Translocation of a Radioactive Plant-Growth Regulator in Bean and Barley Plants

Abstract

The synthesis of radioactive 2-iodo-3-nitrobenzoic acid (INBA) is descr. Two series of reference standards for the radioactivity measurements, one of bean leaf tissue and one of bean petiole tissue, were prepared. For tracing the movement of radioactivity through bean and barley seedlings, INBA was applied to a leaf of these plants as a paste. After treatment the plants were dried and ground and the radioactivity of samples was measured by an Edelmann electrometer-ionization chamber. INBA showed marked inhibitory action on the growth of the bean plant and slight action on that of the barley plant. In the bean the compd. was most effective in inhibiting development of the bud. The compd. was apparently absorbed by the leaves of bean seedlings and translocated to the stems where it accumulated mainly in the terminal buds and in the hypocotyls. INBA was also apparently absorbed by the leaves of barley plants and accumulated mainly in the second leaf. In contrast with bean plants INBA in barley plants was not associated with a significant decrease in their rate of growth. The appearance of radioactivity in the plants following treatment does not prove that the intact INBA molecule actually entered the plant and was translocated as such but it has been shown that the application of elemental iodine, 3-nitrobenzoic acid, or 3-nitrosalicyic acid fails to bring about responses in the bean plant similar to those caused by INBA.