The development of stone cells in Japanese pear fruit

The development of stone cells in Japanese pear (Pyrus serotina cv. Shinseiki) fruit was investigated over a single season to study the processes of stone cell differentiation and lignin accumulation. Stone cells in the flesh were apparent on 22 April, 2 weeks after anthesis, aggregating to form stone-cell clusters (SCCs) during May and early-June. The density of SCCs was highest during Stage II of fruit growth, when fruit enlargement slowed. The young stone cells developed secondary cell walls which grew by the accumulation of lignin. This lignification gave rise to vesicular structures inside the cytoplasm, and the eventual destruction of the cytoplasm. The outer portion of the flesh, outside the network of main dorsal vascular bundles, had a comparatively lower density of smaller SCCs compared with the inner portion, which contained more than 100 stone cells per SCC. Smaller SCCs were relatively more abundant in the epidermal area. Stone-cell formation and development were related to the general growth of fruit in Japanese pear.