Dynamics of fruit and stem expansive growth and photoassimilate translocation in tomato plants (Lycopersicon esculentum Mill.) were analyzed with reference to whole plant water relations as affected by watering and dewatering. Fruit volume and stem diameter were measured on-line by using laser displacement sensor systems newly developed, and sucrose flux through a pedicel was evaluated by applying an EDTA method. Fruit and stem growth and sucrose flux were affected by change in root water condition and appeared in different patterns dependent on xylem water potential. In particular, drastic shrinkage of fruit and dissymmetrical relationship between fruit and stem growth were found under dynamics of root water condition. The results suggest that fruit expansive growth and photoassimilate translocation can be controlled by root water condition through interactive dynamics with water relations of translocation path in stem responding to change in xylem water potential.
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