RT Journal Article SR Electronic T1 Genetic Evidence That the Red-Absorbing Form of Phytochrome B Modulates Gravitropism in Arabidopsis thaliana JF Plant Physiology JO Plant Physiol. FD American Society of Plant Biologists SP 15 OP 19 DO 10.1104/pp.103.1.15 VO 103 IS 1 A1 Liscum, E. A1 Hangarter, R. P. YR 1993 UL http://www.plantphysiol.org/content/103/1/15.abstract AB Hypocotyls of dark-grown Arabidopsis seedlings exhibit strong negative gravitropism, whereas in red light, gravitropism is strongly reduced. Red/far-red light-pulse experiments and analysis of specific phytochrome-deficient mutants indicate that the red-absorbing (Pr) form of phytochrome B regulates normal hypocotyl gravitropism in darkness, and depletion of Pr by photoconversion to the far-red-absorbing form attenuates hypocotyl gravitropism. These studies provide genetic evidence that the Pr form of phytochrome has an active function in plant development.