Using the short-lived isotope C-11 in mechanistic studies of photosynthate transport

Tracer techniques have been central in studies of transport in plants. In the case of carbon, the only readily available radioactive tracer has been C-14, although C-11 was used for a short time before C-14 could be made. Tracers have usually had to be measured by destructive harvesting of the plant, giving a practical limit to the data resolution in both time and space. A major advantage of the short-lived, positron-emitting tracers, of which C-11 is one example, is that in vivo measurement is possible, giving detailed time series of tracer data in many locations and opening up powerful new techniques of data analysis. Medical applications of these isotopes have utilised both dynamic imaging and time courses of uptake or washout. Unfortunately, few plant biology laboratories have realised the potential of these techniques, possibly because of the large physics infrastructure needed. In this paper we review the concepts behind the use of these short-lived tracers in plant physiology, and illustrate with several cases where C-11 was an essential tool.