Rice Genomics and Genetics 2024, Vol.15, No.1, 1-11 http://cropscipublisher.com/index.php/rgg 4 conditions, the vitality of pollen often significantly decreases. Research has shown that an increase in temperature may cause denaturation and oxidation of pollen proteins, thereby affecting the structure and function of pollen particles. Under high temperature conditions, the wax layer on the surface of pollen may change, which in turn affects the water balance and osmotic regulation of pollen particles. These changes directly lead to a decrease in pollen vitality, reducing the success rate of pollen during pollination. Pollen with vitality contains active peroxidase, which can use hydrogen peroxide to oxidize various polyphenols and aromatic amines and produce color. If the pollen grain is red, it indicates the presence of peroxidase, and the pollen is active and can germinate; If it is colorless, it indicates that it has lost vitality and cannot sprout. The strength of pollen activity can be determined by the color of the pollen. Using rice flowering under normal natural climate conditions as a control, this study investigates the effect of high temperature on rice pollen vitality and seed setting rate. For example, in a study by Zhao Qihui et al. (2013), they focused on two varieties: heat resistant strain 996 and heat sensitive strain 4628. The results showed that pollen vitality decreased under high temperatures. On the first day of treatment, the pollen vitality of heat resistant strain 996 and heat sensitive strain 4628 decreased by 7.8% and 13.8% respectively compared to the control, with a significant difference. Moreover, as the time of high temperature stress prolonged, the pollen vitality of the two strains continued to decline until the end of treatment, The pollen vitality of heat-resistant strain 996 and thermosensitive strain 4628 decreased by 19.6% and 32.88% compared to the control, with significant differences. During the entire processing period, the pollen vitality of the heat-resistant strain 996 was higher than that of the thermosensitive strain 4628 (Figure 1) (Zhang et al., 2008). Figure 1 Effects of high temperature stress on rice pollen vigor (Adopted from Zhang et al., 2008) In addition to the decrease in pollen vitality, high temperatures also directly affect the survival rate of rice pollen. Under high temperature conditions, the storage capacity of pollen particles decreases, which may lead to the inability of pollen to survive effectively during pollination. Some experiments have shown that under high temperature conditions, pollen may be more prone to losing vitality, and even exhibit higher mortality rates during storage. 2.2 Effect of high temperature stress on the number of pollen grains on rice stigma High temperature stress has a widespread and significant impact on the reproductive process of rice, one of which is its effect on the number of pollen grains on the stigma. The stigma is a crucial part of rice inflorescence, directly involved in the propagation and pollination process of pollen. In high-temperature environments, the reduction of pollen grains on the stigma may become an important factor in the reduction of rice yield. The seed setting rate of rice depends on the fertilization rate, and normal fertilization first depends on the number of pollen grains on the stigma. If sufficient pollen grains cannot be guaranteed, normal fertilization and seed setting cannot be achieved.
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