Isolation and identification of a light-induced growth inhibitor in diffusates from blue light-illuminated oat (Avena sativa L.) coleoptile tips

The amounts of two growth inhibitors in diffusates from illuminated halves of phototropically stimulated oat (Avena sativa L.) coleoptile tips were larger than those from shaded halves. The less polar inhibitor was isolated from diffusates from oat coleoptile tips illuminated with blue light, and identified as uridine from ¹H NMR spectrum. The distribution of endogenous uridine in diffusates from the illuminated and shaded sides of coleoptile tips unilaterally exposed to blue light for 3 s, causing a first positive phototropic curvature, and from dark-control tips, was determined using a physicochemical assay. The uridine concentration was significantly higher in the diffusates from the illuminated side than in those from the shaded side and the dark-control. Uridine inhibited the growth of etiolated oat coleoptile tips at concentrations of 30 mg/1 and above. These results suggest that uridine plays a role in the phototropism of oat coleoptiles.