Young tomato fruits induced to export carbon by cooling

Abstract

IN phloem translocation systems, sources and sinks are clearly defined: sources are net exporters and sinks net importers of carbon compounds. The overall rate of translocation is largely controlled by ill-defined metabolic processes operating at the source and sink, the transport process itself rarely being limiting^1–3. An understanding of how this control is exerted is needed before the mechanism of phloem translocation can be understood, and may provide the potential for manipulating the yield of the economically important parts of plants. The direction of net translocation is reversed as a growing leaf matures^3,4, or when previously imported material is redistributed from storage organs such as bulbs^5,6. In such cases, however, it is difficult to relate causally the physiology or biochemistry of the organ to the change in the direction of translocation. Previous attempts to convert mature leaves from net exporters to net importers have been only partially successful^7–10. We have now achieved complete reversal of the normal role of a sink, and report here the net export of considerable quantities of carbon from a young, growing tomato fruit.