Dwarf mutants ofBrassica: Responses to applied gibberellins and gibberellin content |
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Authors: | Karen P Zanewich Stewart B Rood Carol E Southworth and Paul H Williams |
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Institution: | (1) Department of Biological Sciences, University of Lethbridge, T1K 3M4 Lethbridge, Alberta, Canada;(2) Department of Plant Pathology, University of Wisconsin-Madison, 53706 Madison, Wisconsin, USA |
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Abstract: | Eight rapid-cyclingBrassica genotypes differing in height were treated with gibberellins (GAs) by syringe application to the shoot tip. The height of two genotypes ofBrassica napus, Bn5-2 and Bn5-8, andB. rapa mutants,dwarf 1 (dwf1) anddwarf 2 (dwf2), was unaffected by exogenous GA3 at dosages up to 0.1 g/plant, a level which increased shoot elongation of normal genotypes. Thus, these dwarf mutants are GA-insensitive. In contrast to theB. napus dwarfs, twoB. rapa mutants,rosette (ros), anddormant (dor), elongated following GA3 application. The dwarfros was most sensitive, responding to applications as low as 1 ng GA3/plant. Furthermore,ros also responded to GA1 and some of its precursors with decreasing efficacy: GA3>ent-kaurenoic acid GA1>GA20 GA19=GA44 GA53. Endogenous GAs were measured by gas chromatography-selected ion monitoring using 2H2]GA internal standards for calibration, from shoots of the GA-insensitive genotypes Bn5-2, Bn5-8 which contained theB. napus mutantdwarf 1, and from a normal genotype Bn5-1. Concentrations of GA1 and GA20 averaged 3.2- and 4.6-fold higher, respectively, and GA19 levels also tended to be higher in the dwarfs than in the normal genotype. |
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