Study On The Decline Process Of Main Photosynthetic Parameters In Rice Flag Leaf

Using two varieties of Oryza Sativa L. Sanyou63 and Xieyou9308 as experimental materials , the turnover point from reversible decline phase to irreversible decline phase of photosynthetic function was studied systemically in rice flag leaf. The results were as follow:It was different that the days after flag leaf full expansion of each photosynthetic parameter declining from full expansion of flag leaf to 50%. In Shanyou63 flag leaf, the change sequence of these photosynthetic parameters was: stomatal conductance, content of light-harvesting protein complex(LHCP), apparent photosynthetic rate, content of chlorophyll, content of PSII core protein, content of Rubisco; in Xieyou9308, the sequence was: stomatal conductance, content of LUCP, apparent photosynthetic rate, content of PSII core protein, content of chlorophyll, content of Rubisco. Stomatal conductance declined earlier obviously than the other photosynthetic parameters done in two varieties.To identify the turnover point from reversible decline phase to irreversible decline phase of photosynthetic function, CTKs hormone that could delay the senescence of leaf was used. The results were as follow:In the experiment of field(in vivo), the decreasing sequence of several photosynthetic parameters was: A, in Shanyou63, stomatal conductance, apparent photosynthetic rate, content of LHCP, content of PSII core protein, content of Rubisco, content of chlorophyll; B, in Xieyou9308, stomatal conductance, content of LHCP, content of PSII core protein, apparent photosynthetic rate, content of Rubisco, content of chlorophyll. The turnover point of stomatal conductance was earlier obviously than that of the other photosynthetic parameters in two varieties. So it is probably a key from reversible decline phase to irreversible decline phase of photosynthetic function, and maybe a initial factor lead to the irreversible photosynthetic function decline in rice(Shanyou63) flag leaf.In the experiment of dark-induced (in vitro), however, the results were distinct. There was no the turnover point of photosynthetic function decline during leaf life span, i.e., 6-BA could always delay the senescence of flag leaf, which showed the senescence mechanism of detached leaf in dark was different with that of attached leaf in natural.Early-declining and irreversible senescence of stomatal conductance were key reason that lead to irreversible senescence of photosynthetic rate in early-declining rice variation(Shanyou63). But these weren't key reason in not-early-declining variation(Xieyou9308).