The relationship between photosynthetic electron transport and photorespiratory 14CO2 release after DCMU treatment in the duckweed, Lemna gibba

The photosynthetic rate of Lemna gibba was measured as ¹⁴CO₂ uptake at the beginning of and after 1 h DCMU treatment during the separate excitation of PS I (703 nm), mainly PS II (662 nm) and the combined excitation of both photosystems (662 + 703 nm) in 2 and 21% oxygen. The results show the Warburg effect. Photosynthesis was significantly reduced by DCMU whenever PS II was excited, at 662 nm and 662 + 703 nm. Photosynthetic enhancement was greater in 21 than in 2% oxygen in both the treated and untreated plants.
Photorespiratory ¹⁴CO₂ release was only affected by DCMU treatment at 662 + 703 nm. It was significantly decreased in 21% O₂ and significantly increased in 2% O₂ as compared to the controls without DCMU. The ¹⁴C-glycolate remaining in the plant after photosynthesis/photorespiration measurements was reduced whenever the electron supply to PS I was low.
These data support the hypothesis that a relationship exists between glycolate metabolism and photosynthesis via the electron transport chain where electrons from the oxidation of glycolate are donated to PS I when the electron supply from water is low.