Abstract
The phytohormone auxin is widely recognized as a regulator of growth and morphogenesis. Since retarded growth and altered developmental patterns in plants are known to follow exposure to ionizing radiation, Skoog (26) investigated the inactivation of auxin by xand ?-rays. His data indicated that both native auxin preparations and pure 3-indoleacetic acid (IAA) in solution were highly labile when irradiated. A marked reduction in auxin levels also occurred when plant tissues were given moderate doses of x-radiation. Auxin thus appeared to be radiosensitive in vitro and in vivo. Skoog pointed out the parallel effects of decreased auxin levels and low doses of radiation in growth and correlation phenomena. His results were used subsequently by other workers to interpret various radiation responses on the basis of auxin radiosensitivity (10, 16, 27). However, certain considerations discussed below cast doubt on the implied direct sensitivity of the auxin molecule, and prompted our reinvestigation of auxin radiosensitivity. Concomitantly, a more precise evaluation of IAA inactivation kinetics was obtained. The present work deals with the destruction of auxin in aqueous solution by ionizing radiation. Auxin sensitivity in the plant, and the biochemical mechanisms whereby auxin levels are lowered in vivo, will be treated in subsequent papers of this series.
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