Effects Of Salt Stress On Rice Growth,Spikelets Development And The Regulation By 1-MCP

Rice?Oryza sativa L.?is more susceptible to the rhizosphere salinity than other cereals.Salinity stress hampers rice growth and development due to its osmotic,ionic and hormonal?ethylene?stresses,while high ethylene productions in rice cultivars under salt stress affect inferior and superior spikelets development.1-Methylcyclopropene?1-MCP?is an excellent ethylene action inhibitor for plants.However,the effects of 1-MCP on rice growth and spikelets development under salt stress have not been studied.This study will analyze the physiological and biochemical characters and the protein expression in rice plants under salt stress,and will also explore the internal mechanism of low rice grain yield and low salt resisitance of rice plants under salt stress.The study will also try to increase rice grain yield and improve the utilization efficiency for salinity soil by 1-MCP regulation.Two pot experiments were conducted in the greenhouse during rice crop seasons?May-November?at China National Rice Research Institute,Zhejiang Province,China in2016 and 2017.The treatments in the first experiment were two rice cultivars with four salt stress levels.Rice cultivars included Liangyoupeijiu?LYP9,indica hybrid?and Nipponbare?NPBA,japonica?;while salt stress included 0?Control,CK?,1.5 g NaCl/kg dry soil?Low salt stress,LS?,4.5 g NaCl/kg dry soil?Medium salt stress,MS?,and 7.5 g NaCl/kg dry soil?Heavy salt stress,HS?.The treatments in the second experiment were two 1-MCP levels?no 1-MCP and 1-MCP applied at the rice booting stage?along with two rice cultivars and four salt stress levels.Rice cultivars and salt stress levels in the second experiment were same with the treatments in the first experiment.The results showed that salt stress reduced seed emergence features?seed emergence rate,seed emergence energy percentage?of rice plants.Salt stress also decreased the growth parameters e.g.root length,plant height,and plant biomass at early seedling stage and maximum tillering stage in LYP9.However,rice seedlings for NPBA were died at the HS level.Salt stress also reduced the photosynthesis activities of rice leaves in both rice cultivars,but this disaster was less in LYP9 than in NPBA.On the basis of total plant biomass reduction rate,LYP9 was categorized as moderately susceptible and susceptible at HS level during seed emergence or early seedling growth and maximum tillering stage,respectively.While NPBA was categorized as sensitive to the HS stress level.The result suggested that LYP9 showed higher resistance under salt stress than NPBA.The application of 1-MCP significantly inhibited ethylene production in inferior spikelets of both rice cultivars compared with those superior spikelets under salt stress.1-MCP was more effective in increasing grain filling rate for inferior spikelets than for superior spikelets in both rice cultivars.The application of 1-MCP improved the net photosynthesis rate,stomatal conductance,transpiration rate,SPAD values,and the leaf area index of rice flag leaves in both cultivars compared with no 1-MCP application.1-MCP was more effective in increasing grain filling rate and grain weight in the LYP9than in the NPBA under all salt stress treatments.As compared to the treatment without1-MCP,the grain yield for LYP9 with 1-MCP treatment was increased by 35.6%,37.6%,and 35.3%for CK,LS and HS treatments,respectively.The results demonstrated the beneficial role of 1-MCP on increasing rice grain yield under salt stress by enhancing rice growth paramters and the spikelets development,particularly inferior spikelets development.1-MCP significantly reduced ethylene production,a key signaling phytohormone for the induction of tolerance when rice experiencing salt stress.1-MCP was helpful for improving biochemical characteristics such as superoxide dismutase production,chlorophyll content?chl a,b,carotenoids?,proline accumulation and protein synthesis,and decreasing malondialdehyde,H₂O₂ in rice leaves.1-MCP also modulated above ground biomass and growth characteristics in LYP9 and NPBA at maturity with increased salt stress.The results revealed that 1-MCP can be employed to modulate plants growth,physiological parameters?P_n,T_r,gs,and SPAD value?,and biochemical activities in rice as a salt stress remedy.Cell membrane injury in rice leaves was higher in NPBA than in LYP9 with increased salt stress levels.Salt stress also badly affected the rice root activities.Rice root activity was higher in LYP9 than in NPBA with increased salt stress levels.Salt stress also affected the protein expression in rice flag leaves.A comparison proteomic expression was studied with LS,MS,and HS salt stress levels with CK.ITRAQ quantification protein analysis showed that,28,368,and 491 up-regulated proteins were detected for LYP9 under LS,MS,and HS treatments compared with CK.Comparisons with LYP9 at LS treatment,LYP9 at MS and HS treatments were detected 425,541 up-regulated proteins,respectively.Compared with LYP9 at MS treatment,LYP9 at HS treatment was detected 324 up-regulated proteins.Whereas for NPBA,239,337 up-regulated proteins were detected under LS and MS treatments compared with CK.To compare with NPBA at LS treatment,NPBA at MS treatment was detected 328 up-regulated proteins.While seedlings for NPBA could not survive under HS treatment due to its high sensitivity.This study suggested that expression of up-regulating proteins in LYP9 was higher than in NPBA.The results showed the genetic potential for LYP9against salt stress.