IR-SNOM analysis of occluding substances in lumina of xylem elements in sapwood of Quercus serrata attacked by Platypus quercivorus.

A new microspectroscopic technique was applied to the analysis of occluding deposits in xylem elements of Quercus serrata. The production of this substance is believed to be a defense response of the sapwood against fungal infection. An occluding substance about 10 μm across was analyzed by Infrared-Scanning Near-field Optical Microscopy (IR-SNOM), which allows for the measurement of IR spectrum with high spatial resolution. The near-field IR spectrum of an occluding substance was different from those of xylem elements and featured a lack of the clear C-H absorption band that should appear at 3000-2850 cm(-1). On the other hand, the absorption band of ester bond exhibited a very strong peak. Among the near-field IR spectra of related compounds, a similar ester absorption peak was observed in the spectrum of pectin and tannic acid. The presence of a C-H absorption band as a very week peak was similar to (+)-catechin and tannic acid.