Biochemical and Cytochemical Cell Wall Changes Across the Cambial Zone

Parallel biochemical and cytochemical investigations on several hardwoods disclosed progressive changes in radial cell wall composition and structure across the cambial zone. Phloem derivatives were characterised by the early deposition of a microfibrillar skeleton and a low amount of xylans. In the radial walls of xylem derivatives, cellulose micro fibrils were few and, at least in some species, xylans were rather abundant. The content in acidic pectins and calcium ions increased from the phloem to the xylem side. The presence of cellulose microfibrils, the activity of enzymes such as xylan synthases or pectin methylesterases might be useful clues to recognise early stages of xylem or phloem determination in the first cambial derivatives.