title: Graviresponse and its regulation from the aspect of molecular levels in higher plants: growth and development, and auxin polar transport in etiolated pea seedlings under microgravity.
abstract: In STS-95 space experiments we have demonstrated that microgravity conditions resulted in automorphosis in etiolated pea (Pisum sativum L. cv. Alaska) seedlings (Ueda et al. 1999). Automorphosis-like growth and development in etiolated pea seedlings were also induced under simulated microgravity conditions on a 3-dimensional (3-D) clinostat, epicotyls being the most oriented toward the direction far from the cotyledons. Detail analysis of epicotyl bending revealed that within 36 h after watering, no significant difference in growth direction of epicotyls was observed in between seedlings grown on the 3-D clinostat and under 1 g conditions, differential growth near the cotyledonary node resulting in epicotyl bending of ca. 45 degrees toward the direction far from the cotyledons. Thereafter epicotyls continued to grow almost straightly keeping this orientation on the 3-D clinostat. On the other hand, the growth direction in etiolated seedlings changed to antigravity direction by negative gravitropic response under 1 g conditions. Automorphological epicotyl bending was also phenocopied by the application of auxin polar transport inhibitors such as 9-hydroxyfluorene-9-carboxylic acid, N-(1-naphtyl)phthalamic acid and 2,3,5-triiodobenzoic acid. These results together with the fact that auxin polar transport activity in etiolated pea epicotyls was substantially reduced in space suggested that reduced auxin polar transport is closely related to automorphosis. Strenuous efforts to learn how gravity contributes to the auxin polar transport in etiolated pea epicotyls in molecular bases resulted in successful identification of PsPIN2 and PsAUX1 encoding putative auxin-efflux and influx carrier proteins, respectively. Based on the results of these gene expression under simulated microgravity conditions, a possible role of PsPIN2 and PsAUX1 genes for auxin polar transport in etiolated pea seedlings will be discussed.
authors.affiliation: College of Integrated Arts and Sciences, Osaka Prefecture Univ., Osaka, Japan.
authors.forename: Kensuke
authors.initials: K
authors.lastname: Miyamoto
authors.forename: Tomoki
authors.initials: T
authors.lastname: Hoshino
authors.forename: Reiko
authors.initials: R
authors.lastname: Hitotsubashi
authors.forename: Eiichi
authors.initials: E
authors.lastname: Tanimoto
authors.forename: Junichi
authors.initials: J
authors.lastname: Ueda
mesh_terms: D029681:Arabidopsis Proteins / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D018548:Cotyledon / Q000254:growth & development; D017343:Genes, Plant; D006112:Gravitation; D018522:Gravitropism / Q000502:physiology; D007210:Indoleacetic Acids / Q000037:antagonists & inhibitors / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism; D018532:Pisum sativum / Q000235:genetics / Q000254:growth & development* / Q000502:physiology; D010940:Plant Proteins / Q000378:metabolism; D012399:Rotation; D018474:Weightlessness Simulation
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D007210:Indoleacetic Acids; D026901:Membrane Transport Proteins; C116363:PIN1 protein, Arabidopsis; D010940:Plant Proteins