| Abstract: | Using radioactive tracers, interactions between flows of photosyntheticassimilate were observed in vivo with several species. Changesin translocation from one source (brought about by repeatedchilling and re-warming which stops and re-starts flow) cancause an immediate and partially compensating change in translocationfrom another source. The rapidity of response implies the transmissionof a physical rather than a chemical signal. The compensationcan be sustained for at least 90 min and involves a change inthe speed of sap flow rather than a change in its concentration.A change in the rate of loading in the source (lamina) is probablyinvolved, but this is not always the case, for it seems thatthe signal calling for extra assimilate is a lowering of sievetube pressure potential and this is transmitted over only rathershort distances of stem (though over quite long distances ofpetiole), because of entry of water and assimilate (loading)from stores in close proximity to the pathway. The responseis buffered therefore and becomes less evident as one movesaway from the site of treatment. Key words: Photosynthate translocation, Phloem loading |
