International Journal of Horticulture, 2025, Vol.15, No.6, 290-298 http://hortherbpublisher.com/index.php/ijh 293 consumers demand in terms of appearance, taste, and storage life and reducing postharvest loss for producers (Tarricone et al., 2020; Quartacci et al., 2022). 4 Mechanisms of Sugar Accumulation Influenced by Leaf Removal 4.1 Photosynthesis and assimilate supply Leaf removal directly alters the photosynthetic pathway of grapevines by reducing the total leaf area available for carbon assimilation. Modest removal within the cluster zone can assist in optimizing light penetration and the microclimate, with the photosynthetic efficiency of the retained leaves being improved and the supply of assimilates to developing berries being increased. Yet, over-removal or excessive reduction of the leaf area-to-fruit weight ratio can limit overall photosynthetic production, retard sugar accumulation, and reduce final sugar concentrations in the fruit (Silva et al., 2017; Wang et al., 2021; Assefa et al., 2025). The balance between sufficient photosynthetic supply and improved microclimate is of utmost significance for optimal sugar accumulation. 4.2 Source-sink relationship regulation Removal of leaves regulates source-sink balance by transforming the ratio of photosynthetic sources (leaves) to sinks (fruits). Partial leaf area reduction may enhance assimilate distribution towards the berries, promoting sugar accumulation, whereas severe leaf area reduction may result in source limitation, constraining sugar availability to the berries. The duration and severity of leaf excision are also critical: early or moderate treatments induce greater sugar translocation, while severe or late leaf excision may reduce the pool size of assimilates and retard fruit ripening (Silva et al., 2017; Arrillaga et al., 2021; O'Brien et al., 2021) (Figure 2). Besides, berry anthocyanin capacity per berry (expressed as equal malvidin-3-glucoside, A/berry) has been shown to be related closely with leaf-to-fruit ratio and grape yield. These correlations can be modeled with non-linear and linear polynomial models (Figure 2A: A/berry vs. leaf-to-fruit ratio; Figure 2B: A/berry vs. grape yield), which indicate that source-sink balance regulation in the dynamic form affects not only sugar accumulation, but also largely contributes to anthocyanin production. Figure 2 Relationship between grape leaves and fruit yield (Adopted from Arrillaga et al., 2021) Image caption: EMG: equivalent malvidin glucoside. Non-lineal-regression and linear polynomic model were fitted; A: anthocyanin potential in berry (A/berry) as a function of leaf to fruit ratio; B: anthocyanin potential in berry (A/berry) as a function of yield per vine (Adapted from Arrillaga et al., 2021) 4.3 Regulation of carbohydrate metabolism-related enzymes and genes Leaf removal, which influences gene expression and enzymatic activity of carbohydrate metabolism in grape berries, was found to increase the transcript level of sugar unloading-related genes such as VvHT3, VvHT5, VvSUC11, VvSUC12, VvSS, and VvcwINV, all of which were positively correlated with reducing sugar and soluble sugar content of berries. These molecular changes facilitate enhanced hexose (glucose and fructose) accumulation,
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