Chlorophyll Fluorescence and Membrane Lipid Peroxidation in the Flag Leaves of Different High Yield Rice Variety at Late Stage of Development Under Natural Condition

With indica ( Oryza sativa L.) hybrid Shanyou 63 as control, the hybrid rice varieties including Peiai 64S/E32, Peiai 64S/9311, X07S/Zihui 100, Guangyou 881 and japonica 9516 were used to study changes of chlorophyll content, photosynthetic response to light intensity and temperature, chlorophyll fluorescence characteristics and membrane lipid peroxidation in their flag leaves at the late stage of development under natural conditions in Nanjing. The results were as follows:. primary photochemical efficiency of PS II ( F-v / F-m), quantum yield of linear electron transport of PS II (phi(PSII)), electron transfer rate (ETR) in these rice varieties decreased with their decrease of chlorophyll content during this period. This kind of impediment to energy conversion induced the transfer of excessive energy to the reducing side of PS I, hence the accumulation of O-2(radical anion) and peroxidation of membrane lipid, and resulting in the accumulation of malondialdehyde (MDA), that is the destroys of photosynthetic pigments and membranes and the consequent, premature senescence. This phenomenon is variable conspicuously in different rice varieties. Under natural condition in Nanjing, F-v/F-m, phi(PSII), ETR and quenching coefficient ( qP) in japonica 9516 tolerant to photooxidation decreased less and the conversion capacity of light energy was stable, premature senescence was unlikely, and consequently the seed-setting rate was higher. While F-v/F-m, phi(PSII), ETR and photochemical qP in Shanyou 63 sensitive to photooxidation decreased more and therefore premature senescence was easy to happen, thus the seed-setting rate and yield were all reduced. The tolerance to photooxidation and premature senescence in other hybrids derived from typical two line or three line crossing laid in the middle. From the rice breeding for super-high-yield, on the basis of the good plant-type of current rice, considering both hybrid vigor and the prevention premature senescence, it would be a notable strategy to use japonica maternal line or maternal. lines with some japonica genotype as the sterile lines in rice breeding.

Effects of Short-term High Temperature Stress on the Photosynthesis of Potato in Different Growth Stages

[Objective] The aim was to study the effects of short-term high temperature stress on the photosynthesis of potato in different growth stages. [Method] Choosing powder potato named Longshu No.3 widely cultivated in Ningxia as test material,the changes of stomata conductance （Gs）,transpiration rate （Tr） and CO2 concentration difference between internal and external leaf chamber,net photosynthetic rate （Pn） and photosynthetic water use efficiency （WUE） in different growth stages under short-term high temperature were analyzed. [Result] During seedling stage,the hysteretic nature of net photosynthetic rate and CO2 concentration difference between internal and external leaf chamber of potato could be found under high temperature stress,while the change trends of stomata conductance and transpiration rate under high temperature stress were consistent to that at normal temperature,but stomata conductance and transpiration rate were higher than those at normal temperature,and CO2 concentration difference between internal and external leaf chamber affected net photosynthetic rate most obviously. During branching stage,the change trends of net photosynthetic rate,CO2 concentration difference between internal and external leaf chamber,stomata conductance and transpiration rate under high temperature stress and normal temperature were similar,but they changed abruptly and reached peak value at noon under high temperature stress,while there existed consistent variation of water use efficiency under high temperature stress and at normal temperature,and CO2 concentration difference between internal and external leaf chamber also affected net photosynthetic rate most greatly,next came transpiration rate. [Conclusion] High temperature stress affected the photosynthesis of potato in different growth stages,and it was more obvious during branching stage than seedling stage,while CO2 concentration difference between internal and external leaf chamber had the most important influence on net photosynthetic rate.