Effects Of Drooping And Roll Traits Of Leaf On Photoinhibition And Senescence Process In Rice

Plants of a medium-maturity Indica rice variety Yangdao6, treated with leaf drooping degrees of5°,30°,50°and70°, as well as roll rates (leaf unfolding width/roll width) of1,1.42, and2.21, were used to investigate the effects of these two leaf orientations on photo-inhibition and the process of senescence.The influences of leaf drooping on photoinhibition and senescence process in rice can be described as:(1) In most period of grain filling, the variation of photosynthetically active radiation (PAR) showed a single peak curve, in3-4hours around noon time, the PAR were about1200-1500μmol.m-2s-1, which were higher than the light saturation point of rice; the air and leaf temperatures varied more gently, and the leaf temperatures of70°and50°drooping degree were markedly higher than the others.(2) the photoinhibition and photooxidation of70°drooping degree were the highest among all treatments, for the value of Fv/Fm decreased most rapidly under high light radiation, the generation rates of the superoxide anion and hydrogen peroxide was the fastest, the membrane lipid peroxidation level was the highest, and the activities of SOD and APX were the smallest; on the contrary, the effects of photoinhibition on leaves of5°and30°drooping degree were relatively smaller.(3) In early stage of grain filling,70°drooping degree treatment had greater advantage in photo synthetic rate, but with the progress of grain filling, its chlorophyll content and photosynthetic rate declined rapidly, resulting in less photosynthetic production and yield;30°and50°treatments may well balance between photoinhibition, light damage and photosynthetic rate, thus their senescence process were relatively gentle, and the mass production and yield were all7%higher than5°and70°treatments; Although the5°treatment had a high photosynthetic potential throughout the grain filling stage (it had highest Fv/Fm, indicating a highest quantum yield of photosynthetic system Ⅱ), it acquired the lowest dry matter production and yield, for the smaller leaf area for light Capture had limited the photosynthetic capacity.Influences of leaf roll on photoinhibition and senescence process in rice can be described as:(1) In most cases, temperatures of different rolled leaf surface were that flat leaf>semi-rolled leaf>rolled leaf.(2) In the entire grain filling period, flat leaf had the most serious photoinhibition and photo-oxidation, for the ratio of Fv/Fm was lower, and the generation rate of active oxygen was higher, while rolled leaves had certain advantages in photoinhibition alleviating and photosynthetic potential (Fv/Fm).(3) Despite their superiority in photosynthetic rate at presence of high PAR, the rolled leaf and semi-rolled leaf treatments had lower photosynthetic rate throughout the grain filling, and were4.8%and13.4%lower in dry mass production,2.4%and3.2%lower in yield than the flat leaf, due to the relatively smaller leaf area of light capture.