Phytochrome Participation in Induction of Haustoria in Cuscuta japonica, a Holoparasitic Flowering Plant

Abstract

Seedlings of Cuscuta japonica pasted on an acrylic plate developed many haustoria in response to far-red light after pre-irradiation with white light. The effect of far-red light was cancelled completely by red light irradiated immediately after the far-red light. In order to elucidate the photoreceptor(s) for photocontrol in the induction of haustoria, action spectra for the photo-induction and its reversion were determined in the wavelength region from 340 nm to 800 nm using the Okazaki Large Spectrograph. The action spectrum for the induction of haustoria had a pronounced peak at 740 nm and a small peak at 420 nm, while the action spectrum for reversal of the induction had a pronounced peak at 660 nm and a small peak at 380 nm. These results indicate that phytochrome is involved in the photocontrol of induction of haustoria in Cuscuta japonica. Considering the far-red /red reversibility, it was suggested that phytochrome B is the photorecepter. This is the first reliable evidence of phytochome participation on development of haustoria in parasitic plants.