Submitted to: Protoplasma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 13, 2010
Publication Date: September 28, 2010
Citation: Bowling, A.J., Vaughn, K.C., Turley, R.B. 2010. Polysaccharide and glycoprotein distribution in the epidermis of cotton ovules during early fiber initiation and growth. Protoplasma. 248:579-590. Interpretive Summary: Cotton is our most important fiber crop but little is known of the early events associated with fiber initiation and elongation. To investigate this, scientists in the Southern Weed Science Research Unit and Crop Genetics and Production Research Unit probed initiating cotton fibers with antibodies that recognize components of the cell wall. These studies indicate that cotton fibers are differentiated from adjacent non-fiber cells with respect to pectin and protein components as early as one day post the opening of the flower. From these data, we could predict the enzyme machinery responsible for the differentiation of the fiber cells from the non-fiber cells and will use these data to determine genes of importance in fiber development.
Technical Abstract: The cotton fiber is a model system to study cell wall biosynthesis because the fiber cell elongates (~3 cm in ~20 days) without mitosis. In this study, developing cotton ovules, examined from 1 day before anthesis (DBA) to 2 days post-anthesis (DPA), that would be difficult to investigate via classical carbohydrate biochemistry, were probed using a battery of antibodies that recognize a large number of different wall components. In addition, ovules from these same stages were investigated in three fiberless lines. Most antibodies reacted with at least some component of the ovule and several of the antibodies reacted specifically with the epidermal layer of cells that may give clues as to the nature of the development of the fibers and the neighboring, non-fiber atrichoblasts. Arabinogalactan proteins (AGPs) labeled the epidermal layers more strongly than other ovular tissue, even at 1DBA. One of the AGP antibodies, CCRC-M7, which recognizes a 1'6 galactan epitope of AGPs, is lost from the fiber cells by 2DPA, although labeling in the atrichoblasts remained strong. In contrast, LM5, that recognizes a 1' 4 galactan RGI side chain, is unreactive with sections until the fibers are produced and only the fibers are reactive. Dramatic changes also occur in the homogalacturonans (HGs). JIM5, which recognizes highly de-esterified HGs, only weakly labels epidermal cells of 1DBA and 0DPA ovules, but labeling increases in fibers cells, where a pectinaceous sheath is produced around the fiber cell and stronger reaction in the internal and external walls of the atrichoblast. In contrast, JIM7-reactive, highly-esterifed HGs are present at high levels in the epidermal cells throughout development. Fiberless lines displayed similar patterns of labeling to the fibered lines, except that all of the cells had the labeling pattern of atrichoblasts. That is, CCRC-M7 labeled all cells of the fiberless lines and LM5 labeled no cells at 2DPA. These data indicate that a number of polysaccharides are unique in quantity or presence in the epidermal cell layers and some of these might be critical participants in the early stages of initiation and elongation of cotton fibers.