| Given the ongoing increases in global temperature,the uneven spatial and temporal distribution of precipitation led to abnormal distribution of drought and humidification in some areas of China.Waterlogging is becoming a challenge factor for maize production in Huang-Huai-Hai plain,which led to significant yield losses of summer maize.Therefore,it is of great significance to explore the influence of waterlogging on the growth and development of summer maize and propose effective managements for maize production against waterlogging,thus ensuring the food security.Application of exogenous 6-BA can effectively enhance the activities of antioxidase,improve the photosynthetic performance,therefore,increasing the crop yield.Exogenous 6-BA has been widely used in the crop production against abiotic stresses.However,the physiological mechanism of 6-BA regulating the crop yield formation needs further study.The waterlogging-induced yield losses was mainly attributed by the decrease in kernels per ear and kernel weight.The kernels per ear and kernel weight are determined by the ear differentiation,florets setting,and grain filling processes.Three waterlogging treatments including waterlogging at V3,V6,and 10VT for 6 days,and non-waterlogging treatment（used as control）were set to study the effect of waterlogging on spike differentiation,photosynthesis,and carbon translocation of summer maize.Additionally,we applied 6-BA on waterlogged plants at the next day after the releasing of waterlogging to explore the underlying mechanism of 6-BA enhancing the yield of waterlogged summer maize by proteomic technology.The main results as follow:1 Waterlogging decreased the grain yield by impeding spike differentiation processesWaterlogging at any growth stage significantly reduced the dry matter accumulation and partitioning to ears,thus impeding the tassel and ear differentiation processes,decreasing the gain yield of summer maize.Among these,waterlogging at third leave stage did most significant damages on summer maize.Waterlogging at V3 significantly decreased the photosynthesis rate of summer maize,which led to reduction of dry matter weight.In addition,waterlogging significantly increased the sucrose-cleaving enzymes of ear leaves,increasing the utilization of sucrose,thus decreasing the carbon export from leaves.The carbon translocation to ears,shanks,and spike nodes were decreased by 53.1%,46.5%,and 71.5%,respectively,in waterlogged summer maize,compared with that of control.The reduction of photosynthesis rate coupling with impediment of carbon translocation resulted in poor development of ears and tassels,reducing the total florets and fertilized florets that were decreased by 15.2%and 20.6%,respectively.Additionally,assimilates were preferentially translocated into tassels,rather ears,which lengthened the ASI.Therefore,the florets setting rate were decreased,resulting in reductions of grain yield of summer maize.2 The regulation mechanism of application of exogenous 6-BA on yield formation of waterlogged summer maize（1）Application of exogenous 6-BA promoted MAPK and hormone signal transductionApplication of 6-BA inhibited the waterlogging-induced increases in ABA content but increased the phosphorylation levels of proteins involved in ABA signaling,such as respiratory burst oxidase 4,MAPK,and Abscisic acid-insensitive 5-like protein 5.Accordingly,the stomatal responsiveness to exogenous ABA was increased.In addition,the application of 6-BA effectively increased phosphorylation levels of proteins involved in EH and JA signaling,such as VQ motif family protein,MKS1,EH insensitive 2,and TIFY 6B,contributing to rapid responses to subsequent stresses.6-BA priming could effectively enhance the accumulation of JA and EH by 29%and 14%,increasing the leaf SPAD,antioxidase activity,and root aerenchyma area of summer maize in response to waterlogging,In summary,application promoted the transduction of MAPK and hormones signaling,which enabled plants to show faster or stronger defense responses to stress.（2）Application of exogenous 6-BA delayed the plant senescenceApplication of exogenous 6-BA significantly affected the protein abundance of peroxidase（A0A1D6E530,B4FBH0,B4FKV6,B4FVT1,C0HHA6）,L-ascorbate peroxidase（A0A1D6QMU5）,glutathione peroxidase（C0P3R8）and the APX3-peroxisome ascorbate peroxidase（B6TM55）in waterlogged summer maize.Accordingly,application of exogenous6-BA increased the activities of superoxide dismutase,peroxidase,and catalase by 6.9%,14.1%,and 18.5%,respectively,and decreased the content of malonaldehyde by 22.1%,compared with that of waterlogging treatment.Additionally,application of exogenous 6-BA significantly affected the abundance of proteins involved in linolenic acid metabolism,alpha-linolenic acid metabolism,and fatty acid metabolism,thus effectively decreasing the activity of lipoxygenase by 13.6%and the content of H2O2by 17.2%.（3）Application of exogenous 6-BA improved the photosynthetic characteristicsApplication of exogenous 6-BA effectively modulated the phosphorylation level of proteins such as Blue-light receptor phototropin 2（PHOT2）,Kinesin-like protein（KCA2）,and Serine/threonine-protein kinase（STY46 and STY17）to mediate the pre-proteins into chloroplast and the movement of chloroplast,which played an important role in improving the structure and function of chloroplasts.Additionally,application of exogenous 6-BA effectively regulated the phosphorylation level of phosphoenolpyruvate carboxylase,Rubisco,NADP-dependent malate dehydrogenase,6-phosphofructokinase,6-phosphogluconate dehydrogenase,sucrose-phosphate synthetase,thus modulating their enzyme activities.As a result,application of exogenous 6-BA effectively increased the photosynthesis rate by 17.8%,compared with that of waterlogging treatment.（4）Application of exogenous 6-BA improved carbon metabolism,promoting spike differentiation processes,enhancing grain yieldAt ear florets differentiation stage,application of exogenous 6-BA effectively increased the content of cytokinin and salicylic acid by 59.3%and 285.5%,and decreased the content of jasmonic acid by 28.8%,thus increasing the sucrose invertase activity by 92.2%.Thereby,the ear sink strength of waterlogged summer maize was increased,which increased the total ear florets by 14.0%.Additionally,application of exogenous 6-BA effectively enhanced the cytokinin content of ear leaf,spike node,and ear by 24.2%,64.2%,and 46.1%,respectively.Besides,the contents of abscisic acid,jasmonic,and salicylic acid were also modulated by application of exogenous 6-BA.Accordingly,the structure of spike node were improved which enhanced the translocation of carbohydrate to ears,thus promoting the development of ear filaments.As a result,the fertilized florets,kernels per ear,and grain yield were increased.In summary,waterlogging decreased the photosynthesis rate of summer maize,reducing dry matter accumulation;and affected the sucrose metabolism,thus impeding the carbohydrate partitioning,which led to insufficient supply of nutrients to spikes.As a result,the spike differentiation processes were impeded,and the dis-coordination between ears and tassels were enlarged,thus the kernels per ear and grain yield of summer maize were decreased by waterlogging.Application of 6-BA increased the cytokinin content of summer maize,thus enhanced the protein phosphorylation processes,which promoted the signal transduction of MAPK and plant hormones,enhancing the plant adaptability to environmental stress.Therefore,the plant protein,energy,reactive oxygen metabolism processes were improved by application of 6-BA,the plant senescence were delayed.Accordingly,the carbon assimilation and translocation capacity of plants were increased,which ensured the energy for spike differentiation and development,leading to increases of grain yield. |
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