The growth promoting effect of red light on internode elongation of Progress seedlings

Red light increased elongation of the apical 10 mm of epicotyls excised from 7-day-old dark grown Progress seedlings. Removal of the basal portion of the plant appears to render the tissue insensitive to the inhibitory influences of light. Addition of gibberellins A1, A3 or A5 further increased elongation. The red light growth response was independent of the gibberellin response; therefore, it was considered to be unrelated to an increase in gibberellin biosynthesis. A study of the time course of growth in the presence of the gibberellins revealed that a 6–8 hr lag period was required before A1 and A5 became effective, while no lag period was associated with A3. It was suggested that A1 and A5 were converted to an A3-like gibberellin.