The primary walls of cotton fibers contain an ensheathing pectin layer

Abstract

Cotton fiber walls (1-2 days post anthesis) are distinctly bilayered compared to those of nonfiber epidermal cells, with a more electron-opaque outer layer and a less electron-opaque, more finely flbrillar inner layer. When probed with antibodies and affinity probes to various saccharides, xyloglucans and cellulose are found exclusively in the inner layer and de-esterified pectins and extensin exclusively in the outer layer. Ovular epidermal cells that do not differentiate into fibers have no pectin sheath, but are labelled throughout with antixyloglucan and cellulase-gold probes. Middle lamellae between adjacent cells were clearly labelled with the antibodies to de-esterified pectins, however. Similarly, cell walls of leaf trichomes have a bilayered wall strongly enriched in pectin, whereas other epidermal cells are not bilayered and are pectin poor. These data indicate that one of the early markers of fiber and trichome cells from other epidermal cells involves the production of a pectin layer. The de-esterified pectins present in the ensheathing layer may allow for expansion and elongation of the fiber cells that does not occur in the other epidermal cells without such a sheath or may even be a consequence of the elongation process.

A Specialized Outer Layer of the Primary Cell Wall Joins Elongating Cotton Fibers into Tissue-Like Bundles

“…1, B-D, and 3G). Second, 2-DPA cotton fibers lacked the distinct cuticle layer that was easily seen in adjacent regular epidermal cells (Vaughn and Turley, 1999), and other images are consistent with an elongating cotton fiber leaving the ovule epidermal cuticle behind at its base (see Fig. 9 in Weis et al, 1999).…”

“…Possibly related to the earliest stages of CFML synthesis, initiating cotton fibers have bilayered primary walls with a thin outer sheath enriched in low-ester, JIM5-reactive HG, whereas the inner layer was enriched in JIM7-reactive HG. The predominant occurrence of JIM5 epitopes in the outer sheath of these young fibers (Vaughn and Turley, 1999) could indicate initial synthesis of the CFML. Alternatively, the outer sheath could be an initiation-specific fiber wall layer, since, unlike the CFML, it was not enriched in XG (Vaughn and Turley, 1999).…”

“…The predominant occurrence of JIM5 epitopes in the outer sheath of these young fibers (Vaughn and Turley, 1999) could indicate initial synthesis of the CFML. Alternatively, the outer sheath could be an initiation-specific fiber wall layer, since, unlike the CFML, it was not enriched in XG (Vaughn and Turley, 1999).…”

“…Previously, there was little specific knowledge about cotton fiber cell wall structure or understanding of how cell walls might control fiber differentiation beyond traditional concepts of thin, extensible, primary walls versus thick, cellulose-rich, secondary walls (Basra, 1999). A notable exception was the demonstration of biphasic distribution of wall polymers in 1-to 2-DPA fibers (Vaughn and Turley, 1999), but functional consequences of this wall structure were unknown. Similarly, the transition stage involves up-regulation of genes putatively encoding cell wall hydrolases as well as the loss of certain neutral cell wall sugars and reduction in pectin and XG mass (Meinert and Delmer, 1977;Shimizu et al, 1997;Tokumoto et al, 2002Tokumoto et al, , 2003Guo et al, 2007), but a cell biological explanation for these developmental events was lacking.…”

Multiscale Frictional Properties of Cotton Fibers: A Review

“…These compounds are collectively called "cotton waxes" [170]. The cotton fiber cuticle also contains some portion of pectins [171]. Due to the presence of waxes and pectins in the cuticle, untreated native cotton fibers are hydrophobic [170].…”