Effects And Mechanisms Of Plant Growth Regulators On The Waterlogging Tolerance Of Oilseed Rape At Radicle Growth

Waterlogging occurs frequently in winter rapeseed production areas in the Yangtze River Basin.The radicle growth is the sensitive phase to waterlogging for rapeseed.With the development of simplified production technology and the rapid expansion of direct rapeseed area,the occurrence of waterlogging after sowing may cause irreparable damage to the crop.It is of important significance to explore the regulatory methods and make clear the mechanism to enhance the waterlogging tolerance of rapeseed at the radicle growth for the crop production.In this study,different concentrations of ethylene synthesis inhibitors?O-?Carboxymethyl?hydroxylamine hemihydrochloride,AOA?,ethylene receptor inhibitors?1-methyl-cyclopropene,1-MCP?,and gibberellin?GA₃?and its synthetic inhibitor(Paclobutrazol,PP₃₃₃)were used to investigate their regulatory effects and mechanism on the waterlogging tolerance of rapeseed?Brassica napus L.?at the radicle growth,under the artificially controlled conditions,using two cultivars of variety of with different waterlogging tolerance,i.e.,Fengyou 737?sensitive?and Huaza62?tolerant?as materials.The major purpose of this study is to provide theoretical basis and regulation technology for combating waterlogging in direct-seeded oilseed rape.The main results are as follows:1.The treatment of waterlogging at the radicle growth significantly reduced the seedling emergence rate and seedling emergence index of rapeseed,and inhibited the growth of seedlings after waterlogging.Among them,Fengyou 737 was more severely affected than Huaza 62.Along with the prolonged waterlogging duration,ethylene release rate significantly increased in seeds of Fengyou 737.2.The pretreatments with AOA and GA₃ at imbibition stage could effectively relieve the waterlogging stress on rapeseed emergence at the radicle growth,increase seedling emergence rate and emergence index,and promote the recovery of seedlings after waterlogging.The effect of AOA was the more significant in Fengyou 737,while the effect of GA₃ was more significant in Huaza62.Low concentration of 1-MCP pretreatment could significantly promote the seedling emergence of Fengyou 737 and the seedling recovery growth after waterlogging at the radicle growth,but it did not promote seedling emergence of Huaza 62 after waterlogging stress.In the pretreatments with1-MCP,AOA,GA₃ or PP₃₃₃ at imbibition stage,the ethylene release rate significantly decreased in the seeds of Fengyou 737 at the radicle growth.However,the pretreatments of 1-MCP,AOA and GA₃ at imbibition stage increased the ethylene release of waterlogged seeds in Fengyou737.Therefore,lowering the ethylene level before waterlogging and maintaining a certain level of ethylene during the waterlogging process may help improve the waterlogging tolerance at the radicle growth of Fengyou 737.3.Different rapeseed cultivars and different pretreatment periods of regulators show different effects on the regulation of seedling emergence and seedling growth of rapeseed after waterlogging.The applications of 1-MCP,AOA,ethephon,GA₃ and PP₃₃₃ at the radicle growth could not effectively promote seedling emergence and seedling growth of Fengyou 737 seeds after waterlogging stress,however,GA₃ and 1-MCP could improve the waterlogging tolerance of Huaza 62 seeds,of which the effect of GA₃ was stronger.4.The action of gibberellin in regulating the waterlogging tolerance may lie on the downstream of that of ethylene.Under the condition that ethylene level was appropriately reduced before waterlogging,the emergence rate of Fengyou 737 seeds after waterlogging was increased by maintaining appropriate level of endogenous gibberellin.Under the condition that ethylene level was not reduced before waterlogging,the treatment with GA₃ led to more severe damage to the seedling emergence Fengyou737 by waterlogging at the radicle growth.However,under the condition that the action of ethylene was inhibited with 1-MCP before waterlogging,maintaining or raising gibberellin levels were not conducive to the seedling emergence and recovery growth of Fengyou 737 seeds after waterlogging at the radicle growth.It implies that the regulation of gibberellin treatment on enhancing the waterlogging resistance of rapeseed may depend on the actions of ethylene.Under the conditions of maintaining or increasing gibberellin levels,appropriately higher ethylene level did not significantly affect the seedling emergence of waterlogged seeds of Fengyou 737.5.The transcriptome datas showed that there were 11 differentially expressed genes in the ethylene metabolism pathway of Fengyou 737 seeds after waterlogging at the radicle growth and 29 in signal transduction pathways.The differentially expressed genes were 56 in the gibberellin metabolic pathway and 166 in signal transduction pathways.There were 41 differentially expressed genes in the synthesis pathway of abscisic acid and 57 in signal transduction pathways.The differentially expressed genes were 54 in the cellular autophagy pathway.This indicates that the endogenous hormone metabolism and signal transduction pathways of oilseed rape after waterlogging at the radicle growth are significantly changed,and the autophagy is involved.