Antisense suppression of tomato endo-1,4-beta-glucanase Cel2 mRNA accumulation increases the force required to break fruit abscission zones but does not affect fruit softening

Plants of tomato (Lycopersicon esculentum Mill. cv. T5) were transformed wi th an antisense endo-1,4-beta-glucanase (cellulase, EC 3.2.1.4) Cel2 transg ene under the control of the constitutive cauliflower mosaic virus 35S prom oter in order to suppress mRNA accumulation of Cel2. In two independent tra nsgenic lines, Cel2 mRNA abundance was reduced by > 95% in ripe fruit peric arp and ca. 80% in fruit abscission zones relative to non-transgenic contro ls. In both transgenic lines the softening of antisense Cel2 fruit pericarp measured using stress-relaxation analysis was indistinguishable from contr ol fruit. No differences in ethylene evolution were observed between fruit of control and antisense Cel2 genotypes. However, in fruit abscission zones the suppression of Cel2 mRNA accumulation caused a significant (P < 0.001) increase in the force required to cause breakage of the abscission zone at 4 days post breaker, an increase of 27% in one transgenic line and of 46% in the other transgenic line. Thus the Cel2 gene product contributes to cel l wall disassembly occurring in cell separation during fruit abscission, bu t its role, if any, in softening or textural changes occurring in fruit per icarp during ripening was not revealed by suppression of Cel2 gene expressi on.