Differences in the response of wheat, soybean and lettuce to reduced blue radiation

Although many fundamental blue light responses have been identified, blue l ight dose-response curves are not well characterized. We studied the growth and development of soybean, wheat and lettuce plants under high-pressure s odium (HPS) and metal halide (MH) lamps with yellow filters creating five f ractions of blue light. The blue light fractions obtained were <0.1, 2 and 6;% under HPS lamps, and 6, 12 and 26% under MH lamps, Studies utilizing bo th lamp types were done at two photosynthetic photon flux levels, 200 and 5 00 <mu>mol m(-2) s(-1) under a 16 h photoperiod. Phytochrome photoequilibri a was nearly identical among treatments. The blue light effect on dry mass, stem length, leaf area, specific leaf area and tillering/branching was spe cies dependent. For these parameters, wheat did not respond to blue light, but lettuce was highly sensitive to blue light fraction between 0 and 6% bl ue. Soybean stem length decreased and leaf area increased up to 6% blue, bu t total dry mass was unchanged. The blue light fraction determined the stem elongation response in soybean, whereas the absolute amount of blue light determined the stem elongation response in lettuce, The data indicate that lettuce growth and development requires blue light, but soybean and wheat m ay not.