Changes in Source-Sink Interaction by Defoliation and Darkening of Source and Sink Leaf in Tomato (Lycopersicon esculentum Mill.)

Changes in source-sink interaction by defoliation and darkening of source and sink were studied.Each source leaf of a tomato plant is connected to all other sink organs with different strengths of the source-sink relation at the 8-leaf stage. Therefore, it occurred that one sink has a strong tie to one source and then it would simultaneously be a weak sink to another source, and they are probably keeping balance with each other independently. Removal of a sink causes two types of responses. One was a small change in source- sink relation by removal of a weak sink and the other was a large change by removal of a strong sink.By removing or darkening 80% of a given source, the remaining and illuminated source leaf decreased its export of the photosynthates. Moreover, the source leaf made a compensatory adjustment in the new source-sink relationship, particularly increasing the percentage of distribution to the young leaves, which will likely support the entire plant in the future, at the expense of root. Furthermore, the additional darkening of the sinks also caused the stronger response on the translocation rate.These responses make up the defense strategy for survival of the plant when the defoliation and darkening of the leaves occur. From these data we discuss possible roles of the source and sink to the source-sink relationship.