Hormonal changes play important roles in the key period of superior and inferior earshoot differentiation in maize

摘要

The upper earshoots with higher superiority usually have higher yield potential and higher efficiency.To determine the key period for the asynchronous differentiation of superior and inferior earshoots and how hormones are involved in this process,a two-year experiment was designed using two maize hybrids:Suyu 41(S41,single-ear hybrid)and AN 101(A101,double-ear hybrid).The results showed that the lag of lower earshoot differentiation was not only caused by the delay of the differentiation starting time but also related to extension of the duration in spikelet differentiation(stageⅡ)and sexual organ formation stage(stageⅣ).From 12 days before silking(DBS),the contents of indole-3-acetic acid(IAA),zeatin riboside(ZR)+zeatin(ZT),and gibberellic acid(GA_(3))in both upper and lower earshoots of the two hybrids increased dramatically and then decreased quickly.ABA slightly increased in the two hybrids and then decreased slowly in S41,while it was maintained at a high level in A101.At 8 DBS,i.e.,the transition period from floret differentiation to sexual organ formation stage,not only the growth of upper-to-lower earshoot difference(ULED),but also the values for ULED of IAA,ZR+ZT and GA_(3)were all significantly higher in S41 than in A101.Furthermore,the upper-to-lower hormone ratios IAA_(U)/AA_(L)and(ZR+ZT)_(U)/(ZR+ZT)_(L)were also much higher in the single-ear hybrid than in the double-ear hybrid,while the GA_(3U)/GA_(3L)and ABA_(U)/ABA_(L)had no significant differences.In addition,the time course of ULED_(hormone)/ULED_(earshoot growth rate)also suggested that the hormones work in different ways in earshoot superiority/inferiority formation.The delayed differentiation of lower ear shoots was conclusively related to the later initiation of differentiation and the longer durations of specific differentiation stages.Compared with the regulating roles of IAA and ZR+ZT in the key period(8 DBS)of superiority/inferiority differentiation,GA_(3) seems to be affected earlier,while ABA contributes little to this process.