Studies on the Cell Wall of Chlorella IV. Incorporation of Glucose-Carbon into Cell Walls of Synchronously Growing Cells of Chlorella ellipsoidea

Uniformly ¹⁴C-labeIled glucose was fed to synchronously growingChlorella cells in the dark or in light. The rate of ¹⁴C-incorporationinto hemicellulose showed two maxima one in the growth phaseand one in the reproductive phase. Significant ¹⁴Cincorporationinto a "rigid wall" was found only in the reproductive phase. (Received April 14, 1983; Accepted June 15, 1983)     

Factors Influencing Induction of Resistance to Dark Abscission by Malformin

Factors influencing induction of resistance to dark abscissionby malformin on cuttings of Vigna radiata during treatment inlight were examined. When light duration (13.5 W m^–2)increased from 0 to 48 h, the effect of malformin on subsequentdark abscission changed from stimulation only (0 to 4 h), stimulationfollowed by inhibition (8 to 12 h), to inhibition only (24 to48 h). Maximum abscission resistance occurred after 48 h whenirradiance was 6.6 W m^–2. Kinetin treatment in light reducedsubsequent dark abscission by controls but did not reduce abscissionon malformintreated cuttings. Hadacidin had no effect on inductionof abscission resistance by malformin. IAA, hydroxyproline,CaCl₂, sucrose, and NH₄NO₃ were inactive. ABA and ethephon completelyblocked induction of abscission resistance by malformin. Inhibitionof abscission induced by kinetin was also blocked by ABA. Becauseboth puromycin and malformin inhibited dark abscission followingtreatment in light, malformin may induce abscission resistanceby inhibiting protein synthesis or promoting formation of othersubstances which inhibit protein synthesis. Leaf blade removalfrom the distal end of the petioles abolished malformin-inducedabscission resistance. It is suggested that in light malformininduces formation of abscission-inhibiting compounds in leaveswhich are responsible for development of abscission resistance. (Received May 17, 1983; Accepted November 8, 1983)     

Studies on the Photoreceptors for the Promotion and Inhibition of Flowering in Dark-Grown Seedlings of Pharbitis nil Choisy

Three-day-old etiolated seedlings of Pharbitis nil were exposedto red light for 10 min and sprayed with N⁶-benzyladenine beforetransfer to a 48-h inductive dark period, after which they weregrown under continuous white light. A second red irradiationpromoted flowering when given at the 5 and 24th hour of theinductive dark period but inhibited flowering at the 10 and15th hour. Far-red light inhibited flowering when given at anytime during the first 24 h of the dark period. Red/far-red reversibilitywas clearly observed at the 0, 5, 10 and 24th hour, but notat the 15th hour when both red and far-red lights completelyinhibited flowering. The action spectrum for the inhibition of flowering at the 15thhour of the inductive dark period had a sharply defined peakat 660 nm and closely resembled the absorption spectrum of theP_R form of phytochrome. The photoreceptors involved in thesephotoreactions are discussed. (Received June 10, 1983; Accepted July 6, 1983)     

Development of Lipid Synthesis from CO2 in Avena Leaves during Greening of Etiolated Seedlings

The development of the lipid synthesizing system in Avena leafsections was examined in connection with carbon fixation duringthe greening of etiolated seedlings under light. During theinitial 2 h illumination there was a low level of CO₂ fixationby PEP carboxylation, but its products, malate and citrate,did not serve as a carbon source for lipid synthesis, althoughlipid synthesis from acetate had already been established. Withthe initiation of Calvin cycle activity after the initial 2h illumination, lipid synthesis began, with CO₂ fixed by RuBPcarboxylation serving exclusively as the carbon source. Fattyacid synthesis in the leaves during the initial 3 h illumination,unlike the fatty acid synthesis thereafter, was insensitiveto thiolactomycin, an inhibitor of type II fatty acid synthetasecontained in the plastids, and was not dependent on light, incontrast to light-dependent activity in greened leaves. The distribution of ¹⁴C incorporated into lipid molecules fromNaH¹⁴CO₃ showed an equal ratio of ¹⁴C in fatty acid, glyceroland choline moieties of labeled phosphatidylcholine, but a denserradioactivity in the galactose moiety than in the residual moietyof mono- and di-galactosyldiacylglycerols. This suggests a regulatedsupply of glycerol, choline and fatty acid moieties for phosphatidylcholinesynthesis, and an excess supply of galactose to diacylglycerolmoiety for galactosyldiacylglycerol synthesis in Avena leaves. (Received October 31, 1984; Accepted January 25, 1985)     

Circadian Rhythms of Potassium and Sodium Contents in the Growing Front of Neurospora crassa

The temporal changes of potassium (K⁺) and sodium (Na⁺) contentsin the growing front of Neurospora crassa (al-2, bd strain)grown on solid medium showed circadian rhythms which persistedfor at least 45 h in the dark. The K⁺ content reached a maximumat about 10 and 30 h after the transfer from light to darkness,while the Na⁺ content was at a minimum at these times. Boththe rhythms were set off by the light to dark transition andwere not observed in constant light. The phase of the circadianrhythm of conidiation of this strain was delayed by 5 h by exposureto 50 min of white light (photon fluence rate 20.7 W/m²) 7 hafter the light to dark transition. The same exposure significantlychanged the ratio of K⁺ to Na⁺ content in the growing frontmeasured 8 h after the exposure. ³ Present address: Pesticides Research Laboratory, TakarazukaResearch Center, Sumitomo Chemical Co., Ltd., 2-1, 4-chome,Takatsukasa Takarazuka, Hyogo 665, Japan. (Received June 26, 1984; Accepted January 11, 1985)     

The Effects of {delta}-Aminolevulinic Acid and Inhibitors of RNA and Protein Synthesis on Phytochrome Mediated Chlorophyll Accumulation in Sorghum bicolor

In 5-d-old etiolated seedlings of Sorghum bicolor, 12 h of darknessafter 5 min in red light eliminated a lag before the accumulationof chlorophylls in subsequent continuous white light. Increasingthe dark period to 24 h and 36 h, increased the rate of chlorophyllaccumulation in the later stages of greening. Exogenous -aminolevulinicacid neither completely removed the lag, nor increased the rateof chlorophyll accumulation. Cycloheximide (25 µg ml^–1)and 6-methyl purine (5.0 µg ml^–1), given continuouslyor only until the 12 h dark period following the red light irradiation,restored the lag and decreased the rate of chlorophyll accumulation.D-threo-chloramphenicol (400µg ml^–1) also decreasedthe rate of chlorophyll accumulation but did not restore thelag. Addition of these inhibitors even 12 h after red lightirradiation decreased the rate of chlorophyll accumulation.Rifampicin (Rifamycin SV, 400 µg ml^–1) did not havesuch effects. Key words: Chlorophylls, Phytochrome, -Aminolevulinic acid, Sorghum bicolor     

Regulation of Protochlorophyll(ide) Levels in Dark-Grown Non-Dividing Euglena 3. Proplastid Structure during Loss and Regeneration of Protochlorophyll(ide)

Cells of Euglena gracilis Klebs var. bacillaris Cori growingin darkness on a complete medium have small undifferentiatedproplastids. On transfer to an incomplete (resting) medium indarkness, the cells cease division within 72 h. During thistime the proplastid expands and several prothylakoids and prolamellarbodies develop even though phototransformable protochlorophyll(ide)[PT-Pchl(ide)] is decreasing. As PT-Pchl(ide) decreases furtherand reaches a stable plateau after 4–5 more days in darkness,the proplastid structure becomes highly reduced. Forty minutesof light plus a one h dark period, or addition of glutamateor malate for 7 h does not change the proplastid structure significantlyeven though PT-Pchl(ide) returns to the level found in growingcells. Upon prolonged incubation in darkness after light treatment(72 h) an expanded proplastid containing prothylakoids, prolamellarbodies and membrane whorls with mitochondria in close associationis seen; most of the cellular paramylum is lost during thisperiod leaving cavities in the cytoplasm. Without light, prolongedincubation in darkness (72 h) with malate leads to accumulationof cellular paramylum but no change in proplastid structurewhile prolonged treatment with glutamate (72 h) allows the formationof a few prothylakoids but no prolamellar bodies. ¹Supported by Grants GM 14595 from the National Institutes ofHealth. ²Permanent address: Department of Microbiology, Tokyo MedicalCollege, 6-1-1 Shinjuku, Tokyo 160, Japan. ³Abraham and Etta Goodman Professor of Biology. (Received July 23, 1983; Accepted September 22, 1983)     

Effects of Preillumination on Dark Nitrogen Fixation and Respiration by Anabaena Cylindrica

In whole filaments of Anabaena cylindrica dark nitrogen-fixingactivity (measured as acetylene reduction) and respiration increasedwith the light intensity of a fixed period of preillumination,saturating at ca. 10,000 lux. With saturating light during preillumination,the amount and duration of dark nitrogen-fixing activity increasedwith length of preillumination, but respiration declined rapidlyin the dark. At dark respiration rates below 250 nmol O₂ uptake mg protein^–1?h^–1(State 1) no significant nitrogen-fixing activity is observed.From 250 to 550 nmol O₂ uptake?mg protein^–1?h^–1(State 2), nitrogen-fixing activity depends on O₂ uptake whileabove 550 nmol O₂ uptake?mg protein^–1?h^–1 (State3), nitrogen-fixing activity no longer increases with furtherincrease in O₂ uptake rate. (Received June 18, 1983; Accepted November 10, 1983)     

Selective Inhibition of Type II Fatty Acid Synthetase by the Antibiotic Thiolactomycin

The antibiotic thiolactomycin inhibits the fatty acid synthesisfrom both [1-¹⁴C]- acetate and [2-¹⁴C]malonyl-CoA of spinachleaves, developing castor bean endosperms and avocado mesocarp.On the other hand, fatty acid synthetases of Brevibacteriumammoniagenes and Corynebacterium glutamicum are much less sensitiveto this antibiotic. As has been indicated that thiolactomycininhibits fatty acid synthetase of Escherichia coli but has littleeffect on the synthetases of yeast and rat liver [Hayashi etal. (1983) Biochem. Biophys. Res. Commun.. 115: 1108], thiolactomycinis suggested to be a selective inhibitor of type II fatty acidsynthetases. (Received November 10, 1983; Accepted December 17, 1983)     

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     

A Comparative Study of Germination Responses to High Irradiance Light

Seeds of 19 native British herbaceous species (14 grasses andfive forbs) were exposed to white light at three photon fluencerates: high (19–2 mol m^–2 d^–1), medium (9·6mol m^–1 d^–1) and low (2·3 mol m^–2 d^–2) These photon doses have been found by previous workers to inhibitgermination in several species. High and low photon doses wereapplied only as continuous light, but the medium dose was appliedas both continuous light and as a 12 h light/12 h dark photoperiod.All four treatments, plus a dark control, were carried out at15 °C; the high and low doses were also applied with a dailyalternation of 10/20 °C. The majority of species (15) fell into one of two groups. Inseven species germination was relatively high and consistentacross all treatments, including darkness; in the other eightspp germination was inhibited only in darkness. Mostly thesedata confirmed published results for the same species In contrast in Agrostis capillaris and A. stolonifera germinationwas high only at alternating temperatures, irrespective of photondose, but was also slightly promoted by a constant temperaturecombined with light/dark alternations. Only in Bromus sterilisand B. ereclus was germination inhibited by light, in B. erectusat all photon doses and in B. sterilis only at the highest photondose These results suggest that inhibition of germination by highirradiance light is not widespread among native British species Aira caryophyllea, Arrenatherum elatius, Festuca ovina, F. rubra, Hordeum murinum, Milhim effusum, Silene dioica, Achillea millefolium, Brachypodium syhaticum, Digitalis purpurea, Holcus lanatus, Leucanlhemum vulgare, Phleum pratense, Poa trivialis, Taraxacum officinale, Agrostis capillaris, A. stolonifera, Bromus erectus, B. sterilis, seed, dormancy, germination, light, High irradiance reaction, alternating temperatures, photoperiod     

The Diurnal Pattern of Nitrate Uptake and Reduction by Spinach (Spinacia oleracea L.)

Spinach plants were grown in bowls of aerated nutrient solutionin a controlled environment chamber for 24 h, and harvestedevery 3·5-5 h to record their growth, nitrate and wateruptake, and plant nitrate concentration. Twelve such experimentsare described, either with a 14/10 h dark/light regime, or continuouslight or darkness. The irradiance was either 110, 320, or 510µmol m^-2 s^-1 (PPFD). All these regimes began at the endof the light period of a 14/10 h dark/light regime (510 µmolm^-2 s^-1) lasting approximately 2 weeks. Nitrate uptake rate per g of dry weight of plant continued almostunabated at about 17 µmol h^-1 through the initial 14-hdark period, and then fell away sharply if the light was notrestored, but increased slightly when it was. With continuouslight at 510 µmol m^-2 s^-1, uptake rate rose steadily forthe first 24 h of light, and then fell sharply for about 6 h.Shoot nitrate concentration increased about three-fold in thedark phase, and declined in the light at a rate which was positivelyrelated to the irradiance. Root nitrate concentration was severaltimes higher than that of the shoot: its diurnal change wassmaller (relative to the mean) than that of the shoot. Nitratereduction occurred to a small extent in the dark, and increasedrapidly as soon as the lights came on, to remain at a roughlyconstant rate (related to the irradiance) throughout the lightphase. Dry matter increase in the light was related to irradiance,but with little increase above 320 µmol m^-2 s^-1. Respiratoryweight loss in the dark was not detectable. Rate of fresh weightincrease was approximately constant throughout light and darkperiods. The results compare quite well with the predictions of a simplesimulation model, based on the pump/leak principle.Copyright1994, 1999 Academic Press Spinacia oleracea, nitrate, uptake, reduction, influx, efflux, diurnal, regulation, model, simulation     

Diurnal Geotropic responses of the Primary Leaves of Phaseolus vulgaris

When seedlings of Phaseolus vulgaris with leaves in the daytimeposition (almost horizontal to the ground) were turned upside-downduring the light period, their leaves moved upward away fromthe ground after about 20 min and ceased moving after about1.5 h. But when seedlings with leaves in the night time position(directed downward) were turned upside-down, their leaves moveddownward toward the ground after about 30 min and stopped movingabout 2 h later. Thus, Phaseolus primary leaves showed positiveor negative geotropic responses that correspohded to the darkor light period. This geotropic response of primary leaves was accompanied bythe redistribution of K⁺, Cl^– and NO₃- in the laminarpulvinus. These facts suggest that the circadian endogenousclock that is assumed to exist in Phaseolus vulgaris has atleast two regulation echanisms; one which measures time andanother which determines leaf postition in relation to gravityby changing the ion distribution in the pulvinus (Received February 12, 1983; Accepted May 17, 1983)     

Identification of Hinesol as a Chlorophyll-Preserving Substance

A chlorophyll-preserving substance was isolated from rhizomesof Atractylodes lancea DC. and identified as (—)-hinesolon the basis of spectroscopic data. Hinesol at more than 0.22DIH was effective for preserving chlorophyll of oat (Avena sativaL. cv Victory) leaves in the dark with 40 to 50% of the initialchlorophyll content being retained at 2.2 mM. However, hinesolstimulated chlorophyll loss with light exposure and at 4.5 mMcaused complete bleaching when measured 4 days after treatment. ¹Dedicated to the memory of the late Professor Joji Ashida. (Received December 9, 1982; Accepted April 22, 1983)     

Induction of Flowering in a Duckweed, Wolffia microscopica, under Non-inductive Long Days, by 8-Hydroxyquinoline

Wolffia microscopica, a duckweed, flowers in response to a singlephotoinductive SD cycle of 16 h dark and 8 h light. Floweringin W. microscopica could be induced, under non-inductive longdays, by 8-hydroxyquinoline (8-HQ). Flowering was initiatedwith 10^–6 M 8-HQ and maximum flowering (ca. 75%) was obtainedat 5 x 10^–6M level. Flowering was accentuated furtherwhen plants, supplied with 8-HQ, were subjected to SD cycles. (Received September 13, 1985; Accepted December 4, 1985)     

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; )     

Isoforms of NADP-dependent Malic Enzyme in Tissues of the Greening Maize Leaf

Scagliarini, S., Pupillo, P. and Valenti, V. 1988. Isoformsof NADP-dependent malic enzyme in tissues of the greening maizeleaf.—J. exp. Bot. 39: 1109–1119. The compartmentation of the isoforms of NADP-dependent malicenzyme (E.C. 1.1.1.40 [EC] ) has been studied in cell-free extractsand in enzymatically-isolated protoplasts of mesophyll tissue(MT) and bundle sheath (BS) strands of greening maize leaves.The etiolated leaf of 10-d-old seedlings contains a cytosolicisozyme with a pl of 5.4 ?0.1 at low specific activity (s.a,45 ? 3 nmol min^–1 mg^–1 protein), found both in MTand BS. The green leaf on the other hand contains the dominantBS chloroplast isozyme with pl 4.6 ? 0.2 at a s.a, of 370 ?40 nmol min^–1 mg^–1 protein (3.2 ? 0.5 µmolmin^–1 mg^–1 chl) and a minor, previously undescribedisoform with pl 6.5 ? 0.1 also localized in the BS at a s.a.of 38 ? 6 nmol min^–1 mg^–1 protein. Green MT protoplastshave only traces of pl 4.6 isozyme. After illumination of dark-grown seedlings, the total leaf activityshows a rapid increase (1.5-fold within 2 h), attributed mainlyto the pl 5.4 isozyme of MT protoplasts and BS strands. Thisis followed by a large increase of enzyme activity due to thecontinued rise of pl 5.4 isozyme for about 24 h and, after aninitial lag of a few hours, to the accumulation of pl 4.6 isozyme.After 18 h illumination, pl 4.6 and 5.4 isozyme activities tendto decline in the MT whereas they are still increasing in theBS, particularly the former. This pl 4.6 species has becomethe major one by 48 h illumination. The final pattern of greenleaves is established around 96 h light, when the chloroplastisozyme has attained its maximum level, the pl 5.4 isozyme ofBS strands has been superceded by the pl 6.5 species (also supposedto be cytosolic) and MT protoplasts retain little residual activity.Some metabolic implications of the changing pattern of NADP-dependentmalic isozymes during maize leaf greening are discussed. Key words: C₄, isozymes, malic enzyme, photodifferentiation, Zea mays     

Photoinhibition of Glucose Uptake in Chlorella

In colorless mutant cells of Chlorella vulgaris (M125), endogenousrespiration in the dark was not affected by 30-min preilluminationwith white light (9,000 mW?m^–2), while exogenous respirationof glucose or fructose was inhibited significantly by the sametreatment in air, but not under N₂. This light effect on exogenousrespiration was accompanied by an inhibition of hexose uptake. When autotrophically grown wild-type cells of Chlorella vulgaris(211-11h) were incubated in glucose medium with DCMU, lightalso greatly inhibited glucose uptake and growth. Blue lightwas very effective, while red light had only a slight effect.This photoinhibitory effect was also observed in algal cellsthat had been grown in a glucose-containing medium in the dark. Using SDS-gel electrophoresis, a new protein peak with a molecularweight of 35–40 kDa was detected in plasma membrane-richcell wall fractions when Chlorella vulgaris (211-11h) cellswere transferred to a glucose-containing medium. This peak disappearedafter the algal cells were returned to the glucose-free medium.These findings suggest that this protein includes the hexose-carrierprotein. Blue light significantly inhibited the formation ofthis protein during incubation in a glucose-containing medium. ¹ Present address: Laboratory of Chemistry, Faculty of PharmaceuticalSciences, Teikyo University, Sagamiko, Kanagawa 199-01, Japan. (Received July 31, 1986; Accepted March 12, 1987)     

Dark uptake of inorganic14C in oligotrophic oceanic waters

Dark uptake of inorganic ¹⁴C by offshore plankton was measuredat two depths at 36 stations in the Atlantic Ocean from 52°Sto 26°N, mainly along 30°W. The samples were incubatedfor 2 h with and without inhibition of biological activity withHgCl₂. In addition, six time course experiments were performed.The mean dark uptake rate varied from 0.68 to 4.82 (µmolC m^–3 h^–1 over the transect and showed a significantpositive relationship with chlorophyll a. The dark uptake wasusually >5% of the maximum photosynthetic capacity (P^m),and higher values relative to P^m were associated with low valuesof P_m and not with high absolute dark values. A linear relationshipbetween dark uptake and P_m was found with a background value(y-axis intercept) of 0.51 (µmol C m^–3 h^–1and a slope of 0.77% of P^m. A major fraction of the dark signal,66–80% of the total signal, persisted in bottles treatedwith HgCl2, indicating that most of the dark signal was independentof biological activity. Time course experiments showed a lineardark uptake with time for the first hours, whereafter the uptakeceased. At stations with low concentrations of inorganic nitrogen[>1 (µmol (NH₄⁺+NO₃^–)], a second stage was observedafter 3–8 h, probably due to an increase in bacterialactivity. The results suggest three mechanisms for the darkvalue in short-term incubations in oligotrophic waters. A backgroundvalue independent of biomass and incubation time which was thedominant part of the dark signal in samples with very low phytoplanktonbiomass (>0.3 p-g Chi a 1"). Another important part was residualsof ¹⁴C associated with plankton, probably adsorbed to compoundsinside the cells. This fraction was dominant in short-term incubationsat chlorophyll concentrations >0.3 p.g Chi a H. Active uptakeby living cells (total minus ‘HgCl2 uptake‘) wasonly a minor part of the dark signal in short-term incubations,but dominated at longer incubation time (>3–9 h), probablydriven by an increase in bacterial activity. A significant enhancementof the non-photosynthetic uptake of ¹⁴C was observed in light,probably associated with a carbon-concentrating mechanism inphytoplankton or light stimulation of ß-carboxylationactivity. The results strongly suggest that dark values shouldbe subtracted from the light uptake. This correction is particularlyimportant when photosynthetic rates are low, e.g. at low lightor in short-term incubations where a time-zero background becomesa significant part of the total uptake in light. Present address: National Environmental Research Institute,Department of Marine Ecology and Microbiology, Frederiksborgvej399, PO Box 358, DK-4000 Roskilde, Denmark     

Effect of Thiolactomycin on Lipid Synthesis in Higher Plants

The effect of thiolactomycin (TLM), an inhibitor of type IIfatty acid synthase, on lipid synthesis in greening tissueswas examined. Pulse-chase experiments with Na[1-¹⁴C]acetatefor greening Avena leaves showed that continuous administrationof TLM (100µg/ml) decisively reduced phosphatidylcholine(PC) synthesis from acetate and blocked the subsequent conversionof PC to monogalactocyldiacylglycerol (MGDG), whereas temporaladministration of TLM (100 µ/ml) reduced PC synthesisfrom acetate by only 50% and did not block the conversion ofPC to MGDG. In the reduced PC synthesis, the ratio of oleicto palmitic acid decreased at earlier stages of greening, reflectingmore suppression of oleic acid synthesis. In later greeningstages the modulated fatty acid composition recovered to thenormal composition. In further steps, the fatty acid compositionwas not affected by TLM throughout the greening stages. Greeningof either etiolated Avena leaves or etiolated Brassica cotyledonsin the presence of TLM led to a marked decrease in the contentsof MGDG, digalactosyldiacylglycerol (DGDG) and phosphatidylglycerol(PG), but only a small change in the fatty acid compositionof their lipids. The only inhibition characteristic of TLM wasthe desaturation of palmitic to 3-trans-hexadecenoic acid inAvena leaf PG. These results suggest the presence of a mechanismby which the modulated fatty acid composition of lipids is normalizedin the flow of the synthesis. Electron microscopic observationsshowed that Avena chloroplasts developed into round forms ratherthan normal ellipse forms and the thylakoid membranes of Brassicachloroplasts were abnormally swollen everywhere in the presenceof TLM. Photosynthetic oxygen evolution in both tissues wasnot inhibited. (Received December 26, 1986; Accepted April 24, 1987)