Gibberellins: Regulators of Plant Height and Seed Germination • GA levels in plants are correlated with stem length. • Play role in seed germination, transition to flowering, and pollen development. Figure 20.1 Effect of exogenous GA1 on wild-type and dwarf mutant maize Figure 20.2 Cabbage can be induced to bolt and flower by applications of GA3 Figure 20.3 Gibberellins induce conebud formation in juvenile conifers Figure 20.4 Gibberellin induces growth in “Thompson Seedless” grapes Ch. 20 In-Text Art, pp. 585–586 Gibberellin structures Figure 20.6 Phenotypes of wild-type and GA-deficient mutants of Arabidopsis Figure 20.8 Histochemical analysis of Arabidopsis plants containing the GA1 promoter Figure 20.24 Phenotypes of floral organs of gamyb mutants of rice Figure 20.9 Phenotypes and genotypes of peas that differ in GA1 content of their vegetative tissue Figure 20.10 Genetically engineered dwarf wheat plants Figure 20.11 Impaired seed development in a GA-deficient mutant of pea Figure 20.12 GA binding properties of GID1 (GA Insensitive Dwarf) Figure 20.13 Phenotypes of gid1a, gid1b, and gid1c mutants of Arabidopsis (Part 1) Figure 20.13 Phenotypes of gid1a, gid1b, and gid1c mutants of Arabidopsis (Part 2) GA receptor mutants exhibit deficient anther development. Figure 20.14 Structure of the GA3-GID1a-DELLA complex Figure 20.15 Model of GA-induced change in the GID1 protein Figure 20.16 Domain structures of the RGA and GAI repressor proteins Figure 20.19 Degradation of the DELLA protein by the 26S proteasome Figure 20.20 Integration of light and GA signaling in Arabidopsis seedlings Figure 20.17 Opposite effects of two different mutations in the same SLN1 repressor gene • GA signals the degradation of negative regulators, e.g. the degradation of DELLA proteins. • Sln1c loss-of-function. Mutated in GRAS domain; unable to repress GA responsive genes even in the absence of GA. • Sln1d gain-of-function. Mutation in DELLA domain prevents the repressor protein from being degraded. Figure 20.21 Structure of barley grain and functions of tissues during germination Figure 23.3 Precocious germination in the ABA-deficient vivipary 14 mutant of maize • Ratio of GA:ABA affects early germination (vivipary). With high levels of ABA, seeds remain dormant.