Rapid CO2 changes cause oscillations in photosynthesis that implicate PSI acceptor-side limitations.

Area of Science:

• Plant physiology
• Photosynthesis research
• Biochemical oscillations

Background:

• Oscillations in CO2 assimilation and fluorescence have been linked to triose phosphate utilization (TPU) limitation for decades.
• The precise physiological conditions triggering these oscillations remain poorly understood.

Purpose of the Study:

• To investigate the physiological conditions necessary to induce oscillations in CO2 assimilation.
• To elucidate the mechanisms behind oscillations observed under TPU-limiting conditions.

Main Methods:

• Utilized dynamic assimilation techniques (DATs) for precise measurement of CO2 assimilation rates.
• Applied controlled CO2 ramps and step changes to induce TPU limitation.
• Conducted optical measurements to assess PSI reduction and cofactor availability (NADP+, ATP).

Main Results:

• TPU limitation alone is insufficient; rapid entry into this state is required for oscillations.
• CO2 ramps induced oscillations proportional to ramp speed, with more severe outcomes than step changes.
• An initial overshoot in CO2 assimilation, driven by phosphate excess, temporarily surpassed steady-state limitations but not Rubisco limitation.

Conclusions:

• Rapid induction of TPU limitation is a critical factor for photosynthetic oscillations.
• Oscillations involve PSI reduction and fluctuating NADP+ and ATP availability.
• Understanding these dynamics offers insights into photosynthetic regulation under stress.