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. 1999 Jun;120(2):623-32.
doi: 10.1104/pp.120.2.623.

Gibberellin dose-response curves and the characterization of dwarf mutants of barley

PM Chandler  1 , M Robertson
Affiliations

Gibberellin dose-response curves and the characterization of dwarf mutants of barley

PM Chandler et al. Plant Physiol. 1999 Jun.

Abstract

Dose-response curves relating gibberellin (GA) concentration to the maximal leaf-elongation rate (LERmax) defined three classes of recessive dwarf mutants in the barley (Hordeum vulgare L.) 'Himalaya. ' The first class responded to low (10(-8)-10(-6) M) [GA3] (as did the wild type). These grd (GA-responsive dwarf) mutants are likely to be GA-biosynthesis mutants. The second class of mutant, gse (GA sensitivity), differed principally in GA sensitivity, requiring approximately 100-fold higher [GA3] for both leaf elongation and alpha-amylase production by aleurone. This novel class may have impaired recognition between the components that are involved in GA signaling. The third class of mutant showed no effect of GA3 on the LERmax. When further dwarfed by treatment with a GA-biosynthesis inhibitor, mutants in this class did respond to GA3, although the LERmax never exceeded that of the untreated dwarf. These mutants, called elo (elongation), appeared to be defective in the specific processes that are required for elongation rather than in GA signaling. When sln1 (slender1) was introduced into these different genetic backgrounds, sln was epistatic to grd and gse but hypostatic to elo. Because the rapid leaf elongation typical of sln was observed in the grd and gse backgrounds, we inferred that rapid leaf elongation is the default state and suggest that GA action is mediated through the activity of the product of the Sln gene.

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Figures

Figure 1
Figure 1
Growth of L1 of wild-type barley. Grains were surface-sterilized, placed in moist paper envelopes, stratified, and incubated as described in Methods. At the indicated times the mean L1 lengths of 10 seedlings were determined, as well as the mean lengths of the blade and sheath. Where not visible, error (se) bars lie within the symbols. Inset, Mean elongation rate of the blade of L1 in the previous 24 h was plotted as a function of days of growth. The LERmax value for this set of data is indicated.
Figure 2
Figure 2
Dose-response curves relating LERmax of L1 to [GA3]. Grains of the indicated lines were surface-sterilized, placed in paper envelopes moistened with the appropriate [GA3], stratified, incubated in low light, and LERmax (mean ± se) of seedling L1 was determined as described in Methods. Curves in the top six panels were fitted using PEST software (Weyers et al., 1987). Note differences in the range of GA3 concentrations in different panels.
Figure 6
Figure 6
LERmax of L1 of elo mutants and a grd mutant growing with or without tetcyclacis and GA3. Grains of M21 (elo1), M626 (elo2), and M117 (grd1) were surface-sterilized, placed in moist paper envelopes containing, where appropriate, 2 μm tetcyclacis or 2 μm tetcyclacis plus 10 μm GA3, stratified, and incubated under low light; and the mean LERmax of seedling L1 was determined as described in Methods. A replicate consisted of 10 seedlings, and there were three replicates for each genotype and treatment. Within a genotype, letters (a, b, or c) indicate significance (P < 0.05) for the differences between the means of each treatment.
Figure 7
Figure 7
LERmax of L1 of Sln1− and sln1sln1 segregants in different genetic backgrounds. Grains from stocks in which the sln1 allele was segregating in different genetic backgrounds (WT, wild type; grd1, M117; gse1, M121; and elo1; M21) were surface-sterilized, placed in moist paper envelopes, stratified, and incubated in low light, and the LERmax (means ± se) of seedling L1 was determined as described in Methods. In an elo1 background, slender (sln1sln1) seedlings cannot be distinguished at the first leaf stage from Sln1− seedlings, but after transplanting and further growth, the early stem elongation characteristic of sln1sln1 plants, which still occurs in an elo1 genetic background, allowed the genotype to be determined.
Figure 3
Figure 3
Dose-response curves comparing the effects of GA3 on either LERmax or final blade length. Grains of the indicated lines were surface-sterilized, placed in paper envelopes moistened with the appropriate [GA3], stratified, and incubated in low light, and LERmax (mean ± se) or final blade length of seedling L1 was determined as described in Methods. To allow direct comparison, response ratios are plotted in which the LERmax or L1 blade length in the absence of GA3 is assigned a value of unity. Curves are the same (minus data points) as shown in Figure 2. Individual data points (▾) are for final blade length.
Figure 4
Figure 4
LERmax (means ± se) of different grd mutants in the presence of GA-biosynthetic intermediates. Grains of M117 (grd1), M359 (grd2), and M411 (grd3) were surface-sterilized, placed in paper envelopes moistened with the indicated GA at 2 μm, stratified, and incubated in low light, and LERmax (means ± se) of seedling L1 was determined as described in Methods. GA44, GA19, and GA20 are successive biosynthetic intermediates in the early 13-hydroxylation pathway leading to the formation of the bioactive GA1.
Figure 5
Figure 5
α-Amylase activity of de-axised grains of the wild type and a gse1 mutant incubated with different [GA3]. The embryonic axes of wild type and M488 (gse1) grains were removed, and the resulting de-axised grains were surface-sterilized, placed in paper envelopes moistened with the indicated [GA3], stratified, and incubated in low light as described in Methods. At the indicated times, duplicate samples (five grains each) were harvested and α-amylase was extracted and assayed. Each data point is the mean of duplicate samples.
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