Time-Lapse Photography of Phototropism in Pellia epiphylla

Abstract

Growth patterns leading to positive phototropism of Pellia epiphylla sporophytes were analyzed by time-lapse photography. Curvature toward 6 W/m2 of unilateral blue light occurred over the entire length of sporophyte setae, and was detected within 10-15 min of continuous illu- mination. Growth rates increased significantly on shaded sides of sporophytes (from 0.50 to 0.96 mm/hr) and decreased on lighted sides (to 0.26 mm/hr). Current interest in the phototropic responses of bryophytes has centered largely on the role played by phytochrome in tip-growing moss filaments (Hartmann & Jenkins 1984). Little is known about phototropism in multicellular organs where, in con- trast to filaments, differences in growth rates on op- posite sides of the structures are responsible for tropic curvature (Garjeanne 1932; Banbury 1959; Newton 1985), and either phytochrome (Fredericq & De Greef 1968; Cove et al. 1978) or some as yet un- identified blue light receptor (Newton 1985) appears to participate in the response. Physiological mech- anisms involved in translation of the light stimulus into growth rate changes have not been elucidated. By analogy to higher plants, Banbury (1959) sug- gests that a growth hormone (probably auxin) is involved.