Effect of Ethephon on IAA Transport, IAA Conjugation, and Antidotal Action of NAA in Relation to Leaf Abscission of Pecan

Abstract Ethephon at 3, 6, and 12 m m induced abscission of mature foliage on pecan [ Carya illinoensis (Wangenh) K. Koch] seedlings. This effect was offset to varying degrees using NAA at 3, 6, or 12 m m in which NAA acted as an effective antidote to ethephon and presumably ethylene. Abscission varied with leaf age and with the relative timing of leaf treatment with ethephon and NAA. Leaves treated with NAA 6 days prior to ethephon treatment were much more sensitive to ethephon induced abscission than those treated one day prior to, at time of, or one day after ethephon sprays. There were no abscission response differences among the 3 latter NAA treatment times. Ethephon greatly reduced 14 C-IAA transport in leaf midrib tissue and increased the amount of IAA conjugated in leaf tissue without changing free IAA levels. It is suggested that ethephon treatment reduces the amount of IAA transported from the leaf blade to the abscission zone by inhibiting auxin transport in vascular tissue. IAA inactivation by conjugation appears to have no influence on the IAA level reaching the cells of the abscission zone. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon); 1-naphthaleneacetic acid (NAA).