Endo-beta-mannanase activity increases in the skin and outer pericarp of tomato fruits during ripening

Activity of endo-beta-mannanase increases during ripening of tomato (Lycope rsicon esculentum Mill.) fruit of the cultivar Trust. beta-Mannoside mannoh ydrolase is also present during ripening, but its pattern of activity is di fferent from that of endo-beta-mannanase. The increase in endo-beta-mannana se activity is greatest in the skin, and less in the outer and inner perica rp regions. This enzyme is probably bound to the walls of the outermost cel l layers of the fruit during ripening, and it requires a high-salt buffer f or effective extraction. The enzyme protein, as detected immunologically on Western blots, is present during the early stages of ripening, before any enzyme activity is detectable. The mRNA for the enzyme is also present at t hese stages; endo-beta-mannanase may be produced and sequestered in a matur e-sized inactive form during early ripening. Most non-ripening mutants of t omato exhibit reduced softening and lower endo-beta-mannanase activity, but a cause-and-effect relationship between the enzyme and ripening is unlikel y because some cultivars which ripen normally do not exhibit any endo-beta- mannanase activity in the fruit.