Translocation of Labeled Assimilates into and Out of Bean Leaves as Affected by 2,4-D and Benzyl Adenine

When a primary leaf on a bean plant was treated with 2,4-D, it imported 14C-labeled assimilates from the opposite primary leaf; the greatest import occurred when the treated leaf was darkened. Benzyl adenine also caused treated leaves to import labeled assimilates when the leaves were darkened but usually not when the leaves were not darkened. Essentially no label was imported by untreated leaves, even when darkened for several days, unless the shoots were debudded; debudding caused darkened leaves to import label. Regardless of the type of treatment, the imported labeled assimilates were confined mainly to the veins. Leaves that were detached from plants following their exposure to 14CO2 translocated labeled assimilates from the mesophyll into the veins in a polar manner; this polar movement was not prevented by any treatment of these leaves, including prior applications of 10,000 ppm of 2,4-D or 7,900 ppm of benzyl adenine. After the veins were loaded, the labeled assimilates were transported basipetally into the petioles; the distribution of the label was relatively uniform from top to bottom of the petioles (except for the pulvinus-upper and lower). The basipetal movement in detached leaves was not prevented by benzyl adenine unless they were assimilate-starved (darkening them for 5 days); basipetal movement was reduced but not prevented by similar treatments with 2,4-D. Basipetal flow out of attached leaves treated with 2,4-D or benzyl adenine occurred in all tests. Labeled assimilate transport in the bean plant was greatly altered by treatment of a primary leaf with 2,4-D and to a lesser extent by benzyl adenine. The greatest alteration occurred when the 2,4-D-treated leaf was kept in the dark; this resulted in most of the exported 2,4-D being confined to the epicotyl. The bulk of the labeled assimilate then migrated into the 2,4-D-containing tissues.