Figure 5.

RGL2 expression in seeds is imbibition inducible. (A) RNA gel-blot analysis of RGL2 expression in wild-type seeds at different stages of imbibition and germination. RGL2 transcripts first become detectable at 24 h after the onset of imbibition at 4°C, then rise to a peak that is maintained for as long as the seeds are kept at 4°C. When wild-type seeds are subsequently moved to 23°C, RGL2 transcript levels begin to fall rapidly, and are barely detectable 48 h after the seeds were moved into the warmth, by which time germination had been completed. (B) RGL2 expression in wild-type seeds is also induced by imbibition at 23°C. Transcript levels rise more rapidly than they did at 4°C, with high levels being achieved by 24 h. (C) RGL2 transcripts remain at high levels in ga1-3 mutant seeds. Unlike RGL2 transcript levels in wild-type seeds, RGL2 transcript levels remained high in ga1-3 seeds following transfer from 4 to 23°C. (D) RGL2 expression is down-regulated in ga1-3 seeds grown at 23°C and treated with GA (10⁻⁴ M GA₃). (E) In situ GUS expression patterns in seeds of rgl2-5 heterozygotes during seed germination. GUS staining is observed in the radicle of seeds that have been imbibed at 4°C (seed coat was removed after staining for observation). Following transfer to 23°C, GUS staining rapidly disappears, being still faintly detectable in the radicle at 24 h and barely detectable at 48 h, by which time germination is relatively advanced. In A, C, D, and E, seeds were chilled at 4°C for 7 d and then moved to a 23°C growth chamber with a 24 hr photoperiod.