Study On Drought Resistance Physiological Characteristic Of Desert Plant Prunus Mongolica Maxim.

Prunus mongolica Maxim. seedlings were drought-stressed continually for 8 days by using naturally-dehydrated-soil drought stress treatment method, in the period of which the soil water content decreased from the normal water supply 14.00% to 2.00% and the corresponding plant water potential decreased from -0.68MPa to -2.86 MPa. After the water stress removed for three days, the leaf water potential of the seedlings recovered to -0.68MPa again. Based that, the Prunus mongolica Maxim. physiological characteristics of drought resistance and dehydration resistance was analyzed dynamically from the photosynthetic characteristics, osmotic adjustment, nitrogen metabolism, plasma membrane permeability and drought-induced protein changes.In the aspect of photosynthetic characteristics of Prunus mongolica Maxim., stomatal conductance and transpiration rate were increased to strengthen the root imbibition motivity to adapt to the drought conditions during the 1st day and 2nd day of drought stress. From the beginning of the 3th day, respiration rate decreased more than photosynthetic rate to raise the hydraulic utilization ratio. Photosynthetic rate showed single peak curve during the drought stress and stoma factor was the main cause of the decrease of the Prunus mongolica Maxim. leaf photosynthetic rate in the preceding period of the drought stress. However, under the sever drought stress condition, the main cause to restrain the Prunus mongolica Maxim. leaf photosynthetic rate was the decrease of mesophyll cell assimilation ability and other nonstomal factors.Prunus mongolica Maxim. seedlings had strong osmotic adjustment ability. Under continuous soil drought stress condition, small molecular organic solvent praline, soluble amino acid and inorganic ion K+,Na+ accumulated in large quantity in the preceding stage of the drought stress, and in the later stage of that, these materials content showed a decrease trend. After the drought stress removed for three days, those materials recovered to the control level. The soluble proteins content showed a decrease trend in the preceding stage of the drought stress while they increased in the later stage, which offered the substance foundation for the Prunus mongolica Maxim. osmotic adjustment tactics.The drought stress had many influences on the Prunus mongolica Maxim. nitrogen metabolism. The nitrate reductase activity, the total nitrogen content and proteinase activity of Prunus mongolica Maxim. Seedlings increased in the former stage of the drought stress. Prunus mongolica Maxim. Seedlings could assimilate nitrate effectively to avoid the accumulation of nitrate that could make the harm to the plant. It enhance the proteinase activity to make the increase of protein degradation and the free amino acid content and increase the solute particles to avoid the harm of Prunus mongolica Maxim.. Under the severe drought stress condition, drought-induced protein was produced and the soluble protein content rose and the soluble protein became the main osmotic adjustment material of Prunus mongolica Maxim. in the later stage of the drought stress.The content of glutathion as non-enzyme active oxygen free radical scavenger of Prunus mongolica Maxim. decreased in the former stage of the drought stress and increased sharply in the later stage while vitamin c (Vc) content accumulated in large quantities and dropped sharply in the later stage. The increase and the decrease made a good compensation. Glutathione and Vc were the effective oxygen free radical scavenger in the later and preceding stage of the drought stress and cowork in the course of Prunus mongolica Maxim oxidation resistance.The maximum increase of the plasma membrane permeability of Prunus mongolica Maxim seedlings in the course of the drought stress was only 67.27% , and after the drought stress removed for three days, the plasma membrane permeability decreased rapidly so it had strong adjustment capacity. The change of malonaldehyde (MDA) content and the plasma membrane permeability had the same trend that they obtained the highest on the 4th day, when they increased by 74.88% compared with that under the normal conditions. The correlation analysis for the change of the membrane permeability and MDA content in the period of the drought stress indicated that they had a significant correlation R=0.768. The change of the leaf plasma membrane permeability of Prunus mongolica Maxim was the result of the peroxidation of the membrane lipid.