Regulation of Dry Matter Production Process in Response to Changes in Photosynthetic Source-Sink Balance by Plant Density

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Soybean (Glycine max Merr.cv.Tsurunoko) plants were grown in the experimental field with high (20 plants/m^2) and law (1.6 plants/m^2) densitites. With progressing of their growth, high density plants were placed under deep mutual shading condition, although low density plants were continuously placed under independently indivitual conditions.(1) Upper leaves on high density plants kept high photosynthetic activities from morning to after noon. Low density plants showed high photosynthetic activities before noon but largely lowered the activities after noon.(2) Sucrose content in leaves of the low density plants was higher than in the high density plants.(3) In the low density plants, the activity of RuBPcase lowered according to lowering of photosynthetic activity. This lowered activity was perfectly recovered with addition of CO_2 and Mg^<2+> into activation medium.(4) The RuBP content in leaves of the lower density plants was significantly higher than in those of the high density plants.It is concluded that the results obtained from the low density plants are consisitent with the those which were observed in the source-sink model plants made from soybean leaves when the source/sink balance was altered (Sawada et al., 1986,1987,1989,1990,1992,1995a, b).