Anatomical and chemical characteristics of the Douglas-fir (Pseudotsuga menziesii (mirb.) Franko) phellem cell

Abstract

The objectives of this study were to 1) characterize the layering in the wall of the Douglas-fir (Pseudotsuga. menziesii (Mirb. ) Franco) phellem cell, 2) determine the pitting present in this cell wall and 3) determine what compounds are present in the middle lamella of this cell. To accomplish the objectives excised Douglas-fir cork was subjected to various chemical treatments (extraction with organic solvents, water, ammonium oxalate and sodium sulfite, saponification by an aqueous sodium hydroxide solution and an ethanolic potassium hydroxide solution). At certain stages in the treatment samples were removed for such analyses as trace mineral, protein and specific gravity. Paralleling this microtomed sections of cork were similarly chemically treated and removed for observation with various types of microscopes. The microscopes used were light, ultraviolet, polarizing, scanning electron and transmission electron. The results of this study showed that the cell wall structure of the Douglas-fir phellem cell is composed of 4 zones or layers. They are 1) a primary wall with randomly oriented microfibrils, 2) a secondary suberin layer composed of alternating lamella of phenolics and waxes which have the wax molecules oriented perpendicular to the cell surface, 3) a wax extractives layer and 4) a layer of cellular debri such as cytoplasm and old membranes lining the lumen. A middle lamella composed of phenolic and pectic substances holds the cells together. The simple pits of the phellem cell are plugged with a material which gives a callose reaction when stained with analine blue. Also the first formed tangential wall of the first formed uncrushed phellem cell in a growth increment has an abnormally thick compound middle lamella.