Study On The Stigma Exsertion Formation Mechanism In Cytoplasmic Inheritance Of Stigma Exsertion Tobacco

Stigma exsertion is a major factor that can increase the opportunity for outcrossing pollination.The efficiency of hybrid seed production can be improved by increasing the percentage of exserted stigma.In order to investigate the stigma exsertion formation mechanism in cytoplasmic inheritance of stigma exsertion tobacco,the floral development characteristics at three different growth periods(initial flowering period,full blossom period,and fruiting period)of three homonuclear-heteroplasmic tobacco materials,MSK326SE with stigma exsertion,MSK326 with normal stigma and K326 planted at Xuchang Scientific and Educational Park in 2018 were compared,and the development characteristics of corolla,style and ovary,changes of endogenous hormones and related gene expression during bud development of three materials at full blossom period were studied.The main results are as follows:The morphological observation of the bud development at three growth periods(initial flowering period,full blossom period,and fruiting period)of three tobacco materials showed that,The daily mean temperature of 10 days before sampling at three growth periods was 29.98?,26.95? and 19.79? respectly.The bud length(43.58 mm?57.33 mm)and corolla length(41.63 mm?56.99 mm)of the three materials had no significant changes.It was also found that the style length(33.40mm?41.99mm)increases with the decrease of temperature,among which the longest style were in K326 at fruiting period,and no significant changes in the stigma exsertion of MSK326SE with the decrease of temperature.The results showed that the temperature conditions at three growth periods in Xuchang in 2018 had a certain effect on the development of floral organs during the growth of tobacco plants,but had no effect on the stigma exsertion of MSK326SE.The developmental morphology of the three materials at full blossom period were compared,it was found that the style of MSK326SE was longer than the other two materials at stage 1-9,and exserted at stage 3.There was no significant difference in style length between the three materials after stage 9,indicating that the style elongation of MSK326SE was earlier than that of the other two materials.The corolla length of MSK326SE was significantly shorter than that of K326 and MSK326(55.48 mm±1.92 mm)after bud length was fixed.The main reason for stigma exsertion was that the corolla of MSK326SE was significantly shorter than the other two materials.According to the relationship between the color,size and relative position of flower organs and the length of flower buds in the division of 19 periods of tobacco buds,the buds of three materials were divided into five developmental phases(T1-T5)by buds length to facilitate subsequent sampling studies.Hormone content and expression of hormone-related genes in different bud organs of three materials at five developmental phases were determined.The results showed that the contents of cytokinin(CTK),auxin(IAA)and ethylene(ETH)related genes in MSK326SE were significantly higher than those in K326 and MSK326 at T1 and T2 phases.At T3 phase,the contents of IAA and GA in the corolla of MSK326SE were significantly lower than those of the other two materials.The expressions of abscisic acid(ABA)and ABA related genes,salicylic acid(SA)and jasmonic acid(JA)related genes were higher than those of the other two materials,ABA content and ABA,SA,JA related genes in MSK326SE style were higher than those of the other two materials.It was suggested that the length of MSK326SE corolla is shorter than that of other two materials after T3 phase,which may be related to the less content of IAA and GA and the vigorous metabolism of ABA,JA and SA.The expressions of genes related to cell division and reactive oxygen species metabolism in different bud organs of three materials at five developmental stages was determined and analyzed.The results showed that the expressions of cell division related genes in the bud of MSK326SE were significantly higher than those of the other materials at T1 and T2 phases;the gene expressions in the corolla were obviously lower than those of the other materials after T4 phase.The expressions of genes related to reactive oxygen species metabolism in the bud of MSK326SE were significantly higher than those of the other materials at T2 phase;the gene expressions in the corolla were obviously lower than those of the other two materials at T3 and T4 phases.The expressions of genes related to stress protein synthesis in the corolla of MSK326SE were lower than those of the other two materials at T3 to T5 phases;the gene expressions in the style were obviously lower than those of the other two materials at T5 phase.The expressions of Polyamines related genes in the bud of MSK326SE were significantly higher than those in K326 and MSK326 at T1 and T2 phases;Polyamines related genes in the corolla were lower than those in K326 and MSK326.The expressions of genes related to carbon and nitrogen metabolism in the bud of MSK326SE were significantly higher than those of the other materials at T1 and T2 phases;the gene expressions in the corolla were lower than those in K326 and MSK326 at T4 and T5 phases.The high expressions of genes related to cell division,Polyamines and active oxygen metabolism in the bud of MSK326S at T1 and T2 phases indicated that the vigorous physical activities of MSK326SE at T1 and T2 phases might be the reason of its stigma exsertion being earlier than the other two materials.When the bud length was fixed,the fact that the corolla of MSK326SE was shorter than the other two materials might be related to the low expressions of genes related to cell division,stress protein,Polyamines,carbon and nitrogen metabolism.In short,the temperature conditions at three growth periods in Xuchang had no effect on the stigma exsertion of MSK326SE,the main reason of its stigma exsertion was that the corolla of MSK326SE became obviously shorter.In the early stage of the bud development,the vigorous metabolism of IAA,GA,CTK,SA,ABA,ETH,JA,Polyamines,carbon and nitrogen in the bud of MSK326SE was the reason that the stigma exsertion was earlier than that of K326 and MSK326.In the late stage of the bud development,the weak metabolism of IAA,GA,CTK,active oxygen metabolism,stress protein synthesis,Polyamines,carbon and nitrogen as well as the vigorous metabolism of ABA,SA and JA in the corolla of MSK326SE was the reason that the corolla length was obviously shorter than that of K326 and MSK326.