Fine structure of the suberized cell walls in the boundary zone and necrophylactic periderm in wounded peach bark

Abstract

Bark on the scaffold limbs of 6-year-old peach (Prunus persica (L.) Batsch cv. Redhaven) trees was mechanically wounded and tissue samples for ultrastructural study were taken after 6, 8, 12, and 14 days. Examination with light and fluorescence microscopy revealed lignification of boundary zone cell walls after 6 days followed by suberization of the lignified cell walls after 8 days. Necrophylactic periderm was present by day 12 and, by day 14, three to five cells of the new phellem were observed. Examination of tissues with transmission electron microscopy revealed suberin lamellae on the inner wall of boundary zone cells. These cells contained senescing cytoplasm with fragments of undifferentiated dense material that formed a thin, discontinuous granular deposit inside the suberin layer. Suberin lamellae did not occlude plasmodesmata. Cells of the new phellem were radially compressed, heavily suberized, and lacked pits or plasmodesmata.