Ultrastructure of parenchyma cell wall in bamboo (Phyllostachys edulis) culms

Abstract

Parenchyma cell wall structure plays a crucial role in the growth and the mechanical properties of bamboo plants, with the secondary cell wall providing strength and rigidity. However, little is known about the ultrastructure of the parenchyma cell wall. The aim of this study was to characterize the anatomical structure of the parenchyma cell wall and determine how it contributes to great mechanical superiority of bamboo culm. We investigated the ultrastructure of the parenchyma cell wall using transmission electron microscopy and field-emission environmental scanning electron microscopy. The key results show that the secondary cell walls of ground and vascular parenchyma cells exhibited tight-loose (light-dark) alternating layers. The pit membrane of the ground parenchyma cells contained numerous pores, and that of vascular parenchyma cells contained some plasmodesmata. Secondary cell walls of most bamboo parenchyma cells contained seven sub-layers, with a maximum of eleven sub-layers of ground parenchyma cells and nine sub-layers of vascular parenchyma cells. The average thickness of ground parenchyma cell wall sub-layers was higher than that in vascular parenchyma cells. The pit membrane thickness of ground parenchyma cells was also higher than that of vascular parenchyma cells, but the diameter of the ground parenchyma cells was smaller than that of the vascular parenchyma cells. The extremely high flexibility of moso bamboo stem could be the consequence of the presence of secondary cell walls in parenchyma cells, and its ultrastructure.