The role of ethylene and cell wall modifying enzymes in raspberry (Rubus idaeus) fruit ripening

This study focuses on four raspberry (Rubus idaeus) genotypes from tno diff erent genetic backgrounds: cvs Glen Prosen and Glen Clova, bred at the Scot tish Crop Research Institute (SCRI) and genotypes bred at Horticulture Rese arch International (HRI), East Mailing (EM), EM 1997 and EM 5007. The ripe fruit of each genotype pair were characterised subjectively by raspberry br eeders as relatively firm or soft, respectively. Different stages of fruit development from each genotype were used to quantify fruit firmness, rates of ethylene evolution and ripening rate. Penetrometry data confirmed suspec ted firmness differences, Firmness correlated,vith rates of ethylene evolut ion. Rates of ethylene production also correlated with receptacle size. Sto rage of green fruits in 20 mu l 1(-1) ethylene reduced fruit firmness, enha nced respiration rate and colour (anthocyanin) development and stimulated t he development of cell wall hydrolase activities. However, during natural r ipening in the field, fruit respiration rate declined, which indicates a no n-climacteric ripening pattern. In drupelets, the activities of polygalactu ronase (PC;). pectin methylesterase (PME)I Cx-cellulase (Cx) and beta-galac tosidase (beta-gal,) increased substantially as ripening progressed, More d etailed studies with ripe fruit of cv. Glen Clova indicated major isoforms of PC at pIs 3.3, 8.6 and 10.1; of PME at pIs 7.2, 8.5, 8.7, 8.8; of Cx at pi 2.4 and of beta-gal. at pIs 6.3 and 6.7.