The Characteristics Of Adaptation To Light Stress And Conversion For Light Energy In Super Hybrid Rice

45 genotypes from rice germplasm were identified under photooxidation and shading condition and divided into four basic types: (l)cultivars tolerant to both photooxidation and shading,(2) cultivars tolerant to photooxidation but sensitive to shading,(3)cultivars tolerant to shading but sensitive to photooxidation, and (4) cultivars sensitive to photooxidation and shading.A comparative study of photosynthetic characteristics between cultivars c.v. differing photooxidation and shading sentivity from Wuyujing 3 is tolerant and Xiangxian is sensitive showed that the PS II and Rubisco activities of the tolerant variety (Wuyugeng) were relatively stable under photooxidation conditions,which is related to the high maintaining activity of Dl protien on PS II and high induced activity of C4 PEPC. And the Rubisco activity and the Rubisco BP content of Wuyugeng were also relatively stable under shading conditions, which concerned with less change of photosynthetic rate, photosynthetic productivity and yield.The above investigation will provide a necessary technique and physiological basis for breeding.Six rice varieties with high yield which were Indica hybrid Shanyou 63, Japonica 9516,intersubspeicific hybrid Peiai 64S/E32,Peiai64 S/9311 ,X07S/Zihui 100,Guangyou 881, were used to study the diurnal variation in chlorophyll fluorescence parameters and the trait tolerant to photooxidation and shading in rice leaves in boot stage. The results showed that the diurnal variation of PS II primarily chemical efficiency (Fv/Fm), quantum yield of PS II linear electron(OPS II) and estimated electron transport rate (ETR) in 6 rice varieties related to light intensity. Under strong light intensity at noon, the functional photosystem II reaction centers were decreased ,which resulted in conspicuous photoinhibition in rice varieties. Fv/Fm in rice varieties tolerant to high light decresed less at noon and showed a lighter photoinhibition. As compared with those in natural light conditions, the diurnal variation of chlorophyll fluorescence after shading treatment decreased more. The changes in Fv/Fm , OPS II and ETR in rice varieties tolerant to low light intensity were less.Chlorophyll fluorescence parameters of leaves in intersubspeicific hybrid Peiai 64S/E32 after shading treatment approached to those in natural light conditions, which proved to be the tolerant variety to photooxidation and shading (wide ranges of light intensities). The statistical analysis showed that ETR and Fv/Fm in rice leaves may be the physiological indexes associated with the stability of yield in rice varieties. This research will provide the physiological indexes and basis on rice breeding for stable and high yield.The mentioned aboved rice varieties were also used to study the changes of chlorophyll content, the photosynthetic response to light intensity and temperature, chlorophyll fluorescence characteristics and membrane lipid peroxidation performance of their flag leaves at the later stage of development under natural conditions of Nanjing . The results were as follows: Fv/Fm (primarily PS II chemical efficiency), O PS II (quantum yield of PS II linear electron transport ), Electron Transfer Rate (ETR) in these rice varieties decreased with their decrease of chlorophyll content during this period .This kind of impediment to energy conversing induced the excessive energy transfer on the reduction side of PS I , then accumulate O2~ ,therefore produced membrane lipid peroxidation and the accumulation of malondialdehyde(MDA), which resulted in the destroy of photosynthetic pigment and membrane and consequently,appeared photooxidation and early aging. This phenomenon is variable conspicuously in different rice varieties. Under natural condition of Nanjing, Fv/Fm, OPS II,ETR and qP in japonica rice variety 9516 tolerant to photooxidation decreased less and exhibited the stable conversion capacity of light energy, which was not easy to appear early aging consequently exhibiting the higher seed-setting rate. While Fv/Fm, OPS II,ETR and qP in indica h...