Absorption and Translocation of 2,4-Dichlorophenoxyacetic Acid and P32 by Leaves

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Abstract
The absorption of 2,4-D by soybean (Glycine max) leaves was increased by surface active chemicals and by increased temperature. In contrast, absorption of P32 applied as a weakly acid phosphate solution exhibited neither of these responses. Absorption of 2,4-D or P32 was not reduced by depletion of leaf carbohydrates. Translocation of both materials was slowed or stopped by a similar depletion. In all cases absorption was a much more rapid process than translocation. Six hours after detached beet (Beta vulgaris) leaf blades were painted with a P32 solution a large portion of the activity was concentrated in the veins, while little remained in considerable areas of the mesophyll. This process, termed "loading", required the presence of available carbohydrate, but occurred in the absence of transport from the leaf blade. It was concluded that absorption and translocation of both experimental materials require actively metabolizing tissue and that loading is a normal process preceding translocation.