| The formation of rice quality is not only affected by heredity, but also by environmental condition. The different panicle weight types of rice varieties have the higher grain yield physiology and structural characteristics, which were hereditary basic suitable to the different panicle weight types of rice varieties, but how environmental factors affect the quality of the different panicle weight types of rice varieties is never reported up to now. Therefore, nine hybrid midseason-rice varieties out of three panicle weight types, heavy panicle type (HPTR), medium panicle type (MPTR) and light panicle type of rice (LPTR), were selected to be cultivated in the six major ecological rice zones of Sichuan Basin, and the effect of meteorological factors in the six major ecological rice zones on the quality of the different panicle weight types of rice varieties and the degrees of the effect were studied. And based on this study characteristics of physiology and biochemistry of formation of rice quality of the different panicle weight types of rice varieties by adopting artificially controlling temperature and light were studied in order to reveal the effect of temperature and light on formation of rice quality of the different panicle weight types of rice and physiological mechanism .The major results were as follows:1. The path analysis and the contribution of determinant coefficient (R2) of meteorological elements to the quality of the different panicle weight types of rice varieties were studied. The results indicated that temperature was the most important meteorological factor considering its effect upon rice quality among meteorological elements, in which main meteorological factors were daily mean maximum air temperature affecting the rate of head rice, chalky rice and chalkiness of HPTR varieties, daily mean minimum airtemperature affecting gel consistency of HPTR varieties, and daily mean air temperature affecting amylase content and protein content of HPTR varieties respectively. But the correlation between the gelatinization temperature of HPTR varieties and meteorological factors was insignificant. However, daily mean minimum air temperature was the most important meteorological factor considering its effect upon the rate of head rice, chalky rice, chalkiness, the gelatinization temperature and amylase content of MPTR varieties, but daily mean minimum air temperature was main meteorological factor affecting protein content of MPTR varieties, and the difference between the gel consistency of MPTR varieties and meteorological elements is insignificant. Daily mean minimumair temperature was the most important meteorological factor considering its effect upon the rate of head rice, chalky rice, chalkiness and protein content of the LPTR varieties ,and main meteorological factor among meteorological elements were daily mean sunshine affecting gel consistency of LPTR varieties and daily mean maximumair temperature affecting amylase content of LPTR varieties respectivly, and the difference between the gelatinization temperature of LPTR varieties and meteorological elements was insignificant. To sum up, the effect of temperature onthe rice quality was obviously different among the different panicle weight types of rice varieties in ecological rice zones of Sichuan Basin, specially, daily mean air temperature was the most important meteorological factor affecting rice quality traits of the different panicle weight types of rice varieties, the second was daily mean minimum air temperature and daily mean maximum air temperature, and daily mean sunshine was less important, but daily mean temperature difference and daily mean relative humidity hardly affected rice quality of the different panicle weight types ofrice.2. After heading, The flag leaf of different panicle weight types of medium India hybrid rice were cultured in two plots at different temperatures. Analysis was conducted on the photosynthetic rate, Rubisco content, Rubisco activity, whole leaf protein, O-2 generation rate, MDA content, and the activity of enzymes involving cell protective enzymes (SOD, CAT,POD) of the flag leaf. The results indicated that that high temperature promoted lower the photosynthetic rate, Rubisco content, Rubisco activity and higher O-2 generation rate, MDA content with the activity of cell protective enzymes weakening earlier; as a result,the senescent process of the flag leaf appeared more than 10 days in advance with respect to normal temperature. Analyses of whole leaf protein showed the high temperature promoted the large subunit (Lsu) of Rubisco and pigment protein (P) greatly to decrease during the medium and last period from full heading to maturity of hybrid midseason-rice, and the high temperature damaged the functional and structural protein of the flag leaf to relative photosynthesis, and the above is important inside reason that the photosynthetic function of the flag leaf decreased and senesced quickly. Considering the senescent process resulting from high temperature of the flag leaf of three panicle weight types during the period after heading, effect of high temperature on the light panicle type of rice is great comparatively followed by effect of high temperature on the medium panicle type of rice, effect of high temperature on the heavy panicle type of rice is relatively poor. The difference of senescent physiological metabolism resulting from high temperature among different panicle weight types was "source" basis of HPTR varieties, whose rice quality traits of the rate of head rice, chalkiness and so on was of better performance than MPTR and LPTR varieties.3. The leaves of different panicle weight types of medium India hybrid rice were cultured in growth chamber at different temperatures. Analysis was conducted on the activity of peroxidase(POD), catalase(CAT) and superoxide dismutase (SOD ) , and their isozymes performance in the leaves. The results indicated that there was an increasing tendency in the activity of protective enzymes (POD, CAT, SOD) of the leaves of HPTR varieties under temperature of 32℃ , 29 ℃ and 24 ℃ ,but there was a decreasing tendency of the activity of protective enzymes in MPTR and LPTR varieties. There were no significant differences between the isozymes pattern of SOD among different panicle weight types of rice varieties, and isozymes expression of SOD weakened with increasing temperature. There were great differences between the isozymes performance of CAT of the different panicle weight type of rice varieties. Especially under high temperature stress (38℃), the CAT isozymes pattern "C-1" of the middle-panicle type and light-panicle type of rice disappeared, however, HPTR varieties showed a new isozymes pattern of CAT "C-0". Therefore, it is concluded that different panicle weight types of rice varieties have possibly different response mechanism to high temperature, this conclusion is the main enzyme basis of explaining thedifference of temperature condition affecting the rice quality of different panicle weight types of rice varieties.4. Rice starch grain development and endosperm transparency were not only controlled by heredity but also affected by environmental temperature. The quality of the different panicle weight types of rice varieties was mainly controlled by heredity at normal temperature and obviously affected by temperature at high temperature when the cultivated rice was the same. The results indicated that the water content was lower, the Q enzyme activity and starch content were reached the peak at 5 and 10 days earlier respectively under high temperature than under normal temperature. An abnormal change of soluble sugar content under high temperature was found too. The significant differences of starch grain morphological development in the central part of grain endosperm were found. LPTR varieties have the best rice quality followed by MPTR varieties, and the quality of HPTR varieties had relatively poor performance under normal temperature. But their metabolism and grain morphological development had opposite performance under normal temperature as compared with under high temperature. In conclusion, HPTR varieties had the better adapt ability to high temperature than MPTR varieties and HPTR varieties.5. The results showed that single starch grains were developed to compound amyloplasts of elliptic or ball shape and smooth edge under normal temperature, and then the compound amyloplasts were developed to polyhedral shape followed by the amyloplasts structure of the compact arrangement. The development time lasted 25 to 30 days. Single starch grains were developed to compound amyloplasts of elliptic shape, loose arrangement and great difference in size under high temperature, and then the compound amyloplasts became " transitional compound amyloplasts" followed by the smooth compound amyloplasts structure of "plum blossom shape", The development time only lasted 20 days, and was shortened about 5 to 10 days compared with normal temperature. Viewing the structure of compound amyloplasts, the former was compact arrangement and its endosperm transparency was high compared with the latter. The amyloplast morphological development and the endosperm transparency foundation varied with the temperature and appeared two different process and models, which wasn't systematically reported up to now. Meanwhile, considering the chalkiness formation and the endosperm transparencyfoundation, the chalkiness of LPTR varieties uneasily formed and their endosperm transparency was higher than MPTR and HPTR varieties under normal temperature. However, the chalkiness formation of LPTR varieties was easier than MPTR varieties followed by HPTR varieties under high temperature. The decreasing tendency of their endosperm transparency was lined in the following order: LPTR varieties >MPTR varieties > HPTR varieties. |
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