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Developmental regulation of H + ‐ATPase‐dependent auxin responses in the diageotropica mutant of tomato ( Lycopersicon esculentum )
Author(s) -
Coenen Catharina,
Bierfreund Nicole,
Lüthen Hartwig,
Neuhaus Gunther
Publication year - 2002
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.2002.1140316.x
Subject(s) - auxin , hypocotyl , guard cell , lycopersicon , mutant , seedling , biology , secretion , etiolation , microbiology and biotechnology , lateral root , biochemistry , botany , arabidopsis , gene , enzyme
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.