CAMBIAL ULTRASTRUCTURE AND BIOCHEMISTRY - CHANGES IN RELATION TO VASCULAR TISSUE DIFFERENTIATION AND THE SEASONAL CYCLE

The original features of cambial cells and their immediate derivatives are reviewed, with special focus on the recent progress resulting from cytological and biochemical approaches. In trees from the temperate zone, many seasonal changes can be correlated with cold acclimation and deacclimation, except those concerning the nuclei and cell walls. Detailed studies of nucleic acid metabolism during the seasonal cycle showed that the nuclei of dormant cells were blocked in the G(1) phase as expected from previous results with apical meristems. Seasonal changes in cell wall structure and composition imply variations in cell wall plastic properties and growth potential. Early wall modifications occurring across the cambial zone, however, may indicate cell commitment; e.g., cellulose biosynthesis appears to be the highest in phloem derivatives, pectin biosynthesis the highest in xylem derivatives. Further studies would benefit from coordinated multidisciplinary approaches.