IMMUNOCYTOCHEMICAL STUDY OF THE DEESTERIFICATION PATTERNS DURING CELL-WALL AUTOLYSIS IN THE RIPENING OF CHERRY TOMATO

The softening process in the ripening of fleshy fruits involves cell wall changes followed by cell separation in the pericarp tissue. Cell separation is brought about by the solubilization of the pectic-rich middle lamella. The modification of pectic substrates was followed in cherry tomato fruits (Lycopersicon esculentum, var. cerasiforme) at different stages of ripening: mature-green, orange and uniformly red. Two monoclonal antibodies (JIM 5 and JIM 7) which recognize homogalacturonic sequences with various degrees of esterification were used, either alone or sequentially for double labelling. Immunolabelling allowed the observation of wall microdomains and the possible analysis of little changes occurring during the differentiation process. A localized loss of labelling with JIM 7, i.e. the disappearance of highly methylated homogalacturonic sequences, occurred. This change in methylesterification was visualized both in time (steps of ripening) and space (in muro observations). It did not occur at random, but seemed to be spatially regulated. The unevenness of distribution of non-methylated homogalacturonan epitopes, recognized by JIM 5. changed during the ripening. In the red stage the labelling was extended evenly throughout the primary cell wall. Data emphasize the importance of a controlled deesterification which renders the wall susceptible to a subsequent enzymatic attack, thus leading to a possible splitting.