Figure 1.

Increased local accumulation of catechin, proanthocyanidins (PAs) and salicylic acid (SA) in the stems of black poplar saplings after infection by P. populi compared to adjacent uninfected stem internodes. Poplar trees of approximately 1 m height were inoculated with the fungus. (A) Representative picture showing a P. populi-infected poplar stem with sampling areas. Infected stem internodes and adjacent uninfected internodes were harvested 6 weeks after inoculation. (B–D) Concentrations of the flavan-3-ol monomer (+)-catechin), the dimer PAB1, and oligomeric PAs. (+)-Catechin and PAB1 were analyzed by LC-tandem mass spectrometry. PA oligomers up to 10 monomeric units were measured by HPLC-FLD. The contents of PAB1 and PA oligomers were equivalent to the content of catechin. (E) Concentration of SA was analyzed by LC-tandem mass spectrometry. Data were analyzed using a paired t-test (**, p < 0.01; and ***, p < 0.001). Bars represent mean ± SE (n = 5). DW, dry weight.