Phototropic response of the stage I Phycomyces sporangiophore to a pulse of blue light

Publisher Website
Google Scholar
Abstract
Positive phototropic curvature of Phycomyces sporangiophores (stage I) induced by a short pulse (10 sec) of blue light has been characterized. The curvature response, measured 40 min after irradiation, increases with increasing fluences up to ≈10 -4 J·m -2 ; it then decreases and becomes nearly 0 at a fluence of ≈10 -1 J·m -2 . The threshold fluence is found near 10 -7 J·m -2 , indicating over 1000-fold higher sensitivity than the first positive phototropism of grass coleoptiles. Positive curvature of the sporangiophore becomes detectable 5 min after irradiation and increases with time up to ≈40 min. During the course of this curvature development, overall elongation growth of the sporangiophore is first stimulated and then inhibited. The relationship between the phototropic response and the response in overall elongation growth is discussed, and it is suggested that the primary mechanisms of these responses are distinct.