Cytological Basis Of Pollen Abortion And Fruit Development In Seedless Pea

Rosa sterilis and Rosa roxburghii Tratt both belong to the Rosaceae genus Rosa,the former had the characteristics of high pollen abortion and the ability to parthenocarpy.In order to better understand the mechanism of pollen abortion in seedless chestnut rose,this study selected chestnut rose as the control.Observing the relationship between the diameter of flower buds and the development period of pollen.Scanning electron microscopy was used to observe pollen morphology.The pollen of seedless chestnut rose and chestnut rose were stained with I₂-KI and magenta acetate solution and cultured in vitro to observe the pollen activity.The systematic observation of meiosis,microspore development,and callose development of pollen mother cells in seedless chestnut rose and chestnut rose was carried out by using the squashing method in order to reveal the cytological basis for high pollen abortion in seedless chestnut rose.At the same time,the anatomical structure of seedless chestnut rose fruit at different development stages was observed.The main results were as follows:1.Relationship between bud size and pollen developmentAs the transverse diameter of the bud increased,pollen development was at different periods,suggesting a correlation between bud size and the period of pollen development.2.Pollen morphological characteristicsThe pollen grains of chestnut rose were mostly spherical in shape and had a plump morphology.The surface of the pollen grains was smooth and flat,with concave holes of varying sizes.Compared with the control,the majority of seedless chestnut rose pollen grains were irregular,with a small portion being spherical in shape,not full in shape,and some were empty and broken,with uneven sizes.3.Pollen vitalityUnder in vitro culture conditions,most of the pollen of chestnut rose germinated into pollen tubes,with a pollen germination rate of 85.13±3.1%,while the pollen germination rate of seedless chestnut rose was 13.87±1.2%.Acetic acid magenta staining showed that 84.21±2.5%of chestnut rose pollen was active,while 9.33±1.9%of seedless chestnut rose pollen was active.In addition,using I₂-KI staining solution,11.89±1.7%of seedless chestnut rose pollen was active,while 80.61±2.8%of chestnut rose pollen was active.4.Meiosis process of pollen mother cellsThe meiosis of the pollen mother cells of the control chestnut rose was normal,while there were abnormal phenomena in the meiosis of the pollen mother cells of the seedless chestnut rose,such as ring chromosome,lagging chromosome,the center of the equatorial plate,asynchronous chromosomes division,Micronuclei,chromosome bridge,broken chromosome,asymmetric arrangement of chromosome,etc.In meiotic prophase I,abnormal chromosome behavior reached 61.11%.At metaphase I,abnormal chromosome behavior reached 54.44%.At anaphase I,abnormal chromosome behavior reached 50.00%.At telophase I,abnormal chromosome behavior reached 49.66%.5.Microspore development processThe pollen mother cells of the control chestnut rose underwent meiosis to form a tetrahedral tetrad,which was also a cross shaped tetrahedral tetrad,crossed tetrads,left-right symmetric tetrad.The microspore underwent mitosis and formed a vegetative nucleus and a reproductive nucleus,indicating that the microspore development process of chestnut rose was normal.Most tetrads of seedless chestnut rose have a normal structure,but some pollen mother cells form triads,pentads,and hexads after meiosis,with the majority of triads.With the development of microspores,the nuclei of seedless chestnut rose underwent disintegration during the binuclear stage.6.Callose development processDuring pollen development,callose was deposited around the mother cell and tetrad stages of the seedless chestnut rose and chestnut rose.With the further development of the tetrad,the callose of chestnut rose was disintegrated,and a large amount of callose deposition was detected after the microspores of seedless chestnut rose were released from the tetrad.7.Fruit developmentSeedless chestnut rose fruit growth and development was a double S-shaped curve growth pattern,unfertilized ovary directly developed pericarp specializes in three thin-walled cell layers,namely,the exocarp,mesocarp and endocarp.Fruits grew rapidly in S1 stage,slowly in S2 stage,rapidly in S3 stage and slowly in S4stage.