Morphological characteristics and cytological study of anther abortion of temperature-sensitive nuclear male sterile line 160S in <italic>Brassica napus</italic>

Abstract

<p indent=0mm>The main purpose of this study was to explore the flower morphologies, anther abortion times and cytological characteristics of the thermo sensitive genic male sterile line 160S in <italic>Brassica napus</italic>. The results will provide a theoretical basis for further study on the molecular regulation mechanism and guide significance for its practical application in two-line hybrid breeding of rape. The 160S were grown at 15℃ and 28℃. The flower morphology, microspore, anther structure and tapetum at different stages of fertile plants (Male Fertile/160S-MF) and sterile plants (Male Sterile/160S-MS) were observed by stereomicroscope with carmine acetate staining, paraffin section, hematoxylin eosin staining and TUNEL staining. The anther was yellow, plump and dehiscent with high pollen viability at 15℃. At 28℃, there was no differences in pistil and potato chips between 160S-MS and 160S-MF flowers, but the petals and the filaments of 160S-MS were smaller and shorter. The stamens of 160S-MS degenerated obviously and its anthers were shriveled in yellowish brown without pollen grains, indicating completely male sterility. But interestingly, the 160S-MF developed normally with higher pollen viability. However, microspore and pollen grains were not observed in 160S-MS due to complete abortion of stamens. Paraffin section results showed that there was no significant difference between 160S-MS and 160S-MF in sporulation and pollen mother cell stages. The morphology and structure of tapetum of 160S-MS appeared some abnormal appearances, such as irregularly cell arrangement, vacuolization, and premature disintegration at meiosis stage. Meanwhile, the development of pollen mother cells were hindered and no tetrads structure were formed leading to the empty pollen sac before the completion of meiosis. TUNEL assay showed that the tapetum of 160-MS began to apoptosis at meiosis stage. In summary, these results showed that 160S belongs to pollen mother cell abortion type male sterile line, whose abortion stage occured during meiosis stage and the tapetum cells degraded prematurely and failed to be transformed to the glandular type, so that the nutrients needed for pollen mother cell development were not provided. The tetrad structures and microspores can not be formed, which leaded to the formation of empty anther sac and resulted in male sterility.