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CANADIAN TRANSLATION OF FISHERIES AND AQUATIC SCIENCES No. 4849 Photosynthesis in the marine world by Y. Fujita Original Title: From: Umi no sekai no kogosei Kagaku 38: 2-9, 1979. Translated by the Translation Bureau (ELC/PS) Multilingual Services Division Department of the Secretary of State of Canada Department of Fisheries and Oceans Arctic Biological Station Ste. Anne de Bellevue, Que. 1982 24 Pages typescript + 4 DEPARTMENT OF THE SECRETARY OF STATE SECRÉTARIAT D'ÉTAT TRANSLATION BUREAU BUREAU DES TRADUCTIONS W. DIVISION DES SERVICES MULTILINGUAL SERVICES CANADA MULTILINGUES DIVISION INTO - EN TRANSLATED FROM - TRADUCTION DE English Japanese AUTHOR - AUTEUR FUJITA Yoshihiko TITLE IN ENGLISH - TITRE ANGLAIS Photosynthesis in the marine world TITLE IN FOREIGN LANGUAGE (TRANSLITERATE FOREIGN CHARACTERS) TITRE EN LANGUE ETRANGÉRE (TRANSCRIRE EN CARACTÉRES ROMAINS) Umi no sekai no kogosei REFERENCE IN FOREIGN LANGUAGE (NAME OF BOOK OR PUBLICATION) IN FULL. TRANSLITERATE^FOREIGN CHARACTERS. REFÉRENCE EN LANGUE ÉTRANGÉRE (NOM DU LIVRE OU PUBLICATION). AU COMPLET, TRANSCRIRE EN CARACTÉRES ROMAINS, Kagaku REFERENCE IN ENGLISH - RÉFÉRENCE EN ANGLAIS Chemistry PAGE NUMBERS IN ORIGINAL NUMEROS DES PAGES DANS L'ORIGINAL PUBLISHER- EDITEUR DATE OF PUBLICATION DATE DE PUBLICATION Unidentified 2-,9 PLACE OF PUBLICATION LIEU DE PUBLICATION YEAR ANNE VOLUME 1979 38 ISSUE r10. NUMERO NUMBER OF TYPED PAGES NOMBRE DE PAGES DACTYLOGRAPHIÉES Unidentified Fisheries and Oceans REQUESTING DEPARTMENT MINISTÉRE-CLIENT BRANCH OR DIVISION DIRECTION OU DIVISION SIPB PERSON REQUESTING DEMANDÉ PAR SIC Hsiao YOUR NUMBER VOTRE DOSSIER NO DATE OF REQUEST DATE DE LA DEMANDE 24 8 TRANSLATION BUREAU NO. NOTRE DOSSIER NO 861177 TRANSLATOR (INITIA LS) TRADUCTEUR ( INITIALES) E . L. C. MAY -. ? '158Z ^ ,^i; March 8, 1982 p^ ? ii....^..._^..,.....o SOS-200•1 0.8 (RE V. 2/68) 7 030-2 1-029-5333 Ié^j' ;}^^^ ^•§h{^,^Ts r^^4yi1^7 ^^?f.:^:..i.._:iî / PS Secrétariat d'Ètat Secretary of State MULTILINGUAL SERVICES DIVISION — DIVISION DES SERVICES MULTILINGUES BUREAU DES TRADUCTIONS TRANSLATION BUREAU aienesNo.—Nocludient Bureau t'Jo. — No du bureau • 861177 Division/Branch — Division/Direction City— Ville Arctic Biological Station Ste Anne Department — Ministère Department of Fisheries and Oceans • • Languege — Translator (Initials) Langue — ELC Japanese Traducteur (Initiales) / PS MAY .- p2 Kagaku (Chemistry) 38 No. • 8, 1979 Pp2 Photobynthesis in thé marine World (Mechanisms used in feeble light) FUJITA Yoshihiko, D.Sc. Scanning elebtron microphotographof a diatom Department of ravine biophysics, Intitute for maritime research, University of Tokyo ' SEC 5- 25 (Rev. 6/78) 7 19tYe 2 1. Introduction It is no exaggeration to say that radiant energy from the sun is 311 the source of support for the activity of%ife on earth. About 70% of the solar radiation which reaches the earth's surface is light energy in the so-calleâ visible wavelength range. Plants which live on thè ground or in the oceans trans-- form this light energy by means of a chain of photosynthetic processes into chemical energy and synthesize the components of living tissues. Organisms which are not photosynthetic range all the way from bacteria to humanity and they obtain the food which they need from other organisms by what is known as he.reronomous nutrition. When the food chain is followed back it leads to the organic nutrients produced by photosynthesis in plants. Since the source of supply of our life energy is the prolific growth of plants on the earth, it can be said that the source of all organic life is the radiant energy from the sun which is utilized by these plants. Everyone knows that photosynthesis occurs in the green leaves of the higher plants, the trees, shrubs and grasses. Green grana -- the chloroplasts which are the photosynthesis organs -- are tightly packed into the cells of green leaves and the leaves are green because they contain chlorophyll which captures the solar energy. When photosynthesis is mentioned, many people will therefore think of the green colour of the green leaves of plants. However photosynthesis is not confined to the activity of these higher plants on the ground. Pond water becomes green in summer, water in goldfish bowls may become green, and this greening mostly results from a luxuriant growth of single cell green algae which are also plants in which photosynthesis occurs. Not only green algae but many other types of algae are active in the waters of lakes, marshes and rivers, and the photosynthesis which occurs in these algae in the same way as in the higher plants produces the life energy for other organisms in the water. 70% of the surface of the globe is covered by Se25. The living activity of organisms in this vast ocean is supported by photosynthesis, and the plants in which this photosynthesis occurs are algae, just as they are in lakes and marshes. Many people will probably associate the idea of marine algae with edible seaweeds such as asakusanori (laver, Porphyra), konbu (tangle, Laminaria) or wakame ( Undaria). However, a major role in photosynthesis in the sea is played by diatoms and flagellates which float or drift as single cells or colonies in the phytoplankton. Except in cases such as the well-known red tide of such algae in the Inland Sea of Japan, the quantity present in sea water is never large, and even when drawing seawater we cannot easily be aware of their presence. Nevertheless, the area of the ocean is, as already mentioned, very large, and as Table 1 shows, photosynthesis in the sea amounts to more than half of the photosynthesis on land. We may say that this shows how important the photosynthesis performed in the oceans by phytoplankton is to the support of life on land. Table 1. Global production of organic substances by photosynthesis Mean quantity per unit area World total (10 9 tons per year) (g/m2 per year) Land total 730 109 Sea 155 55 World total 320 164 4 Photosynthesis by higher plants and by algae procee^s through a complicated chain of reactions, but the overall result can be consolidated in the following equation hV H20 + CO2 CH2O + 02 (1) This reaction not only produces life energy for the organisms but also is of importance in the provision of the oxygen molecules which an extremely large number of organisms require. For this reason, too, it may be said that photosynthesis in the sea must not be neglected in relation to life on earth. p3 2. Light on land, light in the sea ener9Y The ultra violet part of the solar radiation"'is greatly reduced by scattering and absorption in the air and in the ozone layer before it reaches the earth's surface, and as shown in Figure 1(a), the energy distribution in the light which is incident on the surface has its maximum energy in the visible region at about 500 nm. This visible light is the source of energy for photosynthetic plants on land. However the phytoplankton and the marine algae in the sea live mostly in the water and the light which is to be used for photosynthesis has passed through a medium far more dense than the air. The phytoplankton living at depths of some tens of metres to a hundred metres are those of most importance to photosynthesis in the sea, and the solar light which penetrates to such depths has not only been greatly reduced in total energy but has lost much of the visible red light through absorption in the water and has lost the near ultraviolet by absorption or by scattering by dissolved organic matter and by particles suspended in the sea water. The light is finally restricted to a narrow band centred around 5 Figure 1 The energy distribution in the solar radiation (a) On land Open sea (h) Coastal water (a) 1.511.5 ca l /(cm2 .m in .p ) ÉEW -‹ 0.5 - 500 400 1000 500 600 700 (nm) (nm) Figure 2 (a) The absorption spectrum of the green leaves of the higher plants (b) The photosynthesis quantum yield (moles/Einstein) (the number of moles of oxygen evolved per Einstein) (a) Absorption (%) 17,UMSLI:JV'M 4 00 SIDO 6(1)0 700 (nm) eod T A i) ij 0.1 C.; N NR inf.ornld:ion sc;:uk,ir,ent Quantum yield I 0.05 400 500 600 (nm) 700 6 480 nm to 500 nm, as shown by the solid lines in Figure 1(b). Marine algae, other than those which live in the tidal zone, must use this type of light for photosynthesis. In the coastal waters where the algae live, there is more plankton than in the open sea, and once again the near ultraviolet light is greatly diminished by the bodies of these organisms and by the organic compounds which they produce. light which reaches these comparatively shallow The regions is severely limited, as shown by the dotted lines in Figure 1(b). The higher plants which are most important for photosynthesis on land harvest light principally in chlorophyll a and b. Chlorophyll contains magnesium linked to a distorted porphyrin, and its light absorption properties are consequently those of a metal porphyrin with an alpha band in the red at 650 nm to 700 nm and a gamma band in the blue at 430 nm to 450 nm, so that it takes on a green colour. Consequently its efficiency in utilizing light energy for photosynthesis -- the photosynthesis quantum yield -- is high in the red and the blue, and is lower in the 500 nm region ( where the energy distribution in the sun's light has its maximum.' This distinctive feature of photosynthesis by land plants would be quite useless with the light energy distribution which can be used for photosynthesis in the sea. It is therefore to be expected that algae living in the sea will make efficient use of the light in the sea by means quite different from those used by land plants. This fact is considered to be one of the distinctive features of photosynthesis in the sea. The reaction yield per light quantum. Since the photosynthetic reaction is given by equation (1), the quantity of oxygen evolved is a measure of the normal reaction. Consequently it is the molar number of the oxygen molecules evolved per light quantum. 7 3. The principal factors in photosynthesis in the sea Photosynthesis occurs in the sea in familiar algae such as p4 asakusanori. (laver, Porphyra) and konbu (tangle, Laminaria) which are not 3E all, green ^ An abnormal development of phytoplankton in which the sea water becomes clouded with phytoplankton leads to the red tide, but the colour developed is the well-known reddish brown and a green colour is not formed. As these examples show, the photosynthetic organisms in the sea differ from those on land and chlorophyll is by no means the principal photosynthetic pigment. Table 2 shows the answers to questions as to what types of algae the photosynthetic organisms in the sea are, and what pigments they contain. The principal pigments in the green algae are chlorophyll a and b, as they Table 2 Photosynthetic organisms in the sea. Algae and the composition of their photosynthetic pigments Green algae Chlorophyll a b ++ Diatoms Dinofla gellates Red algae Bluegreen algae ++ ++ ++ ++ ++ + + + + + + + + Brown algae + c P-,Carotene + Lutein ++ Fucoxanthin ++ ++ ++ ++ Peridinin Phycoerythrin Phycocyanin ++ Principal pigment + Presence found 8 are in the higher plants on land but as marine algae they practically all live in the tidal zone where the light environment does not differ from that on land, and they are rare among the algae in the phytoplankton. Consequently it may be said that the algae which bear the main burden of photosynthesis in the sea differ greatly from land plants in pigment composition. The most important phytoplankton are diatoms, dinoflagellates and blue-gree algae, whereas the red algae and brown algae are important algae in the sea from the tidal zones to the depths. Comparisons of the photosynthetic pigments in these principal marine photosynthetic organisms with those on land shows that chlorophyll a is common to all organisms but diatoms, dinoflagellates and brown algae contain chlorophyll c instead of chlorophyll b. Of the carotenoids, -carotene is present throughout, but the principal component present in diatoms and brown algae is fucoxanthin and in dinoflagellates it is peridinin (more than 70% of the total). of this, these algae have a brown colour. Because The solid line in Figure 3 (a) is the absorption spectrum of a live diatom cell for comparison with Figure 2 (a). A distinctive feature of red,algae and blue-green algae is their phycoerythrin content. The absorption band at 500 nm to 600 nm in the absorption spectrum of Figure 3 (b) is due to this pigment and is the source of the reddish purple colour. Thus each of the taxonomic groups of the marine algae differs from the others in the composition of its photosynthetic pigments, but one may say that the principal algae, at least, contain carotenoids or phycoerythrin which enable them to absorb light in the vicinity of 500 nm at the peak of the energy distribution of light which has penetrated the sea. In fact, the light energy absorbed by these pigments is used for photosynthesis with high efficiency. The solid lines 9 Absorption (%) 400 500 • 600 700 nm) O. I Quantum yield 0.05 400 500 600 700 (nm) Figure 3. The absorption spectra and quantum yields of diatoms* and red algae (a) Absorption spectrum of red algae Absorption spectrum of diatoms (b) The quantum yield of red algae The quantum yield of diatoms There is an apparent discrepancy between the references to Figure 3 and the captions. I have not tried to adjust these. Translator. 10 in Figures 3(a), (h) show the effective spectrum of the quantum yield of red algae and diatoms, and it is evident that the yields of both in the neighbourhood of 500 nm are higher than those of land plants (Figure 2(b)). It is particularly surprising that the quantum yield of red algae is very greatly reduced in the absorption band of chlorophyll a. It may be said that the substances which work most importantly to bring light energy into photosynthesis in the sea are not chlorophyll but phycoerythrin and the carotenoids fuèoxanthin and peridinin. An attempt will be made, below, to explain the nature of these pigments and how they operate in the living body, but first some description is given of the general mechanism by which photosynthetic pigments harvest light energy. 4. The mechanism of light energy harvesting Neither in the higher plants nor in algae do the photosynthetic pigment molecules participate directly in photochemical reactions. P5 Calculations based on the quantity of oxygen evolved by irradiation with a single short (about 10 microseconds) but sufficiently strong flash, show that in higher plants and algae one unit in which the photochemical reaction occurs is present for about 500 to 600 molecules of chlorophyll. Thus the photosynthetic pigment is present in the chloroplasts in the form of groups, by means of which the excitation energy of a large number of pigment molecules is transferred collectively to the molecules in which the photochemical reaction occurs (the reaction centres). This transfer of excitation energy between the pigment molecules is a weak interaction between the molecules based on a dipole-dipole interaction, and the transfer frequency from molecule j to molecule k can be represented by 1 equation . the following 11 •D T n 1->k • 9000 tc2 In 10 - 128 7r 5 n' NorIC 5" f — — di) ( 2) o kacon In equation 2 N o -113- cs.>) • a coefficient representing the orientation of the dipoles • the refractive index of the solvent = Avogadro's number • the intrinsic lifetime of the excited state of molecule j = the distance between the molecules = the wave number = the molecular light absorption coefficient of the molecule k = the fluorescent emission spectrum distribution of the molecule j. In short, when the overlap integral of the fluorescent emission spectrum of molecule j on the absorption spectrum of molecule k becomes large, n •k becomes large, and it is also inversely proportional to the sixth power of the distance between the molecules. At the present time this is thought to be the most applicable mechanism, and using the fluorescence of the chlorophyll a in the chloroplasts as an index, the excitation energy of the various pigments is transferred as shown in Table 3. Table 3 The transfer of excitation energy between the photosynthetic pigments Efficiency (%) Chlorophyll b p - carotene --> a --> chlorophyll a Chlorophyll c 100 Type of plant Green algae 40 a 90 Brown algae chlorophyll a 90 Diatoms Phycoerythrin chlorophyll a 7 80 Phycocyanin chlorophyll a 86 Fucoxanthin — › Red algae Blue-green algae 12 A first distinctive feature is the high transfer efficiency in light quantum units, a second is the transfer from a molecule in a high energy state to a lower molecule, and these are well explained by the proposed mechanism. In both higher plants and algae the photosynthetic ptiotod lLhlLLi1 reaction progresses through a cooperative two-type Y process2. Consequently each pigment group is attributed to its own reaction centres, and becomes the source from which energy is distributed to them (Figure 4). Each pigment group is linked to individual protein molecules4, and it is believed that the pigment proteins are symmetrically located in the fatty double layer of the photosynthetic membrane (thylakoid membrane) where the distance between the pigment molecules will be sufficiently small (the transfer frequency being inversely proportional to the sixth power of the distance between the molecules). Even so, there is at present little progress in understanding the circumstances, already mentioned, of fucoxanthin-peridinin and of phycoerythrin or the detailed coordination of the pigment molecules, but we will now try to discuss these pigments. 5. The carotenoid-chlorophyll a protein complexes As shown in Figure 5, the basic structures of fucoxanthin and peridinin are the same as that of (? -carotene. The oxidized positions on the ionone rings are the same as in the xanthophylls of the higher plants. The differences are that in fucoxanthin C-8 is oxidized outsieie- the kl}a ^ ionone rings and"C-,6' and C-7' are dehydrated, whereas in peridinin C-,11' and C-19' are oxidized and C-6 and C-7 are dehydrated. However it is not known why, with these structural differences, the excitation energy of the xanthophylls can be efficiently transferred to chlorophyll a and used for p6 13 CHLOROPHYLL D CHLOROPHYLL h Figure 4 3) Butler-Kitajima's three pigment zone model The arrows show the direction of energy transfer, and their thickness shows the magnitude of the transfer. "I" and "II" in the circles show photochemical reaction centres. %^.^^.•^--^ `11 ' \^ ^^3 ^ \ y^ ^-'' ^y ^. I I ki0)\./\OCOCH3 (b) CI-I,CO0 The structure of (a) carotene (b) Fucoxanthin (c) Peridinin 14 photosynthesis. Considering the mechanism of energy transfer already discussed it is necessary that the separation normally present between the xanthophyll and the chlorophyll a should be sufficiently small. Both chlorophyll a and xanthophylls are strongly lipidophile compounds which will be disolved in the fat of the thylakoid membrane, and in this condition there is no restriction on the conshaapproach of the two pigments. In the 50-called higher plants, the chlorophyll is combined with the vmembrane protein and forms r.ous 4 , and the same arrangement will apply in the case of xanthophylls and chlorophyll a. It is known that when the cells of dinoflagellates which contain peridinin as the photosynthetic pigment are destroyed, a red-orange pigment is eluted, and Haxo et al 5 have shown that the pigment is linked to a protein and have purified it by means of ion exchange chromatography and molecular sieve chromatography. The pigment protein shows the absorption spectrum of Figure 6, and the pigments it contains are peridinin and chlorophyll a. The protein portion has an isoelectric point of about 7.5 and is a neutral protein with a reported composition whose distinctive feature is an amino acid structure with more than 50% alanine. The molecular weight is 32000 daltons and it is confirmed to consist of a single peptide chain. Nine molecules of peridinin and two molecules of chlorophyll are linked to one protein molecule. Since the probe.iYt pitymeht is easily extracted froethe compound by any organic solvent it is supposed that there is no covalent bonding to the aminoacids which comprise the peptide chain. As can be seen from the fluorescence excitation spectrum of the chlorophyll a shown in Figure 6, the excitation energy of the peridinin in this pigment protein is transferred to the chlorophyll a with 15 Figure 6 o (VS I (a) The absorption spectrum of peridinin-chlorophyll a protein o (15 (b) o (b-A) The fluorescence excitation spectrum (b-B) The fluorescence emission spectrum o ocrli o: o O 3(J0 400 500 600 700 .(nm ) 2HD HO 0, fle° \CH3 CH3 .-- f\j-)--1 913 -N/Idt-N Kt. / 2 CL /CH2 H I N-- CH3 / Y 642 CH3 \c=cfi 016E133 0 H30.— pmkin Figure 7 The model with two pigments ove the peridinin-chlorophyll a protein . This qualitative diagram shows two types of arrangement of a pair of peridinin molecules at a fixed angle in relation to the molecule of chlorophyll a. UNEDITD î'zr 16 L7: . .; • • 6 extremely high efficiency (100% according to Song et al) . distance between the peridinin and chlorophyll molecules this transfer efficiency by means of equation 2 is 5.8 The effective e.,,pecle.d from R to 6.8 R. Song et al measured the dichroism in circularly polarized light and the polarized light characteristics of this pigment protein, and proposed the arrangement 6 of pigments above (or inside) the protein shown in Figure 7 . Since one protein molecule contains nine peridinin molecules and two chlorophyll a molecules it is thought that the arrangement shown in the Figure is present in sets of two. Such a regular pigment molecule arrangement bonded to a protein may be possible. No such knaNledge has yet been gathered about the fucoxanthin of diatoms. However when fucoxanthin in chloroplasts is compared with that dissolved in organic solvents, the absorption band is said to be displaced by several tens of nanometers to the long wavelength 7 si de . Since displacement of the absorption band to the long wavelength side has been reported for the p -carotene protein complex extracted from higher plants, this fact shows that fucoxanthin bonded to protein in the same way as peridinin may be arranged so as to be close to chlorophyll a The protein complex containing chlorophyll a here present differs from the carotenoids in land plants, and may increase the transfer efficiency of excitation energy. However almost nothing is known about the arrangement 61,e_ on the thylakoid membrane of the pigment proteins containin3 y photosynthesis reaction centres, or about the details of the linking of the pigments to the proteins. For these we must await future studies. Arguing from the presence of peridinin and chlorophyll a proteins one can imagine the relations between the photosynthetic pigments to be as shown in Figure 8. They operate probably in the same way as the chlorophyll a and b proteins in the higher plants and in the green algae. hV hl) CHLOPoPHYLL C PERICI`IN OR FUCO- ^) XANTHiN CHLOROPH LL Figure 8 Photosynthetic pigment relations in dinoflagellates and diatoms CHzOH HO Figure 9 Structure of siphonoxanthin 18 I Green algae have the same photosynthetic pigment composition as the higher plants, and in general the efficiency of utilization of the carotenoid excitation energy is low (see Figure 2 (b) ). However it has recently been found that green algae living in fairly deep places (around la Yn may be- quite different. As Figure 1 (b) shows, the light which penetrates to deep places is restricted to a green region centred around about 510 nm. Investigation of the pigment composition of green algae growing in such places has shown that they contain siphonoxanthin (Figure 9). Figure 10 p8 shows measurements of the absorption spectra of such algae, and also of the fluorescence excitation spectrum of the chlorophyll a which corresponds to the operative photosynthesis spectrum. The absorption spectrum shows the distinctive siphonoxanthin protein band in the neighbourhood of 530 nm, and the same pattern is found in the utilization spectrum. Thus the excitation energy of the siphonoxanthin is efficiently transferred to the chlorophyll a and the photosynthetic quantum yield in green algae is increased. It is a very interesting fact about peridinin, fucoxanthin and siphonoxanthin that in all three there are oxidized carbon atoms outside the ionone rings. Although it is purely speculative, it may be that in the peridinin , chlorophyll a arrangement this structure is geometrically related to the chlorophyll a molecule. Alternatively, it may, for example, easily form a hydrogen bond with the protein. 19 (a) Figure 10 A green algae frond (a) Absorption spectrum (h) Fluorescence excitation spectrum of chlorophyll a . • 400 500 (nm) 600 A: Living at 10 m depth B: v Living at the surface ey . 4" ,:.e e" (-,'-e 0 0 H H il H II -HN-C-C--#----N Ç-C CH2 CH, S Peiv[icle chaill ' (5 HOOC 6=0 Figure 11 Phycoerythrin structure and bonding to protein H 0"N N"0 H H Figure 12 The absorption spectrum in the visible of phycoerythrin from red algae 113' 0 450 500 550 (nm) 600 20 6. Phycoerythrin The characteristic photosynthetic pigment in red algae and blue- green algae, phycoerythrin, differs from chlorophyll and carotenoids, in that it is strongly covalently bonded to protein. The pigment is a cleaved tetrapyrrole porphyrin of the same Yfamily as phycocyanin and allophycocyanin which together are called the phycobili proteins. In light morphogenesis of higher plants the light signal receptor pigment phytochrome is said to belong to the same pigment protein family. The chemical structure of phyco- erythrobiline, in which phycoerythrin is the pigment is shown in Figure 11, and bonds are made to the cystine SH and to the serin OH in the peptide chain. In the red algae, the protein part has a molecular weight of 19500 daltons and consists of two sets of peptides. Three to four protein 8 molecules are bonded to two pigment molecules . Thus one protein molecule is linked to five or six pigment molecules, and the absorption spectrum shows three absorption bands at 500 nm, 540 nm and 565 . nm as shown in Figure 12. This protein is acidic and strongly hydrophilic, and consequently differs greatly in its properties from the chlorophyll protein in the thylakoid membrane. Consequently one must think of the two proteins as present separately on the inside and the outside of the thylakoid membrane. Nevertheless, according to equation (2) they must be sufficiently close together. Electron microscope investigation of the chloroplasts in red algae have shown that phycoerythrin, phycocyanin and allophycocyanin form aggregates of high degree and assume granular structures which are found 9 arranged over the thylakoid membrane (Figure 13) . These granular structures are called phycobilisomes, and phycobilisomes bonded to chlorophyll a have recently been extracted from blue-green algae 10 . It was 21 (0 Y ) Figure 13 ef -.5 % 5_55 r'S, (..., ....) `,....., r-- `, \...) II, I ' 'I' i- - s i .---) r -s l The arrangement of phycobilisomes on • '' ;",; \,_.1,----,2— `,.._.' (--s, •-_ ,'--'', '\--; ■'—', ',---; x ',....,. l' — ‘, (s, — — the thylakoid membranes of red algae I Y (h) (b )( Y (a) Surface Cross-section. The sections - shown are along the lines X and Y in (a) t tt it t: Z7fZZ:t7.12±...MtfZZ Figure 14 Photosynthetic pigment relations in red algae . ' PHYCOCYANIN 1; ( 'Ail° pkycoeyahin 22 I found that chlorophyll a is present at the points of contact between the phycobilisomes and the thylakoid membrane, and that it receives the excitation energy of the phycoerythrin. Consequently the pigment protein p9 outside the thylakoid membrane. in red algae and blue-green algae may be said to operate as an antenna in harvesting light energy. However there is much that is unknown about the arrangement and structure of the pigment proteins in the phycobilisomes or about the way in which the phycobilisomes combine with and there is very little knowledge of the the thylakoid membrane, chlorophyll a arrangement which lies behind the high efficiency of transfer to it of the phycoerythrin excitation energy. Setting up an outline process diagram similar to those given in Figure 4 and in Figure 8 for the operation of photosynthetic pigments such as phycoerythrin results in Figure 14. Characteristic of this case is that the phycobilisome excitation energy is transferred to only a very small number of chlorophyll a. The remaining large number of chlorophyll a cannot distribute this excitation energy to two types of photochemical reaction, and consequently, as can be seen in Figure 3(b), the quantum yield from the light absorbed by the chlorophyll a is lowered. 7. Conclusions This paper has discussed one of the most distinctive features of photosynthesis in the sea by algae, the way in which the photosynthetic pigments match the light energy which penetrates into the sea. In land plants the strongest light energy at about 500 nm is avoided, but algae in the sea have pigment systems which positively and preferentially utilize it. As compared with land plants, algae have an environment in IV 23 ti the sea in which the light energy is extremely low and they possess pigment systems which through long evolutionary stages have been adapted and developed to suit the mode of life in the sea. In writing about photosynthesis in these marine plants, it was originally hoped to discuss them in one or two stages in comparison with land plants. However research into photosynthesis in marine algae lags far behind research on the higher plants. As has already been stated chemical information is particularly lacking even for the photosynthesis systems about which most is known. To some extent this may be due to the author's incapacity but for the moment' we must wait for future studies. This is because the photosynthetic organisms in the sea, the algae and particularly the plankton algae, are difficult to procure. A normal prerequisite for studies with physiological or biochemical objectives is the procurement of considerable quantities of algae or of algal cells. This makE8the artificial rearing of the marine Considering only the phenomenon of photosynthesis, the algae necessary. in Hie- pasb objects usedYhave been land or land water plants, but the algae living in the sea have quite different properties. Some as yet unknown distinctive features such as the photosynthetic production discussed in this paper are probably still hidden from us. In order to bring them to light, artificial means of rearing algae have become essential, and we feel it our duty to promote this in the planning of marine biology. 24 References L_ 1) T. Ftirster, "Comprehensive Biochemistry," cd. by M. Florkin, E. II, Stotz, Vol. 22, p. 61, Elsevier, Amsterdam (1967). 2) R. Hill, F. Benda11, Nature, 186, 136 (1960). 3) W. L. Butler, M. Kitajima, Proc. IIIrd Internatl. Congr. Photosynthesis, ed. by M. Avron, Vol. 1, p. 13, Elseviar, Amsterdam (1975). 4) J. P. Thornber, Ann. Rev. Plant Physiol., 26, 127 (1975). 5) F. T. Haxo, J. H. Kycia, G. F. Somers, A. Bennett, H. W. Siegelman, Plant Physiol., 57, 297. (1976). 6) P.-S. Song, P. Koka, B. B. Prézelin, F. T. Haxo, Biochemistry, 15, 4422 (1976). 7) J. E. Mann, J. Myers, J. Phycol., 4, 349 (1968). 8) A. N. Glazer, G. Cohen-Bazire, Proc. Natl. Acad. Sc j., 68, 1398 (1971). 9) E. Gantt, S. F. Conti, J. Cell Biol., 29, 423 (1966). 10) M. Mimuro, Y. Fujita, "Photosynthetic Organlles," cd. by S. Miyachi et al., p. 23, JSPP Kyoto (1977).