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ARS Home » Southeast Area » New Orleans, Louisiana » Southern Regional Research Center » Cotton Structure and Quality Research » Research » Publications at this Location » Publication #193759
Title: EXTRACELLULAR CU/ZN SUPEROXIDE DISMUTASE IN DEVELOPING COTTON FIBERS

Author
item KIM, HEE-JIN - UNIV OF NEW ORLEANS
item KATO, NAOHIRO - LOUISIANA STATE U
item Triplett, Barbara

Submitted to: Gordon Research Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2006
Publication Date: 7/30/2006
Citation: Kim, H., Kato, N., Triplett, B.A. 2006. Extracellular cu/zn superoxide dismutase in developing cotton fibers. Proceeding of the Gordon Research Conference. 2.

Interpretive Summary:

Technical Abstract: Cotton fibers are unicellular trichomes originating from the ovule epidermis. Fibers elongate to 26-30 mm in an unrestricted manner for about three weeks making these cells an attractive model for plant cell elongation. The activity of superoxide dismutase (SOD), an enzyme that converts superoxide into hydrogen peroxide, is quite high in developing cotton fibers (0-40 DPA). Biochemical evidence from our group suggests that in addition to SOD forms localized in the cytoplasm and plastids, a third form of CuZn-SOD localizes to elongating walls in cotton fiber. We have characterized three different types of CuZn-SOD genes from cotton, analyzed their expression patterns, and have over-expressed them as GFP fusion proteins in Arabidopsis. In this study, GhSOD1 localized to the cytoplasm, GhSOD2a and GhSOD2b were in leucoplasts, and GhSOD3 co-localized in the cytoplasm and cell wall. Interestingly, the extracellular CuZn-GhSOD3 does not contain a classical signal peptide for the secretory pathway. There is in vitro evidence suggesting that hydroxyl radicals (•OH) can cleave the backbones of carbohydrate polymers non-enzymatically via the Fenton reaction. Since there is little peroxidase activity during fiber elongation, we propose that the H2O2 generated by extracellular GhSOD3 may be converted into •OH under Fenton conditions in the cell wall. This generated •OH may break bonds within or between wall matrix polysaccharides, hence contributing to wall loosening. Peroxidase activity increases when cotton fiber elongation is complete, so H2O2 may be used at that time to crosslink walls. We propose that the effective concentration of SODs and peroxidases localized in cell walls may regulate wall loosening and tightening during fiber development.