CELL-WALL METABOLISM IN RIPENING FRUIT .7. BIOLOGICALLY-ACTIVE PECTIN OLIGOMERS IN RIPENING TOMATO (LYCOPERSICON-ESCULENTUM MILL) FRUITS

A water-soluble, ethanol-insoluble extract of autolytically inactive tomato (Lycopersicon esculentum Mill.) pericarp tissue contains a series of galacturonic acid-containing (pectic) oligosaccharides that will elicit a transient increase in ethylene biosynthesis when applied to pericarp discs cut from mature green fruit. The concentration of these oligosaccharides in extracts (2.2 mu g/g fresh weight) is in excess of that required to promote ethylene synthesis. Oligomers in extracts of ripening fruits were partially purified by preparative high-performance liquid chromatography, and their compositions are described. Pectins were extracted from cell walls prepared from mature green fruit using chelator and Na2CO3 solutions. These pectins are not active in eliciting ethylene synthesis. However, treatment of the Na2CO3-soluble, but not the chelator-soluble, pectin with pure tomato polygalacturonase 1 generates oligomers that are similar to those extracted from ripening fruit (according to high-performance liquid chromatography analysis) and are active as elicitors. The possibility that pectin-derived oligomers are endogenous regulators of ripening is discussed.