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Use of a Light-Induced Respiratory Transient to Measure the Optical Cross Section of Photosystem I in Chlorella
Nancy L. Greenbaum, Arthur C. Ley and David C. Mauzerall
Vol. 84, No. 3 (Jul., 1987), pp. 879-882
Published by: American Society of Plant Biologists (ASPB)
Stable URL: http://www.jstor.org/stable/4270733
Page Count: 4
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A method has been developed whereby the magnitude of a transient in O2 uptake attributable to photosystem (PS) I activity, following single-turnover laser flashes of varying energy, can be used to measure the optical cross section of PSI. As measurements are made under the identical physiological conditions for which the cross section of PSII has previously been determined (AC Ley, DC Mauzerall 1982 Biochim Biophys Acta 680:96-105), it is now possible to simultaneously measure the cross section of both photosystems in intact, photosynthetically competent cells, without the use of inhibitors or artificial mediators of electron transport. Plots of light-saturation behavior of the respiratory oscillation following pulses at 596 nanometers indicate a mean optical cross section similar to that of PSII at this wavelength, but suggest significant heterogeneity in the cross section of PSI. If this method measures only PSI activity, this result implies that there exist units with different numbers of identical chromophores, or units having populations of chromophores with different absorption spectra.
Plant Physiology © 1987 American Society of Plant Biologists (ASPB)