Studies on Translocation

Studies have been made on the translocation of C14-labeled solutes (2,4-D, 2,4,6-T and sugar(s)) and labeled solvent (THO or H2O18) in the red kidney bean. Transport of 2,4-D can be controlled by regulating the supply of carbohydrate in the leaves. For the first six hours following treatment of leaves with 2,4-D, the amount of 2,4-D transported to the epicotyl increases linearly with time. Over short time intervals the amount of 2,4-D transported is linearly related to the concentration applied. Over longer time intervals high concentrations of 2,4-D tend to depress transport somewhat. Transport of 2,4-D does not however saturate at concentrations which saturate the growth process of the plant. Essentially the same amount of 2,4-D is transported to the epicotyl of plants grown under 1000 and 2000 f.c. of light. Growth of the epicotyls induced by equivalent amounts of 2,4-D is two to four times larger in plants grown under 2000 than in those grown under 1000 f.c. of light, however. The compounds 2,4-D and 2,4,6-T are equally well absorbed by bean leaves and travel at the same speed in the phloem. The amount of 2,4,6-T which enters the phloem of the leaf, per unit time, is less than the amount of 2,4-D which so enters. TIBA applied as a pre-treatment to petioles inhibits the transport of C14-labeled 2,4-D, 2,4,6-T and sugars (predominantly sucrose). The inhibition of sugar movement may be used to interpret the inhibitory effect of TIBA on 2,4-D and 2,4,6-T transport. Foliarly applied tritium labeled (THO) and O18-labeled (H2O18) water are transported downward in bean seedlings. The carbohydrate status of the leaf does not govern the transport of labeled water in the same manner as it governs 2,4-D transport. The transport of THO takes place equally well or better in girdled as in normal plants. Movement of tritium apparently takes place in the xylem rather than in the phloem