Phototropism

While phototropism has been most intensively studied in higher plants, many other organisms also exhibit phototropism. Phototropism occurs in the filaments and rhizoids of algae, germ tubes and protonemas of mosses, rhizoids and protonemas of ferns, spore-bearing stalks of certain fungi, and numerous other organisms.

Many phototropism experiments have been performed on Phycomyces blakesleeanus, a zygomycete fungus. Phycomyces has slender spore-bearing stalks, referred to as sporangiophores, which bend in response to light and other external stimuli. Incredibly, the sporangiophore of Phycomyces is about as photosensitive as the eyes of humans and about one thousand times more photosensitive than a grass coleoptile. Furthermore, the sporangiophore has the ability to adapt to a one hundred million fold change in ambient light intensity. These and other interesting characteristics of Phycomyces have made it an excellent model organism for investigation of phototropism.