Ultrastructural Studies of Pinus Pinaster Needles: The Endodermis

The endodermis in the needles of Pinus pinaster was examined with light and electron microscopy. The endodermis is composed of very long, radially flattened cells, filled with a large central vacuole, which contains spherical dense bodies whose concentration decreases from the ends of the cell to the middle part. They are individually surrounded by a fine granular matrix. The central vacuole is bounded by a thick tonoplast. Other small, clear vacuoles are limited by a thin tonoplast. The parietal cytoplasm contains relatively few ribosomes, long slender chloroplasts, and lipid bodies. The smooth endoplasmic reticulum is highly developed along the tangential walls and frequently connected, or apposed, to the plasma membrane. Numerous primary pit fields are seen in the radial walls which are lignified and in the tangential walls; the latter exhibit a characteristic loosening of the outer layer of the wall. The lipid bodies are connected to endoplasmic reticulum tubules. The role of the endodermis in the active transport of water inside the needle is discussed in reference to previous physiological studies. The chemical composition of the vacuolar dense bodies is as yet unknown.