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

Irradiation 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 prehausto ria. 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 excis ed 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 no t 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.