The Uptake of Growth Substances: III. INFLUENCE OF INDOLEACETIC ACID AND OTHER AUXINS ON THE UPTAKE OF 2,4-DICHLOROPHENOXY-ACETIC ACID BYCHLORELLA

When 2,4-dichlorophenoxyacetic acid, labelled with 14C, is accumulated by Chlorella pyrenoidosa, an appreciable fraction, which increases with time, is held within the cell in a form which is not removed when the cells are placed in a solution containing the unlabelled compound. The accumulation of this fraction is dependent upon the supply of metabolic energy since it is affected by temperature, light, and the addition of inhibitors or citrate to the external medium. The uptake of this metabolically accumulated 2,4-D follows a pattern which indicates that a single enzymic reaction is a predominant component of the uptake process. In the presence of the other auxins, including indoleacetic acid, 2,4,5-trichlorophenoxyacetic acid and 4-chlorophenoxyacetic acid, the uptake of 2,4-D is depressed and the changes suggest that there is competition at the site of this reaction. The nature of the competition is seemingly of the type where each compound serves as a substrate for the enzyme. It may be significant that the extent to which the individual auxins compete with 2,4-D is in the same order as their general effectiveness as growth regulators for other species.