Study On Characteristics Of Chlorophyll A Fluorescence And Photosynthetic Material Production Of High Yield Japonica Rice

Photosynthesis is the basis for the formation of dry matter.The yield of rice ultimately depends on the photosynthetic capacity from heading to maturity period.Increasing the net photosynthetic rate and photosynthetic efficiency of leaves is an important direction for increasing yield in the future.In this study,typical high yield japonica rice in Liaoning area,Shennong 265,Shennong 9903 and Beijing 3 were selected as test breeds,characteristics of chlorophyll a fluorescence and gas exchange in flag leaves and photosynthetic material production were studied,in order to provide reference for breed improvement of japonica rice and grain bumper.The main results are as follows:1.The net photosynthetic rate（Pn）of flag leaves of Shennong 265,Shennong 9903 and Beijing 3 was maintained at a high level among the 0th to 30th days after flag leaves full expansion,which was beneficial to dry matter accumulation and grain filling.Pn of flag leaves of Beijing 3 was significantly higher than that of Shennong 265 and Shennong 9903 on the 40th day after flag leaves full expansion.The Pn,stomatal conductance（Gs）and intercellular CO₂ concentration（Ci）in flag leaves of tested rice decreased significantly after the 30th day after flag leaves full expansion,which indicated that stomatal factors lead to the reduction of Pn.The Ci in flag leaves was significantly increased on 50th day after flag leaves full expansion,which indicated that non-stomatal factors lead to the decline of Pn.2.The Oxygenation complex in flag leaves of Shennong 9903 and Beijing 3 was damaged since the 40th day after flag leaves full expansion,and the Oxygenation complex of Shennong 265 damaged significantly on the 50th day after flag leaves full expansion.Shennong 265,Shennong 9903 and Beijing 3 fluorescence at J point（2ms）in flag leaves increased slowly since the 30th day afeter flag leaves full expansion,the quantum yield for electron transport（?Eo）and the efficiency for electron transport（?o）significantly decreased among the 30th to 50th days after flag leaves full expansion,which means the electron transfer from Q_A to Q_B was inhibited.The pool sizes at the end of accept side of PSI in flag leaves of the three tested rice breeds decreased after the 30th day after flag leaves full expansion,and the quantum yield for reduction of the end electron acceptors at the PSI acceptor side（?Ro）decreased at the same time.The dissipation flux（DIo/RC）per reaction center increased significantly among the 40th to 50th days after flag leaves full expansion,this is,which plays a protactive role in reaction center.Performance index PI_abs and PI_tot,which means energy conversation from exciton to the reduction of intersystem electron acceptors and to the reduction of PSI end acceptors,in flag leaves of tested varities decreased significantly since the 30th day after flag leaves full expansion,and the PI_tot decreased greaterly than PI_abs.The result indicating that both PSII and PSI were damaged,but PSI was more damaged.3.The extravasation conductivity,malondialdehyde（MDA）content,production rate of superoxide anion radical（O₂?）and hydrogen peroxide（H₂O₂）content in flag leaves of tested rice breeds were increased gradually after flag leaves full expansion.The antioxidant enzyme system in flag leaves of tested rice can effectively purge active oxygen among the 0th to 40th days after flag leaves full expansion,which is beneficial to the photosynthesis of flag leaves of tested rice.4.The yield of three tested japonica rice breeds showed that Beijing 3>Shennong 265>Shennong 9903,because that the number of grains per spike of Beijing 3 was significantly higher than that of Shennong 265 and Shennong 9903.The ratio of dry matter distribution in rice population and single stem of the ear of grain was large from milk-ripening to maturing period,and the photosynthetic assimilates were more used in grain filling.The dry matter of single stem of Shennong 265 and Shennong 9903 kept high output and transport from heading to milk-ripening period,but the dry matter of single stem of Beijing 3 had no output and transport.