CHANGES IN KIWIFRUIT CELL-WALL ULTRASTRUCTURE AND CELL PACKING DURING POSTHARVEST RIPENING

Light, scanning electron, and transmission electron micrographs of ripening kiwifruit were compared at different stages of softening. The three tissues of the fruit, outer pericarp, inner pericarp, and core, differed in packing and cell size. Morphometric studies indicated that the volume of intercellular air spaces increased as the fruit softened. Cell walls swelled in the outer pericarp earlier than in the core and in both tissues well before the climacteric. Except for plasmodesmatal regions, staining of cell wall material markedly declined or was lost in ripe fruit. Middle lamella breakdown was evident in samples taken from both ripe fruit and fruit just prior to ripeness, and electron-dense bodies accumulated between the plasmalemma and cell wall. The results support studies on changes in chemical composition and indicate that kiwifruit cell walls undergo ultrastructural changes during ripening similar to other fruit. However, the extent of cell wall swelling, loss of stainability, and timing of the changes differs.