequently protected embryos from dehydration damage; but when the water content sequentially decreased and exceeds a certain threshold, antioxidaes became inactivation, and eventually led to the complete loss theviability of excised embryos.3. With the dehydration process, the viability of Davidia involucrata excised embryos gradually decreased, meanwhile, the distribution pattern of liposomes in cells converted from irregular to regular(along the inside of the cell membrane). In late dehydration phase, small liposomes merged into the large fat group, and solutions in vacuoles occurred concentration and crystallization and hence the color of vacuoles deepened, and large starch grains occurred split due to dehydration; and plasmolysis phenomenon occurred and the more close to the epidermis, the plasmolysis is more significant.