JXB Advance Access published online on May 12, 2006
Journal of Experimental Botany, doi:10.1093/jxb/erj182
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1 School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK; Present address: Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6 Canada
* To whom correspondence should be addressed. Angiosperm stigmas have long been known to exhibit high levels of peroxidase activity when they are mature and most receptive to pollen but the biological function of stigma peroxidases is not known. A novel stigma-specific class III peroxidase gene, SSP (stigma-specific peroxidase) expressed exclusively in the stigmas of Senecio squalidus L. (Asteraceae) has recently been identified. Expression of SSP is confined to the specialized secretory cells (papillae) that compose the stigma epidermis. The literature on stigma peroxidases and hypotheses on their function(s) is reviewed here before further characterization of SSP and an attempt to determine its function are described. It is shown that SSP is localized to cytoplasmic regions of stigmatic papillae and also to the surface of these cells, possibly as a component of the pellicle, a thin layer of condensed protein typical of ‘dry’ stigmas. Enzyme assays on recombinant SSP showed it to be a peroxidase with a preference for diphenolic substrates (ABTS and TMB) and a pH optimum of
Received February 8, 2006
Accepted March 6, 2006
Oxygen Metabolism ROS and Redox Signalling in Plants Special Issue
The role of stigma peroxidases in flowering plants: insights from further characterization of a stigma-specific peroxidase (SSP) from Senecio squalidus (Asteraceae)
Stephanie M. McInnis 1,
David C. Emery 2,
Robert Porter 3,
Radhika Desikan 4,
John T. Hancock 4,
and
Simon J. Hiscock 3 *
2 Wellcome Laboratories of Integrated Neurosciences, University of Bristol, UK
3 School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
4 Centre for Research in Plant Science, Faculty of Applied Sciences, University of the West of England, Coldharbour Lane, Bristol BS16 1QY, UK
Simon J. Hiscock, E-mail: Simon.Hiscock{at}bristol.ac.uk
Abstract 
4.5. In such assays the peroxidase activity of SSP was low when compared with horseradish peroxidase. To explore the function of SSP and other stigmatic peroxidases, levels of reactive oxygen species (ROS) in stigmas of S. squalidus were investigated. Relatively large amounts of ROS, principally H2O2, were detected in S. squalidus stigmas where most ROS/H2O2 was localized to the stigmatic papillae, the location of SSP. These observations are discussed in the context of possible functions for SSP, other peroxidases, and ROS in the stigmas of angiosperms.
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