Endo-beta-1,4-glucanase activity is involved in the abscission of pepper flowers.

The expression of endo-beta-1,4-glucanase (EGase) and ultrastructural details were examined in the abscission zone (AZ) of pepper flowers. Induction of abscission caused an increase in EGase activity which was due to two isoforms with different isoelectric points (pi 7.2 and 8.5, respectively). In particular, ethylene had a promotive effect on the 7.2 isoform while the basic isoenzyme did not show any significant increase. The observed change of EGase activity was due to de novo protein synthesis, as demonstrated by both RNA and protein blots. By means of a cDNA fragment encoding a pepper EGase and an antibody raised against a pepper fruit EGase, it was possible to show the appearance of a 2.2 kb transcript and a 54 kDa polypeptide, respectively, following activation of flower abscission. A cDNA library was constructed, and the cDNA fragment was used to isolate a 1.8 kb clone which was sequenced and characterised. Ultrastructural analyses of-the cell separation events in the flower AZ showed clear consistency with the demonstrated contribution of the EGase activity to abscission. Massive hydrolysis phenomena were particularly observed at the level of primary wall of the separating cells. Immunolocalization of EGase confirmed both the involvement and the target of the enzyme.