The minimum photon requirement for photosynthesis: an analysis of the data of warburg & burk (1950) and yuan, evans & daniels (1955)
1987
OSBORNE, BRUCE A. | GEIDER, RICHARD J.
Variations in the apparent photon requirement for photosynthesis (Φ⁻¹cₒ₂) or (Φ⁻¹cₒ₂) in the data of Warburg & Burk (1950) and Yuan, Evans & Daniels (1955) can be ascribed to changes in O₂ uptake and energy‐dependent processes which result in aberrant photon requirements in organisms subjected to non‐optimal conditions. The increase in Φ⁻¹cₒ₂ with increases in the gas exchange quotient (γ) in the observations of Yuan et al. (1955) is consistent with increases in photorespiratory production of glycollate, whilst changes in Φ⁻¹cₒ₂ and Φ⁻¹cₒ₂ in the results of Warburg & Burk (1950) can be explained by a variable Kok effect associated with nitrate assimilation at low light levels. When these O₂ and energy‐dependent processes are minimal, the lowest values should be observed. The minimum value obtained when Chlorella is photosynthesizing under optimal conditions is 6 mol photons mol⁻¹O₂. These results provide direct independent evidence for a photon requirement for photosynthesis of less than 8 mol photons mol⁻¹O₂. Such a value is not consistent with the Z scheme of photosynthesis.
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