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 sou rce and sink were studied. Each source leaf of a tomato plant is conne cted to all other sink organs with different strengths of the source-s ink 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 wit h each other independently. Removal of a sink causes two types of resp onses. 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 il luminated source leaf decreased its export of the photosynthates. More over, the source leaf made a compensatory adjustment in the new source -sink relationship, particularly increasing the percentage of distribu tion to the young leaves, which will likely support the entire plant i n the future, at the expense of root. Furthermore, the additional dark ening of the sinks also caused the stronger response on the translocat ion rate. These responses make up the defense strategy for survival of the plant when the defoliation and darkening of the leaves occur. Fro m these data we discuss possible roles of the source and sink to the s ource-sink relationship.