Characterization of Cellulose in Developing Cotton Fibers

During our investigation of cotton fiber development, the  fraction conventionally described as cellulose from fibers of the cultivar DP-50 sampled at ages of 21, 25, 30, 38, 44 and 56 days post anthesis (DPA) were subjected to sequential 6N HCl degradation.  Consistent with literature, we found releases of large amounts of glucose in the early digestions, while such releases quantitatively decreased in later digestions.  Literature asserts that the observed pattern of glucose release occurs because non-crystalline material is degraded rapidly, but crystalline material is more refractive. In contrast to such implied differences in material, observation by light microscopy (200X) of the  residues of the successive hydrolyses revealed no differences; rather microscopic examination consistently found less material with the same apparent structure in decreasing amounts. However, there were differences in chemical composition between the residues of the developing and the relatively more mature cotton fibers. Two groups of glycans, which elute after about 12 minutes as depicted on HPAEC chromatograms of the extractions of the developing fibers, showed a greater relative abundance at all developing stages relative to those from the more mature fibers. These glycans yield several amino acids on hydrolysis. Another difference between the residues from the developing fibers and those of more mature fibers is that at the end of the sequential hydrolyses there is simply nothing left of mature fibers, while the developing fibers yield a series of cello-oligosaccharides in their final hydrolyses. Thus there are apparent differences between developing fibers and fully mature cotton involving all carbohydrate fractions.  Although cotton fibers at 56 DPA are considered mature, changes in composition were occurring in the fibers through the last sampling.