Specific characters of vessel primary walls during the early stages of wood differentiation

Abstract

At the peak of its activity, the cambial zone comprises several layers of undifferentiated, apparently identical cells. In order to find criteria indicating the commitment of cambial cells either to phloem or xylem, early changes in primary wall structure and composition were looked for, using sycamore branches as experimental material. Several chemicals were employed to extract cell wall polysaccharides. Treated specimens were studied by electron microscopy after selective staining. Extracted matrix components were analysed through HPLC. Comparison of ultrastructural and biochemical results indicated that in contrast to phloem derivatives cellulose biosynthesis in xylem derivatives was delayed. Among xylem‐committed cells, the very young vessels were characterized by a nearly complete lack of a cellulose skeleton and a high amount of xylose‐rich hemicelluloses in their primary walls. This organization would cause the wall plasticity necessary for the cell extensive growth in diameter.