Development Characteristics Of Pollen,Embryo Sac And Double Fertilization In Autotetraploid Rice

Rice is one of the important food crops.The research on rice has not stopped.Obtaining rice varieties with high rice yield and rice quality has always been the goal that scientists pursue tirelessly.The breeding of common rice has encountered bottlenecks.Breeders found that the dose effect produced by chromosome doubling had the potential to improve the yield and quality of rice.The agronomic and reproductive development characteristics of different ploidy rice were studied in this paper,which provided theoretical basis for polyploid rice breeding.In this study,5 diploid rice and the corresponding autotetraploid rice,which were obtained by chromosome doubling by colchicine,were used as experimental materials for plant height,panicle length,flag leaf length,flag leaf width,number of filled grains per panicle,seed setting rate,grain length,grain width and 1000-grain weight were compared and analyzed,and the pollen fertility and pollen development characteristics,embryo sac fertility and embryo sac development characteristics,pollen tube growth dynamics and double fertilization process of different ploidy rice were observed and studied by laser confocal microscope.The main findings are as follows:1.There was a significant difference in agronomic characters of rice with different ploidy.The plant height of rice has decreased after the chromosome is doubled,and there is a very significant difference between the different ploidy rice.The reduction of Zijing 4x was the largest,with a decrease of 40.40%.The variation trend of spike length is not uniform,but there is a significant or very significant difference between different ploidy rice.The change trend of flag leaf length was not uniform,However,there were significant or extremely significant differences among different ploidy.The change trend of the flag leaf width is uniform,and it shows an increasing trend.The number of filled grains per panicle and the seed setting of the autotetraploid rice were obviously lower than that of the diploid rice,and a very significant difference was achieved.The 1000-grain weight of the autotetraploid ricehas an obvious advantage,which is higher than that of the corresponding diploid rice.In the two characters of the grain length and the grain width of the rice,most of the tetraploid rice has a rising trend and a very significant difference compared with the diploid rice,and only the shuangpeimiao 4x are reduced in the width level.It can be seen that there is a significant difference in the agronomic characters between different ploidy rice.2.The pollen development of autotetraploid rice and the corresponding diploid rice showed that the pollen development process of different ploidy rice was the same.During meiosis of autotetraploid rice,a variety of abnormal phenomena were observed,such as incomplete degradation of cellulose wall,unsynchronism of daughter cell division,T type tetrad,and so on,which may be the cause of pollen abortion in late stage.During the occurrence of male gametes in autotetraploid rice,there were different forms of cytoplasm concentration,seedless empty flower powder grains,cell wall folds and so on.Autotetraploid rice produced higher frequency abortive pollen at mature pollen stage.In tetraploid rice,the abortion rate of pollen is as high as 51.74%.Statistics of pollen diameter showed that the grain diameter of frontal pollen of autotetraploid rice was significantly higher than that of diploid rice,and the difference was very significant.The increase of pollen diameter may be related to chromosome doubling.After chromosome doubling,autotetraploid rice appeared a certain proportion of double germinating pores or even triple germinating pores,but diploid rice did not have double germinating pores.3.The formation process of embryo sac in different ploidy rice was observed,and the formation process of embryo sac in different ploidy rice was the same.In the mature stage of embryo sac,the percentage of normal embryo sac in diploid rice was higher,the frequency of normal embryo sac was 93.45%-98.32%,while the frequency of normal embryo sac in autotetraploid rice was only 50.12%-75.62%,and the frequency of normal embryo sac in autotetraploid rice was only 50.12%-75.62%,respectively.About 24.38%-49.88% of the embryo sac were abnormal during development(such as degeneration of oocyte,degeneration of female reproductive unit structure and abnormal antipodal cell mass,etc.).4.In the process of double fertilization of different ploidy rice,it was observed that the double fertilization process of different ploidy rice was the same,but because the pollen grains of autotetraploid rice germinated slowly on the stigma,the penetration rate of pollen tube in the style of tetraploid rice was relatively slow.Then the pollen tube enters the embryo sac and the double fertilization is completed.The first division time of zygote and primary endosperm nucleus is later than that of diploid rice.Pollen tube germination on the column appeared abnormal ratio,including abnormal expansion of pollen tube,double pollen tube germination and so on.The agronomic characters of autotetraploid rice and its corresponding diploid rice were significantly different from those of diploid rice after chromosome doubling.The grain length,grain width and 1000-grain weight of autotetraploid rice were significantly better than those of corresponding diploid rice,but the seed setting rate of tetraploid rice was significantly lower than that of corresponding diploid rice.The pollen development and embryo sac development of different ploidy rice were consistent.However,autotetraploid rice produced higher frequency abortive pollen and abnormal embryo sac at mature pollen stage.In addition,the fertilization process of autotetraploid rice will be delayed than that of diploid rice,and even abnormal expansion of pollen tube germination will occur inautotetraploid rice.The above reasons may be the direct reason for the low seed setting rate of autotetraploid rice.In particular,during pollen development of autotetraploid rice,a certain proportion of double germinating pores and even triple sprouting pores were found.During fertilization,some pollens sprouted two pollen tubes from double germinating pores.Some double germinating holes have only one pollen tube germinating.The phenomenon of multiple germination pores and its germination mechanism need to be further studied.