Abstract
Decrease in photosynthetic activity of source-sink model plant of sweet potato under sink-limited conditions was mainly due to the binding of inhibitor to RuBPcase.The inhibitor was suggested to be sugar phosphate. To clarify the structure of inhibitor and its inhibition mechanism of RuBPcase, purifying the inhibitor in large quantities is needed. Steam girdling of stems of sweet potato grown in green house resulted in the decrease in photosynthetic rate and total activity of RuBPcase and the accumulation of photosynthates in leaves. Maximum activity of RuBPcase did not differ from that of control plants, indicating that the girdling treatment resulted in the sink-limited state. Leaf extracts prepared from the plants girdled were mixed with activated RuBPcase to bind inhibitor to this enzyme. Then, the RuBPcase was collected by PEG treatment, and the inhibitor bound to RuBPcase was dissociated with heat treatment. The highly purified inhibitor could be obtained through these treatments.
