title: Developmental regulation of H+-ATPase-dependent auxin responses in the diageotropica mutant of tomato (Lycopersicon esculentum).
abstract: Rapid auxin effects on H+ pumping across the plasma membrane precede auxin-induced elongation growth of hypocotyls and swelling of guard cells, as well as auxin inhibition of root growth. To investigate whether auxin-signalling mechanisms in such diverse cell types are similar, we characterized these responses in various tissues of the diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.). Abraded hypocotyl segments of 4-day-old, etiolated dgt seedlings showed an impaired H+ secretion response to applied auxin. mRNA levels for two PM H+-ATPase isoforms, LHA2 and LHA4, were not reduced in dgt hypocotyl segments as compared to wild-type segments, suggesting that the dgt mutation does not affect H+ secretion by reducing the transcription of major PM H+-ATPase genes. The dgt mutation also disrupted auxin inhibition of growth and H+ secretion in roots of 4-day-old dgt seedlings. However, immediately after germination, dgt seedling roots responded to auxin with a near-normal inhibition of growth. In addition, stomata in epidermal peels from 2-week-old dgt cotyledons demonstrated normal auxin-induced opening. We conclude that an intact DGT gene product is required for auxin-induced H+ secretion in tomato hypocotyl segments and for auxin inhibition of H+ secretion in roots of older seedlings, but that a DGT-independent pathway for auxin responses exists in young root tips and in guard cells. A developmentally controlled switch from DGT-independent to DGT-dependent auxin signalling appears to take place in root tips within 2 days after germination.
authors.affiliation: Biology Department, Allegheny College, Meadville, PA 16335, USA Institut für Biologie II - Zellbiologie, Albert-Ludwigs Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany Institut für Allgemeine Botanik, Universität Hamburg, Ohnhorststrasse 18, D-22609 Hamburg, Germany Corresponding author, e-mail: ccoenen@allegheny.edu
authors.forename: Catharina
authors.initials: C
authors.lastname: Coenen
authors.forename: Nicole
authors.initials: N
authors.lastname: Bierfreund
authors.forename: Hartwig
authors.initials: H
authors.lastname: Lüthen
authors.forename: Gunther
authors.initials: G
authors.lastname: Neuhaus