Effect Of Low Temperature Stress On Chlorophyll Biosynthesis And Chloroplast Development Of Rice (Oryza Sativa L.) Seedlings

Chlorophyll is widely found in photosynthetic organisms,and plays an important role in the growth and development of plants and productivity of crop.Chlorophyll biosynthesis consists of a series of reactions which are catalyzed by 15 enzymes,and the process is affected by various environment factors.Low temperature,a kind of environment stress factor that plants always meet,is also an important factor that affects the chlorophyll biosynthesis and chloroplast development,especially in the early stage of greening process.Rice(Oryza sativa L.)is a kind of thermophilic crop,which is very sensitive to low temperature.In order to explore the response mechanism of rice seedlings to low temperature during greening,we selected rice as experiment materials and investigated the effect of cold stress on chlorophyll biosynthesis,chloroplast development,thylakoid protein accumulation,photosynthesis,and reactive oxygen species accumulation during greening.The main results are follows:1.The biosynthesis of chlorophyll was obviously inhibited and chlorophyll content decreased under low temperature stress during greening.The analysis of chlorophyll precursors under low temperature stress showed that the synthesis of ALA,Proto IX,Mg-proto IX and Chlide were inhibited,while Urogen III and Coprogen III were accumulates massively.At the same time,the activities of enzymes that catalyze the synthesis of ALA,Proto IX,and Chlide were decreased,indicated that the inhibition of enzymes activities might be the main reason for the decreased chlorophyll synthesis.2.Western blotting analysis indicated that the synthesis of PSII and PSI protein was obviously inhibited at 18 ? during greening.The proteins of PSII and PSI could not be detected after 48 h of greening at 12 ?,except for the D2 of PSII.3.Low temperaturw stress of 18 ? had a significant effect on the development of chloroplast,but still formed a typical chloroplast structure.At 12 ?,the development of chloroplast was inhibited,and no thylakoid were formed after 48 h irradiation.4.At 18 ?,Fv/Fm was significantly decreased while NPQ was significantly increased during greening.At 12 ?,the reduction of Fv/Fm and the increase of NPQ were steeper than those at 18 ?.5.Histochemical staining and quantitative analysis indicated that the H2O2 and O2 were accumulated during greening.While the accumulation of H2O2 and O2-were significantly increased under low temperature stress condition during greening,and H2O2 and O2-accumulated more at 12 ? than those at 18 ?.6.The number of leaf cell death was significantly increased under low temperature condition during greening.7.There were no significant effects of low temperature stress on the shape and size of upper and lower epidermal cells,while stomata size was smaller under low temperature condition than control temperature.