The Mechanism Of Selective Maize Kernel Abortion

Maize kernel abortion is frequently occurred on the apical ear,leading to huge loss in production.It is still unclear why kernel abortion occurs on apical ear and how kernel abortion is regulated.In this study,using maize as experimental material,we investigated the underlying mechanism of selective kernel abortion.1.By the approach of delaying pollination to basal kernels,the natural pollination pattern that follows the order from the basal-to the apical-ear was reversed.In synchronous pollination treatment,the middle and basal kernels grew normally from early stage to maturity.Whereas the apical kernel ceased growing and aborted at early stage,with no starch accumulation in the pedicel region,revealing that a deficient in assimilate supply.In the treatments of delaying pollination to basal kernels for 2,4 and 6 days,the growth of basal kernels was suppressed,and increasing the time gaps of delaying pollination inhanced the suppression on basal kernels.The 6-day-delayed-pollination basal kernel abrorted with abundant of starch accumulation in its pedicel region.The results of cell-wall invertase activity in situ localization showed that delaying pollination directly inhibited cell-wall invertase activity in the pedicel region and thus the assimilate unloading process.Moreover,the effect was independent from kernel position.Collectively,we suggest that delayed pollination time and low availability of assimilate supply are major factors causing apical kernel abortion in maize.2.Using the approaches of emasculation and artificial pollination,we investigated how pollination and fertilization processes regulated the key players in apoplastic unloading pathway,including cell-wall invertase,hexose transporters(HT)and SWEET sugar efflux.At 4 hours after pollination(before the fertilization occured),cell-wall inverstase gene and activity as well as HT and SWEET genes were stimulated in style,whereas in ovary they were not influenced then.At 2 days after pollination(after fertilization occurred),cell-wall invertase,HT and SWEET were unregulated in ovary.These results offer experimental evidence to support the regulatory effects of pollination and fertilization on the apoplastic unloading process in pistil.3.The chapter focused on the mechanism how assimilate supply and different gradients of drought stresses regulated maize kernel abortion and their relationships in this process.By increasing the degrees of drought stresses,the completed-pollinated apical kernels showed decreasing kernel number,sugar and spermine concentrations,whereas the ethylene emission increased and starch accumulation showed a slight reduction in pedicel region.Under moderate and severe droght stresses,cell-wall invertase gene expression and activity showed significantly reduction and the ethylene emission rocketed in the completed-pollinated apical kernels at early stage.Under the incomplete pollination treatment,in which the basal kernels were not pollinated thus the assimilate supply to apical kernels was increased,the apical kernels all showed normal growth under different gradients of drought stresses.Even under severer drought stress,the normally grown apical kernels showed increase in sugar and spermine concentrations and decrease in ethylene emission.Notably,the incomplete pollination treatment recovered the cell-wall invertase activity but no its gene expression in apical kernels,indicating that drought stress could suppress cell-wall invertase gene expression,whereas increasing assimilate supply could recover its activity by post-transcriptional regulation.Thus,apical kernels could normally set with an adequate assimilate supply and recovered cell-wall invertase activity,even under the condition of severer drought stress.4.By increasing the druations of ear-three-leaves shading,assimilate supply to the apical kernels was reduced,including dropped sucrose and glucose concentrations,which also results to a synchronously increased endogenous ethylene emission.Correlation analysis showed sucrose and glucose contents were negatively corelated to ethylene in apical kernels,which means adequate assimilate supply and sugar concentration would suppress the synthesis of ethylene.The endogenous balance between sugar and ethylene may play an important role in kernel abortion process.In summary,this study showed that cell-wall invertase,the key enzyme in apopolastic unloading,could be regulated by pollination time gaps and drought stress and its deficiency may relevant to kernel abortion.In addition,adequate assimilate supply could recover cell-wall invertase activity and promote kernel set.The results suggest that shorten the anthesis-silking interval and pollination time gaps among kernels from same ear could reduce kernel abortion in practical maize production.Also,maintaining the assimilate unloading process is crucial for reducing abortion and maintaining crop yield under stress condition.