LIGHT-QUALITY EFFECTS ON ARABIDOPSIS DEVELOPMENT - RED, BLUE AND FAR-RED REGULATION OF FLOWERING AND MORPHOLOGY

Arabidopsis thaliana (L.) Heynh, race Columbia plants were grown in red, blue, red + far-red, blue + far-red and various light mixtures of red + blue + far-red light under 14 h light/10 h dark photoperiods. Each single light source and light mixture maintained a constant irradiance (50 mumol m-2 s-1) and the mixtures of red + blue + far-red maintained a constant ratio of red/far-red light, but varied in the ratio of blue to red + far-red light. Depending on the method used for calculation, values of the fraction of phytochrome in the far-red absorbing form (P(fr)/P(tot)) for these light mixtures were either constant or decreased slightly with increasing percentage of blue light in the mixtures. Arabidopsis flowered early (20 days) in blue, blue + far-red and red + far-red light and late (55 days) in red light. In mixtures of red + blue + far-red light, each of which established a nearly constant P(fr)/P(tot), flowering was in direct relation to time and irradiance level of blue light. Leaf area and petiole length were also correlated with blue light irradiance levels.