Photosynthetic electron transport in single guard cells as measured by scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) is a powerful new tool for studying chemical and biological processes. It records changes in faradaic current as a microelectrode (less than or equal to 7 mu m in diameter) is moved across the surface of a sample. The current varies as a function of both distance from the surface and the surface's chemical and electrical properties. We used SECM to examine in vivo topography and photosynthetic electron transport of individual guard cells in Tradescantia fluminensis, to our knowledge the first such analysis for an intact plant. We measured surface topography at the micrometer level and concentration profiles of O-2 evolved in photosynthetic electron transport. Comparison of topography and oxygen profiles above single stomatal complexes clearly showed photosynthetic electron transport in guard cells, as indicated by induction of O-2 evolution by photosynthetically active radiation. SECM is unique in its ability to measure topography and chemical fluxes, combining some of the attributes of patch clamping with scanning tunneling microscopy. In this paper we suggest several questions in plant physiology that it might address.