Light-induced carbon dioxide and oxygen uptake in plant leaves measured by the photoacoustic method.
Leaf discs, enclosed in a photoacoustic (PA) chamber, generate two types of PA gas-uptake signals under certain conditions. Type I is manifested by a severe signal decrease that develops slowly under very low-light intensity and often reaches negative values. It is partially reversed by low-intensity far-red light. Type II occurs transiently in modulated far-red light. It is manifested by a rapid and dramatic decrease of the PA signal, upon the addition of short-wave background light, which is subsequently reversed. It differs from type-I uptake in that it occurs at much higher total light intensities. A thorough study, including modulation frequency and atmospheric composition dependencies, indicates different mechanisms for the two types of uptakes. Type-I uptake results from CO2 accumulation in the PA cell by leaf respiration and reflects modulations in CO2 solubilization. Type-II uptake likely reflects oxygen photoreduction in photosystem I, occurring prior to the activation of photosynthesis (i.e. during photosynthesis induction). This is supported by the complete suppression of type-II uptake when O2 was removed. Also, type-II uptake was only mildly sensitive to CO2 elimination, whereas type-I uptake was totally dependent on the presence of CO2. Type-II uptake consists usually of two uptake waves. Fluorescence transients measured in parallel give further support to the reality and interpretation of these two uptake waves. PA could thus provide a unique opportunity to monitor oxygen photoreduction in vivo with high sensitivity and time resolution.
Malkin
S
S
CEA-Cadarache, DSV, DEVM, Laboratoire d'Ecophysiologie de la Photosynthèse, Saint-Paul-lez-Durance, France. shmuel.malkin@weizmann.ac.il
Havaux
M
M
D017360:Arabidopsis / Q000378:metabolism*; D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism*; D002734:Chlorophyll / Q000032:analysis; D004579:Electron Transport; D007887:Fabaceae / Q000378:metabolism*; D007259:Infrared Rays; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010084:Oxidation-Reduction / Q000528:radiation effects; D010100:Oxygen / Q000032:analysis / Q000378:metabolism*; D018532:Pisum sativum / Q000378:metabolism*; D010777:Photochemistry; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D018515:Plant Leaves / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013997:Time Factors; D014026:Nicotiana / Q000378:metabolism*
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D002734:Chlorophyll; D002245:Carbon Dioxide; D010100:Oxygen