Modification of cambial cell wall architecture during cambium periodicity in Populus tomentosa Carr.

Cambium periodicity is correlated with changes in the cambial cell wall, but the heterogeneity of cell wall structure and composition makes it difficult to give an accurate interpretation, especially for complex secondary vascular tissues. A combination of different methods is necessary to reveal the structure of this complex cell wall. In this study, the cell wall architecture and composition of active and dormant cambial cells in Populus tomentosa were investigated by a combination of light microscopy, rapid-freezing and deep-etching electron microscopy, Fourier-transform infrared microspectroscopy and immuno-histochemistry. The results showed that the architecture of dormant cambial cell walls displayed a multi-layered structure, denser fibril network, smaller pore size, and fewer crosslinks between microfibrils than active cambial cell walls. The FTIR spectra of cell walls from active and dormant cambium showed differences in the intensity of bands near 1,740, 1,629, 1,537, 1,240, and 830 cm(-1), which reflected differences in cell wall composition. Immuno-labeling indicated that high methyl-esterified homogalacturonan and (1 -> 4)-beta-d-galactan epitopes were abundant and distributed in active cambial cell walls, and relatively de-esterified homogalacturonan and (1 -> 5)-alpha-l-arabinan epitopes had weak labeling in the active cambium, while almost no labeling or very weak labeling for high methyl-esterified homogalacturonan, (1 -> 4)-beta-d-galactan and (1 -> 5)-alpha-l-arabinan epitopes occurred in dormant cambial cells, except for the de-esterified homogalacturonan epitope, which was abundant in dormant cambial cells. These results demonstrate that there are great differences, both in structure and composition, between active and dormant cambial cell walls, which reflect their dynamic changes during cambium activity.