Accumulation of C19-gibberellins in the gibberellin-insensitive dwarf mutantgai ofArabidopsis thaliana (L.) Heynh |
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Authors: | Manuel Talon Maarten Koornneef Jan A D Zeevaart |
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Institution: | (1) MSU-DOE Plant Research Laboratory, Michigan State University, 48824-1312 East Lansing, MI, USA;(2) Department of Genetics, Agricultural University, NL-6703 HA Wageningen, The Netherlands |
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Abstract: | The endogenous gibberellins (GAs) from shoots of the GA-insensitive mutant,gai, ofArabidopsis thaliana were analyzed and compared with the GAs from the Landsberg erecta (Ler) line. Twenty GAs were identified in Ler plants by
full-scan gas chromatography-mass spectrometry (GC-MS) and Kovats retention indices (KRI's). These GAs are members of the
early-13-hydroxylation pathway (GA53, GA44, GA19, GA17, GA20, GA1, GA29, and GA8), the non-3,13-hydroxylation pathway (GA12, GA15, GA24, GA25, GA9, and GA51), and the early-3-hydroxylation pathway (GA37, GA27, GA36, GA13, GA4, and GA34). The same GAs, except GA53, GA44, GA37, and GA29 were detected in thegai mutant by the same methods. In addition, extracts fromgai plants contained GA41 and GA71. Both lines also contained several unknown GAs. In Ler plants these were mainly hydroxy-GA12 derivatives, whereas in thegai mutant hydroxy-GA24, hydroxy-GA25, and hydroxy-GA9 compounds were detected. Quantification of seven GAs by GC-selected ion monitoring (SIM), using internal standards, and comparisons
of the ion intensities in the SIM chromatograms of the other thirteen GAs, demonstrated that thegai mutant had reduced levels of all C20-dicarboxylic acids (GA53, GA44, GA19, GA12, GA15, GA24, GA37, GA27, and GA36). In contrast,gai plants had increased levels of C20-tricarboxylic acid GAs (GA17, GA25, and GA41) and of all C19-GAs (GA20, GA1, GA8, GA9, GA51, GA4, GA34, and GA71) except GA29. The 3β-hydroxylated GAs, GA1 and GA4, and their respective 2β-hydroxylated derivatives, GA8 and GA34, were the most abundant GAs found in shoots of thegai mutant. Thus, thegai mutation inArabidopsis results in a phenotype that resembles GA-deficient mutants, is insensitive to both applied and endogenous GAs, and contains
low levels of C20-dicarboxylic acid GAs and high levels of C19-GAs. This indicates that theGAI gene controls a step beyond the synthesis of an active GA. Thegai mutant is presumably a GA-receptor mutant or a mutant with a block in the transduction pathway between the receptor and stem
elongation.
We thank Dr. L.N. Mander, Australian National University, Canberra, for providing 2H]gibberellins, Dr. B.O. Phinney, University of California, Los Angeles, USA for 13C]GA8, and Dr. D.A. Gage, MSU-NIH Mass Spectrometry Facility (grant No. DRR00480), for advice with mass spectrometry. This work
was supported by a fellowship from the Spanish Ministry of Agriculture (I.N.I.A.) to M.T., by the U.S. Department of Energy
under Contract DE-ACO2-76ERO-1338, and by U.S. Department of Agriculture grant No. 88-37261-3434 to J.A.D.Z. |
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Keywords: | Arabidopsis (gibberellin mutant) Dwarfism Gibberellin (insensitive mutant) Mutant (gibberellin) |
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