RT Journal Article
SR Electronic
T1 Genetic and Transgenic Evidence That Phytochromes A and B Act to Modulate the Gravitropic Orientation of Arabidopsis thaliana Hypocotyls
JF Plant Physiology
JO Plant Physiol.
FD American Society of Plant Biologists
SP 211
OP 216
DO 10.1104/pp.110.1.211
VO 110
IS 1
A1 Robson, PRH.
A1 Smith, H.
YR 1996
UL http://www.plantphysiol.org/content/110/1/211.abstract
AB Hypocotyls of Arabidopsis thaliana exhibit negative gravitropism in the dark, growing against the gravity vector. The direction of growth is randomized in red light (R). In single mutants lacking either phytochrome A or B randomization of hypocotyl orientation in R is retained. However, a double mutant lacks this response, indicating that either phytochrome A or B is capable of inducing randomization and phytochrome A and B are the only phytochromes involved in this process. The induction of randomization was confirmed using lines that express to different levels PHYA and PHYB cDNAs. Overexpression of PHYA cDNAs induced randomization of hypocotyl orientation in the dark. Dark randomization was also seen in the phyB-1 mutant but not in two other phyB alleles, suggesting that dark randomization in the phyB-1 line may be due to a second mutation. When germination was induced by gibberellin, rather than exposure to brief white light, randomization in the dark associated with phytochrome A overproduction was not observed but was retained in the phyB-1 mutant. Overexpression of PHYB cDNAs induced a light-dependent randomization of hypocotyl orientation that responded to R:far-red light ratio. We conclude that the default situation in Arabidopsis hypocotyls is, therefore, negative gravitropism, and either phytochrome A or phytochrome B can mediate randomization.