Negative Phototropism in the Rhizoid of Bryopsis plumosa

Abstract

Negative phototropism in the rhizoid of Bryopsis plumosa was analyzed. The growth zone of the rhizoid was confined to the apical hemisphere, as is typical of tip growth. Upon unilateral illumination, the rhizoid bent away from the light source with a “bulging” manner. The photoreceptive site for phototropism was also restricted to the apical hemisphere. The action spectrum for this negative phototropism was determined from fluence-response curves that were obtained after fixing the duration of illumination at 60 min and varying the fluence rate between 0.1 and 3.0 W m-2. The action spectrum had a large peak at 467 nm and smaller peaks at 378 and 414 nm, resembling the action spectra of certain other blue-light responses.