Comparison of Ethylenediaminetetraacetate-Enhanced Exudation from Detached and Translocation from Attached Bean Leaves

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Abstract
A technique for collection of phloem exudate from detached leaves using 20 mM EDTA (pH 7.0) was previously developed (King and Zeevaart 1974). The efficiency of this technique in relation to undisturbed export from attached leaves was determined. Paired primary leaves of bean seedlings (Phaseolus vulgaris L. cv Montcalm) were used to minimize variations in plant material. Attached leaves, exposed to 14CO2 for 10 min with subsequent excision of 1 of the leaves and collection of the exudate over a 12-h period, showed a 25% export of total assimilated 14C from the attached vs. 15% of total assimilated 14C in the form of exudation from the detached ones. Leaf excision changed the labeling pattern within the leaf, increasing percent total leaf 14C-activity in the ethanolic fraction, while decreasing activity in the starch fraction, as compared to attached leaves. This was presumably caused by a lack of translocation from the detached leaves. Excision did not affect dark respiration. Measurements of total nonstructural carbohydrates in leaf starch and neutral fractions indicated no significant differences between attached and leaves detached in EDTA. In terms of actual C export, and accompanying distribution of nonexported carbohydrate within the leaf, EDTA-enhanced exudation compares favorably with translocation from attached leaves.