Defects in microtubule cytoskeleton during microsporogenesis relate to pollen abortion in male-sterile pepper (Capsicum annuum L.)

Microtubule (MT) cytoskeleton of pepper male-sterile microsporocytes during meiosis was examined to characterise the defects during microsporogenesis by comparison with that of fertile ones. In sterile microsporocytes, after prophase I, abnormal arrangement of MTs occurred until the end of meiosis. At metaphase I, about 10% of microsporocytes initially formed abnormal spindles, including monopolar spindle, non-polar spindle with short kinetochore MTs, and atypical bipolar spindles with two half arrays of MTs not on the same plane. Then, the homologous chromosomes could not separate, or they could move towards the two poles with lagged chromosomes at anaphase I. At telophase I, anisotropic short MTs were formed around the two sister nuclei, or the interzonal MTs depolymerised and nuclei agglutinated. About 10% of microsporocytes degraded in advance from metaphase I to telophase I. About 90% of microsporocytes proceeded to meiosis II. At metaphase II, MTs constructed two spindles at a shallow angle with upper and lower assignment, or four spindles with different size. During anaphase II and telophase II, four nuclei were arranged in a non-tetrahedral distribution with unevenly interzonal MTs between two nuclei; or the cell formed more than four nuclei with different size. The cytokinesis formed the aberrant microspores with different size, irregular shape, and even different-sized nuclei. Therefore, the defects of MTs during microsporogenesis in the male-sterile pepper affected the process of meiosis and cytokinesis, leading to some microsporocytes degraded in advance and the microspores at the end of meiosis completely decayed.