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Cu/Zn superoxide dismutases in developing cotton fibers: evidence for an extracellular form



Hydrogen peroxide and other reactive oxygen species are important signaling molecules in diverse physiological processes. Previously, we discovered superoxide dismutase (SOD) activity in extracellular protein preparations from fiber-bearing cotton ( Gossypium hirsutum L.) seeds. We show here, based on immunoreactivity, that the enzyme is a Cu/Zn-SOD (CSD). Immunogold localization shows that CSD localizes to secondary cell walls of developing cotton fibers. Five cotton CSD cDNAs were cloned from cotton fiber and classified into three subfamilies (Group 1: GhCSD1 ; Group 2: GhCSD2a and GhCSD2b ; Group 3: GhCSD3 and GhCSD3s ). Members of Group 1 and 2 are expressed throughout fiber development, but predominant during the elongation stage. Group 3 CSDs are also expressed throughout fiber development, but transiently increase in abundance at the transition period between cell elongation and secondary cell wall synthesis. Each of the three Gh CSDs also has distinct patterns of expression in tissues other than fiber. Overexpression of cotton CSDs fused to green fluorescent protein in transgenic Arabidopsis demonstrated that Gh CSD1 localizes to the cytosol, Gh CSD2a localizes to plastids, and Gh CSD3 is translocated to the cell wall. Subcellular fractionation of proteins from transgenic Arabidopsis seedlings confirmed that only c-myc epitope-tagged Gh CSD3 co-purifies with cell wall proteins. Extracellular CSDs have been suggested to be involved in lignin formation in secondary cell walls of other plants. Since cotton fibers are not lignified, we suggest that extracellular CSDs may be involved in other plant cell wall growth and development processes.



PlantaSpringer Journals

Published: Jul 1, 2008

DOI: 10.1007/s00425-008-0734-0

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