Early signs of heat stress-induced abnormal development of anther in rice

A continuous high temperature (other than short-term rise in temperature) leads to heat stress in rice at the reproductive growth stage under field conditions. Hence rice can be sensitive to heat stress from meiocyte meiosis to anthesis stage, and not just at anthesis. Rice is likely to respond to heat stress in a cumulative way. Under imitated daily field microclimatic conditions for heat stress, the rice cultivar "Jinyou63" (which is a hybrid rice combination) was treated with a consecutive 3-day heat stress during meiosis in phytotron. Anther and pollen tissues at different development stages after subjected to heat stress were sampled and analyzed for transverse abnormalities. The analysis shows that under heat stress, meiocytes degenerate while tetrad cell dispersion fails at microspore formation phase. During pollen maturation phase, loss of orientation of reproductive cells, abnormal vacuolization of tapetal cells, paramorphia or abortion of anther walls and pollens are observed under heat stress. In addition, pollen activity at anthe-sis decreases significantly under heat stress during meiosis stage. The findings suggest that abnormalities in anther tissues and repro-ductive cells are caused by heat stress before heading. This decreases yield potential of active pollens and destroys dehiscence and pollination, which could be the primary cause of rice sterility under continuously high temperature field conditions.