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1 October 2001 Light-induced Carbon Dioxide and Oxygen Uptake in Plant Leaves Measured by the Photoacoustic Method
Shmuel Malkin, Michel Havaux
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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.

Shmuel Malkin and Michel Havaux "Light-induced Carbon Dioxide and Oxygen Uptake in Plant Leaves Measured by the Photoacoustic Method," Photochemistry and Photobiology 74(4), 593-604, (1 October 2001).<0593:LICDAO>2.0.CO;2
Received: 5 April 2001; Accepted: 1 July 2001; Published: 1 October 2001

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