CELL-WALL METABOLISM IN RIPENING FRUIT .8. CELL-WALL COMPOSITION AND SYNTHETIC CAPACITY OF 2 REGIONS OF THE OUTER PERICARP OF MATURE GREEN AND RED RIPE CV JACKPOT TOMATOES

Pericarp discs were excised from mature green and red ripe tomato (Lyc opersicon esculentum Mill. cv. Jackpot) fruit and kept in sterile tiss ue culture plates for 4 days, in eluding 2 days of incubation with D-[ U-C-13]-glucose, Cell walls were prepared and differentially extracted with dimethylsulfoxide (DMSO), trans-1,2-diaminocyclohexane-N,N,N',N' -tetraacetic acid (CDTA), Na2CO3, 4 M KOH and 8 M KOH. Cell wall nonce llulosic neutral sugar (NS) composition and cell wall synthetic capaci ty (i.e. incorporation of density label into cell wall sugars) were de termined by using a gas chromatograph coupled to a flame ionization de tector and a mass spectrometer, respectively. In the crude cell wall, there was significantly less galactose (Gal) and glucose (Glc) in the ''outer'' 2-mm pericarp region, including the cuticle, compared to the ''inner'' 2-mm region immediately below it (closer to the locules). I n the CDTA-soluble pectin, rhamnose (Rha), arabinose (Ara) and Gal acc ounted for approximately 90% of the total NS. The ratios of these suga rs were very similar in the total (C-12 plus C-13) sugars, and also in the newly synthesized ([C-13]-labeled) sugars, suggesting that newly synthesized NS associated with the chelator-extractable pectic fractio n has a composition very similar to that of preexisting NS, In the 4 M KOH-soluble material, xylose (Xyl) and Glc accounted for approximatel y 70% of the total NS, The ratio of these sugars was very similar in t he total sugars, but much lower in the newly synthesized portion. This suggests that the hemicellulosic polymers synthesized during the ripe ning process are different in type and/or proportion from those presen t in the developing fruit. Because the outer pericarp of tomatoes cont ains at least two distinct tissue types and these have a distinct cell wall composition, analysis of tomato cell wall polysaccharide composi tion by homogenization of the entire outer pericarp will obscure subtl e changes associated with ripening/softening within specific tissue ty pes.