Alan McClain (Sharkey lab)
Date & Location: October 20, 2020, at 12p; Virtual talk
Subject: Co-regulation of the Calvin-Benson cycle and electron transport during phosphate-limited photosynthesis
Abstract: Plants have a maximum photosynthetic rate set by the ability to produce end products from phosphorylated Calvin-Benson cycle intermediates. When the plant is fixing carbon at this maximum rate, the concentration of inorganic phosphate drops, limiting ATP production and capping the rate of photosynthesis. We used a combination of gas exchange, fluorescence, and spectroscopy to study the different components of photosynthetic regulation important to controlling both the electron transport chain and the Calvin-Benson cycle in this paradigm of photosynthesis in Nicotiana benthamiana. We found that initially there is a buildup of electrons on the PS2 electron transport chain that diverts energy into extant non-photochemical quenching. Over the first 5 minutes, energy-dependent quenching builds up and rubisco deactivates by 40%, relieving the pressure on the electron transport chain. After hours of adaptation, accumulation of photoinhibition reduces the importance of energy-dependent quenching. At the end of a day of adaptation, the plants no longer exhibit symptoms of phosphatelimited photosynthesis. We believe this shows that plants will regulate their photosynthesis to never be phosphate-limited for a long period of time. This would explain the common observance that photosynthesis is never phosphate limited in the wild, and it would complicate the role of phosphate limitation in environmental models of photosynthesis.
Speaker Lab: Dr. Thomas D. Sharkey