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Articles

Promotion of Softening and Ethylene Synthesis in Bartlett Pears by 3-Methylene Oxindole ¹

Virginia R. Haddon^b and Joanne M. Smallheer^b

^a Department of Horticulture and Forestry, Cook College, Rutgers—The State University, New Brunswick, New Jersey 08903, Department of Chemistry, Douglass College, Rutgers—The State University, New Brunswick, New Jersey 08903

A purified preparation of 3-methylene oxindole (3-MeOx) was applied to Bartlett pears (Lyrus communis) by vacuum infiltration. The infiltrated fruit were kept at room temperature at atmospheric or at one-twentieth of an atmospheric tension. The rate of softening was markedly enhanced by the application of 0.1 and 1 µM 3-MeOx. At 10 µM 3-MeOx the promotive effect of the compound was diminished. All the employed concentrations of 3-MeOx exceeded the effect of applied ethylene. The enhancement of softening in fruit kept under hypobaric conditions suggests that the action of 3-MeOx is a direct one and not an indirect ethylene effect. 3-MeOx also showed stimulation in the onset of ethylene synthesis, shortening the time required to obtain the peak in ethylene synthesis from 5 days by the control to 3 days by 0.1 µM and 2 days by 1 µM of the applied compound. As with softening, 3-MeOx at 10 µM diminished the rate of ethylene synthesis.

The results suggest that 3-MeOx could function as a senescence promoter in fruit. Also, since auxins retard ripening while 3-MeOx promotes ripening, the action of 3-MeOx may be considered as that of an auxin antagonist. The occurrence and the mode of action of 3-MeOx as a possible senescence factor in fruit are discussed.