CHANGES IN LEVELS OF PYRIDINE NUCLEOTIDES IN CHLORELLA CELLS DURING THE COURSE OF PHOTOSYNTHESIS

1. Using intact cells of Chlorella, the effects of CO₂ on thelevelsof oxidized and reduced forms of DPN and TPN in the lightandin the dark were investigated.
2. It was found that the light-inducedchanges of the DPNH-levelwere not affected by the presenceor absence of CO₂. On theother hand, the light-induced increaseof TPNH was suppressedin the presence of CO₂ and the levelof TPNH which was raisedon illumination in the absence of CO₂was lowered by the provisionof CO₂.
3. On the basis of thesefindings, it was concluded that TPNH,but not DPNH, is participating,in some way, in the mechanismof photosynthesis.
4. Discussionswere made on the difference in the sites of participationofTPNH and of the photogenic reducing agent (R) in the pathofcarbon in photosynthesis.

(Received February 28, 1960; )     

STUDIES ON THE METABOLISM OF A SULFUR-OXIDIZING BACTERIUM II. THE SYSTEM OF CO2-FIXATION IN THIOBAC1LLUS THIOOXIDANS

1. In the early stage of CO₂-fixation by Thiobacillus thiooxidans,which was incubated aerobically in the presence of sulfur, mostpart of the fixed carbon was found in the phosphate ester fraction.
2. The fixation was inhibited by NaF, picolinic acid, PCMB, azide,dipyridyl, o-phenanthroline, monoiodoacetic acid, and arsenite,each in the concentration range where the sulfur oxidation wasnot affected strongly.
3. The crude extract of this organismcould fix CO₂ in the presenceof ATP, R-5-P and Mg⁺⁺. Most partof the fixed carbon was foundin PGA.
4. The crude extract showedthe CO₂-fixation coupled with the H₂S-oxidationin the presenceof ADP.
5. An appreciable reduction of PGA could not be detectedin thepresence of reducing systems, involving TPNH and DPNH.

(Received March 6, 1962; )     

STUDIES ON THE PATHWAY OF SULFIDE PRODUCTION IN A COPPER-ADAPTED YEAST

Metabolism of some sulfur-containing substances was studiedin a copper-resistant strain of yeast (R), its parent strain(P) and respiratory-deficient(RD) mutants from them. The resultsobtained are as follows:

1. Using sulfate, sulfite and thiosulfate as sulfur sources, Rproducedmore H₂S than P, and both of these had the activityhigher than their RD mutants. All of them produced a large amountof H₂S from cysteine, but only little from methionine, cysteinesulfinic acid and S-sulfocysteine.
2. From sulfite and thiosulfate,P and R produced more H₂S inaerobicthan in anaerobic condition.With sulfate and cysteine, however,H₂S production did not differunder those conditions.
3. In both P and R, the sulfate-to-sulfiteand sulfite-to-sulfidereactions were remarkably lowered byiron and zinc deficiencies.But the cysteine-to-sulfide reactionwas not affected by themetal-deficiencies.
4. H₂S productionfrom sulfate was remarkably depressed by highconcentrationsof pantothenate.
5. Rates of reaction steps on a plausible pathway from sulfatetosulfide and to organic sulfur compounds areestimated forthe strainsused. R is characterized by its largecapacity ofthe reaction step from sulfate to sulfite, and excessivesulfitethus formed is liberatedas sulfide not by the way ofcysteine.

¹Present address: Research Reactor Institute, Kyoto University,Kumatori-cho, Sennan-gun, Osaka     

STUDIES ON THE MECHANISM OF GROWTH INHIBITING EFFECT OF LIGHT

1. A substance which inhibits indoleacetic acid (IAA)-and naphthaleneaceticacid (NAA)-induced elongation of Avena coleoptile section andIAA-induced Avena coleoptile curvature was found in an ethersoluble neutral fraction of water extract of sunflower leavesand in agar blocks containing the diffusate from young sunflowerleaves.
2. This substance also inhibits the growth of isolatedsunflowerepicotyl.
3. The R_f value (0.9) of the substance ona paper chromatogramdeveloped with ammoniacal iso-propanolindicates that it isidentical with the inhibitor reported byAUDUS et al. (1956),but not with inhibitor-ß.
4. Theinhibitor can be transported from leaf to stem, and thetransportseems to be accelerated by illuminating the leaf.
5. The auxindiffused from sunflower leaf into agar block may beidenticalwith IAA.
6. A substance, which has the same properties as theinhibitorfrom sunflower leaf, was obtained in crystalline formfrom theleaf of Jerusalem artichoke.
7. The mechanism of growthinhibition caused by this crystallinesubstance seems to involveinactivation of a sulfhydryl group.
8. The reason why the stemgrowth of sunflower seedlings is reducedby strong light isdiscussed: the amount of the inhibitor transportedfrom leafto stem is increased under strong light, and in thestem, growthinhibition is caused by a direct effect of thisinhibitor ongrowth and by its inhibiting effect on the transportof IAAfrom leaf to stem.

¹ Present address: Botanical Garden, Faculty of Science, Universityof Tokyo, Tokyo (Received February 15, 1961; )     

CHANGES IN RESTING POTENTIAL AND ION ABSORPTION INDUCED BY LIGHT IN A SINGLE PLANT CELL

1. Effect of light on ion absorption and resting potential of theinternodal cell of Nitella flexilis was investigated under variousconditions.
2. On illumination, the resting potential increasedby about 30mVin 10^–4 M KCl and by about 60 mV in 10^–4M NaClsolution. A similar photoelectric response was also observedin 10^–3 M KCl, 10^–2 M CaCl₂ and 5 x 10^–2 MCaCl₂ solutions, but not at all in 10^–2 M KCl solution.
3. Absorption of ions by the cell took place in parallel withthelight-induced change in resting potential.
4. Red and bluelights were very effective in increasing the restingpotential,while green light was almost ineffective. These differenteffectsof color lights were in good agreement with their effectsinincreasing the osmotic value of the cell.
5. The photoelectricresponse was not affected by phenylurethane,which, on the otherhand, strongly inhibited the light-inducedion absorption.
6. Theuptake of ions by the cell from the external medium intothevacuole is assumed to proceed in two different steps: thefirstis the process involving the ion movements across theoutermostplasmalemma, and the second is that involved in thetransportof ions through the cytoplasmic layer and tonoplast.The formerprocess is considered to be influenced by the increasein restingpotential probably caused by the light absorbed bychlorophyll.The process was, however, suggested to be independentof photosynthesis.On the other hand, the latter process issupposed to be relatedto photosynthesis. A discussion was madealong this line.

(Received July 26, 1962; )     

COMPONENTS OF THE ELECTRON-TRANSFERRING SYSTEM IN ACETOBACTER SUBOXYDANS AND RECONSTRUCTION OF THE LACTATE OXIDATION SYSTEM

1. Cytochromes a₁⁵⁹⁰, b⁵⁶⁰, c₁⁵⁵⁴ and c₁⁵⁵² were isolated andpurifiedfrom a strain of Acetobacter suboxydans. The proceduresusedwere described in detail.
2. The main cytochrome band at550-560 mµ in intact cellssplitted at liquid air temperatureinto two bands, 551 mµ(strong) and 559 mµ (weak).
3. Optical and physiological properties of the four cytochromeswere investigated. Lactic dehydrogenase activity was found tobe associated with cytochrome c₁⁵⁵⁴. The two c₁-type cytochromes,especially cytochrome c₁⁵⁵⁴, persisted in their reduced formafter the purification through many steps.
4. By some combinationsof isolated components reconstruction ofthe oxygen uptake systemcould be realized.
5. The oxygen-consuming activity of purifiedoxidase preparationswas accelerated by a-tocopherol but notby Emasoll 4130 andTween 80.
6. Some discussions were made onthe nature of terminal oxidase,the role of cytochrome c₁⁵⁵²in the electron-transport system,and persistence of reducedstate of c₁-type cytochromes.
7. A possible scheme of the electron-transferringsystem of Acetobactersuboxydans was presented.

(Received May 16, 1960; )     

Biological activity of phyllosinol, a phytotoxic compound isolated from a culture filtrate of Phyllosticta sp.

1. Phyllosinol is a phytotoxic metabolite of Phyllosticta sp. Thissubstance at 100 µg/ml produced dark grey necrotic lesionson the leaf of red clover. Sensitivities of various plant speciesto phyllosinol differed both quantitatively and qualitatively.
2. Phyllosinol reduced root growth in rice seedlings by 60% at10^–4 M, whereas stimulation of root elongation occurredat a concentration range from 10^–9 to 10^–5 M.
3. Phyllosinolat 2.5x10^–4M promoted adventitious root formationin epicotylsof Azukia cuttings by about 100%. Promotion waspartly reducedby simultaneous application of cysteine.
4. IAA-induced elongationof isolated Avena coleoptile sectionswas inhibited by phyllosinolat a concentration range from 10^–5to 10^–3M.
5. Sulfhydrylcompounds, i.e. cysteine and glutathione relievedinhibitioncaused by phyllosinol in IAA-induced elongation ofAvena coleoptilesections.
6. GA₃-induced elongation of wheat leaf sections wasslightly inhibitedby phyllosinol at 10^–4M.
7. Phyllosinolalso has antibiotic activity. Among the organismstested, Phycomycetesand Gram-negative bacteria appeared mostsusceptible to phyllosinol.

(Received April 21, 1970; )     

NITRATE REDUCTASE IN PHOTOSYNTHETIC BACTERIUM, RHODOSPIRILLUM RUBRUM. ADAPTIVE FORMATION OF NITRATE REDUCTASE

1. A method was discovered for adapting the cells of Rhodospirillumrubrum to grow on a nitrate medium, a capacity initially lackingin the organism. The adapted cells were able to grow with nitrateas the sole source of nitrogen. The growth responses of theadapted cells towards various nitrogenous sources were investigatedunder various conditions of incubation (aero- and anaerobiosis,light and dark).
2. The adapted cells were found to have simultaneouslyacquiredthe capacity for reducing nitrite and hydroxylamineas wellas nitrate. The path of nitrogen in the adapted cellswas assumedto be as follows: NO₃^– NO₂^– NH₂OH CellularNitrogen.
3. Nitrate metabolism of the adapted cells was investigatedundervarious conditions. In the light, nitrate was reducedand furtherassimilated, leaving insignificant amounts of nitritein themedium. In this case, consumption of nitrate was markedlyinhibitedby other forms of nitrogen (e.g., nitrite, hydroxylamine,aminoacids and ammonium salts). In the dark, nitrate was reducedas the terminal hydrogen acceptor in the oxidative breakdownof organic substances (e.g., malate) in the medium (i.e., nitraterespiration). More nitrite was accumulated in this case thanin the light. Molecular oxygen inhibited the reduction of, aswell as the growth on, nitrate in any of the above cases.
4. Theeffects on the rate of nitrate reduction (and respiratoryoxygenuptake) caused by various experimental factors (pH, nitrateconcentration, electron donors, and addition of hydroxylamine)were investigated, using the resting cells of the adapted organism.

¹ This paper was submitted to the University of Tokyo to fulfillthe requirement for the author's doctorate. ² Present Address: Botanical Institute, Kyoto University, Sakyo-ku,Kyoto. (Received February 14, 1963; )     

Effects of Osmotic Stress, Ionic Stress and IAA on the Cell-Membrane Resistance of Vigna Hypocotyls

The cell-membrane resistance (R_m) of Vigna hypocotyls was examined,and the effects of osmotic stress, ionic stress and IAA on R_mwere investigated. R_m decreased by 64 to 77% under osmotic stressin the presence of absorbable solutes (40 mM sorbitol, 15 mMKC1, 30 mM sucrose; or 40 mM sorbitol, 15 mM KC1, 30 mM sucroseplus 10^–4 M IAA) or under ionic stress (50 mM NaCl or50 mM KC1). R_m was not changed by perfusion with 10^–4M IAA. Therefore, the hyper-polarizations of the membrane potentialobserved in both cases should be ascribed totally to the activationof the electrogenic proton pump. Although R_m showed an increaseof 1.6 fold when the hypocotyls were subjected to osmotic stress(100 mM sorbitol or 100 mM sorbitol plus 10^–4 M IAA),83.6% or 92.4% of the hyperpolarization of the membrane potential(V_px was also the result of the activation of the pump. Theresults, calculated on the basis of the current source model,support the viewpoint that the hyperpolarization of the cellmembrane potential of Vigna hypocotyls under osmotic stress,ionic stress or in the presence of IAA is an expression of theactivation of the proton pump, and is not caused by an increasein R_m. ¹ Present address: Researchers and Planners of Natural Environment, Yotsugi Bldg. (2F), 1-5-4 Horinouchi, Suginami-Ku, Tokyo,166 Japan ² Present address: Graduate School of Integrated Science, YokohamaCity University, 22-2 Seto, Kanazawa-Ku, Yokohama, 236 Japan (Received February 14, 1991; Accepted July 24, 1991)     

LIGHT-INDUCED OXYGEN EVOLUTION CAUSED BY HYDROGEN PEROXIDE IN CATALASE-INHIBITED CHLORELLA CELLS

1. Chlorella cells and spinach chioroplasts, whose catalase activityhad been more than 90% inhibited by 10^–5 M azide, werefound to decompose H₂O₂ photochemically to liberate oxygen,indicating that H₂O₂ was used as an oxidant of the HILL reaction.
2. That, however, the observed phenomena cannot be fully accountedfor in terms of the HILL reaction with H₂O₂ was revealed bythe observation that an extract of Chiorella cells, which hadbeen completely freed from chlorophyll, also showed a light-acceleratedO2 evolution from H₂O₂ in the presence of 10^–5 M azide.This extract contained a large quantity of catalase, which seemedto have been, in some way, involved in the reaction in question.
3. The catalatic H₂O₂ decomposition caused by crystalline catalaseof mammalian liver (in the presence of 10^–5 M azide) wasnot accelerated by the effect of light.

¹ Present address: Department of Biology, Faculty of Science,Niigata University, Niigata. (Received June 4, 1961; )     

Photophosphorylation in intact algae: Effects of inhibitors, intensity of light, electron acceptor and donors

The luciferin-luciferase method was used to determine ATP extractedfrom darkmaintained and light-exposed samples of the green algaChlorella pyrenoidosa and of the blue-green alga Anacystis nidulans.A few measurements on Synechococcus lividus (a bluegreen thermophile,clone 65?C) are also reported.

1. The light-minus-dark ATP levels (ATP) from aerobic cells ofChlorella and Anacystis were negative; however, ATP from Synechococcuswas positive. Large positive ATP was obtained in regularly grown(RG: moderate light) Chlorella treated with oligomycin; darklevels were reduced, light levels remained essentially unaffected.In high-light exposed (HLE) Chlorella, oligomycin reduced bothlight and dark ATP levels, but positive ATP was still obtained.However, in Anacystis, which has a different organization ofthylakoid membrane, oligomycin severely reduced both the lightand the dark ATP levels and the ATP remained negative.
2. Theoligomycin (12 µM) treated Chlorella and the untreatedAnacystis and Synechococcus show the presence of cyclic photophosphorylationunder conditions in which the non-cyclic electron flow fromphotosystem II to photosystem I is blocked by 10 µM 3-(3,4-dichlorophenyl)-l,l-dimethylurea(DCMU), or not allowed to operate by the absence of CO₂. Cyclicphotophosphorylation ranged from 10–30% of the maximumATP in RG, to 40–50% in HLE Chlorella. In RG Chlorella,cyclic and non-cyclic (in the absence of DCMU) photophosphorylation(ATP) saturate at about 10³ ergs cm^–2 sec^–1 and10⁴ ergs cm^–2 sec^–1 and 10⁴ ergs cm^–2 sec^–1red (>640 nm) light, respectively; a lag was observed inthe light curve.
3. In Chlorella, the addition of the photosystemI electron acceptormethyl viologen (MV; 1 mM) increased ATPby twofold. Furtheraddition of DCMU (25 µm) reduced thisto the level observedwith DCMU alone. If 1 mM reduced dichlorophenolindophenol orphenazine methosulphate (DCPIPH₂ or PMSH₂, respectively)wasadded along with DCMU, the ATP level was 30–40% ofthecontrol. Further addition of MV increased the JATP to be70–80%of that of the control. These and other resultsconfirm thepresence of both non-cyclic and cyclic photophosphorylationin vivo, the former predominating in Chlorella, and the latterin Anacystis and Synechococcus.

(Received May 1, 1973; )     

Coupling of malate decarboxylation to CO2 fixation and the reduction of 3-phosphoglyceric acid in corn bundle sheath cells,2

1. In the presence of NADP⁺ and Mg⁺⁺, the bundle sheath strandsisolated from corn (Zea mays) leaves by cellulase treatmentsdecarboxylated malate in the light at an initial rate (200 µmoles/mgchl.hr), which was sufficient to account for photosyntheticCO₂ fixation in intact leaves. This rate gradually slowed downand then stopped. The final level of the malate decarboxylatedwas approximately equal to the amount of NADP⁺ added.
2. Rapidand continued decarboxylation of malate was observed whenNADP⁺,3-phosphoglyceric acid and ATP (and Mg⁺⁺) were addedtogether.The addition of ADP instead of ATP showed a similareffect.Light did not show any effect on the malate decarboxylationin the presence of ATP or ADP.
3. When malate was added to thebundle sheath strands in the presenceof exogenous NADP⁺ NADP⁺was rapidly reduced. The reductionstopped after 2 min when,73% of the added NADP⁺ was reduced.The further addition of3-phosphoglyceric acid and ATP broughtabout a decrease in theNADPH-level, which rose again to attaina new steady level.
4. The transfer of radioactivity from (1-¹⁴C-3-phosphoglycericacid to dihydroxyacetone phosphate in the bundle sheath strandsin the presence of ATP and NADP⁺ was greatly enhanced by theaddition of malate.
5. In the presence of ribose 5-phosphateand ATP, the rate of ¹⁴C-transferfrom (4-¹⁴C)-malate to theintermediates of the reductive pentosephosphate cycle was equalto that of ¹⁴CO₂ fixation in the light.

All these results support the current view that in the bundlesheath cells of C₄ plants belonging to the NADP-malic enzyme-group,the decarboxylation of malate is coupled to the fixation ofthe released CO₂ and the reduction of 3-phosphoglyceric acidformed as a result of CO₂ fixation. ¹ Part of this research was reported at the 40th Annual Meetingof the Botanical Society of Japan Osaka, December, 1975. ³ Present address: Laboratory of Chemistry, Faculty of Medicine,Teikyo University, 359 Otsuka, Hachioji-City, Tokyo 173, Japan. (Received April 30, 1977; )     

Light-Dependent CO2 Retrieval in Immature Barley Caryopses

Immature detached caryopses from barley (Hordeum vulgare L.var. distichum cv. Midas) were shown to be capable of light-dependentretrieval of internally-produced CO₂. In the first set of experiments,caryopses were radioactively labelled by supplying (U-14C)-sucroseto detached ears in liquid culture. Caryopses were then removedfrom the ear and given a 12 h chase of non-radioactive sucrosein either the light or dark. More ¹⁴C was recovered in the caryopsesafter the chase in the light than in the dark but the differenceswere not significant. In the second set of experiments, ¹⁴C-labelledcaryopses obtained by a 15 min light incubation in ¹⁴CO₂ weremaintained in either the light or dark for 3 h and any redistributionof label between the tissues recorded. The results show thatunder these conditions, photosynthesis in the Chl-containinggreen layer of the pericarp can prevent losses of internally-producedCO₂, since 3 times as much radiocarbon remained in the caryopsesincubated in the light as in the dark. These differences weresignificant at P=0.001. Experiments with the mutant barley Albinolemma, which has no Chi in the pericarp, showed that there waslittle difference between light and dark treatments. This confirmsthe suggestion that photosynthesis in the pericarp of the normalcultivar Midas may be concerned in the refixation of CO₂. Key words: Barley, pericarp, photosynthesis, carbon dioxide     

Studies on the destruction of indole-3-acetic acid by a species of Arthrobacter I. On the induction of the enzyme responsible for the destruction

1. The induction of an IAA-destroying enzyme in Arthrobacter sp.that can utilize IAA as its sole source of carbon and nitrogenwas investigated.
2. 1. The enzyme was most effectively inducedby 10–³ to2x10–³ M IAA, at pH 6.5.
3. 2. All testedIAA analogs were unable to induce the enzyme.Analogs otherthan indole-3-lactic acid were rather inhibitoryon the inductionwith IAA.
4. 3. The induction period was shortened with the ageof culturein both polypeptone and acetate media.
5. 4. Pretreatmentof the bacterium with IAA caused a shorteningof the inductionperiod.
6. 5. The induction was inhibited by various antibiotics,aminoacid analogs and nucleobase analogs.
7. 6. The inductionwas less remarkable in actively proliferatingcells than itwas in slowly proliferating ones.

(Received July 1, 1967; )     

Effects of Nitrogen Nutrition on Photosynthesis in Cd-treated Sunflower Plants

Increased nitrogen supply stimulates plant growth and photosynthesis.Since it was shown that heavy metals may cause deficienciesof essential nutrients in plants the potential reversal of cadmiumtoxicity by increased N nutrition was investigated. The effectson photosynthesis of low Cd (0, 0.5, 2 or 5 mmol m^-3) combinedwith three N treatments (2, 7.5 or 10 mol m^-3) were examinedin young sunflower plants. Chlorophyll fluorescence quenchingparameters were determined at ambient CO₂and at 100 or 800 µmolquanta m^-2 s^-1. The vitality index (R_fd) decreased approx. three-timesin response to 5 mmol m^-3Cd, at 2 and 10 mol m^-3N. The maximumphotochemical efficiency of PSII reaction centres (F_v/ F_m) wasnot influenced by Cd or N treatment. The highest Cd concentrationdecreased quantum efficiency of PSII electron transport (_II)by 30%, at 2 and 10 mol m^-3N, mostly due to increased closureof PSII reaction centres (q_P). Photosynthetic oxygen evolutionrates at saturating CO₂were decreased in plants treated with5 mmol m^-3Cd, at all N concentrations. The results indicatethat Cd treatment affected the ribulose-1,5-bisphosphate (RuBP)regeneration capacity of the Calvin cycle more than other processes.At the same time, the amounts of soluble and ribulose-1,5-bisphosphatecarboxylase/oxygenase (Rubisco) protein increased with Cd treatment.Decreased photosynthesis, but substantially increased Rubiscocontent, in sunflower leaves under Cd stress indicate that asignificant amount of Rubisco protein is not active in photosynthesisand could have another function. It is shown that optimal nitrogennutrition decreases the inhibitory effects of Cd in young sunflowerplants. Copyright 2000 Annals of Botany Company Helianthus annuus L., cadmium, nitrogen, photosynthesis, Rubisco, sunflower     

Microbiological Synthesis of Fat: THE EFFECTS OF NITROGEN LEVEL ON THE METABOLISM OF PENICILLIUM LILACINUM THOM IN A SUCROSE MEDIUM

1. A study has been made of the relationships between the synthesesof carbohydrate, protein, and fat by Penicillium lilacinum Thomin presence of different amounts of sodium nitrate us a definedsucrose salts medium.
2. Under the defined experimental conditionsincreases in the concentrationof NO^–₂ in the medium werefollowed by increases in therates at which nitrogen and sugarwere taken up by the fungus,in the quantities assimilated,and in total and protein nitrogenin the felt. These conditionsprevailed so long as unassimilatedsugar was available.
3. Mediaof lower NO^–₃ concentration (for example, 0·32or 0·64 per cent. (w/v) NaNO^–₂;) yielded feltsricher in carbohydrate than were those grown in media of higherNO^–₂; content (0·96 or 1·28 per cent. (w/v)NaNO₃ The carbohydrate content of the felts increased graduallyuntil the sugar in the medium was exhausted; carbohydrate contentthen decreased.
4. Media of lower NO^–₃; concentration weremore conduciveto fat synthesis than those of higher NO^–₃;content.

     

EFFECT OF ULTRAVIOLET LIGHT UPON VARIOUS PHYSIOLOGICAL ACTIVITIES OF CHLORELLA CELLS AT DIFFERENT STAGES IN THEIR LIFE CYCLE

1. Using Chlorella ellipsoidea as material, investigations weremade of the effects of ultraviolet irradiation upon variousactivities of cells at different developmental stages in theirlife cycle. Cell activities investigated were photosynthesis,respira tion, over-all growth, modes of synchronous growth andcell division as well as the formation of nucleic acids. Theu. v.- light applied was 30 µµW/cm²in intensityand 2537 Å in wavelength.
2. The most u. v.-sensitive wasthe over-all growth activity, andin this respect the irradiationapplied at the L₂-stage wasmore inhibitive than that givenat the D-stage. The next mostvulnerable was the photosyntheticactivity, the sensitivitybeing the same in the D- and L-cells.The most resistant towardu.v. was the endogenous respirationof D-cells followed by theirrespiration using exogenous glucoseas substrate. The L₂-cellsappeared to be unable to use exogenousglucose as substrateof respiration, but their endogenous respirationwas considerablystronger than that of D-cells, and its u. v.-sensitivitywasthe same as that of glucose respiration of D-cells.
3. WhenD-cells were u. v. irradiated immediately before the startofsynchronous culture, growth and cell division as well astheformation of DNA and RNA were retarded in proportion totheu. v.-dose applied. The division number (n) was normal (around4) at lower u.v.-doses (1-2 minute irradiation), but was reducedto a half (about 2) at a higher dose.
4. When, during the synchronousculture, 1-minute u.v.- irradiationwas applied at various stagesof the ripening phase, the divisionwas retarded, but the cells,after attaining an abnormally largesize, divided into about8. If the irradiation was given atthe L₄-stage, the divisionnumber was practically unmodified(n=4.5), although the divisionwas somewhat retarded comparedwith that of the control culture.When a 1-minute irradiationwas given at the L₂-stage, thereoccurred an apparent stimulationof DNA- and RNA-formation,a phenomenon which corresponds tothe production of a largernumber of daughter cells than itwas the case in control cultures.
5. Thus the cells which were moderately u.v.-irradiated at differentstages of synchronous culture were able to complete their lifecycle, but later a certain portion of irradiated cells becameunable to grow normally.

¹Present address: Department of Biochemistry, Dartmouth MedicalSchool, Hanover, New Hampshire, U.S.A. (Received March 6, 1961; )     

Evidence for Essential Maintenance Respiration of Leaves of Xanthium Strumarium at High Temperature

Mesophyll resistance to photosynthetic carboxylation (r'_m) wasused as a criterion for leaf integrity. It was measured, at25 °C, in the light, before and after periods of high temperature(3 h at 38 °C) in the dark. During the high temperatureperiods, respiration (R_D) of attached leaves of Xanthium strumariumwas suppressed from 27%-36% by either low [O₂] (1.04% or 0.21%v.v.) or high [CO₂] (840 µl 1^–1) in the ambientair. Neither treatment affected rates of R_D or photo-respirationduring the second period at 25 °C. There was no significant increase of r'_m when R_D was not suppressedduring the high temperature treatment. When R_D was suppressedat high temperatures, r'_m increased from about 3s cm^–1before, to about 26 s cm^–1 after the high temperaturetreatment. The increase depended upon the degree of suppression. It is concluded that increased R_D at high temperature in Xanthiumleaves is partly the result of an increase of energy demandingmaintenance. The subsequent rate of carbon dioxide fixationis reduced when this increase of maintenance-induced respirationis inhibited.     

Oxygen enhancement of photosynthesis in Anacystis nidulans cells1

Oxygen enhanced photosynthetic ¹⁴CO₂ fixation in Anacystis nidulanscells. Results obtained under different conditions revealedthe following properties of the oxygen enhancement:

1. The enhancement was most significant at ca. 10% O₂. Furtherincrease in oxygen concentration decreased the enhancing effect.The rate under 100% O₂ was equivalent to or a little higherthan that under N₂ gas.
2. b) With the increase in CO₂ concentration,the magnitude ofthe enhancing effect decreased. No oxygen enhancementwas observedwhen the CO₂ concentration. was raised to 9,000ppm.
3. c) The enhancement was observed only at high light intensities.No enhancement was observed when the rate of photosynthesiswas limited by light intensity.
4. Ribulose 1,5-diphosphate (RuDP)carboxylase activity was demonstratedin the extract obtainedfrom A. nidulans cells. We also foundthat the RuDP carboxylaseactivity in this extract was competitivelyinhibited by oxygen.
5. Based on the above-mentioned results, the possible mechanismunderlying the observed enhancing effect of oxygen was discussed.

(Received May 10, 1976; )     

Light-induced changes in the fluorescence yield of chlorophyll a in Anacystis nidulans II. The fast changes and the effect of photosynthetic inhibitors on both the fast and slow fluorescence induction

1. The intensity dependence and spectral variations during thefast transient of chlorophyll a (Chl a) fluorescence have beenanalyzed in the blue-green alga Anacystis nidulans. (Unlikethe case of eukaryotic unicellular green or red algae, the fastfluorescence induction characteristics of the prokaryotic blue-greenalgae had not been documented before.)
2. Dark adapted cellsof Anacystis exhibit two types of fluctuationsin the fluorescenceyield when excited with bright orange light(absorbed mainlyin phycocyanin). The first kinetic patterncalled the fast (sec)fluorescence transient exhibits a characteristicoriginal levelO, intermediary hump I, a pronounced dip D, peakP and a transitorysmall decline to a quasi steady state S.After attaining S,fluorescence yield slowly rises to a maximumlevel M. From M,the decline in fluorescence yield to a terminalT level is extremelyslow as shown earlier by Papageorgiou andGovindjee (8). Ascompared with green and red algae, blue-greenalgae seem tohave a small PS decline and a very characteristicslow SM rise,with a M level much higher than the peak P.
3. A prolonged darkadaptation and relatively high intensity ofexciting illuminationare required to evoke DPS type yield fluctuationsin Anacystis.At low to moderate intensities of exciting light,the time forthe development of P depends on light doses, butfor M, thisremains constant at these intensities.
4. Fluorescence emissionwas heterogeneous during the inductionperiod in Anacystis;the P and the M levels were relativelyenriched in short-wavelengthsystem II Chi a emission as comparedto D and S levels.
5. Thefast DPS transient was found to be affected by electrontransportcofactor (methyl viologen), and inhibitors (e.g.,DCMU, NH₂OH)in a manner suggesting that these changes are mostlyrelatedto the oxido-reduction level of intermediates betweenthe twophotosystems. On the other hand, the slow SM changesin fluorescenceyield, as reported earlier (5, 15), paralleloxygen evolution.These changes were found to be resistant toa variety of electrontransport inhibitors (O-phenanthroline,HOQNO, salicylaldoxime,DCMU, NH₂OH and Antimycin a). It issuggested that, in Anacystis,even in the presence of so-calledinhibitors of cyclic electronflow, a "high energy state" isstill produced.
6. Measurementsof Chlorophyll a fluorescence and delayed lightemission inthe presence of both DCMU and NH₂OH indicate thatthe slow SMchanges are not due to the recovery of the reactioncenter IIin darkness preceeding illumination.
7. Our results, thus, suggestthat in Anacystis a net electrontransport supported oxidation-reductionstate of the quencherQ regulates only partially the developmentof the DPS transient,but the development of the slow fluorescenceyield changes seemsnot to be regulated by these reactions.It appears, from datapresented elsewhere, that the slow risein the yield resultsdue to a structural modification of thethylakoid membrane.

¹We are grateful to the National Science Foundation for financialsupport. (Received November 21, 1972; )