The Physiological And Molecular Mechanism Of Maize Kernel Development After Ethephon Treatment

Ethephon combined with other plant growth regulators have been widely used in corn production and played an important role in reducing natural disaster and stress-resistance.However,there were some problems of using ethephon such as inconvenient operation,short window period for application and reducting production.In this paper,maize inbred line B73 was used as the experimental material by sprying ethephon in 11-leaf stage to study the effects of ethephon on source,reservoir and flow.Morphological investigation,metabolites determination,microscopic analysis of tissues and organs,comparison of key enzyme activities,expression of related genes,and transcriptome analysis were used to detct the development of endosperm cell.By using a combination of plant related regulators,the effect of ethephon were measured to find if there were some plant growth regulators which can help to reduce the deficient effect of ethephon.Meanwhile,the reasons for the influence of ethephon on the number of kernels and grain weight were discussed.The main results were as follows:1.The photosynthetic rate of the ear-leaf in the ethephon-treated plants decreased significantly and the accumulation rate of photosynthetic products decreased in the grain filling stage.The expression levels of Rubisco,PEPC and NADP-MDH were significantly decreased in the ears of the ethephon treatment plants.Rubisco activities and PEPC were significantly decreased in the ears of the ethephon treatment plants.At 25 DAP,the starch accumulation in the ear-leaf of ethephon-treated plants was significantly decreased,the activities of AGPase and SSS were significantly decreased,simultaneously the expression levels of AGPase and SSS were significantly decreased.2.The number of vascular bundles and vascular bundles in the intemodes and phloem area were significantly reduced in the ethephon-treated plants.The decrease in the number of vascular bundles affected the carbohydrate transport.The number of differentiation of the female florets of the ethephon-treated plants was also decreased,and the number of degraded florets was not significantly different between the control plants and the ethephon-treated plant.The release of ethylene from the grain of the ethephon-treated plants increased,and the activity of ACC synthase was significantly higher than that of the control plants.3.The 100-grain weight and grain number per ear in the ethephon-treated plants decreased significantly,the starch content decreased by 8.5%,and the amylopectin content decreased by 12.5%.The activities of starch synthesis-related enzymes were significantly dropped in the middle and early stages of grain filling stage.In particular,AGPase showed a significant lower level from 10 DAP to 20 DAP.While SSS,SBE,SUS and other enzyme activities also dropped in some degrees.The expression level of ZmSH2 in the ethephon-treated plants was significantly decreased and the expression level of ZmSSI gene was also decreased to some degree.The expression level of ZmSBE?b was obviously decreased from 10 DAP to 20 DAP,while the expression level of ZmSH1 was significantly decreased at 10 DAP.4.The expression levels of CDKA;1,CDKA;3 and CYCA1;2 in the grains of the ethephon-treated plants were significantly decreased.Ethephon regulated the cell cycle by reducing the expression levels of CDKs and cyclin,affecting the conversion of S phase and G/M phase and thus affecting the number of endosperm cells.In 12 DAP,the number of cells in the ethephon-treated plants was 14.9%lower than that of the control plants.5.The number of endoreduplication in the ethephon-treated plants was significantly decreased,and the expression level of cell expansion proteins such as ZmEXPA6 and ZmEXPB13 was also significantly decreased.The area of endosperm cells in the ethephon-treated plants was decreased,and the endoreduplication and expansion were presumed.The protein has a certain degree of promoting effect on the increase of the endosperm cell volume.6.The number and volume of starch granules in the endosperm cells in the ethephon-treated plants decreased,and the distribution of the morphology changed.At 12 DAP,the starch granules in the control plants were mainly medium-sized starch granules,which accounted for 62.17%of the total starch granules.In the ethephon-treated plants,the starch granules were mainly small-sized starch granules,which accounted for 58.99%of the total starch granules.At 30 DAP,the number of large starch granules accounted for 70.84%of the total number of starch granules in the control plants,whereas the ethephon-treated plants accounted for 54.78%of the total number of starch granules.The morphology of amyloplasts in the ethephon-treated plants showed abnormalities at both 12 and 20 DAP,and the expression levels of ZmMinD,ZmFtsZ2-1,and ZmARC5 associated with plastid division,were significantly changed.7.The ear weight of the ethephon-treated plants decreased by 11.2%compared with the control group,and the yield decreased by 11.5%.6-BA can promote the division of the endosperm cells and the expansion of the endosperm cells to increase the storage capacity and thus completely restore the dificient effects of ethephon on kernels weight.1-MCP can restore the adverse effect of ethephon on the grain weight to some extent.After ABA treatment did not significantly affect the grain weight and storage capacity in the ethephon-treated plants.8.Different expression genes related to starch synthesis and metabolism detected by transcriptome sequencing included:SH2,LOX10,APE,GBSS1,GAUT7,GAUT14,glycosyl hydrolase,GTP-binding protein,glucan synthase,phosphoglucomutase,Fructose kinase,SS1,SBE1.Sucrose-phosphatasel,stachyose synthase and fructokinasel were related to sucrose synthesis.Proteins involved in sugar transport include:PMT5,LOC100285023,LOC100282085,LOC100170240,SUT.