Figure 3.

Effect of MONOPTEROS (MP) activity on shoot organ initiation and PIN FORMED1 (PIN1) expression in Arabidopsis.

(a) Apical and (b) lateral views of 17d after germination (DAG) mp nph4 MP-GR seedlings grown in the absence of dexamethasone (DEX).

(c–f) Apical and lateral views of mp nph4 MP-GR (c,d) and mp nph4 MP-GR^er (e,f) seedlings (24DAG) grown in the absence of DEX. The fractions of mp nph4 MP-GR individuals with randomly arranged lateral bulges (c) and of mp nph4 MP-GR^er seedlings with lateral bulges arranged in a linear plane perpendicular to cotyledons (arrows, e) are given. Cotyledons have been removed in (f) to allow visualization of bulges.

(g) Clusters of leaf-like organs (arrowheads) initiated from lateral bulges of mp nph4 MP-GR seedlings transferred to 15μM DEX at 17DAG and grown for an additional 11d.

(h) Apical view of 17DAG mp nph4 MP-GR^er seedling transferred to 15μM DEX at 10DAG.

(i) mp nph4 MP-GR seedling (28DAG) grown in the absence of DEX. Lateral bulges have transitioned to tapered, pin-like structures (arrows).

(j) Flowers (arrowheads) initiated from pin-like SAM outgrowths of 28DAG mp nph4 MP-GR seedlings transferred to 15μM DEX at 17DAG.

(k) PIN1-GFP expression in the shoot apical meristem (SAM) of an mp nph4 MP-GR seedling (13DAG) lacking cotyledons, transferred to 30μM DEX at 0h. Foci of PIN1-GFP expression at 18h presage lateral organ positions.

(l–q) PIN1-GFP expression in dicotyledonous mp nph4 MP-GR^er seedlings (10DAG) transferred to mock (l–n) or 30μM DEX (o–q) at 0h. Appearances of the SAMs at the start (l,o) and end (n,q) of each time course are shown. A uniform ring of PIN1-GFP shows increased expression by 6h of DEX treatment (p). PIN1-GFP foci (arrowheads at 24h) presage lateral organ formation.

Bars: (a,b,d,f,g,i,j) 0.5mm; (c,e) 0.2mm; (h) 1mm; (k–q) 0.2mm.