Rice Genomics and Genetics 2024, Vol.15, No.1, 19-27 http://cropscipublisher.com/index.php/rgg 22 related to stress response, water regulation, and antioxidant activity may be activated, initiating a series of physiological processes to enhance the root system's resistance to drought. Meanwhile, some growth and development related genes may be suppressed to regulate the growth rate of plants and better adapt to water limited conditions. For example, previous studies have found that the decrease in plant hydraulic conductivity (Kplant) of rice under drought conditions is mainly due to the decrease in soil root interface hydraulic conductivity (Ki), as Ki is more sensitive to drought than root and stem hydraulic conductivity, and the soil root interface contributes more than 40% of the overall plant hydraulic resistance to the two crops (Figure 2) (Yang et al., 2023). Figure 2 The mechanism of the plasticity of root morphology and anatomy in regulating plant drought resistance (Adopted from Yang et al., 2023) The regulation of water channel gene expression by rice roots under drought conditions is an important mechanism to ensure effective water absorption by plants. This involves water channel proteins, such as aquaporins in the aquaporin family. Under drought stress, rice roots may regulate the expression of water channel proteins to control water absorption and transportation. On the one hand, the upregulation of aquaporins may increase cell membrane permeability and promote water entry into cells. On the other hand, it is possible to reduce the expression of water channel proteins by regulating the negative regulators of certain water channel proteins, in order to limit water loss (Wu et al., 2020). These molecular level root responses constitute an important component of rice's adaptability under drought conditions. By delving into these molecular mechanisms, we can better understand the stress response of rice in arid environments, providing strong guidance for future breeding work. Understanding the changes in gene expression in rice roots and the regulation of water channel genes is expected to provide more in-depth and precise strategies for developing more drought tolerant rice varieties. This will help improve the adaptability of rice and better respond to extreme climate events brought about by global climate change. 3 Drought Response of Rice Leaves 3.1 Changes in leaf physiological characteristics Rice leaves undergo complex physiological changes under drought stress, including adjustments in water use efficiency and changes in photosynthesis and transpiration. These adjustments are survival strategies adopted by plants to more effectively maintain growth and survival in environments with limited water. The adjustment of water use efficiency is one of the important physiological characteristics of rice leaves under drought conditions. Water use efficiency refers to the biomass produced by plants under unit water conditions, which is the ratio of photosynthetic products to transpiration loss. In arid environments, rice leaves may reduce water loss by adjusting stomatal opening and epidermal conductance. In addition, plants may also improve photosynthetic efficiency by adjusting physiological and molecular responses, thereby more effectively utilizing limited water resources. The changes in photosynthesis and transpiration are another significant physiological feature of rice leaves under drought stress. In situations of water scarcity, plants may reduce stomatal conductance, slow down transpiration,
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