CELL-WALL METABOLISM IN RIPENING FRUIT .6. EFFECT OF THE ANTISENSE POLYGALACTURONASE GENE ON CELL-WALL CHANGES ACCOMPANYING RIPENING IN TRANSGENIC TOMATOES

Cell walls of tomato (Lycopersicon esculentum Mill.) fruit, prepared s o as to minimize residual hydrolytic activity and autolysis, exhibit i ncreasing solubilization of pectins as ripening proceeds, and this pro cess is not evident in fruit from transgenic plants with the antisense gene for polygalacturonase (PG). A comparison of activities of a numb er of possible cell wall hydrolases indicated that antisense fruit dif fer from control fruit specifically in their low PG activity. The comp osition of cell wall fractions of mature green fruit from transgenic a nd control (wild-type) plants were indistinguishable except for trans- 1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA)-soluble pecti ns of transgenic fruit, which had elevated levels of arabinose and gal actose. Neutral polysaccharides and polyuronides increased in the wate r-soluble fraction of wild-type fruit during ripening, and this was ma tched by a decline in Na2CO3-Soluble pectins, equal in magnitude and t iming. This, together with compositional analysis showing increasing g alactose, arabinose, and rhamnose in the water-soluble fraction, mirro red by a decline of these same residues in the Na2CO3-soluble pectins, suggests that the polyuronides and neutral polysaccharides solubilize d by PG come from the Na2CO3-soluble fraction of the tomato cell wall. In addition to the loss of galactose from the cell wall as a result o f PG activity, both antisense and control fruit exhibit an independent decline in galactose in both the CDTA-soluble and Na2CO3-soluble frac tions, which may play a role in fruit softening.