Consequences of high temperature under changing climate optima for rice pollen characteristics-concepts and perspectives

The enhancement in both frequency and intensity of high temperature, besides its large variability will result in up to 40% yield reduction in rice by the end of 21st century. Vegetative growth in rice continues with day time temperature up to 40 degrees C but development of florets is extremely sensitive to temperature higher than 35 degrees C. The effect of night time temperature stress is even more adverse than day. Heat stress results in deprived anther dehiscence, impaired pollination and abnormal pollen germination that cause floret sterility. The decrease in pollen viability is presumably caused by imbalance in proteins expression, abandoned biosynthesis, partitioning and translocation of soluble sugars, imbalance in phytohormones release, and loss of pollen water content. Rice responds to heat stress by adjusting various physiochemical mechanisms viz., growth inhibition, leaf senescence and alteration in basic physiological processes. Antioxidant enzymes, calcium and iron also play an important role in managing heat stress. Response of rice to heat stress varies with plant ecotype, growth stage, heat intensity and time of stress application. High temperature stress can be managed by developing heat-tolerant genotypes. Rice breeding and screening may be based on anther dehiscence, pollen tube development and pollen germination on stigma.