Morphological Studies on Pellicle Development and Removal in Chestnut

Abstract

The developmental processes and the ease of peeling the pellicle in Japanese and Chinese chestnuts were investigated with light phase and scanning and transmission electron microscopes.
During the early growth stage of Japanese chestnut, tannin accumulated in pellicle cells as scattered granules in vacuoles, aggregates along tonoplasts, electron-dense vacuoles, vacuoles with high density of tannin, etc. At harvest, however, most of the pellicle cells were filled with tannin. The tannin cells, which had high electron-dense vacuoles, were located mainly in the middle and outer layers of pellicle, whereas those adjacent to the cotyledons accumulated less tannin.
Various aspects related to the ease of peeling the pellicle, i. e. the adhesive force between pellicle and cotyledon were examined but aspects specific to the variety were not recognized.
In Japanese chestnut varieties, whose pellicles are difficult to peel, tannin accumulated in most of the cells of pellicle tissues; the cells in contact with the cotyledon and those in the middle layers of pellicle were crushed during the growth of fruits. The low electron density matrix and the electron-dense structure of network developed between the pellicle and the epidermis of the cotyledon. The network structure is probably made of tannins which penetrates into the epidermal cells of the cotyledon.
In Chinese chestnut varieties, whose pellicle peels easily, the pellicle cells accumulate little tannin; those in contact with the cotyledon degrade slowly. No penetration of electron-dense structure of network into epidermal cells of the cotyledon occurs.
These finding suggest that the adhesive force between the pellicle cells and the cotyledon depends, not only on tannin accumulation in the pellicle cells, but also on the degradation of the cells contacting the cotyledon.