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The Kok effect revisited.

Xinyou Yin1, Yuxi Niu1, Peter E L van der Putten1

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Summary
This summary is machine-generated.

The Kok effect, a photosynthetic response, is explained by photorespiration and decreasing photochemical efficiency. Photorespiration influences both the CO2 compensation point and light inhibition of respiration.

Keywords:
Kok methodYin methodday respirationphotorespirationphotosystem II efficiencyreassimilation

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Area of Science:

  • Plant Physiology
  • Photosynthesis Research
  • Biochemistry

Background:

  • The Kok effect describes a sharp decline in net photosynthesis near the light compensation point.
  • This phenomenon is traditionally attributed to light inhibition of respiration, enabling estimation of day respiration (Rd).
  • Recent studies highlight the role of photorespiration, quantified by Γ*/Cc, in explaining the Kok effect.

Purpose of the Study:

  • To model and quantify the contributions of varying Rd, Γ*/Cc, Φ2, and alternative electron transport to the Kok effect.
  • To investigate the Kok effect in sunflower under diverse O2, CO2, and temperature conditions.
  • To elucidate the dual role of photorespiration in the Kok effect.

Main Methods:

  • Utilized a model simulating the Kok effect based on key physiological parameters.
  • Measured photosynthetic responses in sunflower plants.
  • Analyzed data across varied oxygen, carbon dioxide, and temperature levels.

Main Results:

  • Decreasing PSII photochemical efficiency (Φ2) accounted for approximately 12% of the Kok effect.
  • Varying photorespiration (Γ*/Cc) explained about 25% of the Kok effect.
  • Real light inhibition of Rd was less than Kok method estimates but increased with photorespiration.

Conclusions:

  • Photorespiration significantly contributes to the Kok effect through both Γ*/Cc and its influence on Rd light inhibition.
  • The Kok effect is a complex interplay of photorespiration, photochemical efficiency, and respiration.
  • Understanding these factors is crucial for accurate photosynthetic measurements and modeling.