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. 1996 Nov 26;93(24):13831–13836. doi: 10.1073/pnas.93.24.13831

Figure 1.

Figure 1

Photoperiod controls floral meristem activity in lfy-6 and ag-1 flowers. (A) LD homozygous lfy-6 flower. lfy-6 flowers show a basipetal to acropetal gradient of phenotypes (16). A typical acropetal LD lfy-6 flower is characterized by the production of sepals (s) and carpels (c) and the absence of petals and stamens. (B) SD homozygous lfy-6 flower. lfy flower development is suppressed under SDs (12, 15). A typical SD “flower” produces an indeterminate number of leaf-like organs (l). (C–F) SD heterozygous lfy-6 flower development. Heterozygous lfy-6 flowers produce a normal complement of organs (C) and are initially indistinguishable from wild type. Later, basipetal flowers are distinguished by a dramatically swollen ovary (so) (D). The swollen ovary often ruptures and a single flower-bearing ectopic shoot (es) emerges (E). The resulting shoot (es) produces several leaf-like organs, numerous flowers, displays internode elongation, and a spiral pattern of phyllotaxis (F). Flowers produced by the ectopic shoot appear either wild type or resemble ap2 mutant flowers. (G) LD ag-1 flower. ag-1 flowers are characterized by the transformation of stamens into petals and an indeterminate pattern of floral organogenesis (sepal, petal, petal)n. (H and I) SD ag-1 flower development. Basipetal SD ag-1 flowers initially produce several whorls of sepals and petals (H). Organogenesis then ceases and is replaced by the production of an ectopic shoot (es) that bears numerous flowers and displays internode elongation (I). (J–L) Ectopic shoot formation in basipetal SD heterozygous lfy-6 flowers. Longitudinal sections (2 μm) were prepared as described in Materials and Methods. An ectopic shoot (es) arises directly from the apical dome of the floral meristem (J). A magnified view of the ectopic shoot is shown in K. At this stage of development the ectopic shoot produces leaf-like organs (l). The ectopic shoot continues to grow and eventually fills the ovary (L). ov, The ovary wall. (Bar = 0.1 mm.) (M) Wild-type flower. Shown is a longitudinal section (2 μm) through a SD wild-type flower. Floral meristem activity is suppressed after carpel primordia are established. (Bar = 0.1 mm.) (N and O) Ectopic shoot formation in SD ag-1 flowers. A 2-μm longitudinal section through a SD basipetal ag-1 flower shows floral buds (fb) emerging from the apex of the floral meristem (N). A LD ag-1 flower is shown for comparison (O). (Bar = 0.1 mm.) (P–R) AG gene expression in SD heterozygous lfy-6 flowers. The spatial pattern of AG gene expression in SD heterozygous lfy-6 (P and Q) and wild-type flowers (R) was determined by in situ hybridization as described. The presence of AG transcripts is revealed by the orange staining. The flowers in P, Q, and R are at stages 3, 8, and 10, respectively (28). es, The ectopic shoot primordium. (Bar = 0.1 mm.)