Nature of light requirement for the flowering of Chenopodium rubrum L. (Ecotype 60° 47' N) : I. Pre-induction light period.

Seedlings of the short-day plant, Chenopodium rubrum L. (Ecotype 60° 47' N) were irradiated with different intensities and qualities of light for 24 h preceding a single inductive dark period (12 h). Our data shows that a relatively low intensity incandescent light (35-100 ft. c.) is not effective as the photoperiod for flowering. The above effect is not due to a requirement for a relatively high level of photosynthesis. Our results suggest a definite promotory role of a blue High Energy Reaction (HER). We could not demonstrate the involvement of a far-red HER. We suggest that ineffectiveness of far-red may have been due to establishment of rather low Phytochrome, P FR , levels, suboptimal for flowering. A certain critical level of P FR (30-40%, that presumably established by blue light) seems to be necessary for photoreactions involved in flowering of C. rubrum. There are indications in our experiments of the operation of a red radiation mediated flower inhibitory photoreaction.