Abstract
The cocoon fiber of Bombyx mori strain F7 features significant fine fibers with irregularly shaped fibroin. We treated cocoon fibers with lithium bromide to swell the fibroin for observation. Optical microscopy revealed linear grooves on the sides of the fibroin. SEM images of fiber cross-sections showed that these grooves were abnormal structures associated with the depression of the fibroin surface. The grooves were present in the outer to middle layers of the cocoon, but not in the inner layers. Slight depressions in the outer layer appeared to indicate the early stage of the structure. On the other hand, fibroin in strain CV, which does not produce the fine fibers, had no grooves. These results suggest that the depression is specific to F7 and may be fundamental to the development of the fine fibers. The F7 fibroin was severely split by the linear grooves, indicating that structural defects may be latent in the fibroins of strains that generate fine fibers.
