Analysis of PtSPL gene expression in eight tissues of Populus trhichocarpa using the qRT-PCR method. Fold changes of transcript levels in young root (Rt), young stems (St), young leaves (L1), mature leaves (L2), developing secondary xylem (X1), developing secondary phloem (P1), developed secondary xylem (X2) and developed secondary phloem (P2) of Populus plants are shown. Transcript levels in roots were arbitrarily set to 1 and the levels in other tissues were given relative to this. Error bars represent standard deviations of mean value from three biological replicates. ANOVA (analysis of variance) was calculated using SPSS. P < 0.05 was considered statistically significant.