Ffects Of Water Defecit On Grain Number Of Wheat And Its Physiological Mechanism During Early Period

Drought is one of the main factors influencing wheat production.In recent years the frequency of winter and spring drought gradually increased and resulted in a lower grain number. Therefore, exploring the effect of water deficit on grain number per spike of wheat and its physiological mechanism has important significance. In this study, Yangmail3 (middle-panicle type) and Yumai49 (small-panicle type) were subjected to ten days water deficit at tillering stage and jointing stage in a pot experiment and drought set two levels of mild water deficit and severe water deficit. This study investigated the effect of water deficit on grain number per spike from growth and development, vascular bundle system, water metabolism, photosynthetic characteristics, antioxidant metabolism, carbon and nitrogen metabolism, and provided a theoretical basis of resilience yield cultivation of China’s wheat. The main results were as follows:1. Effects of water deficit on the yield and the growth of wheat during early period. The treatment of tillering and jointing mild water deficit increased the yield of two varieties and the treatment of severe water deficit significantly reduced the yield. The treatment of tillering and jointing mild water deficit has not significant effect on grain number of, the treatment of tillering severe water deficit reduced the grain number of main stem (the grain number of yangmail3 had not significant difference with the control) and tillering and jointing severe water deficit significantly reduced the grain number of main stem and tillers. The lower yield and grain number had something to do with the decrease of leaf area, dry weight and disruption of vascular tissue. The treatment of tillering and jointing severe water deficit significantly reduced the function leaves area and plant dry matter of two varieties, also affected the dry matter at late growth stage. The number of small vascular bundles, the size of big vascular bundles, catheter diameter and phloem area of main stem and tillers were significantly lower than the normal processing. It showed that severe water deficit during early period affected the plant dry matter and the transport of photosynthetic products to spike, and resulted in lower grain number and yield.2. Effects of water deficit on the physiological characteristics and antioxidant metabolism of wheat during_early period. The treatment of tillering and jointing mild water deficit had little Effects on various physiological indices of two varieties and could quickly restore after restoring the water supply. The treatment of severe water deficit significantly reduced the water potential and SPAD value; MDA content and O2- production rate of wheat also increased significantly, the two varieties had the same trend and it could not eliminate the influence of reactive oxygen species in time, although superoxide dismutase and peroxides activity was rapidly increasing, and cell membrane damage restrained the net photosynthetic rate. The decline of photosynthesis is the main reason of reducing of contract of product and the accumulation of wheat.3. Effects of water deficit on carbon and nitrogen metabolism of wheat during early period. The treatment of tillering and jointing water deficit affected the normal metabolism of carbon and nitrogen in plant of two varieties and the treatment of severe water deficit significantly increased the soluble sugar content of the wheat, at the same time, total nitrogen content of plant significantly decreased, the ratio of sugar to nitrogen significantly imbalanced and higher than the control treatment. Main stem and tillers have the same response. Sugar content and the nitrogen content of main stem is higher than the two tillers, at the same time the impact of water deficit on main stem is larger than the tillers and jointing stage is more significant. Water deficit during early period also affected the normal carbon and nitrogen metabolism of two varieties at booting stage, and soluble sugar content, total nitrogen and ratio of sugar to nitrogen did not restore to the normal level. Differentiation and development of floret is closely related to carbon and nitrogen metabolism and insufficient supply of carbon and nitrogen nutrition and the imbalance of ratio of sugar to nitrogen caused by severe water deficit is the main reason leading to lower grain number.In summary, the treatment of water deficit reduced the water potential, the chlorophyll content, stomata conductance as well as the excess MDA and reactive oxygen species damage the cell membrane. As a result, the water deficit declined the photosynthetic rate and affected the synthesis of photosynthetic products. Leaf area and plant dry weight was significantly lower than the control treatment. Water deficit increased the soluble sugar content, but also reduced the absorption and transport of nitrogen so the total nitrogen content of plant significantly decreased, the ratio of sugar to nitrogen imbalanced. The shorten of spike differentiation process and the short supply of carbon and nitrogen nutrition seriously affected the normal spike differentiation and reduced the grain number of wheat.