Enhancement of Phloem Exudation from Cut Petioles by Chelating Agents

Abstract

The photosynthetic assimilates in leaves of Perilla crispa attached to the plant were labeled by treating the leaves with ¹⁴CO₂. When subsequently detached, these leaves exuded a negligible amount of radioactivity from the cut petiole into water. Ethylenediaminetetraacetate (EDTA), citric acid, and ethyleneglycol-bis (β-aminoethyl ether) N,N′-tetraacetate greatly increased exudation of labeled assimilates into a solution bathing the petioles. The optimal concentration of EDTA was 20 mm, and maximal exudation took place between 2 and 4 hours after excision. Up to 22% of the radioactivity fixed in the leaf was exuded into an EDTA solution as compared to an export of 38% from attached leaves. The amount of radioactivity in the exudate was much reduced at low temperature. Presence of EDTA was required in the collecting solution for only 1 to 2 hours; upon transfer to water, exudation continued as in continuous presence of EDTA. Ca²⁺ completely inhibited the effect of EDTA.