Cortical cell types and their distribution in wool fibres

Abstract

A method of determining cell types in wool fibres by methylene-blue staining has been extended to allow relationships between cortical cell type and cortical diameter to be studied in woolsfrom individual sheep. Application of the method to wools from 12 sheep from six breeds showed that orthocortical cells were the predominant cell type produced. The percentage area occupied by orthocortical cells in a fibre cross-section increased with increasing cortical diameter in either a curvilinear (log-linear) or a linear manner. Nutritional stress or season may have affected the relationship in some sheep. The arrangement of cortical cell type within fibre cross-sections showed less change in linear-type wools as diameter increased than in log-linear-type wools. Proportions and arrangements of cell types sometimes varied along the length of individual fibres, usually in a definite sequence. Orthocortical cells had larger cross-sectional areas than mesocortical-paracortical cells and were most frequently associated with changes in fibre diameter and shape. Mesocortical cells are believed to be true intermediate cells as they ranged in structure from orthocortical-like to paracortical-Iike. Few qualitative differences in wool proteins were found between wools, suggesting that differences in their properties arose mainly from quantitative protein and cellular differences. © 1984 ASEG.