Effect Of Water Deficit On Vascular Bundle System And Partitioning Of Assimilates In Wheat Ear

China is one of 13 major water-poor countries, there is always seasonal water shortages in the Loess Plateau in western China, and in recent years there also was severe drought in south of China. The effects of water deficit have seriously affected China's food production and food security. The objective of this study was to determine the defects of water deficit on the morphological, physiological characteristics of wheat(Triticum aestivum L.) and the vascular bundle system of the wheat ear. Pubing143 and Xinong979 was examined on material grown in pots under water deficit from jointing stage. The contribution to total yield of grain in various organs and the vascular system in the rachis were observed by using physical activity measurement and microscopy paraffin sections. The results in this study are as follows:1. Water deficit will not affect the overall growth of wheat seedlings, but it can change the value of root to shoot; reduce the area of wheat seedling'leaves, lower water potential of leaves and the relative of water content. The chlorophyll content of wheat seedling'leaves will not reduce under moderate water deficit conditions. The MDA content in wheat seedlings first increases and then decreases, as the activities of antioxidant enzymes increase in wheat seedlings. With the strength of osmotic stress increased, it is beyond the antioxidant enzyme defense system's scavenging capacity of wheat seedlings, the value of MDA content increased.2. Under the water deficit condition, the growth of wheat plants was inhibited, stem height decreased, leaf area of wheat was decreased, the over ground biomass was decreased. After flowering stage, the contribution of carbon assimilation in flag leaf, leaf sheath and stem transporting to grain was increasing. However, it is difference between Pubing143 and Xinong979. In filling stage, the flag leaf in vitro which is under adequate moisture conditions is larger than which is under the water deficit.3. Material transferring rate increased with the increasing of sucrose content in vegetative organs; the accumulation of carbon assimilation in grain increased as the sucrose content in vegetative organs with and physical functioning with the increase rate. After flowering 10 to15 days, the carbohydrates stored in the vegetative organs begin to decompose, then the decomposition products was deliveryed to the ear, the soluble carbohydrate content decreased. Under water deficit conditions, the amount of sucrose and starch increased in non-grain composition of ear.4. The number of central and peripheral bundles declined acropetally along the length of the rachis. A significant difference appeared in the rate of declining between the basal spikelet to central and the central to terminal spikelet. While under water-deficit condition, the levels of declining increased significantly. However, little influence on the number of vascular which prolonged and developed to spikelet was showed. On the contrary, the diameter of the large vessel and the area of the vascular which are in the first three floret of each middle spikelet were affected largely by water deficit. Water deficit affects the allocation and transportation of carbon assimilate by affecting the vascular structure significantly under water deficit, which induces a large number of carbon assimilates remaining in wheat ear.