Abstract: Ultrastructure of the storey-side and the shaded side peels of the apple ( Malus pumila Mill. ) fruits stored at 0 ℃ for 4 months and later developed scald at 20 ℃ were observed by electron microscopy. It was found that electron dense matehals (EDM) in the apple cuticle was strongly correlated with scald development. EDM could move firm cuticle to inner cells along the cell walls. The accumulation of EDM on the cells could cause the breakage of plasmalemma and damage internal structure. The EDM could move into the cell as the cell collapsed. It was assumed that EDM could be a compound product of a-fhrnesene oxidation in the cuticle. At the end of cold storage, no scald developed on beth the sunny-side and the shaded side peels of' apples. Little EDM was found in the walls of outer hypodennal cells of the sunny-side fruit peel in which the cells maintained their healthy structure, but some epidermal cells in the shaded side fmit peel were destroyed by EDM. It was also found that much EDM existed in the walls of outer hypodermal cells. There was no scald symptoms develop on the sunny-side peel after the shaded side peel of the fruit severely scalded at 20 ℃. Only a few cells in the outer hypodermis of the sunny-side peel of the fruit were damaged by EDM, most of the cells maintained their healthy structure, but all of the cells in the shaded side peel of the fruit were destroyed and electron-dense was increased. It was suggested that the epidermal and hypodermal cells were damaged by EDM in the cuticle from outside of the cells.

Key words: Apple, Superficial scald, Electron-dense materials, Cuticle, Ultrastructure