Ethylene-enhanced Ion and Sucrose Efflux in Morning Glory Flower Tissue

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Abstract
Rib tissue segments excised from open flowers or buds of Ipomoea tricolor Cav. and floated on aqueous media responded to ethylene treatment by rolling up after 2 to 3 hours; a simple method for quantitating the rolling up is presented. The rolling up response was temperature- and oxygen-dependent and was critically affected by the pH of the medium. The ethylene concentration giving a half-maximal response was 0.1 mul/l; continuous ethylene treatment was not required for the response as a 1-hour ethylene exposure enhanced rolling up.Rib segments rolling up during ethylene treatment unrolled when transferred to 0.5 m sucrose, indicating that rolling up was due to asymmetric turgor changes in the segments. Compartmental analysis of (36)Cl(-) efflux from rib segments showed a fast and a slow phase; the slow phase, with a half-time of about 6 hours, is tentatively identified as efflux from the vacuolar compartment. During ethylene treatment, the rate of (36)Cl(-) efflux in the slow phase rose markedly as the rolling up response developed. A similar result was obtained with the efflux of (86)Rb(+). The release of (14)C-metabolites, labeled either by a period of (14)CO(2) fixation in darkness or by exposure to (14)C-(U)-glucose, also increased during ethylene-induced rolling up.These results suggest that ethylene causes an increase in membrane permeability in certain cells of the rib tissue.