BIOCHEMICAL AND CYTOCHEMICAL CELL-WALL CHANGES ACROSS THE CAMBIAL ZONE

Parallel biochemical and cytochemical investigations on several hardwo ods disclosed progressive changes in radial cell wall composition and structure across the cambial zone. Phloem derivatives were characteris ed by the early deposition of a microfibrillar skeleton and a low amou nt of xylans. In the radial walls of xylem derivatives, cellulose micr ofibrils were few and, at least in some species, xylans were rather ab undant. 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 methylestera ses might be useful clues to recognise early stages of xylem or phloem determination in the first cambial derivatives.