| To study formation mechanism of grains weight and the effects of environmental condition on grain weight during booting stage and grain filling period in rice, pot experiment and field experiment were carried out with two japonica varieties, Ruyu 1 (27g/1000-grain weight) and Qianchonglang 2 (19g/1000-grain weight). There were compared with grain filling characteristics, physiological characteristics of glume, stuctures of glume, pericarp and endosperm in growth and development of glume and caryopsis between two cultivars. The effect of shading, high-temperature or low-temperature stress on grain weight were also studied. The major results were as follows:1. In the process of glume development, length, width, area and dry weight of glume tested cultivars were in order of superior grains > middle grains > inferior grains, and the development process of glumes in the different positions within a panicle presented S-curve, but there was significant difference between two japonica varieties. At the mature stage, length, width, thickness, and weight of grains and brown rice ,and grain plumpness were in order of superior grains > middle grains > inferior grains, and there were very significantly positive correlation between grain length, grain width, grain thickness and grain plumpness with grain weight.Glume length and width would increase with internal cells of glume elongation, the time of the faster rate of glume synchronized internal cells of glume. Compared with Qianchonglang 2, intermal cell of Runyu 1 is the larger, and there is a closely relationship between the epidermal size and glume. There was not significant difference between number of epidermal cell in two varieties.2. It was major difference that exited two tested cultivars of grain filling rate or different positions within a panicle. Grain filling rate for superior grains of tested cultivars started early, and average grain filling rate and maximum grain filling rate were the highest, and followed by middle grains, inferior grains in the minimum. Compared with Qianchonglang 2, the average and maximum filling rate of superior grain, middle grain and inferior grain in Runyu 1 were the higher, and filling time of Runyu 1 was the longer and grain plumpness of Runyu 1 was the higher, but grain filling of Runyu 1 started the later. The average filling rate of Qianchonglang 2 was higher, and lasting time of filling was shorter than that of Runyu 1 during the primary stage of filling. The average filling rate of Runyu 1 exceeded Qianchonglang 2 in middle filling stage and was large in late filling stage. Compared with caryopsis of Runyu 1, the caryopsis of Qianchonglang 2 grew faster , accumulated more dry marerials and had faster proliferation of endosperm cells during the primary stage of growth. However, it was just the opposite in the later stage of development. Compared with Qianchonglang 2, the pericarp of Runyu 1 developed more vigorously and its cells were with longer life cycle.3. The chlorophyll content of glumes at different positions of panicle showed the changes of superior>middle>inferior at heading stage, and the higher chlorophyll content, the earlier filling starting, and the average filling rate was also larger at earlier stage. Qianchonglang 2 showed faster decline of chlorophyll content of glumes in different parts of panicle after flowering, and that of Runyu 1 decreased slowly.The chlorophyll content of different parts glume of Runyu 1 was significantly higher than Qianchonglang 2 at late filling stage.The Runyu 1 had the higher chlorophyll content for top-three leaves compared to Qianchonglang 2 in late filling stage, and the former still maintained a high net photosynthetic rate(NPR), and Qianchonglang 2 had only a higher NPR and chlorophyll content for the flag leaf, but chlorophyll content and NPR were significantly reduced for the second and third leaf from the top.4. The emperature stress significantly reduced plant height, area of the top-three leaves and total dry matter accumulation of the test varieties at booting stage, the decreased range of the plant height, leaf area and dry matter accumulation under stress was the largest in leaf-remainder 2.0 time, and which was the smallest in leaf-remainder 0.0 time. Compared with the control, the tested variety under high or low temperature stress at the filling stage showed small proportion of dry matter distribution in the stem and sheath and a larger proportion in panicle, the dry matter exportation rate of stem and sheath were higher. However, the exportation rate of stem and sheath were lower than that of control under highor low temperature stress at the booting stage.5 The panicle and primary length, primary and secondary branch numbers, the number of grains per panicle, grain density and seed-setting rate were reduced significantly by low or high temperature treatment during booting stage. It was at leaf-remainder 1.0 time that there had the greatest effects on the panicle characters after low or high temperature stress. Low or high temperature stress had little effect on the secondary branches number and grain number, the seed-setting rate, and primary length of upper part per panicle, and had little effect on those of the middle and lower parts per panicle during booting stage, and there was a significant difference between two tested varieties. Low or high temperature stress had little effect on the seed-setting rate, and had little effect on the secondary branches number and grain number, and primary length during filling stage, and there was no difference between two tested varieties.6. The high or low temperature stress resulted in obvious decrement of the grain and brown rice length, width, area, volume ,thickness and weight compared with CK (no low temperature treatments) during booting stage, and there was a significant difference among different positions grain. Compared with stress at booting stage, high or low temperature stress had little effect on grain characters at filling stage, and they had large effect on brown rice characters at filling stage. The weights of superior grains were reduced obviously by low or high temperature at leaf-remainder 1.0 time, and the inferior grains were at leaf-remainder 0 time.7. As for Qianchonglang 2, high or low temperature stress decreased the grain plumpness and glume sizes of different positions at booting stage, and the stress had little effect on grain plumpness at filling stage. High or low temperature stress had little effect on grain plumpness at booting stage ,and they had large effect on grain plumpness at filling stage.8. he high or low temperature stress lowered the activities of SOD and POD , and enhanced MDA content and the content of chlorophyll in the flag leaf. Compared with CK, the content of soluble sugar in the flag leaf was lower after high temperature stress, and the content was higher after low temperature stress. The rice plant harmed were placed under nature condition after some time, and it returned to normal growth and development by depending on it's own physiological mechanism regulation.9. After low temperature stress, the change rule of glume sizes of different treatment at full heading stage was similar to the change rule of glume sizes at maturity stage. Change rule of average cell sizes and vascular bundle area of glume was consistent with glume sizes among different treatment. Glume length and width will increase with epidermal, fibre and parenchymatous cells of glume elongation. Low temperature stress had little effect on cell numbers of glume ,and had large effect on cell sizes.10. The weak light during booting stage increased plant height, leaf area of the top three leaves and reduced dry matter accumulation of two japonica rice varieties compared with CK (no shading treatments). Compared with CK, the weak light made dry matter partition ratio of stem and sheath reduced, and made the dry matter exportation rate of stem and sheath increased. However, the result was opposite at the booting stage.11. Panicle length, primary length, secondary branch numbers, and grain density were reduced significantly by shading treatment during booting stage. It was at leaf-remainder 1.0 time that had the greatest effects on the panicle characters after shading treatment. Low temperature harm had little effect on primary branches number ,and had large effect on secondary branches number.12. The weak light during booting stage resulted in obvious decrement of the grain and brown rice length, width, area, volume and thiceness compared with CK (no low temperature treatments), and there was a significant difference among different positions grain. Compared with weak light at filling period, weak light at booting stage had a larger effect on grain characters. It was at filling stage that thickness of brown rice of two varieties was decreased significantly by weak light13. Grain plumpness of Qianchonglang 2 was decreased at different positions by shading treatment during booting stage and grain filling period. As for Runyu 1, change range of grain plumpness at different positions was little. Weak light of different stage made the 1000-grain and brown rice weight decreased. It was at leaf-remainder 1.0 time that there had the greatest effects on the 1000-grain and bulled rice weight. |
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