An auxin-inhibiting substance was isolated from light-grown maize shoots and its structure determined by spectral data as 6-methoxy-2-benzoxazolinone. It inhibited both the auxin-inducing bending in the Avena curvature test and the auxin-inducing elongation in the Avena coleoptile section test. The elongation inhibition against the coleoptile section test appeared in the presence of auxin, but not without auxin. The inhibition caused in the presence of auxin could be overcome by additional auxin. The present results suggest that the inhibitor is a potent antiauxin. It also inhibited the shoot and root elongation in etiolated timothy grass and Amaranthus seedlings.
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