Green Light Drives CO2 Fixation Deep within Leaves

Maximal ^l4CO₂-fixation in spinach occurs in the middle of thepalisade mesophyll [Nishio et al. (1993) Plant Cell 5: 953],however, ninety percent of the blue and red light is attenuatedin the upper twenty percent of a spinach leaf [Cui et al. (1991)Plant Cell Environ. 14: 493]. In this report, we showed thatgreen light drives ¹⁴CO₂-fixation deep within spinach leavescompared to red and blue light. Blue light caused fixation mainlyin the palisade mesophyll of the leaf, whereas red light drovefixation slightly deeper into the leaf than did blue light.¹⁴CO₂-fixation measured under green light resulted in less fixationin the upper epidermal layer (guard cells) and upper most palisademesophyll compared to red and blue light, but led to more fixationdeeper in the leaf than that caused by either red or blue light.Saturating white, red, or green light resulted in similar maximal¹⁴CO₂-fixation rates, whereas under the highest irradiance ofblue light given, carbon fixation was not saturated, but itasymptotically approached the maximal ¹⁴CO₂-fixation rates attainedunder the other types of light. The importance of green lightin photosynthesis is discussed. ¹Supported in part by grants from Competitive Research GrantsOffice, U.S. Department of Agriculture (Nos. 91-37100-6672 and93-37100-8855).     

Responses of Stomata to IAA and Fusicoccin at the Opposite Phases of an Entrained Rhythm

The stomata of Commelma communis showed reduced opening responsesto light and low CO₂ concentrations during the night phase oftheir entrained circadian rhythm. Increased supplies of potassiumions, and treatments with indol-3-ylacetic acid and fusicoccin,failed to promote opening during the night phase to a levelequivalent to that in the day phase. The inability of fusiccocinto overcome the suppression of opening during the night phasecontrasts with its ability to counteract the closure inducedby agents such as CO₂, darkness and abscisic acid. It is concludedthat there are at least two basic mechanisms by which the turgorof guard cells can be regulated, one which is susceptible tooverriding control by fusicoccin and another which is unaffectedby fusicoccin. Several previous studies had shown a positive correlation betweenmalate in the epidermis (mainly located in guard cells) andstomatal opening. In the present experiments the aperture/malatecorrelation was broken in epidermis treated with fusicoccinduring the night phase of the rhythm. The amount of malate presentexceeded that associated with the same stomatal aperture inthe day phase. Possible explanations are (1) that fusicoccinstimulates similar proton fluxes out of the guard cells duringboth phases of the rhythm, but an unknown factor imposes a restrictionon stomatal opening during the night phase; (2) that there arelower proton fluxes in the night phase (limited, for example,by a reduced supply of ATP) but chloride availability or transportis reduced to an even greater extent so that a larger productionof malate in the guard cells is required. Key words: Stomata, IAA, Fusicoccin, Rhythms     

The Comparative Effects of Blue and Red Light on the Stomata of Allium cepa L. and Xanthium pennsylvanicum

Stomatal responses to blue and red light were compared in leavesof Xanthium pennsylvanicum (which contain starch in their guardcells) and in onion leaves (which are devoid of starch). Bluelight was found to be more effective than red in opening stomatain both species. However, a significant difference in the ratiosof blue to red light required to produce equal stomatal openingwas found between Xanthium pennsylvanicum and onion. It is concludedthat blue light may promote stomatal opening by its effect onenzymes controlling the starch and soluble polysaccharide contentof guard cells.     

Differential Stimulation of PEP-carboxylation in Guard Cells and Mesophyll Cells by Ammonium or Fusicoccin

Dark CO₂-fixation in guard cells of Vicia faba was much moresensitive to ammonium than in mesophyll cells. Addition of ammonium(5.0 mol m^–3; pH₀ 7.6) caused up to a 7-fold increasein dark CO₂-fixation rates in guard cell protoplasts (GCP),whereas in leaf slices, mesophyll cells, and mesophyll protoplaststhe increase was only about 1.4-fold. In both cell or tissuetypes, total CO₂-fixation rates were higher in the light (2–12-foldhigher in GCP and 28-fold in mesophyll); these rates were onlyslightly changed by ammonium treatment. However, separationof ¹⁴C-labelled products after fixation of CO₂ in the lightby GCP revealed a large ammonium-induced shift in carbon flowfrom starch and sugars to typical products of C₄-metabolism(mainly malate and aspartate). In contrast, in mesophyll cellsamino acid and malate labelling was only moderately increasedby ammonium at the expense of sucrose. The data suggest thatin vivo ammonium might facilitate stomatal opening and/or delaystomatal closing through an increased production of organicacids. Key words: PEP-carboxylation, guard cell protoplasts, ammonium, fusicoccin     

Effects of Light Quality on Formation of 5-Aminolevulinic Acid, Phycoerythrin and Chlorophyll in Cryptomonas sp. Cells Collected from the Subsurface Chlorophyll Layer

Phycoerythrin obtained from the cells of Cryptomonas sp. (Cryptophyceae)which had been isolated from the subsurface chlorophyll layerin the western Pacific Ocean showed peaks in absorption andfluorescence spectra at 545 and 586 nm, respectively. The rateof photosynthetic O₂ evolution under green light was higherthan those under blue and red light. The rate of 5-aminolevulinic acid (ALA) accumulation in thepresence of levulinic acid was higher under green light thanunder blue and red light. The effects of light quality on therates of O₂ evolution and ALA formation closely resembled eachother. On the other hand, the formation of phycoerythrin andALA was suppressed during growth under blue light. Possible effects of light quality on the formation of photosyntheticpigments in Cryptomonas sp. were discussed. (Received January 31, 1984; Accepted May 14, 1984)     

Carbon Dioxide Fixation by Guard Cell Protoplasts of Commelina communis

Biochemical studies of epidermal tissue may not reflect metabolismof the guard cells which represent less than 5% of the tissuevolume. Pure samples of guard cell protoplasts of Commelinacommunis were therefore used to investigate CO₂ fixation ratesand ¹⁴C-labelling patterns of metabolites in the light and thedark. Qualitatively, results were similar in most respects tothose obtained in a previous study (Schnabl, 1980) for guardcell protoplasts of Vicia faba. CO₂ fixation rates by guardcell protoplasts of C. communis were the same in the light andthe dark but about 50 times lower than the values Schnabl obtainedfor V.faba. The ¹⁴C-labelling pattern of metabolites in C. communiswas also similar in the light and the dark: over 60% of thetotal fixed was in malate with only 1% in sugar phosphates.Label was also detected in starch, aspartate, glutamate andcitrate but not in glycollate as previously recorded in V. fabaguard cell protoplasts. The results confirm the view that the reductive pentose phosphatepathway does not occur in guard cells of C. communis. Key words: CO₂ fixation, Guard cell protoplasts, Stomata     

Stomatal Opening in Light of Different Wavelengths: Effects of Blue Light Independent of Carbon Dioxide Concentration

Stomatal opening in Xanthium pennsylvanicum was found to besignificantly greater in blue light than in red. Experimentsin which leaves were placed in a closed system and allowed toestablish their own steady-state carbon dioxide concentrationshowed that when the CO₂ concentration was about the same asthat in red, opening was much greater in blue light. Blue lightof low intensity could cause as great an opening as red of higherintensity, even though the CO₂ concentration was much higherin blue. Stomatal opening in light is considered as involvingat least two reactions: (1) a response to the removal of CO₂by photosynthesis; (2) a response to blue light not dependenton the removal of CO₂. Blue light became increasingly effective, relative to red, asthe length of night was increased over the range 2 to 14 hours.This might, in part, explain previously observed effects ofnight length on rate of opening in light. The initial very rapid phase of closure in darkness appearedto be independent of CO₂ accumulation, for it was not preventedby flushing the intercellular spaces with air free of CO₂. Itis suggested that closure in darkness, like opening in light,should be considered as involving components both dependentupon, and independent of, CO₂ concentration.     

Effects of dark preincubation and chloramphenicol on blue light-induced CO2 incorporation in Chlorella cells

Chlorella cells incubated in the dark longer than 12 hr showedpronounced blue light-induced ¹⁴CO₂ fixation into aspartate,glutamate, malate and fumarate (blue light effect), whereasthose kept under continuous light showed only a slight bluelight effect, if any. 2) During dark incubation of Chlorellacells, phosphoenolpyruvate carboxylase activity and the capacityfor dark ¹⁴CO₂ fixation decreased significantly, whereas ribulose-1,5-diphosphatecarboxylase activity and the capacity for photosynthetic ¹⁴CO₂fixation (measured under illumination of white light at a highlight intensity) did not decrease. 3) In cells preincubatedin the dark, intracellular levels of phosphoenolpyruvate and3-phosphoglycerate determined during illumination with bluelight were practically equal to levels determined during illuminationwith red light. 4) The blue light effect was not observed incells incubated widi chloramphenicol, indicating that blue light-inducedprotein synthesis is involved in the mechanism of the effect. (Received April 9, 1971; )     

Phytochrome and blue light-mediated stomatal opening in the orchid,paphiopedilum

Guard cells of the orchid genus, Paphiopedilum have been reported to lack developed chloroplasts and detectable chlorophyll a autofluorescence. Paphiopedilum stomata lack a photosynthesis-dependent opening response but have a blue light-specific opening. The present study found that low fluence rate green and red light elicited stomatal opening in Paphiopedilum and this opening was reversed by far red light, indicating the presence of a phytochrome-mediated opening response. Phytochrome-dependent, red light-stimulated opening was largest under low fluence rates and decreased to near zero as fluence rate increased. A recently discovered green light reversibility of blue light-specific stomatal opening was used to probe the properties of the blue light response in Paphiopedilum stomata. Blue light-stimulated opening was completely reversed by green light in the presence of far red light. Red light enhanced the blue light response of Paphiopedilum guard cells when given as a pretreatment or together with blue light. Analysis of guard cell pigments showed that guard cells have small amounts of chlorophyll a and b, zeaxanthin, violaxanthin, antheraxanthin and lutein. Zeaxanthin content increased in response to blue light or ascorbate and declined in the dark or under illumination in the presence of dithiothreitol, indicating the presence of an active xanthophyll cycle. Thus Paphiopedilum stomata possess both a blue light-mediated opening response with characteristics similar to species with normal chloroplast development and a novel phytochrome-mediated opening response.     

Effects of Light Quality on Photosynthetic Carbon Metabolism in C4 and C3 Plants: Rapid Movements of Photosynthetic Intermediates Between Mesophyll and Bundle Sheath Cells

The influence of varying light intensity and quality on thecarbon labelling patterns in Rumex vesicarius (a C₃ plant),Setaria italica (a malate-formingC₄ plant), and Amaranthus paniculatus(an aspartate-forming C₄ plant) was studied. In A. paniculatusand B. vesicarius blue light decreased the transfer of radioactivityto sugars and starch but in S. italica only slightly decreasedradioactivity in sugar phosphates, sucrose, and insolubles.Negligible transfer was observed from the C₄ acids to sugarphosphates, sucrose, and starch under dim blue-green and blue-yellowlights in S. italica and A. paniculatus. Blue light favouredthe formation of malate, aspartate, and alanine in all threeplants. The differential effect of blue and red light suggesteda variation in the mechanisms of C₄-photosynthesis in Setariaand Amaranthus. Leaves of S. italica and A. paniculatus were allowed to photosynthesizein ¹⁴CO₂ for 5 s and then the distribution of the labelled productsbetween the mesophyll and the bundle sheath cells was determinedduring subsequent photosynthesis in ¹²CO₂. Malate and aspartatewhich appeared initially in the mesophyll layer moved rapidlyinto the bundle sheath cells. Phosphoglyceric acid originatingin the bundle sheath moved swiftly to the mesophyll layer. Sugarphosphates were recovered from both the mesophyll and the bundlesheath cells. Most of the starch was found in the bundle sheathcells while sucrose and alanine were localized in the mesophyllcells.     

Sugar and Organic Acid Accumulation in Guard Cells of Vicia faba in Response to Red and Blue Light

Changes in neutral sugar and organic acid content of guard cells were quantitated by high-performance liquid chromatography during stomatal opening in different light qualities. Sonicated Vicia faba epidermal peels were irradiated with 10 [mu]mol m-2 s-1 of blue light, a fluence rate insufficient for the activation of guard cell photosynthesis, or 125 [mu]mol m-2 s-1 of red light, in the presence of 1 mM KCl, 0.1 mM CaCl2. The low-fluence-rate blue light stimulated an average net stomatal opening of 4.7 [mu]m in 2 h, whereas the saturating fluence rate of red light stimulated an average net opening of 3.8 [mu]m in 2 h. Under blue light, the malate content of guard cells increased to 173% of the initial level during the first 30 min of opening and declined as opening continued. Sucrose levels continuously rose throughout the blue light-stimulated opening, reaching 215% of the initial level after 2 h. The starch hydrolysis products maltose and maltotriose remained elevated at all times. Under red light, guard cells showed very little increase in organic acid or maltose levels, whereas sucrose levels increased to 208% of the initial level after 2 h. Total measured organic metabolite concentrations were correlated with stomatal apertures in all cases except where substantial malate increases occurred. These results support the hypothesis that light quality modulates alternative mechanisms of osmotic accumulation in guard cells, including potassium uptake, photosynthetic sugar production, and starch breakdown.     

Studies on the Mechanisms of Action of the Antitranspirant Phenylmercuric Acetate, and its Penetration into the Mesophyll

Experiments have examined the effect of phenylmercuric acetate(PMA) on the guard cells of Commelina communis. In one series,PMA was supplied to the leaf surface; after different time intervalsthe epidermis was removed and the ability of the stomata toopen was determined. In the other series, different concentrationsof PMA were included in the medium used for inccubating epidermalstrips with which ion-stimulated stomatal opening was assayed.At concentrations of 10^-54 M and above the effect of PMA wassevere and the structural integrity of the guard cells was affected;they were unable to accumulate neutral red. At concentrationsarpound 10^-6 M the guard cells were less affected and PMA broughtabout a transient stimulation of stomatal opening by releasingsubsidiary-cell turgor pressure. A solution of 5 x 10^-4 M PMA applied to leaves reduced by halfthe photosynthetic ¹⁴CO₂ incorporation into C. communis mesophyll.In Zea mays it increased the CO₂ compensation point and alsothe resistance to diffusion in the gas phase (R_A, but therewas a proportionately greater increase in the apparent liquidphase resistance (R_t). This direct inhibition of mesophyll photosynthesisundermines one of the major objectives of applying anatitranspirants,and for this reason it is suggested that PMA is unsuitable forgeneral application to crops.     

Guard Cell Metabolism in Epidermis of Commelina communis L. During Stomatal Opening and Closing

The rates of CO² incorporation into the epidermis of C. communiswere linear and were similar during the completion of opening(2 h) and closing (1 h) movements of stomata. The kinetics of¹⁴C turnover between metabolites and the rates of ‘leakage’of metabolites were determined for opening and closing movements.When stomata were opening there was a slow turnover of ¹⁴C frommalate chiefly into sugars. Upon stomatal closure ¹⁴C was initiallymainly in sugars, malate, and sugar phosphates. Thereafter,there was a slight loss of label from sugar phosphates witha corresponding increase in malate. Starch became labelled duringopening and closing movements. Rates of incorporation of CO₂found in the ‘leakage’ fraction were greatest whenstomata were opening. Of the labelled compounds Most‘from the tissue, malate was the most highly labelled whetherstomata were opening or closing. Although interpretation of the turnover patterns is difficultwithout knowledge of pool sizes for the metabolites it is suggestedthat a pool of sugars exists within the guard cells, which havefairly direct and reversible access to carbon from starch andmalate. The implications of loss of malate from guard cellsduring stomatal opening and closing are discussed.     

Induction of CAM in Mesembryanthemum crystallinum Abolishes the Stomatal Response to Blue Light and Light-Dependent Zeaxanthin Formation in Guard Cell Chloroplasts

Facultative CAM plants such as Mesembryanthemum crystallinum(ice plant) possess C3 metabolism when unstressed but developCAM under water or salt stress. When ice plants shift from C3metabolism to CAM, their stomata remain closed during the dayand open at night. Recent studies have shown that the stomatalresponse of ice plants in the C3 mode depends solely on theguard cell response to blue light. Recent evidence for a possiblerole of the xanthophyll, zeaxanthin in blue light photoreceptionof guard cells led to the question of whether changes in theregulation of the xanthophyll cycle in guard cells parallelthe shift from diurnal to nocturnal stomatal opening associatedwith CAM induction. In the present study, light-dependent stomatalopening and the operation of the xanthophyll cycle were characterizedin guard cells isolated from ice plants shifting from C3 metabolismto CAM. Stomata in epidermis detached from leaves with C3 metabolismopened in response to white light and blue light, but they didnot open in response to red light. Guard cells from these leavesshowed light-dependent conversion of violaxan-thin to zeaxanthin.Induction of CAM by NaCI abolished both white light- and bluelight-stimulated stomatal opening and light-dependent zeaxanthinformation. When guard cells isolated from leaves with CAM weretreated with 100 mM ascorbate, pH 5.0 for 1 h in darkness, guardcell zeaxanthin content increased at rates equal to or higherthan those stimulated by light in guard cells from leaves inthe C3 mode. The ascorbate effect indicates that chloroplastsin guard cells from leaves with CAM retain their competenceto operate the xanthophyll cycle, but that zeaxanthin formationdoes not take place in the light. The data suggest that inhibitionof light-dependent zeaxanthin formation in guard cells mightbe one of the regulatory steps mediating the shift from diurnalto nocturnal stomatal opening typical of plants with CAM. (Received July 5, 1996; Accepted December 12, 1996)     

Tentoxin Suppresses Stomatal Opening by Inhibiting Photophosphorylation

Tentoxin and, to a lesser extent, dihydrotentoxin (both at 10mmol m^–3) reduce stomatal opening in epidermal stripsof Commelina communis in the light but not in darkness. Thiseffect was significantly greater in normal air than in CO₂-freeair. Fusicoccin overcame the tentoxin effect. However, tentoxindid not inhibit stomatal opening in the light in epidermal stripsof Paphiopedilum harrisianum, a species which lacks guard cellchloroplasts. It is concluded that tentoxin exerts its actionon stomata not by an ionophorous effect in the plasmalemma ofguard cells but by the inhibition of photophosphorylation intheir chloroplasts. The effects of DCMU and tentoxin on guardcells are discussed in terms of their effects on chloroplastsand the extent to which energy is supplied from this organelleduring stomatal opening in the light. The results indicate thatneither photophosphorylation nor non-cyclic electron transportin guard cell chloroplasts are essential for stomatal opening. Key words: Commelina, epidermal strips, Paphiopedilum, photophosphorylation, stomata, tentoxin     

Some Biochemical Characteristics of Guard Cell and Mesophyll Cell Protoplasts from Commelina communis L.

Guard cell and mesophyll cell protoplasts of Commelina communisL., were isolated and used to investigate their various biochemicalcharacteristics. Contamination of the samples by other celltypes was very low and viability of the protoplasts, assessedby the use of neutral red, Evans blue and fluorescein diacetate,was high (89–98%). Mesophyll cell protoplasts containedmore chlorophyll (x 47), more soluble protein (x 10), more totalN (x 36) and more DNA (x 9) than guard cell protoplasts. Theabsorption spectra of protoplast extracts were similar for bothcell types except that below 400 nm there was a large increasein absorption by the guard cell protoplast extract. In guardcell protoplast extracts, high levels of activity of phosphoenolpyruvatecarboxylase (E.C. 4.1.1.31 [EC] ), NAD malate dehydrogenase (E.C.1.1,1.37), NADP malic enzyme (E.C. 1.1.1.40 [EC] ) and carbonic anhydrase(E.C. 4.2.1.1 [EC] ) were detected while only low levels of pyruvate-orthophosphatedikinase (E.C. 2.7.9.1 [EC] ) activity were detected. Glycollate oxidase(E.C. 1.1.3.1 [EC] ), ribulose-l,5-bisphosphate carboxylase (E.C 4.1.1.39 [EC] ),NADP malate dehydrogenase (E.C. 1.1.1.82 [EC] ) and NAD malic enzyme(E.C. 1.1.1.39 [EC] ) were not detected in guard cell protoplast extracts.High levels of ribulose-1, 5-bisphosphate carboxylase, glycollateoxidase, NAD malate dehydrogenase and carbonic anhydrase weredetected in mesophyll cell protoplast extracts which is typicalof C₃ plants. A pathway of carbon flow during stomatal openingand closing is proposed. Key words: Carbon metabolism, Commelina communis, guard cell protoplasts, mesophyll cell protoplasts, stomata     

Stomatal Responses to Two Herbicidal Auxins

The effects of 1-naphthylacetic acid (NAA) and 2-naphthoxyaceticacid (NOXA) on stomatal opening on illumination of excised,turgid leaves of Stachytarpheta indica were investigated bymicroscopic examination of abaxial epidermises fixed in absoluteethanol. Both chemicals were effective in restricting, but notcompletely preventing, stomatal opening and suppressing starchhydrolysis and potassium accumulation in the guard cells. Therepressive effects were only partly reversed by CO₂-free air.It is concluded that NAA and NOXA do not greatly affect passiveopening mediated by changes in the leaf water balance, but partlysupress photoactive opening by arresting starch hydrolysis andpotassium accumulation in the guard cells and partly by disturbingthe intercellular CO₂ concentration. A possible link betweenstarch hydrolysis and potassium accumulation in the guard cellsis briefly mentioned.     

Change in Levels of Starch and Sugars in Epidermis of Commelina benghalensis during Fusicoccin Stimulated Stomatal Opening

The concentrations of malate, starch and sugars were determinedin presonicated epidermal strips of Commelina benghalensis.During opening, the starch content of epidermis decreased whilethe level of sugars or malate increased. Fusicoccin (FC) stimulatedstomatal opening and elevated the levels of malate and sugars.However, the contribution from sugars was nearly 50% of theosmotic effect of malate and it increased to more than 60% inthe presence of FC. We conclude that FC stimulates stomatalopening by enhancing not only potassium influx into guard cellsbut also hydrolysis of starch into sugars (and malate). Significantcorrelations were noticed between the width of stomatal apertureand epidermal starch (negative), malate and sugars (both positive).The negative relationship between starch and malate or sugarswithin epidermis indicated that starch hydrolysis lead to formationof sugars as well as malate. Starch—sugar interconversioncan therefore play a significant role in modulating the solutepotential of guard cells. Key words: Commelina benghalensis, Stomatal opening, Fusicoccin, Epidermal starch and sugars     

Functional Stomata in a Variegated Leaf Chimera of Pelargonium zonale L. without Guard Cell Chloroplasts

Fluorescence microscopy indicated that chlorophyll was absentfrom epidermal and guard cells overlying all white areas andgreen areas (of certain leaves) in variegated leaves of Pelargoniumzonale, cv. Chelsea Gem. Stomata with chlorophyll-free guardcells, in general, responded normally to light and CO₂ as gaugedby direct measurements of stomatal aperture and by transpirationalwater loss studies, although stomata from white regions of variegatedleaves were more reluctant to open than stomata from green regionsof the leaves. Thus, functional stomata without guard cell chloroplastshave been discovered in another genus, namely Pelargonium, besidesthat originally discovered in Paphiopedilum. When stomata withchlorophyll-free guard cells opened, K⁺ accumulated in the guardcells. This indicates that chloroplasts are not essential forthe normal functioning of stomata and that the energy sourcefor driving stomatal movements can come from sources other thanphotophosphorylation. Key words: Guard cell chloroplasts, Leaf chimera, Pelargonium, Stomata     

Wavelength effects on photosynthetic carbon metabolism in Chlorella

To study the wavelength-effect on photosynthetic carbon metabolism,¹⁴C-bicarbon-ate was added to Chlorella vulgaris 1 lh suspensionunder monochromatic blue (456 nm) and red (660 nm) light. Thelight intensities were so adjusted that the rates of ¹⁴CO₂ fixationunder blue and red light were practically equal. Analysis of¹⁴C-fixation products revealed that the rates of ¹⁴CO₂ incorporationinto sucrose and starch were greater under red light than underblue light, while blue light specifically enhanced ¹⁴CO₂ incorporationinto alanine, aspartate, glutamate, glutamine, malate, citrate,lipid fraction and alcohol-water insoluble non-carbohydratefraction. Pretreatment of the algal cells in phosphate mediumin the dark, which was essential for the blue light enhancementof PEP carboxylase activity, was not necessary to induce theabove wavelength effects. Superimposition of monochromatic bluelight at low intensity (450 erg.cm^–2.sec^–1) on thered light at saturating intensity caused a significant decreasein the rate of ¹⁴CO₂ incorporation into sucrose and increasein incorporation into alanine, lipid-fraction, aspartate andother related compounds, indicating that the path of carbonin photosynthesis is regulated by short wavelengdi light ofvery low intensity. Possible effects of wavelength regulationof photosynthetic carbon metabolism in algal cells are discussed. ¹ Part of this investigation was reported at the XII InternationalBotanical Congress, Leningrad, 1975 and the Japan-US CooperativeScience Seminar "Biological Solar Energy Conversion", Miami,1976. Requests for reprints should be addressed to S. Miyachi,Radioisotope Centre, University of Tokyo, Bunkyo-ku, Tokyo 113,Japan. ⁴ Present address: Department of Chemistry, Faculty of PharmaceuticalSciences, Teikyo Univ., Sagamiko, Kanagawa, Japan. (Received August 6, 1977; )