Fig. 4. ROXY1 expression. (A) RT-PCR analysis of ROXY1 in wild-type organs. For first-strand cDNA synthesis, RNA was isolated from roots (R), stems (S), leaves (L), inflorescences (I), mature flowers (F) and siliques (Si). 18S rRNA was used as a control. (B-F) In situ analysis of ROXY1 expression in wild-type flowers. (B,C) Longitudinal (B) and transverse (C) sections through the tip of an inflorescence. Onset of ROXY1 expression is visible in the inflorescence apex where a future primordium will be initiated (pre-stage 1). Then, signal is detectable when a flower primordium emerges (stage 1), in a flower primordium (stage 2) and in the area where the sepal primordia are formed (stage 3). (D,E) ROXY1 expression in longitudinal sections of a wild-type flower at stage 4 (D) and stage 7 (E). Expression is detected in petal (arrowhead) and stamen primordia (arrow) that are just initiated (D). ROXY1 mRNA is still expressed throughout young petals but confined to the vasculature in stamens (E). (F) Cross-section through a bud at stage 8 shows that the signal becomes restricted at a later stage to the central vasculature of both older petals and stamens. (G) Top view of a transgenic inflorescence meristem revealing expression of the ROXY1-GFP fusion protein comparable to the in situ staining shown in C. (H) Arrowheads indicate ROXY1-GFP expression in petal primordia in a flower bud at stage 8. se, sepal; pe, petal; st, stamen; ca, carpel. 1, 2, 3 indicate developmental stages (Smyth et al., 1990). Asterisks in C and G indicate the position of the inflorescence meristem (im). Scale bar: 50 µm.