Evidence for yellow light suppression of lettuce growth

Researchers studying plant growth under different lamp types often attribut e differences in growth to a blue light response, Lettuce plants were grown in six blue light treatments comprising five blue light fractions (0, 2, 6 % from high-pressure sodium [HPS] lamps and 6, 12, 26% from metal halide [M H] lamps). Lettuce chlorophyll concentration, dry mass, leaf area and speci fic leaf area under the HPS and MH 6% blue were significantly different, su ggesting wavelengths other than blue and red affected plant growth. Results were reproducible in two replicate studies at each of two photosynthetic p hoton fluxes, 200 and 500 mu mol m(-2) s(-1). We graphed the data against a bsolute blue light, phytochrome photoequilibrium, phototropic blue, UV, red :far red, blue:red, blue: far red and 'yellow' light fraction. Only the 'ye llow' wavelength range (580-600 nm) explained the differences between the t wo lamp types.