Abstract
In the northern part of Japan, cool-weather damage in rice production is very severe in climate damages. And it has occurred about 25 times during the past century (once every 4 years on an average) in Hokkaido. Rice plants has 2 types of cool-weather damage; delayed growth type and destructive sterile one. Between them, it is very important for the latter to solve physiological mechanism to cool stress and to establish the countermeasures for conquering cool-weather damage. Destructive sterility to cool stress mainly suffer the damage at booting stage and flowering one during pollen developmental process. The most sensitive stage, the trough in fertility curve to cool stress at booting stage is the early microspore stage from tetrad to early microspore phase. And the next sensitive stage is just before pollen germination at flowering stage. At booting stage, the decrease of pollen number per anther to the stress is closely related to the sterility. Pollen activity to the stress, however, is not clear to the tolerance. At flowering stage, the cool tolerance is influenced after decision of pollen number in an anther. So, one of the important reaction to coolness is the abnormal digestion of starch to sucrose just before the germination of the pollens. Besides pollen differentiation and development mechanism, it is necessary for more strong cool tolerance to solve the mechanism of fertilization on the stigma, and more stable and higher in-vitro germination because of very short longevity of rice pollens.
