title: The plasma membrane aquaporin NtAQP1 is a key component of the leaf unfolding mechanism in tobacco.
abstract: Epinastic leaf movement of tobacco is based on differential growth of the upper and lower leaf surface and is distinct from the motor organ-driven mechanism of nyctinastic leaf movement of, for example, mimosa species. The epinastic leaf movement of tobacco is observed not only under diurnal light regimes but also in continuous light, indicating a control by light and the circadian clock. As the transport of water across membranes by aquaporins is an important component of rapid plant cell elongation, the role of the tobacco aquaporin Nt aquaporin (AQP)1 in the epinastic response was studied in detail. In planta NtAQP1-luciferase (LUC) activity studies, Northern and Western blot analyses demonstrated a diurnal and circadian oscillation in the expression of this plasma membrane intrinsic protein (PIP)1-type aquaporin in leaf petioles, exhibiting peaks of expression coinciding with leaf unfolding. Cellular water permeability of protoplasts isolated from leaf petioles was found to be high in the morning, i.e. during the unfolding reaction, and low in the evening. Moreover, diurnal epinastic leaf movement was shown to be reduced in transgenic tobacco lines with an impaired expression of NtAQP1. It is concluded that the cyclic expression of PIP1-aquaporin represents an important component of the leaf movement mechanism.
authors.affiliation: Department of Botany, Applied Plant Sciences, TU Darmstadt, D-64287 Darmstadt, Germany.
authors.forename: Franka
authors.initials: F
authors.lastname: Siefritz
authors.forename: Beate
authors.initials: B
authors.lastname: Otto
authors.forename: Gerd Patrick
authors.initials: GP
authors.lastname: Bienert
authors.forename: Alexander
authors.initials: A
authors.lastname: van der Krol
authors.forename: Ralf
authors.initials: R
authors.lastname: Kaldenhoff
mesh_terms: D051398:Aquaporin 1; D020346:Aquaporins / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D002462:Cell Membrane / Q000502:physiology / Q000528:radiation effects; D002940:Circadian Rhythm; D017930:Genes, Reporter; D008027:Light; D008156:Luciferases / Q000032:analysis / Q000235:genetics; D018515:Plant Leaves / Q000254:growth & development / Q000502:physiology*; D010940:Plant Proteins / Q000502:physiology* / Q000528:radiation effects; D011401:Promoter Regions, Genetic / Q000235:genetics; D011994:Recombinant Proteins / Q000032:analysis; D014026:Nicotiana / Q000254:growth & development / Q000502:physiology*
chemical_list: D020346:Aquaporins; D010940:Plant Proteins; D011994:Recombinant Proteins; D051398:Aquaporin 1; D008156:Luciferases