Proteins which are specifically expressed in developing cotton fibers (0-20 days post anthesis) were identified. These proteins were discovered by using a fiber specific antiserum for the immunodetection of proteins unique to the fiber. This serum was generated by immunizing rabbits with total fiber and ovule proteins. The resulting serum was cross-absorbed with proteins extracted from a fiberless mutant, naked seed, which produces no fiber. Cross-absorption inactivated all antibodies which would react to ovule proteins and proteins common to both fiber and ovule, thus yielding the fiber specific antiserum. The cross-absorbed serum was used to selectively identify fiber specific proteins among total fiber and ovule proteins following separation by single dimension, discontinuous buffer, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by electroblotting onto nitrocellulose paper (Western blotting). Binding of the fiber specific antiserum to proteins on blots was assayed by using peroxidase linked goat anti-rabbit IgG. Densitometry of the banding pattern of each ovule age (0-20 days postanthesis taken at two day intervals) was used to determine the relative degree of variation in the amount of each fiber specific protein during the study period.

Using these methods 15 major fiber specific proteins with apparent molecular weights ranging from 160,000 to 48,000 were detected. Several of the proteins occur from 0 through 20 days post anthesis, although their relative amounts appear to fluctuate. Some of the proteins seem to appear during the 20 day period. Functional roles have not been assigned to any of these fiber specific proteins.

This research initiated an effort to study gene regulation during cell development in a higher plant. Cotton fiber provides an interesting and useful model system because the fiber is a single cell, it has been well characterized physically and biochemically, and at least four fiber mutants are available for study. Long term objectives of this research include investigating gene regulation in an angiosperm, and identifying important genes which may be manipulated by classical and molecular genetic methods to modify cotton fiber. Characterization of the proteins expressed specifically during the development of fibers is the first step in this study of cellular development.