In vivo temperature dependence of cyclic and pseudocyclic electron transport in barley

• Published in: Planta 2001-04, Vol.212 (5/6), p.808-816
• Main Authors: Clarke, Joanne E., Johnson, Giles N.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Barley; Biological and medical sciences; Biological Transport, Active; Chlorophyll - metabolism; Chloroplasts; Economic plant physiology; Electron Transport - physiology; Fluorescence; Fundamental and applied biological sciences. Psychology; High temperature; Hordeum - physiology; Hydrogen-Ion Concentration; Leaves; Light; Light-Harvesting Protein Complexes; Low temperature; Metabolism; Net assimilation, photosynthesis, carbon metabolism. Photorespiration, respiration, fermentation (anoxia, hypoxia); Nutrition. Photosynthesis. Respiration. Metabolism; Oxidation-Reduction; Oxygen; Oxygen - metabolism; Photosynthesis, respiration. Anabolism, catabolism; Photosynthetic Reaction Center Complex Proteins - metabolism; Photosynthetic Reaction Center Complex Proteins - radiation effects; Plant Leaves - physiology; Plant Leaves - radiation effects; Plant physiology and development; Plants; Temperature; Temperature dependence; Thylakoids; Thylakoids - physiology; Thylakoids - radiation effects
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s004250000432

The effect of temperature on the rate of electron transfer through photosystems I and II (PSI and PSII) was investigated in leaves of barley (Hordeum vulgare L.). Measurements of PSI and PSII photochemistry were made in 21% O2 and in 2% O2, to limit electron transport to O2 in the Mehler reaction. Measurements were made in the presence of saturating CO2 concentrations to suppress photorespiration. It was observed that the O2 dependency of PSII electron transport is highly temperature dependent. At 10 °C, the quantum yield of PSII (ΦPSII) was insensitive to O2 concentration, indicating that there was no Mehler reaction operating. At high temperatures (> 25 °C) a substantial reduction in ΦPSII was observed when the O2 concentration was reduced. However, under the same conditions, there was no effect of O2 concentration on the ΔpH-dependent process of non-photochemical quenching. The rate of electron transport through PSI was also found to be independent of O2 concentration across the temperature range. We conclude that the Mehler reaction is not important in maintaining a thylakoid proton gradient that is capable of controlling PSII activity, and present evidence that cyclic electron transport around PSI acts to maintain membrane energisation at low temperature.