Tannin cell morphology as a structural marker for classification of persimmon cultivars

Large amounts of tannins (proanthocyanidins) accumulate in specialized tannin cells of persimmon (Diospyros kaki Thunb.) fruit, contributing to the sensation of astringency. However, there is no clear consensus on whether tannin cells within the same cultivar group share common morphological characteristics. In this study, mature fruits were used as experimental material, and tannin cells were examined using a filtration–clarification method combined with soft-fruit pressure smearing. The results showed that: (1) tannin cell morphology was highly diverse and clearly distinct from that of parenchyma cells; (2) tannin cells were generally slender in pollination-constant non-astringent (PCNA) cultivars and wider in non-PCNA types. Pollination-variant non-astringent (PVNA) cultivars contained numerous spine-like tannin cells, whereas tumorous tannin cells were predominant in pollination-variant astringent (PVA) and pollination-constant astringent (PCA) cultivars; (3) browning tannin cells were observed in both PCNA and non-PCNA types, but occurred at lower frequency in Chinese PCNA (C-PCNA) and PCA; (4) across different de-astringent types, most tannin cells were of the coagulated type, while a small proportion of coacervate tannin cells occurred in Japanese PCNA (J-PCNA) and PVNA, and contracted tannin cells were detected in J-PCNA, C-PCNA, and PVNA. Overall, tannin cell morphology exhibited consistent characteristics within cultivar types, indicating its potential as a structural marker for the classification of persimmon cultivars. Persimmon (Diospyros kaki Thunb.) fruits accumulate large amounts of tannins (proanthocyanidins), which are stored in specialized flesh cells known as tannin cells. Although tannin cell morphology is highly diverse, there has been no clear consensus regarding the relationship between tannin cell morphology and cultivar classification. The morphology of tannin cells exhibited consistent characteristics within the same cultivar types. Across different persimmon types, most tannin cells were of the coagulated type. Browning tannin cells were observed to varying degrees, among different de-astringent persimmon types. This study may shorten the identification cycle of persimmon types, simplify identification procedures, and provide a new, reliable approach for the classification and identification of persimmon genotypes.