Smallseed dodder (Cuscuta planiflora) phototropism toward far-red when in white light

White light-grown seedlings of smallseed dodder were (a) provided with unilateral far-red (700 to 800 nm) at photon irradiances ranging from 20 to 110 mu mol m(-2) s(-1) against a background of cool white light (400 to 700 nm) from above at 77 mu mol m(-2) s(-1), or (b) transferred to darkness and provided with unilateral white light at 20 mu mol m(-2) s(-1), unilateral blue light (400 to 500 nm) at 10 mu mol m(-2) s(-1), unilateral red light (600 to 700 nm) at 10 mu mol m(-2) s(-1), unilateral far-red at 50 mu mol m(-2) s(-1), or (c) in experiments utilizing bilateral irradiations, provided with unilateral far-red perpendicular to unilateral white light, Positive phototropic curvature was induced by unilateral white light and by unilateral blue light in otherwise darkness and by unilateral far-red in a background of cool white light, Seedling vines were also phototropic toward unilateral far-red when provided with unilateral white light perpendicular to unilateral far-red, Phototropism to unilateral white light was inhibited in seedlings treated with 200 mu M norflurazon and 50 mM potassium iodide, Norflurazon- and potassium iodide-treated seedlings remained phototropic toward unilateral far-red when provided with unilateral white light perpendicular to unilateral far-red, Seedling vines were not phototropic to unilateral red or to unilateral far-red in otherwise darkness, and seedlings in cool white light were neither skototropic (i,e,, tropic toward unilateral darkness) nor tropic to or from infra-red (radiation with wavelengths greater than 900 nm), Phototropism toward regions of lowered red:far-red may aid smallseed dodder in chlorophyllous host location and attachment.