Effect Of Light Intensity On Photosynthetic Characteristics Of Super Rice And Conventional Rice In Seeding Stage

Rice is an important crop which is the staple food of half the world's population.The promotion of hybrid rice has increased the yield of rice by 10%.However,in the field production of super hybrid rice,due to poor growth conditions and improper field management measures,it is difficult to realize its super high yield.In the middle and lower reaches of the Yangtze river in China,because of the rainy weather in summer,the low light environment inhibit rice growth,and the production decreased.Therefore,studying the photosynthetic characteristics of super rice under low light stress,it is important to realize the mechanism of production formation in super rice.A hydroponic experiment in the greenhouse with simulated low light stress induced by different illumination intensity was conducted in two rice cultivars,including super hybrid indica(‘Guodao 6' and‘Liangyou 084')and conventional indica('Yangdao 6'),which aims to study the effects of low light stress on leaf photosynthetic characteristics and chloroplast development.The mechanism of photosynthetic process of super rice and conventional rice in response to low light stress was discussed,and the difference of chloroplast structure between super rice and conventional rice was compared from the perspective of chloroplast development.The main results are as follows:1.Under low light stress,the growth of rice was significantly inhibited,the content of nitrogen in the leaves decreased,and the nitrate accumulation was caused by the decrease of NR activity.The distribution of nitrogen to chlorophyll in super rice was promoted,and the distribution of nitrogen to Ribulose-1,5-bisphosphate carboxylase/oxygenase(Rubisco)was decreased.Under low light stress,the growth of super rice was better than that of conventional rice,but the nitrogen content of the leaves and and the root xylem sap rate was significantly lower than conventional varieties.Under low light stress,the leaf nitrogen content of conventional rice is higher than super rice,and more leaf nitrogen stored in Rubisco.2.The inhibited photosynthesis rate under low light intensity was mainly due to the decreased leaf quantum efficiency of PS ?(?ps?)and the decreased CE resulted from gm.The different responses of photosynthesis rate to low light stress in different rice cultivars were resulted from the higher Rubisco activity and gm in super hybrid indica cultivar.3.Under low light stress,chloroplasts and grana became thicker,increasing the capture efficiency of the light and increasing the contact area with CO2.Under low light stress,super rice‘Guodao 6' and 'Liangyou 084' are larger than the conventional rice'Yangdao 6',which can help it have larger mesophyll conductance in low light.4.Under low light stress,conventional rice was more sensitive to nitrogen concentration than super rice.The photosynthetic rate decreased significantly with the decrease of light and nitrogen concentration.Whether normal illumination or under low light stress,low nitrogen supply promote 'Liangyou 084','Yangdao 6 ' chloroplast starch grains accumulated.With the increased of nitrogen concentration,larger chloroplast,thinner cell wall promoted the transmission of CO2,improved the photosynthetic capacity.In conclusion,the inhibited photosynthesis rate under low light intensity was mainly due to the decreased leaf quantum efficiency of PS ?(?ps?)and the decreased CE resulted from gm.The different responses of photosynthesis rate to low light stress in different rice cultivars were resulted from the higher Rubisco activity and gm in super hybrid indica cultivar.Under low light stress,the chloroplast of super rice is larger than conventional rice,which can help it have larger mesophyll conductance under low light,and with the increased of nitrogen supply,the decline of rice biomass decreased gradually,larger chloroplast,thinner cell wall promoted the transmission of CO2,improved the photosynthetic capacity of plants.