8-Epixanthatin, a light-induced growth inhibitor, mediates the phototropic curvature in sunflower (Helianthus annuus) hypocotyls

• Published in: Physiologia plantarum Vol. 106; no. 3; pp. 326 - 330
• Main Authors: Yokotani-Tomita, Kaori, Kato, Jun, Yamada, Kosumi, Kosemura, Seiji, Yamamura, Shosuke, Bruinsma, Johan, Hasegawa, Koji
• Format: Journal Article
• Language: English
• Published: Copenhagen Munksgaard International Publishers 01.07.1999; Blackwell
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Economic plant physiology; Fundamental and applied biological sciences. Psychology; Movements; Plant physiology and development; Tropism and nastic movements; Tropism; Auxin; Growth; Phototropism; Compositae; Oil plant(vegetal); Helianthus annuus; Hypocotyl; Dicotyledones; Indoleacetic acid; Angiospermae; Plant growth substance; Inhibitor; Spermatophyta; Inhibition
• ISSN: 0031-9317; 1399-3054
• DOI: 10.1034/j.1399-3054.1999.106310.x

The distribution of the endogenous auxin‐inhibiting substance, 8‐epixanthatin, was determined in the lighted and shaded sides of phototropically‐stimulated, de‐etiolated sunflower (Helianthus annuus L. cv. Taiyo) hypocotyls. From 40 min after the onset of phototropic stimulation, the growth rate at the lighted side was inhibited, whereas that at the shaded side showed no change. In the lighted side, 8‐epixanthatin increased by 20 min after the onset of unilateral illumination and, after 40 min, reached a 3‐fold larger concentration than that in the shaded side. Unilateral application of 8‐epixanthatin suppressed the growth of etiolated hypocotyls at the applied side only, causing the hypocotyls to bend at the site of application. It is concluded that phototropic curvature in sunflower hypocotyls is caused by a lateral gradient of the auxin‐inhibiting substance 8‐epixanthatin.