Volcano plots of microarray analyses to identify genes differentially expressed during compression and opposite wood formation. The common logarithm of the p-value was represented as a function of the binary logarithm of the background-corrected and normalized opposite:compression fluorescence ratio (log2 Fold Change) for each spot. Vertical bars delimit the spots showing up-regulation in developing compression xylem by at least 1.5-fold compared to developing opposite xylem (Up-regulated in Cx) or spots showing up-regulation in developing opposite xylem by at least 1.5-fold compared to developing compression xylem (Up-regulated in Ox). The horizontal line delimits the spots showing significant up-regulation under the criteria of an adjusted p-value ≤ 0.001. Therefore, the upper left and right sectors delimited by the horizontal and vertical lines include the spots (in red) containing probes for genes significantly up-regulated in developing compression or opposite xylem respectively. The number of spots corresponding with genes significantly up-regulated in Cx or Ox are shown in the top side of the sector. (a) Results from the analysis of microarray 1 constructed with cDNA clones from the composite library. (b) Results from the analysis of microarray 2 constructed with cDNA clones from subtractive libraries.