Fig. 7
Expression profile of the gene CO1 used to indicate freezing tolerance. The level of gene expression is expressed as delta delta threshold cycle (ddCt), which is the relative difference between the gene of interest and reference genes (genes that did not show any significant difference in expression). Measurements were performed at four different occasions, Sept. 9, Sept. 23, Oct. 9, and Oct. 23, 2013, for Norway spruce seedlings previously subjected to SD (short day) treatments with a photoperiod of 11 h of various lengths (0, 7, 14, 21, and 28 days) starting on July 15. After SD treatment, seedlings were either kept indoors or moved outdoors. Each sampling day, eight apical buds were collected from each SD treatment and growing environment and then analyzed for gene expression as one general sample