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Abscission of the leaflets of Sambucus nigra is stimulated by ethylene. Associated with cell separation is an increase in the activity of β 1,4 glucanase (cellulase) and polygalacturonase (PG) and this rise is restricted to the cells comprising the abscission zone. A cDNA library has been generated from mRNA extracted from separating abscission zone cells and screened using a heterologous s 1,4 glucanase probe from Phaseolus vulgaris. A number of positive cDNAs have been isolated from the S. nigra library and the largest clone designated pJET1 has a size of 1.7Kb. pJET1 has been sequenced and exhibits over 70% deduced amino acid homology with the protein encoded by the P. vulgaris cDNA. Using a differential screening strategy over 20 abscission-related cDNAs have been isolated from the library. None of these hybridizes to pJET1 and their role in abscission remains to be determined.

Different strategies were compared for the concentration of polygalacturonase, ß-glucosidase and ß-galactosidase produced by two strains of Aspergillus niger. Ultrafiltration was more successful than vacuum evaporation for all three enzymes but produced concentrates with high solids contents. The use of mineral adsorbents enabled almost complete separation and concentration of polygalacturonase and ß-glucosidase activities from one culture filtrate. Concentration of all three enzymes using adsorbents led to preparations with higher specific activities and lower solids contents than the corresponding ultrafiltration concentrates.

Cell-wall degradation occurs in a wide variety of situations. First, it is important at certain points in the normal life of the plant, such as seed germination, xylem-vessel formation, fruit ripening, abscission and it perhaps growth (Section 4.5). Secondly, it is an important part of the process by which other organisms degrade plant material, whether in the process of pathogenic or saprophytic attack by microorganisms or during digestion by herbivores. Thirdly, cell-wall degradation is a key process underlying several industrial processes.

Exposure of tomato plants to salinity enhances the ripening process in their fruits. Thus, all the ripening parameters measured, e.g. CO2 and ethylene evolution rates, pigment concentration, fruit softening, polygalacturonase activity, and taste, were higher than in their respective controls (4).