Physiological and Biochemical Changes in Microcystis aeruginosa Qutz. in Phosphorus Limitation

Effects of phosphorus limitation on the physiological and biochemical changes of the freshwater bloom alga Microcystis aeruginosa Qutz. are reported in the present study. As a result of phosphorus limitation, biomass was controlled to some extent and the protein content per cell in vivo decreased. However,the carbohydrate content per cell was higher in phosphorus limitation over the 8 d of cultivation. Soluble proteins were distinct in the media, whereas phosphorus deficiency induced the presence of a unique protein (16.2 kDa). Under conditions of phosphorus limitation, the activities of both superoxide dismutase and peroxidase per cell in vivo were lower than under normal conditions in the last cultivation. The in vivo absorption spectra of cells showed chlorophyll absorption peaks at 676 and 436 nm, over 10 nm red-shifted from the normal position; cells showed an absence of a chlorophyll c with an in vivo absorption peak at 623nm and an extraction absorption peak at 617 nm. The chlorophyll a/carotene and chlorophyll a/xanthophylls ratios decreased under conditions of phosphorus limitation, photosynthetic efficiency (Fv/Fm) was clearly lower, and the low-temperature fluorescence emission spectra indicated a higher peak at 683 nm and a lower peak at 721 nm relatively, with the 721 nm peak drifting slightly to the red and the 683 nm peak strengthened with a weakened 692 nm shoulder peak.     

Some physiological and biochemical changes in marine eukaryotic red tide alga Heterosigma akashiwo during the alleviation from iron limitation

Some physiological and biochemical changes in the marine eukaryotic red tide alga Heterosigma akashiwo (Hada) were investigated during the alleviation from iron limitation. Chlorophyll a/carotenoid ratio increases as a result of iron alleviation. In vivo absorption spectra of iron-limited cells showed a chlorophyll (Chl) absorption peak at 630 nm, 2 nm blue-shifted from the normal position. Low-temperature fluorescence emission spectra of the cells have one prominent Chl emission peak at 685 nm. The cells showed a decrease in fluorescence yield from 685 nm band during alleviation from iron limitation. Low-temperature fluorescence excitation spectra and room-temperature fluorescence spectra indicated an efficient excitation energy transfer in the cells alleviated from iron limitation. Photosynthetic efficiency and carbohydrate content per cell increased after alleviation from iron limitation. Total protein decreased in iron-limited cells, while iron deficiency induced the appearance of specific soluble proteins (17 and 55 kDa).     

Changes in Pigment Composition and Photosynthesis Induced by Iron-Deficiency in the Blue-Green Alga Anacystis nidulans

Absorption spectra and photosynthetic action spectra have been determined for living Anacystis grown in complete and iron-deficient inorganic media. The absorption studies have shown a spectral shift from 679 nm to 673 nm in the chlorophyll a absorption peak when the algae had to grow without iron. The shift is believed to reflect a changed ratio between at least two chlorophyll a forms denoted Ca670 and Ca680 in this work. Action spectra determinations have revealed a similar shift from 677 nm to 672 nm in the photosynthetic activity peak of chlorophyll a when Anacystis was transferred to a medium without iron. It is proposed that both Ca670 and Ca680 participate in light absorption for photo-system I.     

The State of Protochlorophyll and Chlorophyll in Corn Roots

The protochlorophyll(ide) present in primary roots of dark-grown corn (Zea mays) seedlings has an in vivo absorption maximum at 634 nm. Red light converts the pigment to chlorophyll(ide) a with an absorption maximum at 675 nm.     

The Light Induced Protochlorophyll–Chlorophyll a-Transformation and the Succeeding Interconversions of the Different Forms of Chlorophyll

Curve resolution into Gaussian components of the absorption spectra during the varying stages of the Shibata shift in dark grown, irradiated leaves of barley indicates that the chlorophyll a forms formed after irradiation consist of the same main components which have been reported to be present in all hitherto investigated plant materials (peak values in the red region 662, 670, 677 and 683 nm, respectively) but in varying proportions. The spectra during the Shibata shift proper can be satisfied by a mixture of two single components gradually changing their proportions, although a four component system gives a still better fit to the measured absorption curves. It is also shown that curves taken before and after the shift and added together in the appropriate proportions will match the absorption spectrum measured with peak at the isosbestic point (after ca. 15 min at room temperature).     

Water-soluble chlorophyll protein of Brassica oleracea var. Botrys (cauliflower)

A water-soluble chlorophyll protein was prepared from Brassica oleracea var. Botrys (cauliflower) and purified by (NH₄)₂SO₄ fractionation and by chromatography on a DEAE-cellulose column. The chlorophyll protein contained chlorophylls a and b in the ratio 6:1, and no carotenoids. The molecular weight, determined by means of gel filtration on Sephadex G-100, was 78000. The chlorophyll protein showed absorption peaks at 273, 340, 384, 420, 438, 465, 628, 674 and 700 nm. Since the three bands at 384, 420 and 438 nm all have approximately the same height, the spectrum is different from that of chlorophyll a in organic solvents. The fluorescence of the chlorophyll protein showed a peak at 683 nm, with shoulders at 706 and 745 nm at room temperature, and peaks at 685, 706 and 744 nm at the temperature of liquid N₂. An apo-protein was prepared by removing the chlorophylls with 2-butanone and purified by precipitation with (NH₄)₂SO₄. The apo-protein thus prepared had an absorption band at 273 nm but none at longer wavelengths. The apo-protein could be combined with chlorophylls, forming a chlorophyll protein which had spectral characteristics similar to those of the original.     

Distribution of Chlorophyll between the Two Photoreactions in Photosynthesis of the Blue-Green Alga Anacystis nidulans Grown at Two Different Light Intensities

Anacystis nidulans was grown in white light of two different intensities, 7 and 50 W ·m^?2. The in vivo pigmentations of the two cultures were compared. The ratio phycocyanin/chlorophyll a was 0.96 for cells grown at 7 W · m^?2 and 0.37 for cells grown at 50 W · m^?2. Phycocyanin-free photosynthetic lamellae (PSI-particles) were prepared, using French press treatment and fractionated centrifugation. Algae grown in the irradiance of 50 W · m^?2 showed a chlorophyll a/P700 ratio of 260, while algae grown at 7 W · m^?2 had a value of 140. Corresponding PSI-particles showed values of 122 and 109 respectively. Light-induced absorption difference spectra measured between 400–450nm indicated different ratios between cytochrome f and P700 in the two algal cultures. Enhancement studies of photosynthetic oxygen evolution were carried out. When a background beam of 691 nm was superimposed upon a signal beam of 625 nm, good enhancement was observed for both cultures. With the wavelengths 675 and 691 nm together a pronounced enhancement could be detected only in algae grown at the higher light level. Absorption spectra recorded on whole cells at 77°K revealed a small shift of the main red chlorophyll a absorption peak caused by light intensity. It is proposed that the reduction of the phycocyanin/chlorophyll a ratio in high light-grown cells is accompanied by an increased energy distribution by chlorophyll a into PSII.     

Relation between the Light-Harvesting Chlorophyll a-Protein Complex LHCPa and Photosystem I in the Alga Chlamydobotrys stellata

The light-harvesting chlorophyll protein system of the alga Chlamydobotrys stellata consists of an as yet uncharacterized algal chlorophyll a-protein, called LHCPa, and a common photosystem II-related chlorophyll a/b-protein, called LHCPb (Brandt, Kaiser-Jarry, Wiessner 1982 Biochim Biophys Acta 679: 404-409). For further characterization, this LHCPa was isolated from the organism by polyacrylamide isoelectrofocusing and reelectrophoresis. It contains only chlorophyll a and has only one apoprotein (32,000 daltons). When separated from autotrophically grown cells, its absorption peak is at 674 nm and its isoelectric point at 5.3. Photoheterotrophic cultivation of the algae shifts the absorption maximum of LHCPa to 679 nm and its isoelectric point to 4.8. This LHCPa is a component of photosystem I particles. In relation to the total chlorophyll a content, the amount of LHCPa is low in autotrophic algae, but increases under photoheterotrophic growth conditions, where the organisms do not have the ability to assimilate CO₂ photosynthetically.     

PHOTOSYNTHETIC LIGHT-HARVESTING FUNCTION OF VIOLAXANTHIN IN NANNOCHLOROPSIS SPP. (EUSTIGMATOPHYCEAE)1

Whole cell absorption spectra of the Eustigmatophycean algae Nannochloropsis salina Bourrelly and Nannochloropsis sp. reveal the presence of a distinct absorption peak at 490 nm. The lack of chlorophylls b and c in these species indicates that this peak must be attributed to carotenoid absorption. In vivo fluorescence excitation spectra for chlorophyll a emission show a corresponding maximum at 490 nm. This peak is more clearly resolved than carotenoid maxima in other algal classes due to the absence of accessory chlorophylls. The carotenoid composition of the two Nannochloropsis species shows that violaxanthin and vaucheriaxanthin are the main contributors to 490 nm absorption. Violaxanthin accounts for approximately 60% of the total carotenoid in both clones. We conclude that light absorption by violaxanthin, and possibly by vaucheriaxanthin, is coupled in energy transfer to chlorophyll a and that violaxanthin is the major light-harvesting pigment in the Eustigmatophyceae. This is the first report of the photosynthetic light-harvesting function of this carotenoid.     

An automatic device for in vivo absorption spectra acquisition and chlorophyll estimation in phytoplankton cultures

In order to aid the study of photoacclimation, a new programmable deviceis described which provides automatic on-line acquisition of in vivo cellabsorption in phytoplankton cultures. The system was used for a long-termstudy of Rhodomonas salina grown at constant photon flux density ina nitrate-limited continuous culture with different dilution rates. Particulate absorption measured at the red chlorophyll a (Chl a)maximum was not a good proxy of biomass, because of the large variabilityof cellular chlorophyll induced by nitrogen limitation. However, thedevice is well suited to automatic assessment of Chl a andphycoerythrin (PE) concentrations in phytoplankton cultures, if algal cellsize and concentration are measured in parallel to correct the packagingeffect. The effects of nitrogen limitation on Chl a and PE contentsand particle absorbance are discussed.     

Adaptations in Pigment Composition and Photosynthesis by Far Red Radiation in Chlorella pyrenoidosa

Chlorella pyrenoidosa has been cultivated in radiation of wavelengths between 690–975 nm for several months. Absorption spectra and action spectra of photo-synthesis have been determined for far red and “white” light brown cultures, In vivo spectrophotometric analyses and action spectra showed that fur red growth Chlorella adapted to the extreme light conditions by an increase both in absorption and photosynthesis above 700 nm. It is proposed that som of the in vivo normal chlorophyll a forms were converted to a far red absorbing chlorophyll a form, giving the far red exposed suspension an increased photosynthetic activity between 700–740 nm. The analyses of far red grown Chlorella have also shown an increased photosynthesis in the blue part of the spectrum, presumably due to a decrease in photosynthetically inactive carotenoid content. By culturing Chlorella in a “white” light gradient between 0.5 × 10⁴ and 3.7 × 10⁴ erg cm^?2 s^?1, it has been demonstrated that light intensity did not influence pigment ratios between 500–750 nm. In the blue part, however, high light levels caused increased absorption because of increased carotenoid content. Some ecological aspects of this far red effect have also been discussed.     

Light- and nutrient-limited periphyton in low order streams of Oahu,Hawaii

To date, most studies of light- and nutrient-limited primary productivity in forested streams have been carried out in deciduous forests of temperate, continental regions. Conceptual models of light and nutrient limitation have been developed from these studies, but their restricted geographic range reduces the generality of such models. Unlike temperate continental streams, streams on tropical high islands are characterized by flashy, unpredictable discharge and riparian canopies that do not vary seasonally. These contrasting conditions suggest that patterns of light and nutrient limitation in tropical streams may differ from those in temperate streams. The effects of light, and nitrogen and phosphorus availability on periphyton accrual (measured as chlorophyll a per unit area) were investigated using field experiments in 4 low-order streams on the island of Oahu, Hawaii. Levels of chlorophyll a in partially-shaded stream pools were significantly greater than in heavily-shaded pools, and nutrient-enrichment increased the level of chlorophyll a in partially-shaded pools but not in heavily-shaded pools. In each stream, phosphate enrichment resulted in an increase in the level of chlorophyll a, but nitrate enrichment had no effect. Spates following rainstorms occur frequently in these streams, and may increase periphyton productivity by increasing the flux of nutrients to algal cells. However, differences in inorganic nitrogen and phosphorus concentrations measured during spates and baseflow were small, and during some spates, concentrations of these two nutrients declined relative to baseflow concentrations. These observations suggest that phosphorus limitation was not alleviated by spates.     

Studies on the cytochromef ofBryopsis maxima in vivo andin vitro

Cytochromec (553.7Bryopsis maxima) isolated fromB. maxima had absorption maxima at 553.7, 523.0, 417.1 and 317.5 nm in its reduced form. Isosbestic points in the reduced minus oxidized difference spectrum were located at 561, 543, 528, 511, 436, 411 and 334 nm. The purified protein exhibited a molecular weight of 10,700. The midpoint potential for the cytochromec was estimated to be 372±5 mVin vitro at pH 7.0 and 365±5 mVin vivo.In vivo 80% of the cytochromec was in the reduced form. This cytochrome was located only in chloroplasts indicating that it functions in the photosynthetic electron transport as cytochromef. Chloroplasts contained one molecule of this cytochrome per 360 molecules of chlorophyll. The magnitude of the chemically induced absorbance changes for the cytochromoesin vivo were much smaller than the light-induced absorbance change at 561 nm. It is concluded that the light-induced 561 nm absorbance change characteristic of this alga is not mainly attributable to the redox reaction of cytochromesb andf in the chloroplasts.     

Absorption and fluorescence spectra of chlorophyll-proteins isolated from Euglena gracilis

A spectroscopic study of chlorophyll-protein complexes isolated from Euglena gracilis membranes was carried out to gain information about the state of chlorophyll in vivo and energy transfer in photosynthesis. The membranes were dissociated by Triton X-100 and separated into fractions by sucrose gradient centrifugation and hydroxyapatite chromatography. Four different types of chlorophyll-protein complexes were distinguished from each other and from detergent-solubilized chlorophyll in these fractions by examination of their absorption, fluorescence excitation (400–500 nm) and emission spectra at low temperature. These types were: (1). A mixture of antenna chlorophyll a- and chlorophyll ab-proteins with an absorption maximum at 669 and emission at 682 nm; (2) a P-700-chlorophyll a-protein (chlorophyll: P-700 = 30 : 1), termed CPI with an absorption maximum at 676 nm and emission maxima at 698 and 718 nm; (3) a second chlorophyll a-protein (CPI-2) less enriched in P-700, with an absorption maximum at 676 nm and emission maxima at 680, 722 and 731 nm; (4) a third chlorophyll a-protein (CPa₁) with no P-700, absorption maxima at 670 and 683 nm, and an unusually sharp emission maximum at 687 nm. Treatment of CPa₁ with sodium dodecyl sulfate drastically altered its spectroscopic properties indicating that at least some chlorophyll-proteins isolated with this detergent are partially denatured. The results suggest that the complex absorption spectra of chlorophyll in vivo are caused by varying proportions of different chlorophyll-protein complexes, each with different groups of chlorophyll molecules bound to it and making up a unique entity in terms of electronic transitions.     

Chlorophyll composition of Photosystems IIα, IIβ and I in tobacco chloroplasts

The antenna composition of the Photosystems II_α, II_β and I was studied in tobacco chloroplasts. Absorbance spectra, recorded at 4 K, were analyzed for the wild type and the mutants Su/su and Su/su var. Aurea, containing higher concentrations of the photosystems. With chloroplasts of Su/su we measured the action spectra of the three photosystems from 625 to 690 nm. Above 675 nm absorption by Photosystem I dominated. This sytem had a maximum at 678 nm and a shoulder at 660 nm. Of the long-wavelength chlorophyll a forms, absorbing at 690, 697 and 705 nm at 4 K, which are generally assigned to Photosystem I, the 697 nm form occurred in an amount of four molecules per reaction center of Photosystem I in each type of chloroplast. The Photosystem II_α spectrum was characterized by maxima at 650 and 672 nm, showing clearly the participation of the chlorophyll a and b containing light-harvesting complex. In the mutants the light-harvesting complex has a chlorophyll a to chlorophyll b ratio of more than 1; the amount of the 672 nm chlorophyll a was normal, whereas the amount of chlorophyll b was markedly decreased in the mutants relative to the wild type. The Photosystem II_β spectrum mainly consisted of a band at 683 nm.     

Analyses of absorption and fluorescence spectra of water-soluble chlorophyll proteins,pigment System II particles and chlorophyll a in diethylether solution by the curve-fitting method

Absorption and fluorescence spectra in the red region of water-soluble chlorophyll proteins, Lepidium CP661, CP663 and Brassica CP673, pigment System II particles of spinach chloroplasts and chlorophyll a in diethylether solution at 25°C were analyzed by the curve-fitting method (French, C.S., Brown, J.S. and Lawrence, M.C. (1972) Plant Physiol. 49, 421–429). It was found that each of the chlorophyll forms of the chlorophyll proteins and the pigment System II particles had a corresponding fluorescence band with the Stokes shift ranging from 0.6 to 4.0 nm.The absorption spectrum of chlorophyll a in diethylether solution was analyzed to one major band with a peak at 660.5 nm and some minor bands, while the fluorescence spectrum was analyzed to one major band with a peak at 664.9 nm and some minor bands. A mirror image was clearly demonstrated between the resolved spectra of absorption and fluorescence. The absorption spectrum of Lepidium CP661 was composed of a chlorophyll b form with a peak at 652.8 nm and two chlorophyll a forms with peaks at 662.6 and 671.9 nm. The fluorescence spectrum was analyzed to five component bands. Three of them with peaks at 654.8, 664.6 and 674.6 nm were attributed to emissions of the three chlorophyll forms with the Stokes shift of 2.0–2.7 nm. The absorption spectrum of Brassica CP673 had a chlorophyll b form with a peak at 653.7 nm and four chlorophyll a forms with peaks at 662.7, 671.3, 676.9 and 684.2 nm. The fluorescence spectrum was resolved into seven component bands. Four of them with peaks at 666.7, 673.1, 677.5 and 686.2 nm corresponded to the four chlorophyll a forms with the Stokes shift of 0.6–4.0 nm. The absorption spectrum of the pigment System II particles had a chlorophyll b form with a peak at 652.4 nm and three chlorophyll a forms with peaks at 662.9, 672.1 and 681.6 nm. The fluorescence spectrum was analyzed to four major component bands with peaks at 674.1, 682.8, 692.0 and 706.7 nm and some minor bands. The former two bands corresponded to the chlorophyll a forms with peaks at 672.1 and 681.6 nm with the Stokes shift of 2.0 and 1.2 nm, respectively.Absorption spectra at 25°C and at ?196°C of the water-soluble chlorophyll proteins were compared by the curve-fitting method. The component bands at ?196°C were blue-shifted by 0.8–4.1 nm and narrower in half widths as compared to those at 25°C.     

Photoconversion of long-wavelength protochlorophyll native form Pchl 682/672 into chlorophyll Chl 715/696 in Chlorella vulgaris B-15

By spectral methods, the final stages of chlorophyll formation from protochlorophyll (ide) were studied in heterotrophic cells of Chlorella vulgaris B-15 mutant, where chlorophyll dark biosynthesis is inhibited. It was shown that during the dark cultivation, in the mutant cells, in addition to the well-known protochlorophyll (ide) forms Pchlide 655/650, Pchl(ide) 640/635, Pchl(ide) 633/627, a long-wavelength protochlorophyll form is accumulated with fluorescence maximum at 682 nm and absorption maximum at 672 nm (Pchl 682/672). According to the spectra measured in vivo and in vitro, illumination of dark grown cells leads to the photoconversion of Pchl 682/672 into the stable long wavelength chlorophyll native form Chl 715/696. This reaction was accompanied by well-known photoreactions of shorter-wavelength Pchl (ide) forms: Pchlide 655/650Chlide 695/684 and Pchl (ide) 640/635Chl (ide) 680/670. These three photoreactions were observed at room temperature as well as at low temperature (203–233 K).Abbreviations Chl chlorophyll - Chlide chlorophyllide - Pchlide protochlorophyllide - Pchl protochlorophyll - PS I RC Photosystem I reaction centres. Abbreviations for native pigment forms: the first number after the pigment symbol corresponds to maximum position of low-temperature (77 K) fluorescence band (nm), second number to maximum position of long-wavelength absorption band     

Photosynthetic enhancement spectra in higher plants

Enhancement spectra for photosynthesis of intact leaves of higherplants were investigated by means of the rate of CO₂ absorptionunder atmospheric conditions. Enhancement spectra for photosystem(system)II measured with a reference beam of 700 nm had twopronounced peaks at about 480 and 650 nm and lower humps at540–600 nm in all of the nine species tested. By the useof a rice mutant which lacks chlorophyll b, it was revealedthat the 650-nm peak and the middle humps in the spectrum canbe attributed mostly to chlorophyll b absorption, whereas the480-nm peak must be due to the absorption of carotenoids andchlorophyll b. Enhancement for system I in wheat had a peakat about 715 nm, and the maximum was much higher than that ofthe enhancement for system II. Enhancement between a red anda farred light for wheat was much greater for the farred lightthan for the red light in the presence of an excess amount ofthe other light. These results demonstrate that the enhancementphenomenon in higher plants is essentially the same as thatin green algae. (Received November 30, 1977; )     

Far-red induced changes of the protochlorophyllide components in wheat leaves

Biosynthesis of chlorophyll is partly controlled by the phytochrome system. In order to study the effects of an activated phytochrome system on the protochlorophyllide (PChlide) biosynthesis without accompanying phototransformation to chlorophyll, wheat seedlings (Triticum aestivum L. cv. Starke II Weibull) were irradiated with long wavelength far-red light of low intensity. Absorption spectra were measured in vivo after different times in the far-red light or in darkness. The relationship between the different PChlide forms, the absorbance ratio _{650nm636 nm} changed with age in darkness, and the change was more pronounced when the leaves were grown in far-red light. Absorption spectra of dark-grown leaves always showed a maximum in the red region at 650 nm. For leaves grown in far-red light the absorption at 636 nm was high, with a maximum at the 5 day stage where it exceeded the absorption at 650 nm. At the same time there was a maximum in the total amount of PChlide accumulated in the leaves, about 30% more than in leaves grown in darkness. But the amount of the directly phototransformable PChlide, mainly PChlide_650–657, was not increased. The amount of PChlide_628–632, or more probably the amount of (PChlide_628–632, + PChlide _636–657) was thus higher in young wheat leaves grown in far-red light than in those grown in darkness. After the 5 day stage the absorption at 636 nm relative to 650 nm decreased with age, and at the 8 day stage the spectra were almost the same in both types of leaves. Low temperature fluorescence spectra of the leaves also showed a change in the ratio between the different PChlide forms. The height of the fluorescence peak at 632 nm relative to the peak at 657 nm was higher in leaves grown in far-red light than in dark-grown leaves. – After exposure of the leaves to a light flash, the half time for the Shibata shift was measured. It increased with age both for leaves grown in darkness and in far-red light; but in older leaves grown in far-red light (7–8 days) the half time was slightly longer than in dark-grown leaves. – The chlorophyll accumulation in white light as well as the leaf unrolling were faster for leaves pre-irradiated with far-red light. The total length of the seedlings was equal or somewhat shorter in far-red light, but the length of the coleoptile was markedly reduced from 8.1 ± 0.1 cm for dark-grown seedlings to 5.2 ± 0.1 cm for seedlings grown in far-red light.     

Orientation of the pigments in Photosystem II: A low-temperature linear dichroism and polarized fluorescence emission study of chlorophyll-protein complexes isolated from Chlamydomonas reinhardtii

The orientation of the various absorbing and fluorescing dipoles in Photosystem II have been investigated by linearly polarized light spectroscopy at 5 K, performed on macroscopically oriented PS II complexes derived from Chlamydomonas reinhardtii. Linear dichroism and absorption spectra show that the Q_Y transitions of the chlorophyll molecules are mostly tilted at less than 35° from the plane of largest cross-section of the particle (which in vivo coincides with the plane of the thylakoid membrane). The chlorophyll forms absorbing at 676 and 683 nm are oriented closer to the membrane than the forms absorbing at 665 and 670 nm which are tilted at approximately 35° from the plane. A dip observed around 680 nm in the LD/absorption spectra indicates a component tilted at a larger angle away from the membrane plane than the 676 nm- and 683 nm-absorbing species. A component weakly absorbing around 693 nm and exhibiting a negative LD (tilt larger than 35°) is clearly resolved. The amplitude of the LD at 693 nm relative to that observed at the maximum (676 nm) varies from sample to sample. In the blue spectral region, two populations of carotenoids are observed; one absorbs around 460 and 490 nm, while the other absorbs around 510 nm. They are oriented out of and near to the thylakoid plane, respectively. Comparison of polarized absorption and fluorescence spectra from the same oriented samples allows the assignment of the 695 nm fluorescence emission to the dipoles responsible for the LD signal at 693 nm.