Cellulase Activity in Separation Zones of Citrus Fruit Treated with Abscisic Acid under Normal and Hypobaric Atmospheres1

Abscisic acid (ABA) introduced through the stem of ‘Pineapple’ and ‘Valencia’ oranges stimulated cellulase activity in the separation zones. ‘Pineapple’ orange was affected more than ‘Valencia’. Cellulase activity was greatest under normal atmospheres in which ethylene accumulated in the treated fruit. Under one-fifth atmosphere with little ethylene accumulation, cellulase was 2 to 2.5 times greater in separation zones of treated fruit than in non-treated fruit. ABA introduced through the stem was more effective than spray applications. ABA sprayed on the fruit was partly absorbed but did not increase ethylene production or cellulase activity, or decrease fruit removal force.