Effect Of Soil Drought Stress On The Physiological Activities In Seeds And Roots Of Prunus Mongolica Maxim.

Prunus mongolica Maxim. is a special deciduous shrub, xerophytes, in the desert area and desert steppe of Mongolia Plateau, one of the plants with strong stress-resistant ability and wind break and sand fixation ability, and it plays extremely important functions in stabilization and rehabilitation of the fragile ecological environment. In this paper, we cultivated the Prunus mongolica Maxim. seeds on the culture medium of quartz sand which were simulated by the solutions of polyethylene glycol (PEG-6000) with -0.04MPa,-0.12MPa and -0.30MPa osmotic potentials of water stress and studied the effect of drought stress on respiratory metabolism of Prunus mongolica Maxim. during seed germination. The results showed that the respiratory quotient and total respiratory rate were increased first and decreased afterwards, so were the alternative pathway(AP).The respiration in EMP increased from the beginning of the seed germination and arrived the maximum respiratory rate at 4^th day. Namely,it was 74.33,70.29,70.24 and 62.16O2μl·g^-1FW·h^-1 respectively in the control,-0.04MPa,-0.12MPa and -0.30MPa PEG-6000 water stress. But EMP respiratory rate declined gradually. At the same time,the EMP—TCA rate increased correspondingly. The hexose monophosphate pathway(pentose phosphate pathway)was operated in higher speed in the early period of seed germination of Prunus mongolica Maxim., and it was declined with prolonging of seed germination. The light water stress(-0.04MPa of osmotic potentials)accelerated the respiratory substrate metabolic rate. In whole seed germination course of Prunus mongolica Maxim., the operative activity of cytochrome pathway(CP) was enhanced, but the contribution of CP to total respiration declined slowly as germination time processed. Furthermore, the contribution of AP to total respiration increased gradually. Cyanide-resistant respiration was enhanced during the seed germination under the light stress. There were a decrease of the contribution of the AP and an increase of the contribution of CP along with the stress intensity strengthen. Moreover, Cyanides contents during the seed germination of Prunus mongolica Maxim. showed the trends which first rose then declined, and the light stress accelerated the accumulation of it.In this paper, we simulated different soil drought stress by controlling the water content of the soil, and studied the effect of soil drought stress on root physiological characteristics of Prunus mongolica Maxim. seedlings. The results showed that nitrogen metabolism level including the total nitrogen (TN), nitrate reductase (NR) activity and protease activity was enhanced rapidly along with the stress intensity strengthen. When the soil water content dropped to 3.96%,the leaf water potential decreased to -2.48MPa, above three physiological index reached the highest level, namely, TN in levels increased 35.55%, NR 164.06% and protease activity 651.63% over the sufficient water supply (control), respectively. From then these values decreased gradually and come to be balanced. It is obvious that the roots of Prunus mongolica Maxim. Seedlings have the good capability to make osmotic adjustment on the drought stress, and it is apparent of the accumulation of proline,free amino acid and K⁺, Na⁺ in the early period of stress, the maximum contents were 2.63, 7.29, 1.45, 0.60mg·g-1DW, and the levels increased 16.44, 0.83, 1.62 and 1.36times over the control, respectively. At the late stage of stress, the content of these minor molecular osmotic solutes was decreased and the content of the big molecular soluble matter including the soluble protein and soluble sugar were enhanced meantime. In the other words, the most osmotic solutes are praline,free amino acid and K⁺, Na⁺ in the early period of stress and the soluble protein and soluble sugar are the main osmotic matters in the late stage of stress. It has a good antioxidant capacity in the roots of Prunus mongolica Maxim. seedlings. Glutathione (GSH) contents declined rapidly and ascorbic acid (ASA) accumulated quickly in the early period of the stress, the trends was on the contrary in the late stage of the drought stress. It indicated that the two kinds of not enzyme free radical scavengers are well compensated each other. The results showed that soil drought intensify the roots membrane lipid peroxidation of Prunus mongolica Maxim. seedlings. Malonic dialderhyde (MDA) was accumulated more and caused an increase of membrane permeability with the extent of stress, and the cell membrane permeability was related to the added value of the MDA (R²=0.706). After the treatment of the drought stress, the roots activity of Prunus mongolica Maxim. seedlings showed a decrease first, then increase and then decrease trend. Under the drought stress, root hydraulic conductivity in individual root and whole root system level of the Prunus mongolica Maxim. seedlings was declined rapidly, and when the soil water content dropped to 1.23%,the leaf water potential decreased to -3.48MPa, two values decreased 88.38% and 94.59% compared with the CK, it showed that the soil drought stress caused the sharply drop of the capacity of water transmitting. The result of hydrolysis of starch in root-cap of Prunus mongolica Maxim. seedlings under drought stress demonstrated that the content of starch in root-cap decreased with the increase of drought stress, and it was resulted from the roots injuries of seedlings.In this study, we cultivated the Prunus mongolica Maxim. seedlings of 3 0～40cm high for 60days under four levels of water supply treatment, such as adequate water available(CK), light drought stress, modest drought stress, and severe drought stress, during the seedling stage, and then measured all related index. The result showed that under the light drought stress, all the roots length, roots volume, root thickness, active absorbing area of roots, root/shoot ratio, root surface area/leaf area ratio and roots activity in the levels increased over the control(CK). Above index declined with the water stress strengthen, at the same time the roots cytoplasmic membrane permeability increased. It was obvious of the accumulation of the organic solute including soluble sugar, free amino acid as well as praline, but it was not apparent of the accumulation of K⁺ and Na⁺, and there was a decline of soluble protein in the roots under the different level drought stress. It is probably an exhibition that the roots of Prunus mongolica seedlings adaptated to the long term drought stress.