Figure 2
Average expression stability values (M) and ranking of candidate reference genes determined by geNormPLUS. Candidate reference genes ordered from least stable (left) to most stable (right) in shoot tips/buds, young leaves, mature leaves and bark of both genotypes (P. trichocarpa and P. tremula x P. alba). The red line indicates the limit above which genes are considered non-stable (M = 0.5).