SummaryIrradiation of 4‐day‐old dark‐grown seedlings of Cuscuta campestris Yuncker and Cusctira indecara Choisy with I min of red light stimulated coiling and prehaustoria formation in excised upper 4‐cm segments of seedlings during a 48‐h dark period in which zeatin was applied. Coiling and prehaustoria development were completely reversed when irradiated with 2 min of far‐red light applied directly after red light. When deetiolated segments were subjected to prolonged exposure of pure blue light, or mixtures of ultraviolet‐A/far‐red, blue/far‐red or red/far‐red light, coiling and prehaustona development were induced. Blue light at photon fluxes lower than 1 μmol m‐2 s‐1 did not promote coiling and formation of prehaustoria. Mechanical stimulation caused tendrils to coil and form prehaustona in biue and blue/far‐red light, but not in darkness. Zeatin substituted for high irradiance blue light and mechanical stimulation caused coiling and prehaustoria formation.
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 μmol m−2 s−1 against a background of cool white light (400 to 700 nm) from above at 77 μmol m−2 s−1, or (b) transferred to darkness and provided with unilateral white light at 20 μmol m−2 s−1, unilateral blue light (400 to 500 nm) at 10 μmol m−2 s−1, unilateral red light (600 to 700 nm) at 10 μmol m−2 s−1, unilateral far-red at 50 μmol 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 μM 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.
SummaryIrradiation of excised stem segments from de‐etiolated seedlings of Cuscuta planiflora for 24 h with mixtures of red and far‐red light with red to far‐red ratios between 0.02 to 1.0 enhanced coiling and formation of prehaustoria. Maximum number of prehaustoria were recorded when red:far‐red was near 0.1. Coiling and prehaustoria were observed whenever estimated in vivo Pfr/Ptotal at photoequilibrium was between 0.06 and 0.67. Irradiation of excised stem segments from white light grown seedlings with 12 h blue light also promoted coiling and prehaustoria formation after another 38 h in darkness. Coiling and prehaustoria were not observed in segments pulsed with 10 min red light at the end of 12 h in blue light. Coiling and prehaustoria were observed after photoreversible end‐of‐day far‐red/red/far‐red pulses but not after red/far‐red/red pulses. A far‐red pulse may not reverse inhibition by end‐of‐day red pulse when far‐red is given more than 12 h after the red pulse.
Phytohormones were screened for their effects on induction of coiling and prehaustoria in de-etiolated excised dodder seedlings under different light treatments. Zeatin stimulated coiling and the formation of prehaustoria under all light tested, even in darkness. A synergistic effect was observed with zeatin and far-red light (700-800 nm) but not with red light (600-700 nm) on the formation of prehaustoria. Application of indole-3acetic acid inhibited zeatin-induced coiling and prehaustoria development under blue (400-SO0 nm) and a mixture of red plus far-red light. but not in blue plus far-red light. Ethylene had no effect on coiling and prehaustoria development. Observations suggest that zeatin-induced coiling and prehaustoria development may be mediated by phytochrome.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.