TRANSGENIC ANALYSIS OF TOMATO ENDO-BETA-1,4-GLUCANASE GENE-FUNCTION -ROLE OF CEL1 IN FLORAL ABSCISSION

Endo-beta-1,4-glucanase (EGase) expression in ripening tomato fruit an d abscising tomato flowers reflects the overlapping accumulation of st ructurally divergent gene transcripts, including EGase1 (Cel1) and EGa se2 (Cel2). Transgenic plants in which cell expression was specificall y inhibited were evaluated in order to assess the potential role(s) pl ayed by Cel1 during fruit ripening and floral abscission. The constitu tive expression of an antisense cel1 gene driven by the 35S promoter o f cauliflower mosaic virus resulted in the reduction of Cel1 mRNA to t race levels in both ripening fruit and abscising abscission zones of t ransgenic tomato plants. Transgenic fruit in which cell expression was reduced to less than 0.1% of wild-type levels exhibited normal growth and softening behaviour. Transgenic floral abscission zones expressin g 5-7% of wild-type levels of Cel1 mRNA exhibited an incidence of absc ission reduced by up to one third. The incomplete loss of abscission a bility by transgenic flowers may indicate that the contribution of Cel 1 activity is insufficient to account for all floral abscission and at tests to the presence in tomato abscission zones of additional cell wa ll hydrolase activities, including Cel2.