Rice Genomics and Genetics 2024, Vol.15, No.1, 19-27 http://cropscipublisher.com/index.php/rgg 23 and lower the rate of water loss. This adjustment helps to maintain leaf water balance and prevent excessive water loss. However, this may also lead to a decrease in photosynthesis, as stomatal closure restricts the entry of CO2 and affects the process of photosynthesis. Therefore, rice leaves may balance the relationship between photosynthesis and transpiration by adjusting the expression of photosynthetic enzymes and other related genes to maximize growth and survival (Buckley, 2019). The changes in physiological characteristics of these leaves indicate that rice has adopted a series of physiological adjustments under drought conditions to adapt to environments with limited water. Understanding the molecular mechanisms and physiological processes of these adjustments can help us better understand the response mechanisms of plants to drought and provide theoretical support for future drought tolerance breeding. In depth research on the adjustment of water use efficiency and changes in photosynthesis and transpiration of rice leaves will provide strong scientific basis for formulating more effective drought management strategies in rice. 3.2 Leaf metabolic regulation Rice leaves undergo complex metabolic regulation under drought stress, involving changes in carbon metabolism and accumulation of antioxidant substances, which are key physiological responses of plants in response to drought conditions. Under drought conditions, the carbon metabolism of rice leaves undergoes significant changes. Under limited water conditions, plants may adjust their carbon metabolism pathways to adapt to changes in photosynthesis and carbon fixation. Usually, plants adjust enzyme activity, such as regulating the activity of RuBisCO enzyme to improve carbon fixation efficiency. In addition, plants may also adjust sugar metabolism pathways to maintain a balance between energy and carbon. This may include increasing sugar accumulation as a reserve of energy and signaling molecules to maintain normal growth and metabolic activity under drought conditions. So, when rice leaves face drought stress, they will accumulate more antioxidant substances. Due to the oxidative stress caused by drought, excessive accumulation of reactive oxygen species occurs. Rice leaves alleviate oxidative stress by adjusting the synthesis and accumulation of antioxidant substances. Antioxidants include superoxide dismutase (SOD), peroxidase (POD), ascorbic acid peroxidase (APX), etc. These enzymes can clear free oxygen radicals in cells, protect cell membranes, proteins, nucleic acids, and other biomolecules from oxidative damage (Wang et al., 2018). These changes in metabolic regulation constitute important physiological characteristics of rice leaves under drought conditions. By adjusting carbon metabolism pathways, plants can more effectively utilize limited water resources and protect cells from oxidative damage by accumulating antioxidant substances. This adaptation strategy helps rice maintain basic growth and survival functions in arid environments. Deeply understanding the mechanisms of metabolic regulation not only helps to understand the physiological response of rice to drought, but also provides scientific basis for developing rice varieties with better drought tolerance. 3.3 Molecular level leaf response The response of rice leaves under drought conditions involves complex molecular level regulation, including regulation of leaf gene expression and activation of signal transduction pathways. These molecular level regulatory mechanisms are key components for plants to respond quickly and accurately to drought stress. Drought stress can trigger the regulation of gene expression in rice leaves, which is a direct response to environmental pressure. By changing the expression level of specific genes, plants can quickly adapt to drought environments (Wang et al., 2019). In the leaves, a series of genes related to drought resistance may be activated or suppressed. This may include genes encoding dehydratin response elements, transcription factors, and signaling molecules, whose expression regulation directly participates in the plant's stress response to drought. Through the regulation of gene expression, rice leaves can initiate a series of physiological processes to enhance their drought resistance. For example, previous studies on Yangdao 6 and Shanyou 63 have shown that compared to normal water
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