Development of the structure of the russeted apple skin

The epidermal, cuticular, and periderm layers of the apple “Golden Delicious” were studied electron microscopically in the period during which the skin russets, with special reference to the cutin and suberin containing layers. Naturally occurring russeting and the artificially induced form (by iron or copper compounds or mechanical injury) are identical on the EM level. The stages of development are as follows: Firstly, a strong cutinization is observed in the anticlinal and periclinal inner cell walls of the epidermis forming a cuticular epithelium. Secondly, a suberization of the divided cells under the “second cuticle” is described. Thirdly, the suberized cells become located on the outside and they give rise to russeting. The suberin wall consists of alternating wax and suberin lamellae. These suberin lamellae appear to end in globules located in the tertiary cellulose wall. The fibrillar structure of the cuticle is discussed in connection with the lamellar structure of the suberin.