title: Light as stress factor to plant roots - case of root halotropism.
abstract: Despite growing underground, largely in darkness, roots emerge to be very sensitive to light. Recently, several important papers have been published which reveal that plant roots not only express all known light receptors but also that their growth, physiology and adaptive stress responses are light-sensitive. In Arabidopsis, illumination of roots speeds-up root growth via reactive oxygen species-mediated and F-actin dependent process. On the other hand, keeping Arabidopsis roots in darkness alters F-actin distribution, polar localization of PIN proteins as well as polar transport of auxin. Several signaling components activated by phytohormones are overlapping with light-related signaling cascade. We demonstrated that the sensitivity of roots to salinity is altered in the light-grown Arabidopsis roots. Particularly, light-exposed roots are less effective in their salt-avoidance behavior known as root halotropism. Here we discuss these new aspects of light-mediated root behavior from cellular, physiological and evolutionary perspectives.
authors.affiliation: Department of Plant Cell Biology, Institute of Cellular and Molecular Botany, University of Bonn Bonn, Germany ; Department of Biological Sciences, Tokyo Metropolitan University Tokyo, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Yokawa
authors.affiliation: Department of Pharmacy, University of Salerno Fisciano, Italy.
authors.forename: Rossella
authors.initials: R
authors.lastname: Fasano
authors.affiliation: Department of Plant Cell Biology, Institute of Cellular and Molecular Botany, University of Bonn Bonn, Germany.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Kagenishi
authors.affiliation: Department of Plant Cell Biology, Institute of Cellular and Molecular Botany, University of Bonn Bonn, Germany.
authors.forename: František
authors.initials: F
authors.lastname: Baluška
keywords: light response; plant hormones; reactive oxygen species; root; root tropism