Photoacoustic detection of photosynthetic activities in isolated broken chloroplasts

Nehama Lasser-Ross, Shmuel Malkin, David Cahen

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Methodology and demonstration how to utilize the photoacoustic technique in photosynthesis research are presented. Photoacoustic signals were obtained from suspensions of isolated broken chloroplasts. In the presence of strong, continuous (non-modulated) background light the signals were normally larger than without the background light. The effect of the background light was saturable and was absent when non-active (e.g. heat-treated) samples were used, showing that the normal smaller signal in the absence of background light is a genuine reflection of the loss of heat due to the competing photochemistry. The effect of the background light is to close the reaction-centers and hence to inhibit the photochemical process. The percent difference of the photoacoustic signal (± background light) is taken as a measure of the photochemical activity ('photochemical loss'). Initial results demonstrate the wavelength dependence of the 'photochemical loss'. As expected there was a 'red-drop' decrease of the 'photochemical loss' for λ > 690 nm, when the cofactor methyl viologen was present. Surprisingly, however, there was a 'red-rise' increase for λ > 690 nm when no cofactor was present. These findings indicate that under the last conditions there is an unsuspected photoactivity of PS I which was not detected hitherto by the conventional techniques. The dependence on the background light intensity confirms this result. This photoactivity can be explained tentatively as a cyclic electron flow around PS I, present without any added cofactor. Initial results on the modulation frequency dependence in the presence of electron acceptors are also demonstrated.

Original languageEnglish
Pages (from-to)330-341
Number of pages12
JournalBiochimica et Biophysica Acta - Bioenergetics
Issue number2
StatePublished - 3 Dec 1980
Externally publishedYes


This work was supported by the US-Israel Binational Science Foundation, Jerusalem. Thanks are due to Mr. Shlomo Gershon for his technical assistance.

FundersFunder number
US-Israel Binational Science Foundation


    • (Broken chloroplast)
    • Photoacoustic spectroscopy
    • Photochemical loss
    • Photosynthesis
    • Photosystem I


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