Early changes in the radial walls of storied fusiform cambial cells during fiber differentiation

Abstract

There is little information about the ultrastructural changes taking place in the radial walls of fusiform cambial cells during differentiation into xylem derivatives. The present study reports the early events occurring in the radial walls of fusiform cambial cells (FCCs) during fiber elongation in Holoptelea integrifolia, a deciduous tropical tree with storied cambium. Serial tangential sections of active cambial zone cells demonstrate the initiation of intrusive cell wall elongation from gabled ends of FCCs during fiber development. The elongation at the tip is followed by the axial extension of the entire cell. It was evident from ultrastructural observations made on the tangential sections that the thick beaded pattern on FCC radial walls disappear following cell elongation. PATAg staining, specific for wall polysaccharides showed that, initially, the beaded structures undergo wall loosening following hydrolysis of pectic polysaccharides in the middle lamella. Then the loosened primary walls come together with the axial extension of cells. Thus the beaded nature disappears in the differentiating cambial cells. This study highlights the cell wall changes associated with the differentiation of FCCs into fibers.