Enhancement of the Release of Protoplasts and Pectin from Tomato Locular Gel by Pectin Methylesterase

Pectin methylesterase (PME, EC 3.1.1.11) was added to locular gel and pericarp of ripening tomato ( Lycopersicon esculentum Mill.) and cell wall alterations were examined. Treatment of mature tomato locular gel with purified PME resulted in release of protoplasts. No protoplasts could be detected from immature locular gel or pericarp at any ripening stage examined under similar conditions. Net solubilization of pectins occurred with PME treatment in both tissues. Pectins solubilized with buffer or PME were of high molecular weight. Maximum protoplast release and pectin solubilization occurred at pH 5.0. Increased pectin solubilization in locular gel and pericarp is a result of polygalacturonase action on PME-induced deesterified pectin, the preferred substrate. Release of protoplasts from PME-treated mature locular gel suggests that maturation in this tissue involves alterations in cell wall structure that do not occur in pericarp.