Microfibrillar Orientation of the Innermost Surface of Conifer Tracheid Walls

Abstract

The orientation of the microfibri1s deposited on the innermost surfaces of the tracheid wall was observed in three conifer species, Larix leptolepis, Picea jezoensis, and Picea abies, using field emission scanning electron microscopy (FE-SEM). The microfibrillar orientation is different in each tracheid and exhibits either an S- or a Z-helix. The latest microfibrils deposited were normally joined into small bundles having various widths and had a different orientation from the microfibrils beneath them. When the latest deposited microfibrils on the innermost surface were oriented in an S-helix, the microfibrils beneath them were oriented in either a flatter S-helix or in a Z-helix, and when they were oriented in a Z-helix, the microfibrils beneath them were oriented in a steeper Z-helix. This is because, as seen from the lumen side, the microfibrillar orientation changes counterclockwise from the outer S23 to the innermost S3. These microfibrillar orientations varied throughout a single annual ring in each of the three species. The commonly observed angles of these microfibril were: Larix leptolepis: 70-80°, Picea jezoensis: 60-70°, and Picea abies: 40-50° in an S-helix, and the maximum range of angles was limited in extent to about 90 degrees in all species.