Fig. 5

Autofluorescence images obtained by fluorescence microscopy (a–c) and emission spectra obtained by confocal laser-scanning microscopy (d) of transverse sections of tissue around the pith of branches of Robinia pseudoacacia L. var. inermis. a A transverse section from near the apical region of a branch (NA sample). b A transverse section, from around the pith, of upper region of tissue with four annual rings in xylem that lacked dark-colored heartwood (LH-1 sample). c A transverse section, from around the pith, of tissue with four annual rings in xylem and dark-colored heartwood (IH sample). d Averaged emission spectra of autofluorescence under fluorescence excitation at 405 nm from cell walls of xylem and pith cells around the pith, namely, from sections in (a blue dots and line) and (c green dots and line) (n = 6 in each case). Arrows indicate yellow–green fluorescence. Arrowheads indicate ray parenchyma cells that emitted no yellow–green fluorescence. The left side of the micrographs corresponds to the outer side of the branch. AP Axial parenchyma cell surrounding vessel elements, P pith, PZ perimedullary zone (with double-headed arrow), RP ray parenchyma cell, V vessel element, Xy xylem. Bars 100 μm