The Use of Radioactive Iodine in the Study of a Plant Growth-Regulator

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Abstract
2-iodo-4-chlorophenoxyaCetic acid (ICPA) labelled with I 131 was applied in the form of a 0·25 per cent. olive oil solution (using 2·5 per cent, ethyl alcohol as accessory solvent) to the upper leaf surface of young broad bean and oat plants at the rate of 0·01 ml. solution per plant. The initial activity of the solution was 3·75 mc. per ml. Epinastic effects were induced in the bean but not in the oat. The movement of the I 131 within the plattt was followed by means of autoradiographs. Results indicate rapid absorption and translocation of a high proportion of the applied material in the broad bean, radioactivity appearing in quantity in every part of the plant within 27 hours of treatment, with a marked cáncentration at the upper end of the stem and another at the lower end of the stem and top of the tap root. In the oat, on the other hand, absorption and translocation were much slower; only under the most favourable conditions did a small amount of of I 131 reach the root in 27 hours, and the amount absorbed was much less than in the bean. There was no upward movement of the I 131 into untreated leaves of the oat.