The response of Cuscuta planiflora seedlings to red and far‐red, blue light and end‐of‐day irradiations

Abstract

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.