NAA-induced Ethylene and ACC in `Delicious' Spur Tissues: Changes with Temperature and Time

These studies with apple (Malus domestica Borkh.) spur tissues were conducted to investigate the mechanism whereby NAA may stimulate fruit abscission in the spring but acts to prevent fruit drop in the fall. NAA-induced ethylene evolution from `Delicious' spurs in vivo was similar to that evolved from excised leaf and fruit tissues that later were treated in the laboratory and incubated in darkness at 20C. The peak in ethylene production occurred 24 hours after treatment at 30C, 48 hours after treatment at 20C, and production was still increasing 72 hours after treatment at 10C. Leaf tissue showed the greatest induction of ethylene from NAA followed by fruit and petiolar tissues. Induction was greatest early in the season and declined steadily until about “June drop.” After this time, none of the tissues showed significant capacity for ethylene induction. Chemical names used: 2-(1 -naphthyl) acetic acid (NAA).