Action Spectra for the Inhibition of Hypocotyl Growth by Continuous Irradiation in Light and Dark-Grown Sinapis alba L. Seedlings

Abstract

Action spectra for the inhibition by continuous (24 h) irradiation of hypocotyl growth in 54 h old S. alba L. seedlings were measured using seedlings which had had 4 different pretreatments. These seedlings were either dark-grown with a high total phytochrome level, dark-grown with a low total phytochrome level, light-grown with chlorophyll, or light-grown with no chlorophyll [treated with 4-chloro-5- (methylamino)-2-(.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl)-3(2H)-pyridazinone (San 9789)]. The resulting action spectra show that the blue, red and far-red (716 nm) wavebands are most inhibitory for dark-grown plants with high phytochrome content, whereas hypocotyl growth in dark-grown plants with a low phytochrome content are only slightly inhibited by blue and far-red radiation. In light-grown plants, the effectiveness of blue and far-red light almost disappears. The position of red light effectiveness in chlorophyll-containing plants is shifted to lower wavelenghts compared with those containing no chlorophyll.