APICAL GROWTH OF PROTONEMATA IN ADIANTUM-CAPILLUS-VENERIS .3. ACTION SPECTRA FOR THE LIGHT EFFECT ON DARK CESSATION OF APICAL GROWTH AND THE INTRACELLULAR PHOTORECEPTIVE SITE

Action spectra for the effect of light treatment on subsequent apical growth in the dark were determined before and after compensation of the phytochrome effect in single-celled protonemata of the fern Adiantum capillus-veneris grown initially under continuous red light. The irradiation lowered the growth rate in subsequent darkness and shortened the final length. The action spectrum before compensation showed peaks at 450 and 470-480 nm with a shoulder in the near-ultraviolet region and another peak at 730 nm, whereas after compensation the action spectrum was similar in the blue and near-ultraviolet region but totally lost the peak at 730 nm. Narrow-beam irradiation of the filamentous protonemata with blue light was effective only when the nuclear region of the protonemal cell was exposed. Polarised blue light having different directions of electrical vectors was equally effective in inducing the inhibitory effect. The experimental evidence supports the conclusion that a blue and near-ultraviolet light absorbing pigment located in the nuclear region of the filamentous protonema controls a process of growth cessation in the dark, in addition to the previously reported phytochrome effect. © 1979.