Plant Gene and Trait 2025, Vol.16, No.4, 152-161 http://genbreedpublisher.com/index.php/pgt 154 3.2 Physiological traits: chlorophyll fluorescence, water retention, antioxidant activity Physiologically, the chlorophyll fluorescence values of heat-tolerant tea plants are generally high, indicating that their photosynthetic systems can still function normally in hot weather. The leaves of this type of tea tree have a strong water retention capacity, which can reduce water loss and also prevent the cell membrane from being damaged by high temperatures. Their antioxidant enzyme activities, such as POD and SOD, are also higher than those of common tea plants, which can eliminate reactive oxygen species produced at high temperatures and reduce cell damage (Seth et al., 2021; Huang et al., 2024). In addition, more regulatory substances like proline accumulate in the leaves of these tea plants, helping cells maintain a stable state. 3.3 Genetic basis and heritability of heat-tolerant traits Heat resistance is also related to genes. Research has found that under high-temperature conditions, heat-tolerant tea trees will activate some “emergency” genes, such as HSP90, HSP70 and HSP18.1, as well as the transcription factor HSFA2 that regulates them. These genes can regulate the heat stress response and help tea plants adapt to high temperatures (Seth et al., 2021). There are also some genes, such as FLS, which can promote flavonoid synthesis and enhance the antioxidant capacity of tea plants (Huang et al., 2024). The expression differences of these genes are the key to improving the heat tolerance of tea plants. Studies have also found that the heat tolerance traits of different tea tree varieties vary greatly and have relatively strong heritability, which provides a theoretical basis for the subsequent breeding of heat-tolerant tea trees (Driedonks et al., 2016). 4 Field Performance of Heat-Tolerant Tea Cultivars 4.1 Evaluation indicators and experimental methods When evaluating heat-tolerant tea trees in the field, researchers usually look at three aspects of indicators: physiological, biochemical and molecular levels. The commonly observed physiological aspects include leaf water content, chlorophyll content, whether the cell membrane is damaged, and the level of photosynthetic pigments (Figure 2) (Seth et al., 2021; Huang et al., 2024). The biochemical aspects mainly include the activities of antioxidant enzymes (such as SOD, APX and POX), regulatory substances like proline and betaine, and the accumulation of reactive oxygen species (H₂O₂, O₂⁻) in the body (Nalina et al., 2021). At the molecular level, we look at the expression of some key genes, such as heat shock proteins (HSPs) and heat shock transcription factors (HSFs) (Seth et al., 2021). Usually, when conducting such experiments, field treatment is carried out in a high-temperature environment, and then leaves are taken for physiological, biochemical, transcriptomic and metabolomic analyses (Shen et al., 2019). 4.2 Yield and quality maintenance under heat stress High temperatures can affect the yield and quality of tea trees. However, heat-resistant varieties will perform better. When it is hot, their leaves can retain more water, chlorophyll is less likely to decline, and cell membranes are relatively stable, so the yield is relatively stable (Seth et al., 2021). In terms of quality, heat-tolerant tea trees can accumulate more flavonoids and antioxidants, which can reduce the influence of high temperature on the flavor and composition of tea (Huang et al., 2024). Also, these tea plants activate more heat shock proteins and chaperone proteins when they are hot, which helps maintain protein stability and also helps protect cells, thereby ensuring the quality and yield of tea (Shen et al., 2019). 4.3 Effects of genotype ×environment ×management (G×E×M) interactions The heat tolerance of tea plants is also jointly influenced by variety, environment and management methods. Different varieties of tea trees react differently under the same high temperature. Some heat-resistant varieties can reduce tropical damage through more effective antioxidant and regulatory mechanisms. Environmental factors such as soil moisture content and temperature changes can also affect the expression of heat-tolerant genes and the accumulation of substances (Huang et al., 2024). If combined with reasonable management measures, such as irrigation or shading, it can also help tea plants better cope with high temperatures, maintain leaf function and improve field performance (Nalina et al., 2021). Therefore, for tea plants to grow well in summer with stable leaves and high yield, a good combination of variety, environment and management is the key.
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