Poster: Cell Walls

Abs # 1270: Pectin Polymer Metabolism in Green Tomato Fruit

Presenter:	Prody, Gerry A, prody@chem.wwu.edu
Authors	Prody, Gerry A (A)   Greve, L. Carl  (B)   An, Hyun-Joo  (C)   Lebrilla, Carlito B (C)   Lurie, Susan  (D)   Labavitch, John M (B)
Affiliations:	(A): Department of Chemistry, Western Washington University (B): Department of Pomology, University of California, Davis (C): Department of Chemistry, University of California, Davis (D): Volcani Institute, Bet-Dagan, Israel

For several years, we have been testing the hypothesis that pectin-derived oligosaccharides (PDOs) generated during metabolic cell wall pectin modification play an important role in initiating ripening in tomato fruit. Initial investigations have shown that, when applied to excised mature green (MG) tomato fruit pericarp discs, PDOs from citrus pectin promote ethylene synthesis and red color development (Campbell and Labavitch, Plant Phys. 97:706-713, 1991). In addition, we have shown that PDOs extracted from tomato fruits that had just begun to ripen also promoted fruit ethylene production (Melotto et al., Plant Phys. 106:575-581, 1994). The most active of these endogenous PDOs had degrees of polymerization (DPs) in the 7-11 range, based on HPLC analysis and contained neutral sugar as well as the expected galacturonosyl residues, suggesting that they had been generated by the metabolism of branched-chain pectin polymers. In this study, we have collected tomatoes at various pre-ripening developmental stages and cut them in half. We have extracted cell wall fractions one set and prepared enzyme extracts from the other. When combined with these enzyme extracts, the wall polysaccharides undergo a dramatic size change based on size exclusion chromatography. We have also developed methods to unequivocally determine the identities of the sugars present at both the reducing and non-reducing ends of the oligosaccharides generated and are now using MALDI Fourier Transform Ion Cyclotron MS techniques to obtain additional details about the structures of these biologically active oligosaccharides. These methods, along with more classical chemical analyses, provide evidence for pectin polymer backbone-cleaving enzymes in extracts of young, rapidly growing green tomato fruit.