Photon requirement for O₂‐Revolution in red (λ= 680 nm) light for some C₃ and C₄ plants and a C₃–C₄ intermediate species*

Abstract

Photon requirements for O2‐evolution in red (λ=680nm) light (Фr) were measured for six C3 species, one C3‐like, C3–C4 intermediate species, and three C4 species, including examples of NADP‐malic enzyme and PEP‐carboxykinase C4 sub‐groups. Variation in Фr within the C3 species was small with a mean value of 7.96 ±0.12 mol photon mol−1 O2, whereas the mean value for the C4 species was 12.27± 1.53 mol photon mol−1 O2, with the lowest value, 9.24 ±0.13 mol photon mol−1 O2, for the PEP‐carboxykinase C4 species Spartina townsendii. The C3–C4 intermediate species Panicum milioides had a value of 9.05 ±0.29 mol photon mol−1 O2, approximately 1 mol photon mol−1 O2 greater than the C3 species. The possibility that this extra cost is due to PEP‐carboxylase‐dependent recycling of CO2 is discussed. No correlation was found between Фr and chlorophyll content or leaf absorptance. Based on white (ФW) and red light measurements of the photon requirement, values in red light were approximately 20% higher than white‐light estimates. These results are discussed with reference to accepted mechanisms of energy transduction in thylakoid membranes (Z‐scheme), expected inefficiencies and losses during light‐harvesting and electron transport reactions, and the influence of respiratory processes.

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Is acclimation required for success in high light environments? A case study using Mycelis muralis (L.) Dumort (Asteraceae)

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