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. 2008 Dec 8;105(50):20032–20037. doi: 10.1073/pnas.0805617106

Fig. 2.

Fig. 2.

pBpCRE1::AtCKX2 poplar lines with a high expression level of the transgene display reduced cytokinin content and responsiveness, together with a thin-stemmed phenotype. (A) WT and pBpCRE1::AtCKX2 poplar lines 5, 8, 7, 9, and 11 (4-month-old trees). Lines 7, 9, and 11 with a strong transgene expression have elongated internodes and show premature leaf senescence (indicated by white arrows). (Scale bar: 20 cm.) Height vs. age ratio (B) and width vs. height ratio (C) in WT and pBpCRE1::AtCKX2 poplar lines 5, 8, 7, 9, and 11 (n = 3). pBpCRE1::AtCKX2 poplar lines 5 and 8 have a WT-like phenotype, and lines 7, 9, and 11 display a thin-stemmed phenotype (error bars = SD). (D) AtCKX2 and PtTUA2 expression in WT and pBpCRE1::AtCKX2 poplar lines 5, 8, 7, 9, and 11 by qRT-PCR shown in a gel. Both t-zeatin (E) and ZOG (F) are below the detection limit (*) in the shoot of lines 7 and 11. Three biological replicates (A–C) are shown per line (error bars = SD). (G) Cytokinin responsiveness assay. Medium with indole acetic acid (IAA) at 0.5 mg/L IAA and 0, 0.5, 1.5, 2.5, or 15 mg/L t-zeatin. A low cytokinin-to-auxin ratio induces root regeneration, and a high cytokinin-to-auxin ratio enhances shoot regeneration. The following lines were analyzed: WT, pBpCRE1::GUS, and pBpCRE1::AtCKX2 lines 7 and 11. WT and pBpCRE1::GUS regenerate shoots from medium to high cytokinin concentrations (1.5–15 mg/L), whereas lines 7 and 11 regenerate shoots only in a high (15 mg/L) cytokinin concentration. Emerging shoots are indicated by yellow arrows. (Scale bar: 1 cm.)