| Leaf colour mutants are ideal materials for the studies of photosynthesis system structure and function, chlorophyll biosynthesis and regulation mechanism.They also have very wide application in hybrid rice as the trait marker. It is significant and valuable to study there photosynthetic mechanism as well as physiological biochemistry characteristic.Two leaf color mutants, ygl5 and pygll,were identified from the progeny of Jinhui 10, which was an excellent restorer line bred in the Rice Research Institute of Southwest University, treated with EMS.All leaf color of ygl5 in the whole growth period was yellow and pygll's was greenish, these two characters had stable genetic. Compared with the wild type, these two mutants had lower height. In this research, the synthesis of chlorophyll precursors, the photosynthetic characteristics as well as physiological biochemical characteristics of mutants were investigated, Jinhui 10 as an control. The main results are as follows:1.Synthesis of chlorophyll precursors of ygl5 and pygll were blocked at synthesis of uroporphyrinogenâ…¢from porphobilinogen, it might be related to the abnormal activity of porphobilinogen deaminase and uroporphyrinogen synthase III.Multiple analysis indicated that, the difference of protochlorophyllide content between ygl5 and pygll were not achieve significant level, but the light conversion efficiency of protochlorophyllide showed that, ygl5 generate the least chlorophyllide, and the consumption as well as the consumption rate of chlorophyllide for synthesis of chlorophyll a were least, it might be one important reason for the lowest chlorophyll content of ygl5.Compared with ygl5, pygll had higher light conversion efficiency of protochlorophyllide, generated higher content of chlorophyll a. It was supposed that the abnormal activity of chlorophyllide a oxygenase(CAO) would be the main reason leading to the large degree of decrease in chlorophyll b content.2.Compared with Jinhui 10, ygl5 and pygll were chlorophyll-deficient mutants, the total chlorophyll content respectively decreased by 67.51% and 51.07%. The chlorophyll b content of pygll decreased by 98.97%, which showed that, pygll was a chlorophyll b-deficient mutant, and ygl5 was a total chlorophyll-deficient mutant.3.Chloroplast ultrastructure of these two mutants showed that, compared with Jinhui 10, the number of grana and grana lamella reduced, stacking arrangement of grana was loose, had larger electronic transparency.4. Compared with Jinhui 10, net photosynthetic rate, light compensation point, light saturation point, apparent quantum yield and carboxylation efficiency were higher in mutants, with lower CO2 compensation point and CO2 saturation point. Diurnal variation of photosynthesis showed that, mutants had better tolerance to strong light and lower photoinhibition. In low-light conditions, mutants had lower net photosynthetic rate, this is consistent with the results of light response curve.5.Chlorophyll fluorescence parameters showed that mutants had higher PSII activities, primary light energy conversion efficiency as well as actual quantum yield of photochemical.6. The malondialdehyde(MDA) content and relative conductivity of wild type and mutants continued to increase during the growth period. Compared with Jinhui 10, the MDA content and relative conductivity of ygl5 was lower, but the growth range of MDA content was higher. The changes of soluble sugar and soluble protein content in ygl5 was consistent with that of Jinhui 10 and had a lower degrees of decrease, with higher superoxide dismutase(SOD) and peroxidase(POD) activity. This indicated that the resistance of ygl5 did not reduce due to the decrease of chlorophyll content, but remained at a high level. pygll had the highest growth range, meanwhile its soluble sugar and soluble protein content were at a low level, it was showed that the generated reactive oxygen species and free radicals can not be removed by the increase in superoxide SOD and POD activity,cell membrane in pygll suffered larger degrees of damage.
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