Plant Gene and Trait 2025, Vol.16, No.4, 152-161 http://genbreedpublisher.com/index.php/pgt 155 5 Summer Leaf Functional Stability 5.1 Definition and importance of functional stability in summer leaves Leaf functional stability means that the leaves of tea plants can still function normally during hot or dry summers, such as continuing photosynthesis, transpiration and maintaining cellular moisture. This ability is extremely important because it ensures that the tea plants are still growing leaves when it is hot and can still be picked. High temperature and water shortage can damage leaves, deteriorate photosynthesis, potentially damage cells, and make leaves prone to premature aging, ultimately affecting yield and quality (Peguero-Pina et al., 2020; Cao et al., 2024). Figure 2 Summarized illustration of physiological and molecular insights underlying heat stress associated thermotolerance in tea (Adopted from Seth et al., 2021) Image caption: The higher temperature leads to an increase in leaf surface temperature with decreased water content, cellular oxidizing ability, and chlorophyll content, while an increase in the membrane damage due to high electrolyte leakage. The heatmap represents gene enrichment in heat sensitive (HS) and tolerant (HT) cultivars under control (HS_Ct; HT_Ct) and under heat treatment (HS_H; HT_H) (Adopted from Seth et al., 2021) 5.2 Key evaluation indicators: SPAD, leaf temperature, turgor regulation The SPAD value can reflect the amount of chlorophyll and is an indicator for judging the photosynthetic capacity and health status of leaves. When the weather is hot, if the SPAD value can still remain stable, it indicates that the leaves can still retain chlorophyll, which is conducive to maintaining photosynthetic efficiency and heat resistance (Gao et al., 2025; Hočevar et al., 2025). In addition, the temperature of the blades is also very crucial. When the temperature is high, the temperature of the leaves will also rise. If the leaves can dissipate heat through transpiration, they can be maintained at a relatively suitable temperature, which also indicates that it has a certain heat resistance capacity (Peguero-Pina et al., 2020; Cao et al., 2024). The turgor pressure loss point (πtlp) is an indicator used to determine whether leaves can retain cellular moisture when they are dry. The better this value is, the more drought-resistant the leaves will be. If the turgor pressure regulation ability of the leaves of a tea plant is strong, it is not easy to wither in the dry and hot summer, and the cell function can also be maintained better (Zhu et al., 2018; Trueba et al., 2019). 5.3 Relationship between functional stability, plucking quality, and economic return Those tea trees with good stability in leaf function can still continuously grow high-quality fresh leaves in summer. Even if the weather is very hot, it is not easy for the leaves to get injured or for their quality to deteriorate. In this way, not only can the quality of the picked tea be guaranteed, but also better economic benefits can be brought (Zhu et al., 2018; Peguero-Pina et al., 2020; Cao et al., 2024; Gao et al., 2025). This stability mainly depends on several aspects: for instance, if the SPAD value remains high, it indicates that the chlorophyll in the leaves has not dropped too much; If the temperature of the leaves is well controlled, the cells are less likely to go bad. Another
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