Action Spectrum of Phototropic Tip-Curvature of Avena.

Abstract

Action spectra of the 1st positive tip-curvature of A. sativa, Victory 2020, were determined from 350 to 520 m[mu]. A detailed description of the equipment and procedures for the isolation of narrow band-widths of radiant energy is given. Curvatures were produced by 15-second uni-lateral irradiances of the upper 0.5 cm of coleoptiles. A plot of the curvature in degrees versus the log. of the incident energy was linear from 3 to 30[degree]. The slopes were found to be a function of wavelength. Action spectra were plotted as the reciprocal of the moles of incident quanta necessary to produce 0, 5, 10 and 20[degree] responses. Peaks of activity were obtained at 370-375, 410-415, 440-445 and 470-475 m[mu]. An analysis of the meaning of the slope as a function of wavelength indicates that the 370-375 m[mu] peak may be primarily due to increased attenuation by an inactive secondary pigment. Curvatures in the visible spectral range appear to be mediated by the active photoreceptor alone.