tailieunhanh - Báo cáo khoa học: "Control ofxylogenesis within the whole treeR."

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài: "Control ofxylogenesis within the whole treeR. | 267s Ann. Sci. For. 1989 46 suppl. 267S-272S Forest Tree Physiology E. Dreyer et al. eds. Elsevier INRA Control of xylogenesis within the whole tree R. Aloni Department of Botany The George s. Wise Faculty of Life Sciences Tel Aviv University Tel Aviv 69978 Israel Introduction The problems to be dealt with here concern the control of organized differentiation of the wood within a whole tree. Anatomically the wood is the xylem and it has a different structure and composition in different parts of the tree. In mature organs the wood is produced by a lateral meristem the vascular cambium. The wood produced by the vascular cambium is termed secondary xylem. It is a complex tissue comprised of several types of cells. Xylem differentiation within the plant is characterized by a high degree of order. The vascular and supporting elements as well as the parenchymatic cells differentiate in a predictable three-dimensional structure typical for each species. Therefore a tree species can be identified solely by its xylem. Xylogenesis within the whole tree is an open type of differentiation which continues as long as the tree grows by apical and lateral meristems. Thus there is a continuous development of new xylem tissues that are in a dynamic relationship with one another. This complex developing system raises many questions about control mechanisms and these have enormous economic impor tance in terms of improving wood quality and forest productivity. Wood quality depends upon the form and size of a tree as well as on the wood s anatomical structure and chemical composition. The quality of an isolated piece of wood is the result of the quantitative relationship between the type of xylem cells their size and density as well as their physical structure and chemical composition. The problems to be dealt with here will be restricted to the control of xylem development and structure from the level of individual cells to that of the entire plant. In order to clarify how the wood .