Abstract
The evidence showing that phototropism is caused by blue light-induced local accumulation of growth inhibitor(s), interfering with the action of evenly distributed auxin, has been presented and the search for growth inhibitor(s) has been evolved in several plant species. Caprolactam and 8-epixanthatin have been isolated and identified as candidates for inhibitors in sunflower seedlings. Recently, we have confirmed the presence of growth inhibitor(s) showing stronger activity than these compounds. Here, we isolated a new potent, blue light-induced growth inhibitor from sunflower hypocotyls and identified as 8-O-β-D-glucopyranosyl-1,9,14-pentadecatriene-4,6-diyne-3,8-diol (designated "helian") from 1H and 13C NMR and HRFABMS spectra. It inhibited the growth of cress root at concentrations higher than 2.6 Χ 10-6 M. The distribution of helian was much higher in the illuminated halves than in the shaded ones in phototropically stimulated sunflower hypocotyls. These results suggest that helian may play an important regulatory role in phototropism of sunflower hypocotyls.
