1807 De-esterified pectins in the cell walls of cotton fibers: a study of fiber mutants

In the wild-type cotton (DP 5690), the cell walls of elongating cotton fibers are bilayered, with the outer layer enriched in de-esterified homogalacturonan (HGA), and an inner layer enriched in xyloglucans and cellulose. This bilayer is conspicuously absent in the cell walls of the ovule epidermal cells and in the fiber of the short fiber mutants Ligon lintless 1 and Ligon lintless 2. The highly-reduced quantity of de-esterified HGA in the Ligon lintless lines does not appear to be due to decreased pectin methylesterase (PME) activity, however. The use of a mild CDTA extraction of intact ovules (3 days after anthesis) releases similar amounts of PME activity from both normal and short fiber lines. Comparison of protein profiles derived from the CDTA extracts of each line indicates that a few differences occur between the “enriched cell wall” proteins of the wild-type and the Ligon lintless lines. Very few proteins are detectable in the fiberless SL 1-7-1 ovule profiles. The largest protein spot in the 2D PAGE profiles is an acidic protein (pI 4.4) with a molecular weight of 17 kDa and is unique to the Ligon lintless lines. Heterologous expression was used to produce a putative cotton PMEI protein in Pichia pastoris. These data indicate that a decrease in the levels of de-esterified HGA in the Ligon lintless lines are not caused by a decrease in PME, but by a decrease in PME activity by an environmental or enzymatic mechanism in muro.