| Pot-cultivation experiment was conducted to explore effects of middling water stress on growth, photosynthesis characteristics, active oxygen metabolism, and yield of different drought-tolerance-type maize. The correlation between the drought-tolerance of hybrids and that of their own parents was also researched. This experiment included two factors: variety and content of water in soil. Three maize hybrids and their own parents were selected in this experiment and water stress was performed in the whole life of maize. The main results were as follows:1. The growth and organ forming were significantly affected by water stress, and the effects were obviously different between different hybrids and their own parents. The function period of leaves was shortened, the plant height and stem diameter were reduced, and the anthesis and silking date, especially the silking date, were postponed under water stress. Therefore the anthesis-to-silking interval (ASI) was prolonged, which caused asynchrony between pollen shed and silking. The influence of water stress was larger on Yedan 13 than on the other two hybrids, and it was the least on Yedan 2 in term of growth and organ forming, while the drought-tolerance of Yedan 2 was bigger than that of Yuyu 22, whose drought-tolerance was larger than Yedan 13. The sensitivity of D340 and 478 who were the parents of Yedan 13 was higher than that of the parents of Yuyu 22 and Yedan 2. It showed that their parents determined the difference of drought -tolerance between hybrids.2. Water stress cumbered dry matter accumulation of maize. The dry weight of both root and shoot was decreased by waster stress, especially the dry weight of shoot, and therefore the root/shoot rate was increased in the whole life of maize. The order of the influence of water stress on dry matter accumulation was: Yedan 13> Yuyu 22> Yedan 2, while the drought-tolerance order is: Yedan 2> Yuyu 22> Yedan 13.3. The content of chlorophyll, especially that of chlorophyll a, was decreased by water stress in maize leaves. Water stress decreased the net photosynthesis rate (Pn) and transpiration rate (Tr), and also lowered the peak of the diurnal variations of photosynthesis rate and transpiration rate in silking stage. At the same time, water stress changed the diurnal variations of fluorescence parameters. Under water stress, the chlorophyll fluorescence parameters Fv/Fm, ΦPSⅡ and qP decreased, while NPQ increased, and this trend is more obvious from 10:00 to 14:00. weak drought-tolerance-type maize, Yedan 13 and Dan 340, manifested photosynthetic midday depression under water stress. Yedan 2, Yuyu 22 and their own parents were affected slightly by the water stress in terms of the photosynthesis parameters and fluorescence parameters when compared with Yedan 13 and its parents.4. Under water stress the superoxide production rate and the content of H2O2 in maize leaves were increased in the whole growth stage, and the activities of SOD, CAT and ASP and the content of ASA were increased in the early period, while all of them were decreased in the late period. The content of MDA in leaves was increased by water stress in the whole growth stage. These results suggested that the ability of maize to scavenge Active Oxygen Species (AOS) was decreased rapidly in the late period of growth, the accumulation of AOS was increased, and the damage of cell membrane system was aggravated by water stress. The superoxide production rate and the content of H2O2 in leaves of D340 and 478 were increased more significantly than others. The activity of SOD,CAT,ASP and the content of ASA were decreased more obviously in the later growth stage of D340 and 478. This showed D340 and 478 were weak drought-tolerance. So did theirs hybrids, Yedan 13. 5. The relation between AOS and AOS scavengers indicated that the rate of the activities or content of AOS scavengers under water stress against normal water irrigation (WS/CK) was very important to remain the balance of active oxygen metabolism. To SOD, the high ratio of WS/CK in t...
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