[Phytochrome-induced regeneration of adventitious roots in the mustard seedling (Sinapis alba L.)].

Isolated cotyledons and hypocotyl cuttings ("Restkeimlinge") taken from young (36 h old) etiolated mustard seedlings at a stage of development at which nutrients are not yet limiting require active phytochrome (Pfr) to regenerate roots. The influence of photosynthesis on rooting (Lovell et al., 1969, 1972, 1973) appears to be limited to cotyledons depleted of storage materials. These conclusions are based on the following experimental results: 1. Continuous far-red irradiation ("Dauer-DR") is as effective as continuous red irradiation ("Dauer-HR") in stimulating rooting (Fig. 1). 2. Continuous far-red irradiation can be largely replaced by a series of 5 min red/12 h dark cycles. Five min far-red irradiations have no detectable effect if given alone, but fully reverse the action of red if given subsequently to the red irradiation (Fig. 3).Phytochrome-mediated rooting in mustard is limited to cuttings taken from seedlings not older than about 60 h under our experimental conditions (Fig. 2). However, rooting is stimulated by continuous far-red light not only in the case of irradiated cuttings but also in the case in which seedlings are irradiated before dissection and the cuttings subsequently kept in darkness (Fig. 4).-It appears from these data that Pfr increases the capacity for rooting in intact seedlings as well as in cuttings, but has no influence on the time-course of rooting set in motion by dissection. There is no evidence for a function of the plumule in the rooting response. It rather appears that phytochrome is needed to produce a hormonal rooting factor in the cotyledons.