Fig. 7. Marker gene expression in CLV1::WUS-expressing wild-type and stm5 mutant plants. Longitudinal sections hybridized in situ with CLV3 (A,B), KNAT1 (C,D,F,G), KNAT2 (H-J) antisense and KNAT1 sense (E) riboprobes. CLV3 and KNAT2 sense riboprobes did not produce any staining (not shown). (A) In CLV1::WUS-expressing wild-type plants 14 days after germination, cells in the three outermost layers of the meristem show strong CLV3 expression. (B) CLV1::WUS-expressing stm5 mutant plants 14 days after germination exhibit CLV3 expression in a band at the top of the induced structure inside the fused cotyledon petioles. The same result was obtained when analyzing 10 day old seedlings (not shown). (C) In non-transgenic wild-type seedlings, KNAT1 expression is detected at the base and periphery of the SAM and close to the base of young leaf primordia (black arrow), but is absent from the central zone of the SAM (white arrow). In addition, expression is detected in cells close to the vasculature (arrowhead). (D) In CLV1::WUS-expressing wild-type plants 10 days after germination, KNAT1 expression is detected at the periphery of the enlarged meristem (black arrows) and adjacent to the vasculature (arrowhead). Although weak, this staining was consistent throughout serial sections. The central region of the meristem (white arrow) shows only weak background staining that is also found in leaves (asterisk) and in sections hybridized with a KNAT1 sense probe (compare with E). (E) Hybridization with a KNAT1 sense riboprobe produces only weak non-specific staining. (F,G) While no KNAT1 mRNA can be detected in the induced structures of 10 day old CLV1::WUS-expressing stm5 mutant seedlings (F), plants of the same genotype at 14 days after germination (G) exhibit clear KNAT1 expression at the base (arrow) and in patches on the flanks of the induced structures (arrowhead). However, no expression is seen close to the vasculature in either seedling. (H) KNAT2 mRNA can be detected in the periphery of the enlarged meristem of CLV1::WUS-expressing wild-type plants 14 days after germination (black arrows), while only weak and even staining is visible in the centre of the meristem (white arrow) and in leaves (asterisk) which most likely represents non-specific background staining. (I,J) In 10-day old CLV1::WUS-expressing stm5 mutant seedlings (I), no KNAT2 expression can be detected, which is however seen in seedlings of the same genotype 14 days after germination (J) on the flanks (arrow) and at the base (arrowhead) of the induced structure. The asterisk in I indicates a fragment of the vasculature which appears darker because of its secondary cell wall. Scale bars in A-J are 100 µm.