Abstract
The chlorophyll a fluorescence in Chlorella pyrenoidosa can be enhanced by 4-9% if the excitation light beam is parallel to an external magnetic field or decreased by 4-9% if the light beam is oriented perpendicular to a magnetic field of about 16 kgauss or more. These effects cannot be explained in terms of the small changes in light absorption which are also observed. It is suggested that these observations are due to a reorientation of pigment molecules in the magnetic field.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 486-491 |
| Number of pages | 6 |
| Journal | BBA - Bioenergetics |
| Volume | 226 |
| Issue number | 2 |
| DOIs | |
| State | Published - Mar 2 1971 |
ASJC Scopus subject areas
- Biophysics
- Biochemistry
- Cell Biology
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In: BBA - Bioenergetics, Vol. 226, No. 2, 02.03.1971, p. 486-491.
Research output: Contribution to journal › Article › peer-review
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TY - JOUR
T1 - Magnetic field effect on the chlorophyll fluorescence in Chlorella
AU - Geacintov, Nicholas E.
AU - van Nostrand, Francis
AU - Pope, Martin
AU - Tinkel, Jack B.
N1 - Funding Information: The experiments were performed at the Francis Bitter National Magnet Laboratory at the Massachusetts Institute of Technology in one of the Bitter coil solenoid magnets*. The Chlorella was grown in Pirson and Ruppel's 1 medium. The experiments were performed in the same medium. The age of the culture at the time of the experiments varied from 3 to 6 days. The experimental arrangement is shown in Fig.1. The Chlorella suspensions were placed in a 1 cm × 1 cm X 5 cm square bottomed cell (E) to which were attached two prisms C and C' (at right angles to each other) and two 3-cm-long, 7-mm-diameter light guides A and B. A was cemented to the prism C and B was cemented to the bottom of the cell. The entire assembly was situated in the 2-inch bore of the magnet J. The magnetic field was homogeneous and variable from 0 to 145 kgauss. The light source was a 100-W mercury lamp; the light was filtered with a Coming CS 4-72 filter (band pass 340-620 nm). A 9-ft-long 7-mm-diameter bent quartz rod G was used as a light guide. By Abbreviation: DCMU, 3-(3,4-dichtorophenyl)-l,l-dimethyl urea. "~rhe National Magnet Laboratory is supported by the Air Force Office of Scientific Research. Funding Information: where \[Q\]i s the concentration of fluorescence quenching traps which decreases with increasing light intensity, k\[Q\]i s the term due to photosynthesis, kF is the radiative rate constant of chlorophyll a in Chlorella and kH is the sum of all other nonradiative rate constants. We measured F(H)/F(O) as a function of light intensity. In the perpendicular orientation the negative effect is nearly independent of light intensity. In a typical example, the effect is -6.3% when F/1 is maximum (at high light intensity) and is -5.3 -+ 0.5% at low light intensities where ~ = F/I -~ 0.03; at the low light intensity the signal is noisy and there is consequently a + 10% uncertainty associated with the measured value of-5.3%. The magnitude of the effect in the perpendicular orientation does not change (within limits of +0.7%) when the photosynthetic poison 3-(3,4-dichlorophenyl)-l, 1-dimethyl urea (DCMU) is added. Since it is well known that DCMU eliminates the intensity dependence of ~ (the quenching process k\[Q\]- ~ 0), the magnetic effect in the perpendicular orientation does not appear to operate on the term k \[Q\]. In the parallel orientation, there is a pronounced intensity dependence of F(tO/F(O). For example, in a particular sample, the effect was +6.0% at high light intensities when F/I was maximum and decreased to 3.3 + 0.5% at low light intensities. Addition of DCMU does not affect F(H)/F(O) in the high intensity limit, but eliminates the intensity dependence which is observed in the absence of this poison. We first note that any intensity dependence of the magnetic effect is most likely due to a variation in one of the terms in the denominator of Eqn. 1. Furthermore, we assume that kF is independent of the magnetic field, which is based on the lack of a magnetic field effect on the fluorescence of chlorophyll a in solution. If k\[Q\]w ere the magnetic field sensitive term, F(H)/F(O) would be expected to increase with decreasing light intensity since \[Q\]i ncreases. At high light intensities and in the presence of DCMU, \[Q\]~ 0, yet F(tt)/F(O) is largest under these conditions. We therefore concluded that at least part of the magnetic effect in the parallel orientation is operative on the term kI~ in Eqn. 1. The magnetic field may also be affecting the amount of light absorbed, which effectively would change I in Eqn. 1 and therefore F as well. Experiments currently in progress indicate that the absorption of polarized and unpolarized light is indeed magnetic field dependent; this effect depends on the wavelength of the exciting light and will be described in detail in a future publication. However, quantitative comparisons between magnetic field induced changes in both the absorption and the fluorescence, indicate that changes in I alone cannot account for the observed changes in the fluorescence (the parallel orientation effect in particular, which is intensity dependent, cannot be explained in this manner). For example, in the perpendicular orientation there is a decrease in the overall transmitted light, corresponding to an increase of 0.4-2.0% (depending on the sample) in the total amount of light absorbed by the Chlorella; yet the fluorescence always decreases when the magnetic field is turned on in the perpendicular orientation. In the parallel orientation there is a decrease of about 1-2% in the amount of light absorbed, yet the fluorescence increases by 4-9% in the presence of the magnetic field. The changes in fluorescence (and light absorption) induced by magnetic fields may be due to a reorientation of the pigment molecules which may give rise to changes in energy transfer efflciencies. Such orientation phenomena can be explained in terms of cooperative effects between molecules with anisotropic magnetic susceptibilities, which are known to align small muscle fibers s and molecules in liquid crystals 6 ,7 Biochim. Biophys. Acre, 226 (1971) 486--491 Conformational changes have been previously proposed to explain changes in the fluorescence intensity under varying experimental conditions. Papageorgiou and Govindjee 8 have invoked conformational changes in the lamellar system to explain the slow decline of fluorescence during the "second wave" in the fluorescence induction curve. Murata 9 proposed the idea that the illumination of a photosynthetic organism with light preferentially absorbed by system I or system II changes the efficiency of excitation transfer between chlorophyll molecules. This author has also suggested that Mg 2+ changes the mutual orientations of pigment molecules in chloroplasts, thus altering the rate of excitation transfer from chlorophyll molecules in pigment system II to those in pigment system 1l °. Bonaventura and Myers 3 have also proposed that conformationa\] changes control the distribution of excitation energy between the two pigment systems. Duysens 11 explains the observed changes in the fluorescence following preillumination with photosystem I or II light in terms of a reorientation of pigment molecules in systems I and II. This gives rise to more efficient energy transfer from system II to I, and thus to a decrease in the fluorescence n . The magnetic field effects reported here, if they are indeed due to a reorientation of pigments as suggested above, may prove to be an important new tool in the study of conformational changes in Chlorella pyrenoidosa, and perhaps other organisms as well. We finally note that Stacy et aL t2 examined the delayed fluorescence of ChloreUa in a magnetic field of 18 kgauss and found no effect (within an error limit of + 2%). We are grateful to Larry Rubin and his staff of the National Magnet Laboratory for their generous assistance. We thank R.S. Knox and C. Weiss for several helpful suggestions and C. Swenberg, W. Arnold, Govindjee and W. Bertsch for stimulating discussions. We would also like to thank S.5. Brody of New York University for kindly providing the Chlorella cultures. This work was supported in part by the U.S. Atomic Energy Commission. N.E.G. is a Visiting Scientist, Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Mass. F. Van N. is a New York University Predoctoral Fellow. Copyright: Copyright 2014 Elsevier B.V., All rights reserved.
PY - 1971/3/2
Y1 - 1971/3/2
N2 - The chlorophyll a fluorescence in Chlorella pyrenoidosa can be enhanced by 4-9% if the excitation light beam is parallel to an external magnetic field or decreased by 4-9% if the light beam is oriented perpendicular to a magnetic field of about 16 kgauss or more. These effects cannot be explained in terms of the small changes in light absorption which are also observed. It is suggested that these observations are due to a reorientation of pigment molecules in the magnetic field.
AB - The chlorophyll a fluorescence in Chlorella pyrenoidosa can be enhanced by 4-9% if the excitation light beam is parallel to an external magnetic field or decreased by 4-9% if the light beam is oriented perpendicular to a magnetic field of about 16 kgauss or more. These effects cannot be explained in terms of the small changes in light absorption which are also observed. It is suggested that these observations are due to a reorientation of pigment molecules in the magnetic field.
UR - http://www.scopus.com/inward/record.url?scp=0015207656&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0015207656&partnerID=8YFLogxK
U2 - 10.1016/0005-2728(71)90118-6
DO - 10.1016/0005-2728(71)90118-6
M3 - Article
C2 - 5575169
AN - SCOPUS:0015207656
SN - 0005-2728
VL - 226
SP - 486
EP - 491
JO - BBA - Bioenergetics
JF - BBA - Bioenergetics
IS - 2
ER -