Berhanu A. Tsegay1*, Jorunn E. Olsen2 , and Olavi Juntttila
Plants sense the quality, quantity, and duration of light signals and use them to optimise their growth and development. These signals are perceived by special light receptors of which the phytochrome pigment system is one of the most important for photomorphogenetic responses. Using special diodes that emit monochromatic light, we studied the effect of red (R), far-red (FR) and R+FR combinations on hypocotyl elongation of latitudinal ecotypes of Betula pendula. Continuous R and FR inhibited hypocotyl elongation equally, but inhibition was higher when seedlings were irradiated by continuous R+FR. In all cases, inhibition increased with increasing irradiance, from 0.75 µmol m-2 s -1 to 76 µmol m-2 s -1 . Moreover, seedlings treated by R or R+FR synthesised more anthocyanins than those exposed to FR. Accumulation of anthocynins increased with increasing irradiance up to about 19 µmol m-2 s -1 .
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