White spruce and poplar HD-Zip III transcript profiles across several organs and tissues. Steady-state RNA levels were determined by RT-qPCR with gene-specific primers. The Y-axis is the number of RNA molecules/ng total RNA (determined from a standard curve), which has been normalised based on the transcript accumulation level of a gene. A) Mean RNA level in P. glauca was analysed in duplicate in two independent biological replicates (one tree per replicate) ± SD (error bar), and normalised based on the transcript accumulation levels of reference gene EF1a. B) Mean RNA level in P. trichocarpa × P. deltoides (clone H11-11) from duplicate analyses of two biological replicates (two trees per replicate) ± SD (error bars), normalised with a CDC2 reference gene. The recently duplicated poplar paralogues are colour-matched. The tissue codes (see Methods): shoot apex (A), portion of the main undergoing primary growth (1T), young needles from upper tree crowns (YN, in spruce); young leaves (YF, in poplar); mature leaves (MF); old leaves (OF); bark (B); stem secondary xylem (2X) and phloem (2P); root secondary xylem (R2X); phloem/phelloderm (RPP); and young root tips (R).