Changes in Steady-State Photosynthetic ^<14>C-Incorporation into cellular Metabolites of Chlorella pyrenoidosa during Transitions from High to Low Irradiance

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Changes in the levels of ^<14>C-labelled metabolites were monitored in Chlorella pyrenoidosa cells during a transition from high to low irradiance, i.e.; from 700 to 430 μmol quanta (400-700 nm) m^<-2> s^<-1>. Chlorella cells assimilated ^<14>CO_2 photosynthetically (steady-state ^<14>C-labelling) for 12 min at the high irradiance and then 10 min at the low irradiance. With the transition to low light, the level of ^<14>C-labelled ribulose 1,5-bisphosphate (RuBP) did not decrease, even though the rate of total ^<14>C-incorporation decreased by 80%. The data suggest that RuBP carboxylase deactivates rapidly (within 1 or 2 min) on exposure to low light, causing RuBP pool sizes to be maintained (or even increased) in spite of a decreased rate of RuBP regeneration. There was also evidence of light modulation of other enzymes, including some enzymes involved in sucrose synthesis. The rate of sucrose synthesis decreased with decrease in light intensity while the level of uridine diphosphoglucose increased, but within a few minutes, both returned to their former levels.
日本植物生理学会の論文