In Vivo Veritas: Radiotracers in Studies of Phloem Transport of Carbohydrate.

Opportunities and challenges in the use of radiotracers to measure phloem transport are discussed, with an emphasis on noninvasive techniques to trace photoassimilate, carbon's short-lived isotope C, and an eye to pitfalls and traps to avoid. We discuss in turn the rationale for using tracers, the limitations and complications with using short-lived radiotracers like C, the physics of decay and detection that need to be known when data are interpreted, and methods of analysis.