Analysis of self-repair mechanisms of Phaseolus vulgaris var. saxa using near-infrared surface-enhanced Raman spectroscopy

We used surface-enhanced Raman spectroscopy (SERS) to investigate ultrastructural changes in cell-wall composition during the self-repair of lacerated hypocotyls of Phaseolus vulgaris var. saxa. A detailed study of self-repair mechanisms requires localized information about cell-wall structure and morphology in addition to the chemical cell-wall composition. Characteristic Raman and SER spectra yielded two-dimensional maps of cross sections of P. vulgaris var. saxa visualizing chemical compositions in the walls of different cell types and during various repair phases. SERS substrate particles were produced by the reduction of gold chloride on the plant tissue surface and characterized with absorption spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The SERS results were compared with stained cross sections of the same plant using dark-field microscopy with focus on lignin and suberin contents in repairing cells. In addition, SERS measurements revealed Au cyanide compounds on the cell surface, indicating the formation of hydrogen cyanide during the self-repair phase.