Anisotropy of photosynthetic membranes and the degree of fluorescence polarization

J. F. Becker, J. Breton, N. E. Geacintov, F. Trentacosti

Research output: Contribution to journalArticlepeer-review


The degree of fluoresence polarization, P, of unoriented and magnetically oriented spinach chloroplasts as a function of excitation (400-680 nm) and emission wavelengths (675-750 nm) is reported. For unoriented chloroplasts P can be divided into two contributions, PIN and PAN. The latter arises from the optical anisotropy of the membranes which is due to the orientation with respect to the membrane plane of pigment molecules in vivo. The intrinsic polarization PIN, which reflects the energy transfer between different pigment molecules and their degree of mutual orientation, can be measured unambiguously only if (1) oriented membranes are used and the fluorescence is viewed along a direction normal to the membrane planes, and (2) the excitation is confined to the Qy (≈ 660-680 nm) absorption band of chlorophyll in vivo. With 670-680 nm excitation, values of P using unoriented chloroplasts can be as high as +14%, mostly reflecting the orientational anisotropy of the pigments. Using oriented chloroplasts, PIN is shown to be +5±1%. The excitation wavelength dependence studies of PIN indicate that the carotenoid and chlorophyll Qy transition moments tend to be partially oriented with respect to each other on a local level (within a given photosynthetic unit or its immediate neighbors).

Original languageEnglish (US)
Pages (from-to)531-544
Number of pages14
JournalBBA - Bioenergetics
Issue number3
StatePublished - Sep 13 1976

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology


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