Cooperative effects of blue and red light in the inhibition of hypocotyl elongation of de-etiolated castor bean

The effect of irradiating the cotyledons and hypocotyl on elongation of the hypocotyl was investigated in de-etiolated seedlings of castor beans. Continuous irradiation of the cotyledons does not appear to have photomorphogenetic effects on hypocotyl elongation, while continuous irradiation of the hypocotyl itself affected its elongation. Continuous far red light (FR) enhanced elongation; continuous red (R), blue (B) or near ultra violet light (NUV) were ineffective, but simultaneous irradiation with R and B or R and NUV inhibited elongation. We suggest that cooperative effects between different photoreceptors may be involved in the regulation of plant growth by the light environment.