ACTION SPECTRA FOR THE POSITIVE AND NEGATIVE PHOTOTROPISM OF PHYCOMYCES SPORANGIOPHORES

Abstract

Action spectra for phototropism of P. blakesleeanus (G-5, + strain) were obtained by using the curvature of the sporangiophores to balance a standard blue light (spectral center about 460 m[mu]) against narrow band emission from either a GE H85C3 mercury lamp or a GE ribbon-filament tungsten lamp monochromator source. The spectrum in the visible (positive curvature) showed a maximum of effectiveness at 445 m[mu], a shoulder at 470 m[mu]. and a secondary maximum near 370 m[mu]. The spectral sensitivity of the negative curvature in the ultraviolet of wave lengths shorter than 312 mu using a small germicidal lamp shining through a Corning 9683 filter showed a single peak near 280 m[mu], a trough near 250 m[mu] and a steady rise below this. Growth promotion accompanies the curvature in both visible and ultraviolet, and in the visible range the Light Growth Reaction shows probably the same spectral sensitivity as does the curvature. The evidence suggests that the Light Growth Reaction and phototropism in Phycomyces are initiated by the same light reaction. The visible action spectrum for Phycomyces is almost identical with that of Avena coleoptiles. The photoreceptors in the 2 plants are essentially identical and probably carotenoids.