Study On The Mechanism Of Silicon Alleviating The Decrease Of Photosynthetic Function Of Liangyoupeijiu Under Drought Stress

Drought stress is one of the important abiotic stresses that severely restricts crop yields.Many studies show that silicon plays the important role in improving the drought resistance of plants.Previous studies have focused on revealing the mechanisms of silicon enhances drought resistance in rice through testing changes in physiological levels.Whereas studies on the changes in structure and composition of rice thylakoid under drought stress are relatively rare.In this study,high-yielding hybrid rice named Liangyoupeijiu(LYP9)was the experimental material,and then we used polyethylene glycol(PEG-6000)to simulate drought stress to test effects of silicon on spectral characteristics,structure and composition of LYP9 seedlings thylakoid membrane and its physiological levels under PEG stress.This study provides a theoretical basis for elucidating the physiological,biochemical and molecular mechanisms of silicon on improving drought resistance of rice and rational use of silicon fertilizer.The results of the study are as follows:(1)Drought stress affected the growth of rice seedlings.Under drought stress,rice seedlings were short,leaf color was chlorotic,and wilting was serious.However,after treating with silicon,the wilting of rice seedlings leaves have been significantly reduced under PEG stress.Through the determination of photosynthetic pigment content,we found that silicon can increase the photosynthetic pigment content of rice seedlings under drought stress.The chlorophyll a fluorescence transient dynamics analysis indicated a timely and constant responsive pattern related to PSI and PSII.Under drought stress,the occurrence of K points in OJIP curves and the parameter of ET0/RC,ET0/CS0 and ?E0 of rice seedlings were decreased.It indicated that the rice oxygen-evolving complexe were damaged under drought stress and the electron transfer between the photosynthetic systems were strongly suppressed.While silicon could reduce the damage of drought stress to the photosynthetic system.(2)The BN-PAGE technique was used to isolate thylakoid membrane proteins from drought-stressed and silicon-treated rice seedlings.By analyzing the changes of thylakoid membrane protein complexes,it was found that silicon treatment can relieve the thylakoid damage caused by drought stress and slow down the degradation of Supercomplexes,PSIcore+LHC,PSIcore,F1-ATPase&Cytb6/f,PSII core,Trimeric LHC? and Monomeric LHCII and increase the stability of thylakoid membranes.The BN-SDS-PAGE technique was used to analyze the differential-proteins in different treatment groups.CK-PEG treatment group successfully identified 23 of the 41 differential protein spots.Compared with CK,21 protein spots in PEG were down-regulated.Only 2 protein spots were upregulated.The PEG-PEG+Si treatment group successfully identified 21 of the 30 differential protein spots.Compared with PEG,14 protein spots in the PEG+Si treatment group were up-regulated and 7 protein spots were down-regulated.Most of the identified protein spots are related to photosynthetic,pigment synthesis and energy metabolism.The protein spots of cytochrome b6/f complex,photosystem ? CP47 protein,phosphoenolpyruvate carboxylase,ATP synthase CF1? subunit and carotene desaturase were down-regulated in the PEG treatment group.These results suggest that drought stress affects the synthesis of photosynthetic pigments and also decreases the photosynthetic capacity and carbon assimilation ability.Compared with PEG treatment,phosphoenolpyruvate carboxylase,photosystem I-PsaO subunit,photosystem ? CP47 protein and ATP synthase CF1?subunit protein were up-regulated in the PEG+Si treatment group.(3)Effects of silicon on physiological and biochemical characteristics of rice seedlings under drought stress have also been studied.The drought stress inhibited the growth of rice and influenced the accumulation of material on shoot.But the root material accumulation was higher than the control.The addition of silicon could alleviate the inhibiting of drought on rice growth and increase the accumulation of material in shoot and root.Silicon application increased the relative water content of rice seedlings under drought stress and reduced the osmotic adjustment substance soluble sugar,proline,superoxide anion free radical(O2-)and membrane lipid peroxidation product malondialdehyde(MDA)accumulation.Silicon application made the activities of peroxidase(POD)and ascorbate peroxidase(APX)reducing,the activity of catalase(CAT)increasing and ascorbic acid(AsA)decreasing.It also reduced Glutathione(GSH)accumulation in rice seedlings under drought stress.