Figure 3.

RGL2 is a GA-response negative regulator of seed germination. Germination begins when quiescent dry seeds are imbibed. Following this, the radicle begins to elongate. Germination becomes visible when the radicle protrudes outside of the seed coat. In these experiments, the frequency of radicle protrusion was used as a measure of germination. (A) Seed germination of RGL2 alleles on medium containing PAC. All three alleles (rgl2-1, rgl2-5, and rgl2-12) confer strong resistance to the inhibitory effects of PAC on seed germination. The gai spy-7 gar2-1 mutant line also displays PAC-resistant seed germination (Peng et al. 1999b) and was used here as a positive control. (B) A genomic DNA fragment containing RGL2 complements the rgl2-1 phenotype in five independent transgenic lines, PJR369, 376, 378, 379, and 381. Vector control, pCambia1300 (Cambia, Australia). (C) Comparison of the effects of increasing concentrations of PAC on the seed germination of wild-type and of the rgl2-1, rgl1-1, gai-t6, and rga-t2 mutants. At the highest PAC concentration, only the rgl2-1 mutant, and the gai spy-7 gar2-1-positive control seeds can germinate. (D) Suppression of the nongerminating phenotype of ga1-3 by the rgl2-1 mutation, but not by rgl1-1, gai-t6, rga-t2, or by gai-t6 rga-t2 in combination. Seeds were germinated on SM medium. All tests yielding germination rates between zero and <2% were given a value of 2% for the convenience of drawing the histogram. The seed germination experiments were repeated multiple times and the results shown are those of a single experiment and are clearly representative of what was seen in the repeat experiment.