CELL-WALL METABOLISM IN RIPENING FRUIT .9. SYNTHESIS OF PECTIC AND HEMICELLULOSIC CELL-WALL POLYMERS IN THE OUTER PERICARP OF MATURE GREEN TOMATOES (CV XMT-22)

Discs of outer pericarp were excised from mature green tomato (Lycoper sicon esculentum Mill.) fruit and kept in sterile tissue culture plate s for 4 d, including 2 d of incubation with D-[U-C-13]glucose. Cell wa lls were prepared and the water-soluble, pectic, and hemicellulosic po lymers were extracted. Cell wall synthetic capacity was determined by gas chromatography-mass spectrometry analysis of incorporation of the heavy isotope label. The ''outer'' 2-mm pericarp region, which include d the cuticle, had a lower cell wall synthetic capacity than the ''inn er'' 2-mm region immediately below it (closer to the locules), based o n the percentage of labeling of the neutral sugars. There were no sign ificant differences in relative abundance of glycosidic linkages in th e two tissue regions. Label was incorporated into neutral sugars and l inkages typical for each polysaccharide class were identified in the c ell wall preparations. Galacturonic acid and glucuronic acid were labe led to an extent similar to that of the neutral sugars in each tissue region.