Preferential water uptake and differences in the anatomical structure of the distal end of grape berry may jointly lead to cracking in vitro soaking

The distal end of grape berries preferentially cracks during the soaking process in vitro, which may be related to preferential water uptake and cell anatomy. Thus, the relationship between water uptake and cell anatomical structure was assessed using 49 grape varieties. In vitro immersion experiments were performed on mature berries to measure the differences in berry-cracking properties. A whole-berry in vitro staining method was used to trace the water uptake of the vascular bundles, and paraffin sections were used to observe and analyze the structural parameters of the different tissues. The results showed that the berry-cracking rate and water uptake of the distal end of berries prone to cracking were significantly higher than that of the resistant berries. Compared with the berries that were resistant to cracking, the berries that were prone to cracking possessed a thin cuticle, epidermis and sub-epidermis. Dye accumulated in the distal end of the cracking-prone berries, which even exhibited cracking during the dyeing process. However, less dye accumulated on the surface of the cracking-resistant varieties and was only sporadically distributed on the surface. In addition, cracking of the distal end of the berry may also be related to other shape and size parameters of the cells in cell layer. Analysis of vascular bundle water transport and the differences in the cell structure characteristics of the different varieties, offered a preliminary explanation for why the distal end of the berry is prone to cracking, providing theoretical support for further research on the mechanisms of berry cracking.