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. I nduction 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 inc rease. The observed change of EGase activity was due to de novo protei n synthesis, as demonstrated by both RNA and protein blots. By means o f a cDNA fragment encoding a pepper EGase and an antibody raised again st a pepper fruit EGase, it was possible to show the appearance of a 2 .2 kb transcript and a 54 kDa polypeptide, respectively, following act ivation of flower abscission. A cDNA library was constructed, and the cDNA fragment was used to isolate a 1.8 kb clone which was sequenced a nd characterised. Ultrastructural analyses of-the cell separation even ts in the flower AZ showed clear consistency with the demonstrated con tribution of the EGase activity to abscission. Massive hydrolysis phen omena were particularly observed at the level of primary wall of the s eparating cells. Immunolocalization of EGase confirmed both the involv ement and the target of the enzyme.