Rice Genomics and Genetics 2024, Vol.15, No.1, 1-11 http://cropscipublisher.com/index.php/rgg 5 Research has shown that high temperature stress can lead to a significant decrease in the number of pollen grains on the stigma. For example, in previous studies, under high temperature treatment conditions, the average number of pollen grains on the stigma of the heat-resistant strain 996 was 35, while the average number of pollen grains on the thermosensitive strain 4628 was 19, indicating a significant difference between the two; Under natural conditions in the field, the average number of pollen on the stigma of the heat-resistant strain 996 is 125, while the heat sensitive strain 4628 is 132, with no significant difference between the two. Further analysis shows that the number of pollen on the stigma is determined by the cracking condition of the anthers, and there is a significant positive correlation between the two, with a correlation coefficient of 0.8476 (Figure 2) (Zhang et al., 2008). Figure 2 Effects of high temperature stress on rice pollen grains on the stigma of rice (Adopted from Zhang et al., 2008) Therefore, the impact of high temperature on the number of pollen grains on rice stigma involves complex physiological and ecological mechanisms, including pollen development and physiological adaptation of the stigma. A deeper understanding of this impact mechanism not only helps to explain the adverse effects of high temperature on rice yield, but also provides important scientific basis for the future development of high-temperature resistant varieties and the formulation of agricultural management strategies. The reduction of pollen caused by high temperature may be related to the sensitivity of pollen development and changes in the physiological state of the stigma. Under high temperature stress, pollen development may be disrupted, leading to incomplete development or early death. At the same time, the stigma is stimulated by high temperature, which may cause dehydration of the stigma cells and degeneration of the cell wall, affecting the reception and support ability of the stigma, thereby reducing the survival and attachment ability of pollen on the stigma. This influence may also affect the fertilization process and final yield of rice. The number of pollen on the stigma is not only related to pollen release and pollination efficiency, but also directly affects the success rate of fertilization. In fact, studies have confirmed the close relationship between high temperature and the decrease in rice pollen grain count and yield. 2.3 The effect of high temperature stress on the size of rice pollen grains High temperature stress is a common environmental stress during the growth and development of rice, which has a significant impact on the morphology, structure, and size of pollen. The size of pollen grains is directly related to their movement and deposition during pollination, so the impact of high temperature on pollen size may have a significant impact on the success of rice reproduction and yield. Case studies have shown that under high temperature stress, the size of rice pollen grains usually changes. Under suitable temperature conditions, pollen grains usually have a relatively uniform shape and larger size, which is conducive to their stable carrying during wind or insect transmission. However, in high-temperature environments, pollen grains often exhibit a shrinking trend, sometimes even exhibiting irregular shapes. This change may be related to factors such as high-temperature induced denaturation of cell membrane lipids and inhibition of protein synthesis (Chaturvedi et al., 2021).
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