Cell wall metabolism during ripening and storage of nonclimacteric sour cherry (Prunus cerasus l., cv. Kántorjánosi)

Ripeness: The colour of green (ripeness stage I), pit hardening (II), light red (a, b) (III, IV), red (V) and dark red (VI) sour cherry fruits ( Prunus cerasus cv. Kántorjánosi) were characterised by CIELAB L*, a* and b* values. L* and b* decreased as a function of ripeness, a* intensively increased between green (I) and pit hardening (II) stages. The cell wall of green fruit was intact, but the electron dense cytoplasm concentrated along the cell wall and showed a number of degradation signs. The pit hardening stage (II) resulted in more structural break down in the cytoplasm and in the cell wall. Large numbers of plastoglobuli were in the plastids resulting in chloroplast-gerontoplast conformation. The most striking feature of light red fruits is the dissolution of the walls. Middle lamellae almost completely disappeared. In ripe fruits, the wall degradation was even more prominent. The regular structure of the cytoplasm had almost completely disappeared. The total pectin content between pit hardening and light red stages was the highest. The autolysis of pectin increased between pit hardening (II) and light red-a stage (III), then it slowly decreased. The largest activity of β-galactosidase was in the green (I) stage, and then in the pit hardening stage (II) it suddenly decreased. In light red-a/b (III/IV) stages the activity of β-galactosidase again started to increase. The activity of polygalacturonase did not depend on the grade of ripeness. Storage: In the first period of storage, the activity of β-galactosidase and polygalacturonase of sour cherry decreased, then in the second period of storage increased