Ultrastructure in Microspore Abortion of Genic Male Sterile Line in Sesame(Sesamum indicum L.)

Sesame(Sesamum indicum L.) is an important oil-seed crop with great nutritional value,and the sesame hybrid has remarkable heterosis in many characters,especially in productivity.To investigate the abortion mechanism of genic male sterile(GMS) line in sesame,a comparative study was conducted on the fertile and sterile microsporogenesis of ms86-1 derived from the male sterile line discovered by Osman using transmission electron microscopy(TEM) techniques.According to the morphologic characteristics of the microspores,the developmental process of sesame pollen could be tentatively divided into seven stages,including microsporocyte formation stage,microsporocyte meiosis stage,tetrad stage,early microspore stage,middle microspore stage,late microspore stage,and pollen maturation stage,respectively.The abnormal phenomena observed in the sterile anthers indicated that male sterility might arise in microsporocyte formation stage.With the growth and development of the sterile anthers,the following abnormal features were observed evidently.The cell wall of the sterile microsporocytes was irregular during their formation stage.In the meiosis stage,the cell walls were getting distorted obviously,and the microsporocytes failed to form the early exine component designated as probaculums on the outside of the plasma membrane.Subsequently,abnormal villiform de-posits were observed on the outside of the callose wall during the tetrad stage.As soon as the tetrad cells disintegrated,the re-leased sterile microspores represented aberrantly dumbbell-shaped,and their exines were undergrown without any baculum.Ac-companying with the delay of the degeneration process,inclusions of the tapetum cells became more abundant and few abnormal ubisch bodies were secreted.Later on,the sterile microspore was gradually crimpled as its cytoplasm agglomerated to an electron dense clot,and ultimately degraded to the complete abortion.In this paper,compared with the fertile pollen development,the abortion process and characteristics of the sterile anthers were disclosed,providing a foundation for the greater insight into theabortion mechanism of GMS line in sesame.