Figure 3. Two-dimensional (A) score and (B) scaled and centered loading plots of orthogonal partial least square regression (OPLS) of S-nitrosylated proteins (normalized by whole-cell extract) in poplar leaf samples determined using biotin switch assay and LC-MS/MS.

The explained variance (in percentage) and the number of principal components (PC) are reported in the x- and y-axes in both (A) and (B) plots. The ellipse in (A) indicates the tolerance based on Hotelling’s T² with the significance level of 0.05. The outer and inner ellipses in (B) indicate 100% and 75% explained variance, respectively. (A) control = black circles, ozone-treated = grey triangles; (B) each functional group of proteins (according to Figure 1C) is indicated with different symbols, zoomed symbols with a dot represent the significantly different proteins between C and O plants tested independently with Student’s t-test (P<0.05 applying a FDR of 5%). Symbol legend: dark red circles = Amino acid metabolism and Protein synthesis, folding and degradation; blue diamonds = Redox and Signaling; cyan triangles-up = Primary metabolism; yellow square = Secondary metabolism; red triangles-down = Stress; dark green squares = Structural function; grey triangles-down = other; grey squares = not assigned or not identified. The black diamond indicates the Y-variable, i.e. ozone-treatment.