CELLULAR CHANGES OF TRACHEIDS AND RAY PARENCHYMA CELLS FROM CAMBIUM TO HEARTWOOD IN <em>CUNNINGHAMIA</em> <em>LANCEOLATA</em>

Abstract

SONG K, LIU B, JIANG X & YIN Y. 2011. Cellular changes of tracheids and ray parenchyma cells from
cambium to heartwood in Cunninghamia lanceolata. Cellular changes of the cell wall and protoplasm in tracheids
and ray parenchyma cells during heartwood formation were investigated in a 26-year-old Cunninghamia
lanceolata at micro- and ultrastructure levels. Cell morphological and ultrastructural features changed
significantly from the cambium to inner heartwood. In the cambial zone, the thickness of fusiform and
ray cell walls were thin and their radial walls were much thicker than tangential walls. Fusiform cells were
highly vacuolated with the protoplasm confined to the periphery of cell lumen. At the time of wood cell
differentiation, differentiating xylem mother cells began to lose the protoplasm. Concomitantly, their walls
thickened and showed characteristically distinct wall layers. In comparison, ray cell walls appeared as typical
polylamellate structure and had thinner walls than the tracheids. Tracheids completed their differentiation
and left hollow dead tracheary elements to decline into sapwood, while the xylem ray cells remained alive.
The ray cells contained cell protoplasm, although the amount, shape and size altered when shifting towards
intermediate wood. Subsequently, the ray cells disintegrated their protoplasm, including the nuclei, organelles
and reserve materials, which marked the formation of heartwood.