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

A water-soluble, ethanol-insoluble extract of autolytically inactive t omato (Lycopersicon esculentum Mill.) pericarp tissue contains a serie s of galacturonic acid-containing (pectic) oligosaccharides that will elicit a transient increase in ethylene biosynthesis when applied to p ericarp 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-performan ce liquid chromatography, and their compositions are described. Pectin s were extracted from cell walls prepared from mature green fruit usin g chelator and Na2CO3 solutions. These pectins are not active in elici ting 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 oligo mers are endogenous regulators of ripening is discussed.