Premature breakdown of tapetum associated with reverse thermo-sensitive genic male-sterile line Huiyou50S in rapeseed (Brassica napus)

Thermo-sensitive genic male-sterility (TGMS) has great advantages in hybrid crop production. Different from common TGMS in Brassica napus, a reverse TGMS line named Huiyou50S is male sterile when it is cultivated in low temperature, but highly fertile when exposed to high temperature. To gain further insights into the developmental aberrations leading to this male sterility, the anther development of Huiyou50S was observed by light and electron microscopy. Firstly, it was suggested by light microscopy that the abortion of anther occurred at the tetrad to early uninucleate microspore stage. A premature breakdown of tapetum is associated with protoplast degradation in the uninucleate microspores. Under transmission electron microscope, the tapetum exhibited vacuolization from pollen mother cell (PMC) stage to tetrad microspore stage and was then disrupted before late microspore stage. Alterations in the tapetal cells included abnormal plastids and a loss of recognizable elaioplast. However, the endoplasmic reticulum seemed to be normal as in the fertile plant. The formation of primexine on the surface of tetrad microspores was postponed to the uninucleate microspore, and hence exine construction was delayed. The evidences suggested that a premature breakdown of tapetum characterized by vacuolization, less secretory activity and abnormal elaioplast, rather than programmed cell death in normal plant, was associated with microspore abortion in Huiyou50S.