ON THE EFFECT OF SOIL DROUGHT DURING THE PERIOD FROM THE END OF FLOWERING TO RIPENING ON THE GRAIN FILLING AND MATTER TRANSLOCATION IN THE WHEAT PLANT
Wang Wan-li;Lin Zhi-ping;Zhang Xiu-ying;Wu Ya-hua Shanghai Institute of Plant Physiology,Academia Sinica
The effect of soil drought after flowering on the grain filling and matter tran- slocation in the wheat plant was investigated in the phytotron. The principal findings are as follows: 1. During the time of soil drought, the younger organs in the upper part of the wheat plant, such as the ear, the upper part of the stem, the flag-leaf sheath and the flag-leaf blade, were better supplied with water than the older organs. As a result, these younger organs Were able to carry on their physiological functions for a relatively longer time. 2. Soil drought reduced the photosynthetic capacity of the wheat plant both by the direct effect of water deficit and by the accelerated senescence of the green photosynthetic organs. The shortage of assimilates for the grains was the main cause of decrease in the yield. The yield of plants stressed in the earlier half of grain- filling stage showed a remarkable decrease, as these plants had lost more photosyn- thetic products. However, the mobilization of the reserves for grain-filling in the vegetative parts of the plant was intensified under drought. 3. Matter translocation in the sieve tubes was not inhibited under moderate and even almost severe water stress. On the contrary, because of the accelerated senescence, the nitrogen and phosphorus in the leaves and the carbohydrate re- serves in the stems of the stressed plants were exported more rapidly. As compared with the control, about the same amount of nitrogen was transported to the grains per ear at full ripening, but the amount of phosphorus that had been transported to the grain per ear was reduced significantly under drought. The protective adaptation of the wheat plant to soil drought after flowering was also discussed.