Orientation of photosystem-I pigments. Investigation by low-temperature linear dichroism and polarized fluorescence emission

Abstract The mykotrophic orchid Neottia nidus-avis does not evolve oxygen in the light but is able to perform photophosphorylation. The low temperature fluorescence emission spectrum lacks the 680 and 690 nm bands. Hence, the spectroscopic chlorophyll a forms which are attributed to photosystem II do not occur in plastids of this orchid. The low temperature excitation spectrum of photosystem I fluorescence exhibits a maximum at 666 nm. The position of this maximum appears not to be influenced by energy transfer and corresponds to the absorption maximum of the chlorophyll form which emits the photosystem I fluorescence. Energy migration, however, occurs from carotenoids whose absorption spectrum is shifted to longer wavelengths and which cause the yellow-brown color of the Neottia plastids. Room temperature fluorescence emission shows after the onset of light no variable part. Despite the fact that plastids of the tobacco mutant NC 95 at most evolve only traces of oxygen the low temperature emission spectrum shows the three bands which are usually observed with fully functioning chloroplasts. However, the two bands at 680 and 690 nm are distinctly lower than with the wild type. The variable portion of room temperature fluorescence is barely detectable. In line with the very low capacity for oxygen evolution, rates of electron transport partial reactions in the region of photosystem II are extremely low. In agreement with this observation no 690 nm absorption change signal is detected. However, a normal P+700 signal is seen. In the presence of electron donors like reduced phenazine methosulfate the decay time of the P+700 signal is faster than with the wild type. The yellow tobacco mutant Su/su var. aurea which exhibits at high light intensities higher rates of photosynthesis than the wild type shows at low temperature an emission spectrum with stronger photosystem II bands than the wild type.

Download Full-text

Low-temperature fluorescence emission spectra and chlorophyll-protein complexes in mutants of Chlamydomonas reinhardtii: Evidence for a new chlorophyll-a-protein complex related to Photosystem I

Biochimica et Biophysica Acta (BBA) - Bioenergetics ◽

10.1016/0005-2728(86)90076-9 ◽

1986 ◽

Vol 851 (3) ◽

pp. 395-406 ◽

Cited By ~ 22

Author(s):

Jacques Garnier ◽

Jeannine Maroc ◽

Denise Guyon

Keyword(s):

Low Temperature ◽

Chlorophyll A ◽

Photosystem I ◽

Protein Complex ◽

Protein Complexes ◽

Fluorescence Emission ◽

Emission Spectra ◽

Fluorescence Emission Spectra ◽

Chlorophyll Protein Complexes ◽

Chlorophyll Protein

Download Full-text

Total Electron Yield Detector Working at Low Temperature for Linear Dichroïsm Studies on Monocrystalline Samples

Journal de Physique IV (Proceedings) ◽

10.1051/jp4/1997213 ◽

1997 ◽

Vol 7 (C2) ◽

pp. C2-325-C2-326

Author(s):

C. Revenant-Brizard ◽

J. R. Regnard ◽

J. Mimault ◽

D. Duclos ◽

J. J. Faix

Keyword(s):

Low Temperature ◽

Linear Dichroism ◽

Total Electron Yield ◽

Total Electron ◽

Electron Yield

Download Full-text

The light-harvesting complexes of higher-plant Photosystem I: Lhca1/4 and Lhca2/3 form two red-emitting heterodimers

Biochemical Journal ◽

10.1042/bj20101538 ◽

2011 ◽

Vol 433 (3) ◽

pp. 477-485 ◽

Cited By ~ 62

Author(s):

Emilie Wientjes ◽

Roberta Croce

Keyword(s):

Photosystem I ◽

Light Harvesting ◽

Fluorescence Emission ◽

Light Response ◽

Native State ◽

Higher Plant ◽

Light Harvesting Complexes ◽

Light Harvesting Complex ◽

Wavelength Emission

The outer antenna of higher-plant PSI (Photosystem I) is composed of four complexes [Lhc (light-harvesting complex) a1–Lhca4] belonging to the light-harvesting protein family. Difficulties in their purification have so far prevented the determination of their properties and most of the knowledge about Lhcas has been obtained from the study of the in vitro reconstituted antennas. In the present study we were able to purify the native complexes, showing that Lhca2/3 and Lhca1/4 form two functional heterodimers. Both dimers show red-fluorescence emission with maxima around 730 nm, as in the intact PSI complex. This indicates that the dimers are in their native state and that LHCI-680, which was previously assumed to be part of the PSI antenna, does not represent the native state of the system. The data show that the light-harvesting properties of the two dimers are functionally identical, concerning absorption, long-wavelength emission and fluorescence quantum yield, whereas they differ in their high-light response. Implications of the present study for the understanding of the energy transfer process in PSI are discussed. Finally, the comparison of the properties of the native dimers with those of the reconstituted complexes demonstrates that all of the major properties of the Lhcas are reproduced in the in vitro systems.

Download Full-text