Involvement of Extracellular Cu/Zn Superoxide Dismutase in Cotton Fiber Primary and Secondary Cell Wall Biosynthesis

Authors: KIM, HEE JIN - UNIV. OF NEW ORLEANS; Triplett, Barbara

Submitted to: Plant Signaling and Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2008
Publication Date: 12/15/2008
Citation: Kim, H., Triplett, B.A. 2008. Involvement of Extracellular Cu/Zn Superoxide Dismutase in Cotton Fiber Primary and Secondary Cell Wall Biosynthesis. Plant Signaling and Behavior. 3(12):1119-1121.

Interpretive Summary: Cell walls govern the shape, rigidity, and size of plant cells and plant cell wall thickness plays an important role in plant growth. While plants are growing actively, plant cells must make thin walls (primary cell walls) to permit cell elongation because the growth stops as soon as thick walls (secondary cell walls) are synthesized. Thus, productions of both primary and secondary cell walls are accurately regulated in a temporal, spatial, and developmental manner throughout growth and development. Recent advances in the biochemistry of plant cell walls suggest a chemical called hydrogen peroxide, may be involved in signaling the transition between primary and secondary cell walls. There are several processes that can form hydrogen peroxide in plants, including a reaction catalyzed by the enzyme superoxide dismutase. Previously, our team identified a superoxide dismutase enzyme in the secondary cell wall of cotton fibers and showed it was distinct from other superoxide dismutases. In this study, we present evidence showing that the cell wall form of superoxide dismutase is present in not only thickening secondary walls, but also thin and elongating primary walls of cotton fibers. Three different assays show that the cell wall form of superoxide dismutase is detected in cotton fiber cells containing both primary and secondary walls. Based on our results, we propose that the cell wall form of superoxide dismutase is commonly involved in the production of both primary and secondary walls for controlling the level of hydrogen peroxide. Scientists working on plant cell wall biochemistry, most notably bioenergy researchers and cotton fiber molecular biologists, will be the primary target audiences for this manuscript.

Technical Abstract: Extracellular Cu/Zn superoxide dismutases (CSDs) that catalyze the conversion of superoxide to hydrogen peroxide have been suggested to be involved in lignification of secondary walls in spinach, pine and aspen. In cotton fibers, hydrogen peroxide was proposed to be involved in the induction of secondary cell wall biosynthesis. Recently, we identified extracellular CSDs from developing cotton fibers using both immunological and epitope tagging techniques. Since cotton fibers are not lignified, we suggested that extracellular CSDs may be involved in plant cell wall growth and development processes other than lignification. In this addendum, we have further characterized the extracellular CSD in cotton fiber. Immunoblots, enzyme activity assays, and transcript levels show that an extracellular CSD is present in elongating primary walls as well as thickening secondary walls of cotton fibers. We propose a working model that the level of extracellular hydrogen peroxide regulated by redox status-related enzymes including extracellular CSDs and peroxidases may affect the processes of wall loosening and wall tightening.