ACTION OF BLUE OR RED MONOCHROMATIC LIGHT ON STEM INTERNODAL GROWTH DEPENDS ON PLANT SPECIES

Authors:	T. Hirai, W. Amaki, H. Watanabe
Keywords:	light emitting diode (LED), Lactuca sativa, photomorphogenesis, PPF, Solanum melongena, stem elongation
Abstract: We investigated the effects of different monochromatic lights at various PPF on the stem elongation of eggplant and leaf-lettuce seedlings. Each of LEDs was used as a sole light source for cultivation of seedlings. The peak wavelengths of blue, blue-green, green and red LEDs were 470, 500, 525 and 660 nm, respectively. Each of four monochromatic lights was supplied at 20, 50, 100 and 150μmolm^-2s^-1 PPF with 16hr-light/8hr-dark cycles to seedlings since at the stage of having two unfolded true leaves. Stem length of eggplant was remarkably increased in proportion to the PPF increment of blue light up to 100μmolm^-2s^-1, but there was a little difference in stem length under other monochromatic lights. On the other hands, stem length of leaf-lettuce was longer under red light, compared with that under other monochromatic lights, and blue light remarkably suppressed the internodal stem growth. In some previous reports, blue light suppressed stem elongation. But our results showed promotive action of blue light on stem elongation in eggplant. The response on stem elongation under blue or red monochromatic light was dependent on plant species.
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