Abscisic acid,ethylene and antioxidative systems in rice grains in relation with grain filling subjected to postanthesis soil-drying

【作者】 张耗； 刘凯； 王志琴； 刘立军； 杨建昌；

【机构】 扬州大学江苏省作物遗传生理国家重点实验室培育点/粮食作物现代产业技术协同创新中心；

【摘要】 [Objective]Grain filling is the final growth stage in cereals when fertilized ovaries develop into caryopses.The filling degree and rate of rice（Oryza sativa L.） spikelets differ largely with their positions on a panicle.Grain filling is generally believed to be a regulated process either genetically or environmentally.Water or drought stress is one of the most important factors limiting crop yields world-wide.The mechanism underlying the decrease or increase in grain filling under soil-drying is yet to be well understood.Abscisic acid（ABA） and ethylene are two major phytohormones generally suggested to be involved in linking plant responses to stress.It has been reported that many adversities could induce membrane damage,membrane lipid permeability increase,and biological free radicals accumulation,such as malondialdehyde（MDA）.Moreover,drought,like other abiotic stresses,results in oxidative stress through an increase in reactive oxygen species（ROS）,such as superoxide radical(O^2-).To clear these ROS,plants have developed a complex antioxidative enzymes system（AES）,including catalase（CAT）,peroxidase（POD）,and superoxide dismutase（SOD）.Although the AES and ROS in rice under water stress are well documented,little is known about relationships of ABA,ethylene,AES,and ROS with grain filling of superior and inferior spikelets of rice under different soil water statuses.This study tested the hypothesis that abscisic acid（ABA） and ethylene may mediate the effect of postanthesis soil-drying on grain filling of rice through regulating antioxidative systems;[Method]The experiment was conducted at a farm belonging to Yangzhou University,Yangzhou,China during the rice growing season（May to October）.Two rice cultivars,Wuyunjing 8（japonica） and Yangdao 6（indica）,were pot-grown.From 9 DPA until maturity,three levels of soil water(Ψ_soil) potentials were imposed by controlling water application.The well-watered（WW）treatment was flooded with 1-2 cm water depth in the pot(Ψ_soil^i = 0 kPa) by manually applying tap water,a moderate soil-drying（MD） treatment was maintained at-20±5 kPa,and a severe soil-drying（SD） treatment was maintained at-40±5 kPa.Soil water potentials in the soil-drying treatments were monitored in the 15-20 cm soil depth.The pots were placed in a field and sheltered from rain by a removable polyethylene shelter which was placed over them during rain.Levels of ABA and ethylene,CAT,POD,and SOD,and contents of O₂^- and MDA and their relationships with grain filling rate were investigated;[Result]The results showed that,when compared with the WW treatment,the MD treatment increased,whereas the SD treatment decreased,grain filling rate and activities of CAT,POD,and SOD in both superior and inferior spikelets.Both MD and SD treatments increased contents of ABA,superoxide anion and MDA in grains,with more increases under the SD than under the MD.The MD treatment decreased,whereas the SD treatment increased,ethylene evolution rate and 1-aminocycopropane-1-carboxylic acid（ACC） content.The ratio of ABA to ACC（ABA/ACC） was the highest under the MD and the lowest under the SD among the three soil-drying treatments.ABA content,activities of CAT,POD,SOD,and ABA/ACC very significantly and positively,while the levels of ethylene and ACC and contents of superoxide anion and MDA significantly and negatively,correlated with grain filling rate.Application of cobalt ion（inhibitor of ethylene synthesis） or ABA at early grain filling stage significantly decreased contents of superoxide anion and MDA,and increased activities of CAT,POD,SOD and grain filling rate.Spraying with ethephon（ethylene-releasing agent） or fluridone（inhibitor of ABA synthesis） had the opposite effect;[Conclusion]The results suggest that an increase in ABA and decrease in ethylene in the grains under postanthesis moderate soil-drying could enhance the activities of antioxidative enzymes and reduce free radicals in grains,and therefore,accelerate the grain filling rate of rice.更多还原

【Abstract】 [Objective]Grain filling is the final growth stage in cereals when fertilized ovaries develop into caryopses.The filling degree and rate of rice（Oryza sativa L.） spikelets differ largely with their positions on a panicle.Grain filling is generally believed to be a regulated process either genetically or environmentally.Water or drought stress is one of the most important factors limiting crop yields world-wide.The mechanism underlying the decrease or increase in grain filling under soil-drying is yet to be well understood.Abscisic acid（ABA） and ethylene are two major phytohormones generally suggested to be involved in linking plant responses to stress.It has been reported that many adversities could induce membrane damage,membrane lipid permeability increase,and biological free radicals accumulation,such as malondialdehyde（MDA）.Moreover,drought,like other abiotic stresses,results in oxidative stress through an increase in reactive oxygen species（ROS）,such as superoxide radical(O^2-).To clear these ROS,plants have developed a complex antioxidative enzymes system（AES）,including catalase（CAT）,peroxidase（POD）,and superoxide dismutase（SOD）.Although the AES and ROS in rice under water stress are well documented,little is known about relationships of ABA,ethylene,AES,and ROS with grain filling of superior and inferior spikelets of rice under different soil water statuses.This study tested the hypothesis that abscisic acid（ABA） and ethylene may mediate the effect of postanthesis soil-drying on grain filling of rice through regulating antioxidative systems;[Method]The experiment was conducted at a farm belonging to Yangzhou University,Yangzhou,China during the rice growing season（May to October）.Two rice cultivars,Wuyunjing 8（japonica） and Yangdao 6（indica）,were pot-grown.From 9 DPA until maturity,three levels of soil water(Ψ_soil) potentials were imposed by controlling water application.The well-watered（WW）treatment was flooded with 1-2 cm water depth in the pot(Ψ_soil^i = 0 kPa) by manually applying tap water,a moderate soil-drying（MD） treatment was maintained at-20±5 kPa,and a severe soil-drying（SD） treatment was maintained at-40±5 kPa.Soil water potentials in the soil-drying treatments were monitored in the 15-20 cm soil depth.The pots were placed in a field and sheltered from rain by a removable polyethylene shelter which was placed over them during rain.Levels of ABA and ethylene,CAT,POD,and SOD,and contents of O₂^- and MDA and their relationships with grain filling rate were investigated;[Result]The results showed that,when compared with the WW treatment,the MD treatment increased,whereas the SD treatment decreased,grain filling rate and activities of CAT,POD,and SOD in both superior and inferior spikelets.Both MD and SD treatments increased contents of ABA,superoxide anion and MDA in grains,with more increases under the SD than under the MD.The MD treatment decreased,whereas the SD treatment increased,ethylene evolution rate and 1-aminocycopropane-1-carboxylic acid（ACC） content.The ratio of ABA to ACC（ABA/ACC） was the highest under the MD and the lowest under the SD among the three soil-drying treatments.ABA content,activities of CAT,POD,SOD,and ABA/ACC very significantly and positively,while the levels of ethylene and ACC and contents of superoxide anion and MDA significantly and negatively,correlated with grain filling rate.Application of cobalt ion（inhibitor of ethylene synthesis） or ABA at early grain filling stage significantly decreased contents of superoxide anion and MDA,and increased activities of CAT,POD,SOD and grain filling rate.Spraying with ethephon（ethylene-releasing agent） or fluridone（inhibitor of ABA synthesis） had the opposite effect;[Conclusion]The results suggest that an increase in ABA and decrease in ethylene in the grains under postanthesis moderate soil-drying could enhance the activities of antioxidative enzymes and reduce free radicals in grains,and therefore,accelerate the grain filling rate of rice.更多还原