Ethylene and Auxin Transport and Metabolism in Peach Fruit Abscission

Abstract Interaction of exogenous ethylene and embryoctomy with auxin transport and metabolism through the abscission zone located between fruit and receptable (AZ3) was studied in ‘Andross’ peach. At the end of stage I of fruit development, abscission was induced physically by embryoctomy, or chemically be using ethephon as the ethylene releaser, and/or TIBA as an auxin transport inhibitor. Ethephon was applied to the fruit (Ef) or to the pedicel (Ep), and TIBA to the pedicel, alone (TIBAp) or in combination with ethephon to the fruit (TIBAp + Ef). Embryoctomy induced a quick activation of AZ3 cells, with all fruits abscising in one week; Ef, Ef + TIBAp, TIBAp and induced a fruit drop of 80−85%. Ethephon applied to the pedicel was totally ineffective in hastening fruit drop. Abscission was preceded by a reduction of ( 1−14 C)IAA transport through AZ3 cells, an increase of its decarboxylation and changes in partitioning of the radioactivity among the different solvents. Radioactivity in the EtOH fraction declined in those treatments that were effective in promoting abscission, while it decreased in the NaOH and residue fractions. Changes in the H 2 O fraction were variable. As far as metabolites in the EtOH soluble fraction are concerned, higher levels of ( 1−14 C)IAA and lower amounts of ( 1−14 C)IAASp were detected in explants excised from treatments effective in promoting abscission. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon); and 2,3,5-triiodobenzoic acid (TIBA).