Xanthoxin: A Growth Inhibitor in Light-grown Sunflower Seedlings,Helianthus annuusL.

Methanol extracts from light- and dark-grown sunflower seedlings, Helianthus annuus L., var. ‘Inra No. 6501’, were subjected to solvent partition. The neutral diethyl ether fraction from the light-grown seedlings contained material(s) which inhibited cress seed germination. Such inhibition was scarcely detectable in extracts of the etiolated seedlings. Sometimes inhibition also occurred in the petroleum spirit fraction. A mixture of cis, trans- and trans, transxanthoxin showed the same partition characteristics as the inhibiting substance(s); the latter co-chromatographed with xanthoxin in all paper, thin layer, and high pressure liquid chromatography separation procedures tried. The inhibition was also detectable with the Avena colcoptile straight growth bioassay. It is concluded that xanthoxin is formed during illumination of sunflower seedlings; its role in the phototropic response of these seedlings is discussed.