Cytological Mechanism Of Pollen Abortion In Populus Tomentosa Clone ’Baotoubai’

Due to a severe pollen abortion,the excellent traits of P.tomentosa clone ’baotoubai’ have not been efficiently exploited.In the present study,to reveal the cytological mechanisms of pollen abortion in P.tomentosa clone ’baotoubai’,the law of meiosis and the observation of pollen morphology was conducted by comparing with a diploid clone ’lumao50’ with good fertility.Then,chromosomal behaviors and microtubule skeleton during meiosis,cytokinesis,tapetum development were systematically carried out by the methods of cytology and indirect immunofluoresence.The main findings were as follows:(1)The meiotic process of pollen mother cells in P.tomentosa clone ’baotoubai’ was related to the color of anthers.When meiotic stage of pollen mother cells(PMCs)was from leptotene to tetrad stage,the color of anthers changed from peak green,yellow green,slightly red,to crimson.Therefore,the color of anthers could be considered as a primary morphological marker for judging the meiotic stages of PMCs.However,no correlation between meiotic stages and the colors of anthers was seen in P.tomentosa clone ’lumao50’.Therefore,the color of anthers could not be considered as a primary morphological marker for judging the meiotic stages of PMCs.(2)The anthers of P.tomentosa clone ’lumao50’ could dehisce normally and a large amount of pollen grains could be released.Its pollen grains were full,with relatively smooth and uniform surface structure,and no cracks were seen.The proportion of abortive pollen was 3.47±0.45%.However,the pollen production in P.tomentosa clone ’baotoubai’ was lower than that of clone’lumao50’.a large number of empty and broken pollen grains were observed and the pollen grains partially showed obvious fold,unbalanced,and even cracks on the surface textures.The proportion of aborted pollen could be up to 28.08±4.04%,suggesting that the pollen abortion in P.tomentosa clone ’baotoubai’ was more serious than that in clone ’lumao50’.The abnormal dehiscence of anthers mainly accounted for the abortion type in P.tomentosa clone ’baotoubai’.(3)The abnormal chromosomal behaviors were observed during meiosis of PMCs both in clone’lumao50’ and ’baotoubai’,The ratios of lagging chromosomes and chromosome bridges at anaphase Ⅰ and anaphase Ⅱ in P.tomentosa clone ’baotoubai’ were dramatically higher than clone’lumao50’.Generally,these abnormal chromosomal behaviors would result in daughter cells with unbalanced genetic material,and leading to pollen abortion(4)The microtubule skeleton appeared dynamical organization during meiosis.No significant differences in was observed between P.tomentosa clone ’lumao50’ and ’baotoubai’.In addition,bipolar microtubules connected with chromosomes at the anaphase I in some PMCs were showed.The balanced pull force of bipolar microtubules caused the lower segregation of chromosome,and formed lagging chromosomes(5)The proportion of distorted,broken,and insufficiently developed cell plates in clone ’Iumao50’was 5.67±0.78%,0.52±0.95%,3.09±1.25%,respectively.However,the proportion of distorted,broken,and insufficiently developed cell plates in clone ’baotoubai’ was 54.88±8.1%,11.59±2.4%,17.07±4.6%,respectively,significantly higher than that of in clone ’lumao50’.This suggested that insufficient accumulation of callose during cell plate formation could lead to pollen abortion(6)There were no significant differences of tapetum during the meiosis of PMCs in P.tomentosa clone ’lumao50’ and ’baotoubai’.However,during the development of microspores,the tapetum of clone ’lumao50’ degraded in time.While the degradation of tapetum in P.tomentosa clone’baotoubai’ was delayed,affecting the development of microspores and the indehiscence of anthers.Eventually pollen abortion occurredIn conclusion,pollen abortion in P tomentosa clone ’baotoubai’ could occurred during meiosis of PMCs,cytokinesis and the development of microspore.stick chromosomes,lagging chromosomes and chromosome bridges at anaphase of meiosis would result in daughter cells with unbalanced genetic material,and leading to pollen abortion.Insufficient accumulation of callose during cytokinesis could cause the formation of distorted,broken,and insufficiently developed cell plates,resulting in pollen abortion.During the development of microspores,the degradation of tapetum was delayed,which affect the development of microspores and the indehiscence of anthers,eventually inducing the occurrence of pollen abortion.