Journal Article

Requirement for the Gravity-Controlled Transport of Auxin for a Negative Gravitropic Response of Epicotyls in the Early Growth Stage of Etiolated Pea Seedlings

Tomoki Hoshino, Kensuke Miyamoto and Junichi Ueda

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 47, issue 11, pages 1496-1508
Published in print November 2006 | ISSN: 0032-0781
Published online November 2006 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcl015
Requirement for the Gravity-Controlled Transport of Auxin for a Negative Gravitropic Response of Epicotyls in the Early Growth Stage of Etiolated Pea Seedlings

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Gravity-controlled transport of auxin was studied for a negative gravitropic response in the early growth stage of etiolated pea (Pisum sativum L. cv. Alaska) seedlings, in which epicotyl bending was observed near the cotyledon nodes of the seedlings grown continuously from seeds germinated in a horizontal or an inclined position. Increased expression of an auxin-inducible gene, PsIAA4/5, was observed in the elongated side of epicotyls grown in a horizontal or an inclined position. Regardless of the conditions of seed germination, polar auxin transport in the proximal side of the first internodes of the seedlings was significantly higher than in the distal side. Polar auxin transport in the proximal side of epicotyls grown in an inclined position was significantly lower than in those grown in a horizontal position. In contrast, lateral auxin distribution from the proximal to distal sides in epicotyls grown in an inclined position was significantly higher than in epicotyls grown in a horizontal position. Accumulation of PsPIN1 mRNA encoding a putative auxin efflux facilitator, which was observed in vascular tissue, cortex and epidermis in the proximal and distal sides of epicotyls, was markedly influenced by gravistimulation. These results strongly suggest that gravistimulation induces changeable polar auxin transport and one-way lateral auxin distribution in epicotyls as well as asymmetric auxin accumulation in the proximal and distal sides of epicotyls, resulting in a negative gravitropic response of epicotyls in the early growth stage of pea seedlings.

Keywords: Auxin distribution; Auxin efflux facilitator; Graviresponse; Pea epicotyl; Polar auxin transport; PsPIN1

Journal Article.  7386 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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