Fig. 1. Activated STM-GR rescued the meristem in stm1 mutants and inhibited leaf development. (A) 35S::STM-GR seedlings grown on medium without dexamethasone. One of the seedlings is homozygous for stm1 (arrow). Bar: 5 mm. (B) 35S::STM-GR seedlings (including one-quarter of stm1 homozygotes), grown on medium with 1 µM dexamethasone. Bar: 5 mm. (C) Scanning electron micrograph of the apex of a 35S::STM-GR seedling two weeks after germination on medium with 1 µM dexamethasone. The meristem (m) is surrounded by leaf primordia (p) in the normal spiral phyllotaxis. The arrows indicate stipules, whose identity was confirmed using a stipule-specific reporter gene (not shown). Bar: 100 µm. (D) Cryo-scanning electron micrograph of a leaf from a 2-weeks old 35S::STM-GR seedling grown on medium with 1 µM dexamethasone. Arrows indicate ectopic stipules between leaf lobes. Bar: 100 µm. (E) Tip of a leaf from a 35S::STM-GR seedling grown for 2 weeks on medium with 1 µM dexamethasone. The arrow indicates a pair of guard cells. Bar: 100 µm. (F,G) 35S::STM-GR plants grown for 2 weeks on soil, sprayed once a day for 4 days with 0.015% v/v Silwet L-77 (F) or 0.015% v/v Silwet L-77 with dexamethasone 0.1 µM (G) and photographed 20 days after germination (moved to agar medium only for photography). The area around in the centre or the rosette in G is contains arrested leaf primordia similar to those seen in B, and early floral buds. Seedlings similar to the one shown in G were seen after spraying with 0.1-10 µM dexamethasone, although the degree of growth arrest was more severe at higher steroid concentrations. Bar: 5 mm.
