Cytochromes in the Cultured Mycobiont of a Lichen, Cladonia vulcani Sav

Cytochromes in a cultured cells of the mycobiont of Cladoniavulcani Sav. were studied, b-and c-type cytochromes and aa₃-typecytochrome c oxidase were found in the membrane fraction, whileb- and c-type cytochromes were found in the soluble fraction.Soluble cytochrome c-549.5 was purified, and some of its molecularproperties were determined. (Received June 27, 1994; Accepted October 3, 1994)     

Respiratory Properties of Mitochondria from Rice Seedlings Germinated under Water and Their Changes during Air Adaptation

Respiratory activities were compared among rice seedlings germinated in air for 6 days (aerobic seedlings), those germinated under water for 5 days (submerged seedlings), and those grown in air for 1 day after 5 days' submerged germination (air-adapted seedlings). The respiratory activity of the submerged seedlings increased rapidly on transfer to air and reached a plateau at 16 hours in air. Respiration of the submerged seedlings was as sensitive to cyanide as those of aerobic and air-adapted seedlings. 2,4-Dinitrophenol had no effect on the respiration of the submerged seedlings, but stimulated those of the other two types of seedlings. Mitochondria from three types of seedlings did not differ in the ADP/O ratio and the respiratory control ratio (RCR) when succinate was oxidized. However, mitochondria from submerged seedlings (submerged mitochondria) showed poor RCR of about unity when malate was oxidized. Both the rate of succinate oxidation and succinate dehydrogenase activity were low in submerged mitochondria, but increased during air adaptation. Although submerged mitochondria oxidized malate very slowly, this activity increased after exposure to air without any increase in malate dehydrogenase activity. When NAD⁺ was added to submerged mitochondria, oxidation of malate was restored to the level of the aerobic controls. Addition of NAD⁺ enhanced the state 3 rate in submerged mitochondria, and RCR recovered to nearly the same value as that of the aerobic controls. Similar effects of NAD⁺ on 2-oxoglutarate oxidation were observed. All these defects in submerged mitochondria were repaired during air adaptation. These results suggest that NAD⁺-linked substrate oxidation was low in submerged mitochondria because of NAD⁺ deficiency, and that the oxidation increased with an increasing level of NAD⁺ during air adaptation.     

Activities of isolated mitochondria and mitochondrial enzymes from aerobically and anaerobically germinated barnyard grass (echinochloa) seedlings

Activity of mitochondria isolated from whole seedlings of Echinochloa crus-galli (L.) Beauv. var oryzicola germinated under aerobic and anaerobic conditions for 5 to 7 days was investigated. Mitochondria from both treatments exhibited good respiratory control and ADP/O ratios. Although O₂ uptake was low in anaerobic mitochondria, activity rapidly increased when the seedlings were transferred to air. Mitochondria from both aerobically and anaerobically grown seedlings of E. crus-galli var oryzicola maintained up to 66% of their initial respiration rate in the presence of both cyanide and salicylhydroxamic acid, and the inhibitory effects of cyanide and azide were additive. In addition, antimycin A was not an effective inhibitor of respiration. Reduced-minus-oxidized absorption spectra revealed that cytochromes a, a₃, and b were reduced to a greater extent and cytochrome c was reduced to a lesser extent in anaerobically germinated seedlings relative to that in aerobically germinated seedlings. An absorption maximum in the cytochrome d region of the spectrum was reduced to the same extent under both germination conditions and an absorption maximum at 577 nm was present only in anaerobically germinated seedlings. Anaerobically germinated seedlings contained 70% of the cytochrome c oxidase activity found in air grown seedlings. Upon exposure to air, the developmental pattern of this enzyme in anaerobically germinated seedlings was similar to air controls. Succinate dehydrogenase activity in anaerobic seedlings was only 45% of the activity found in aerobically germinated seeds, but within 1 hour of exposure to air, the activity had increased to control levels. The results suggest that mitochondria isolated from E. crus-galli var oryzicola differ from other plants studied and that the potential for mitochondrial function during anaerobiosis exists.     

Isolation and Purification of a Ubiquinone-Cytochrome b-c1 Complex from a Photosynthetic Bacterium, Rhodopseudomonas sphaeroides

A ubiquinone-cytochrome b-c₁ complex was removed from chromatophoremembranes of a Rhodopseudomonas sphaeroides green mutant bydeoxycholate-cholate treatment of the chromatophores. The complexwas purified by ammonium sulfate fractionation and gel filtration. The molecular weight of the purified complex was 240,000 (240kD) and it was composed of seven subunits with molecular weightsof 47 kD, 42 kD, 38 kD, 32 kD, 30 kD, 24 kD and 16 kD. The complexcontained 1.54 and 3.42 nmol of cytochrome c₁ and two differentcytochrome b species per mg protein, respectively. It also contained7.07 nmol of ubiquinone, 6.37 nmol of non-heme iron and about3 nmol of carotenoids per mg protein. No flavins were detected.Heme staining indicated that the 32 kD-and 24 kD-subunits werecytochromes. The midpoint potential of cytochrome c₁ was 245 mV, and thevalues for the cytochromes b were 60 mV and –75 mV atpH 7.2. The peak of the -band of the reduced-minus-oxidizeddifference spectrum of cytochrome c₁ was located at 552.5 nm,arid peaks of the b-type cytochromes with higher and lower midpointpotentials were located at 562 nm and 563 nm. The chemical and the subunit compositions of the purified complexreported here were similar to those obtained for the inner membranesof mitochondria of various organisms. (Received April 5, 1982; Accepted June 14, 1982)     

Contents of Cytochromes, Quinones and Reaction Centers of Photosystems I and II in a Cyanobacterium Synechococcus sp.

The contents of photosystem I and photosystem II reaction centers,cytochrome c-553, cytochrome c-550, cytochrome f, cytochromeb-559, cytochrome b-563, plastoquinone and vitamin K₁ in thecyanobacterium Synechococcus sp. were determined. About threephotosystem I reaction centers were present for each photosystemII reaction center. The amounts of cytochromes functioning betweenthe two photosystems were approximately half those of the photosystemI reaction center. Plastocyanin was not detected, while plastoquinoneand vitamin K₁ were present in excess of other electron carriersand reaction centers. The results indicate the importance ofplastoquinone and cytochrome c-553 for cooperation of the tworeaction centers through electron transport. ¹Present address: Toray Basic Research Laboratory, 1111 Tebiro,Kamakura, Kanagawa 248, Japan. (Received June 17, 1982; Accepted January 17, 1983)     

The respiratory chain of Paramecium tetraurelia in wild type and the mutant Cl1 I. Spectral properties and redox potentials

1. Purified mitochondria have been prepared from wild type Paramecium tetraurelia and from the mutant Cl₁ which lacks cytochrome aa₃. Both mitochondrial preparations are characterized by cyanide insensitivity. Their spectral properties and their redox potentials have been studied.2. Difference spectra (dithionite reduced minus oxidized) of mitochondria from wild type P. tetraurelia at 77 K revealed the α peaks of b-type cytochrome(s) at 553 and 557 nm, of c-type cytochrome at 549 nm and a-type cytochrome at 608 nm. Two α peaks at 549 and 545 nm could be distinguished in the isolated cytochrome c at 77 K. After cytochrome c extraction from wild type mitochondria, a new peak at 551 nm was unmasked, probably belonging to cytochrome c₁. The a-type cytochrome was characterized by a split Soret band with maxima at 441 and 450 nm. The mitochondria of the mutant Cl₁ in exponential phase of growth differed from the wild type mitochondria in that cytochrome aa₃ was absent while twice the quantity of cytochrome b was present. In stationary phase, mitochondria of the mutant were characterized by a new absorption peak at 590 nm.3. Cytochrome aa₃ was present at a concentration of 0.3 nmol/mg protein in wild type mitochondria and ubiquinone at a concentration of 8 nmol/mg protein both in mitochondria of the wild type and the mutant Cl₁. Cytochrome aa₃ was more susceptible to heat than cytochromes b and c,c₁.4. CO difference spectra at 77 K revealed two different Co-cytochrome complexes. The first, found only in wild type mitochondria, was a typical CO-cytochrome a₃ complex characterized by peaks at 596 and 435 nm and troughs at 613 and 450 nm. The second, found both in mitochondria of the wild type and the mutant, was a CO-cytochrome b complex with peaks at 567, 539 and 420 nm and a trough at 558-549 nm. Both complexes are photo-dissociable.5. Spectral evidence was obtained for interaction of cyanide with the a-type cytochrome (shift of the α peak at 77 K from 608 to 605 nm), but not with the b-type cytochrome.6. The mid-point potentials of the different cytochromes at neutral pH are as follows: cytochrome aa₃ 235 and 395 mV, cytochrome c,c₁ 233 mV, cytochromes b 120 mV.     

Development and endocrine regulation of mitochondrial cytochrome biosynthesis in the insect fat body: δ-[14C]aminolevulinic acid incorporation

The rate of incorporation of [¹⁴C]aminolevulinic acid (ALA) into cytochrome hemes was used to measure mitochondrial cytochrome synthesis in the fat body of adult male Blaberus discoidalis cockroaches. The hemes of cytochromes aa₃+b and c+c₁, were chemically separated to observe differential rates in their synthesis and regulation. [¹⁴C]ALA was linearly incorporated into cytochrome hemes for at least 8 h. No significant pool of endogenous ALA was detected relative to the amount of administered [¹⁴C]ALA. Peak cytochrome synthesis occurred 4 to 6 days after adult emergence. Endocrine disruption by corpora cardiaca-corpora allata extirpation or cervical ligation eliminated the 4-day developmentally related increase in the rate of cytochrome aa₃+b synthesis but had no effect on the production of cytochromes c+c₁. Injections of corpora cardiaca extracts into cervically ligated animals stimulated the rate of production of cytochromes aa₃+b by 2.5 times but did not affect cytochromes c+c₁. By comparison, juvenile hormone injections did not affect the rate of synthesis of either cytochrome fraction. These findings indicate that a neurohormone regulates the rate of synthesis of cytochromes a+b in insect fat body mitochondria.     

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; )     

Resistance to Oxidative Injury in Submerged Rice Seedlings after Exposure to Air

Rice (Oryza sativa L.) seedlings were germinated under waterin darkness for 5 or 6 days (submerged seedlings) and then inair for 1 day. Control seedlings were germinated in air, indarkness, for 5 or 6 days (aerobic seedlings). Changes in levelsof antioxidants and in the extent of oxidative damage afterexposure of submerged seedlings to air were studied. -Tocopherol,which inhibits lipid peroxidation, was present in submergedseedlings at about 3 times the level found in aerobically growncontrols, and higher levels than in controls were maintainedfor 24 h after transfer of the seedlings to air. Products oflipid peroxidation were present at a one-third of the levelsfound in aerobic controls, and their levels increased aftertransfer to air. However, these levels remained lower than thosein aerobic controls even after 24 h of contact with air. Carotenoids,which are considered to protect chlorophyllous compounds againstphotooxidation, were not found in submerged seedlings, but theirlevels increased after exposure of the seedlings to air. Lightat an intensity that did not cause photooxidative damage tochlorophyllous compounds in aerobic controls induced photobleachingof these compounds in submerged seedlings during the early stagesof adaptation to air. However, the extent of photobleachingdiminished as adaptation to air proceeded, and photobleachingwas no longer detected after 24 h of adaptation to air. Thus,the system for protection of cellular membranes from lipid peroxidationin the post-hypoxic phase appeared already to exist in submergedseedlings. However, the system for protection of pigments fromphotobleaching was poorly developed in submerged seedlings andwas fully active only after 24 h of adaptation to air. ¹Present address: Department of Biology, Faculty of Science,Shizuoka University Shizuoka, 422 Japan ²Present address: Research Institute for Bioresources, OkayamaUniversity, Kurashiki, 710 Japan     

Chromatic Regulation of Cytochrome Composition and Electron Transfer from Cytochrome b6-f Complex to Photosystem I in Anacystis nidulans (Tx 20)

Cytochrome composition of the cyanobacterial photosyntheticsystem was studied with Anacystis nidulans (Tx 20) in relationto the chromatic regulation of photosystem composition. Comparisonof cytochrome compositions in cells with a high PS I/II ratio(3.0, grown under weak orange light) and with a low ratio (1.6,grown under weak red light) indicated that cytochrome compositionwas also changed in the chromatic regulation of photosystemcomposition. Two types of cytochrome change were observed: 1)contents of cytochromes C₅₅₃ and c₅₄₈ were changed in parallelwith the changes in PS I content, and 2) cytochrome b₅₅₃ andcytochrome b₆-f complex were held at a constant molar ratioto PS II. The molar ratio, PS II : cytochrome b₅₅₉ : cytochromeb₆-f complex : cytochrome c₅₅₃ : PS I : cytochrome C₅₄₈, inthe red-grown cells was 1 : 2.5 : 1.3 : 0.17 : 1.6 : 0.67, andthe ratio in the orange-grown cells, 1:2.4:0.9:0.32:3.0:1.2.In both types of cells, almost all cytochrome f in the cytochromeb₆-f complex was rapidly oxidized after multiple flash activation,indicating that all cytochrome b₆-f complexes in cells of bothtypes are functionally connected to PS I, even when the molarratio to PS I is largely changed. The content of cytochromeC₅₅₃ was at most 0.14 of PS I, suggesting that the cytochrometurns over several times per one turnover of PS I. ¹Present address: Department of Biology, Faculty of Science,Tokyo Metropolitan University, Fukazawa 2-1-1, Setagaya, Tokyo158, Japan. (Received January 20, 1986; Accepted March 17, 1986)     

The electron transport systems of Fasciola hepatica mitochondria.

The electron transport systems of Fasciola hepatica mitochondria were investigated spectrophotometrically at room temperature and at −196°. The mitochondria were found to contain substrate reducible a-, b- and c-type cytochromes. All of the cytochrome components of the classical mammalian type of respiratory chain were present, although the concentration of cytochromes aa₃ was low. In addition to the mammalian type of respiratory chain, the Fasciola mitochondria contained a substrate reducible b-type cytochrome component (557 nm) which included a CO reactive o-type cytochrome. The results suggest that F. hepatica mitochondria contain a branched electron transport system including a mammalian type of chain and involving two terminal oxidases and at least two b-type cytochromes.     

Properties of Ascaris muscle mitochondria. I. Cytochromes

1. The cytochrome system in Ascaris muscle mitochondria was further characterized using purer preparations.2. Difference spectra (at 22 °C and ?196 °C) of the mitochondrial preparations using succinate and ascorbate plus N,N,N′,N′-tetramethyl-p-phenylenediamine show that Ascaris muscle mitochondria contain cytochromes c₁, c and aa₃, and also at least three b-type cytochromes. The b-type cytochrome is the predominant component.3. Cytochrome c and Ascaris cytochrome b-560 can be extracted from the mitochondrial preparations with 150 mM KCl, leaving the membrane-bound cytochromes c₁, b and aa₃ in the KCl residue.     

Changes in cytochrome contents and respiratory activity of Bacillus cereus Strain T during germination, vegetative growth and sporulation

Vegetative cells of Bacillus cereus Strain T contain cytochromeb-562, a minor b-type component, in addition to known components,cytochrome a+a₃, cytochrome b-557 and cytochrome c-551. Also,the spores contain low but definite amounts of cytochromes b-562and c-551, which were oxidized when the spores were shaken withair. Contents of cytochromes a, b and c per cell and per cellnitrogen, and the activity of glucose oxidation increased duringspore germination and elongation. During the stage precedingfirst cell division, cytochrome contents per cell increasedin parallel with the increase of cell nitrogen, while the activityof glucose oxidation decreased. During early exponential growth,the content of cytochrome b per cell nitrogen and respiratoryactivity with glucose again increased. When cells entered thesporulation stage, characterized by structural changes insidethe cells, the activity of glucose oxidation began to decrease,while that of acetate or succinate oxidation started to increase.During the sporulation process, the contents of the three cytochromecomponents continued to increase and reached the highest levelin cells containing completed spores, but the activity of respirationwith endogenous or added substrates was negligible in thesecells. (Received November 10, 1975; )     

Respiratory Activities, Cytochrome Composition and Cytochrome c Oxidase Subunit II Levels of Mitochondria from Alloplasmic Wheats Having Aegilops Cytoplasms

Respiratory activities, cytochrome composition and cytochromec oxidase (EC 1.9.3.1 [EC] ) subunit II (COXII) levels of isolatedmitochondria in one euplasmic and four alloplasmic lines ofwheat (Triticum aestivum), having cytoplasms of Aegilops columnaris,Ae.crassa (4x),Ae. mutica and Ae. triuncialis, which show variousgrowth abnormalities, were studied. Cytoplasm-specific variationon the respiratory activities has been revealed among the cytoplasmsof five Triticum and Aegilops species. The cyanide-resistantrespiratory pathway does not seem to contribute to the variationin activity. The low level of state 3 and cytochrome oxidaseactivities were evident in lines having Ae. columnaris and Ae.triuncialis cytoplasms, which also show growth inhibition. Thelow cytochrome oxidase activity in both cytoplasms is consistentwith the low amount of cytochrome aa₃ and the severe reductionin COXII levels. The relatively low amount of cytochrome aa₃in Ae. mutica is also consistent with the reduced level of theCOXII. On the other hand, relatively low amounts of cytochromeb (b-557) are found in the Ae. crassa cytoplasmic line. Theseresults suggest that the growth abnormalities found in the alloplasmicwheat lines are related to the variation in respiratory activitiesand cytochrome composition. In particular, growth inhibitionfound in the alloplasmic wheats having Ae. columnaris and Ae.triuncialis may be caused by the severe depression of respiratoryactivity due to the impaired cytochrome oxidase activity oftheir mitochondria. ³Present address: Department of Biochemistry, Dalhousie University,Halifax, NS, Canada B3H 4H7     

Properties of the Cytochrome c Oxidase Activity of Cytochrome b561 from Photoanaerobically Grown Rhodopseudomonas sphaeroides

Cytochrome b₅₆₁ from Rhodopseudomonas sphaeroides had cytochromec (c2) oxidase activity and a pH optimum at 6.0 for this activity.The activity was affected by the ionic strength of the reactionmixture. The apparent K_m and maximal velocity (V_max) valuesin the absence of addea salts were 14 µM and 120 nmoloxidized per min per mg protein for horse heart cytochrome c.Reduced horse heart cytochrome c was reoxidized in first-orderkinetics by this cytochrome b₅₆₁. The specific activity was0.7 s^–1 per mg protein at 20°C at the concentrationof 30 µMM cytochrome c. Activity was inhibited by KCN and NaN₃, but not by antimycin.The addition of a low concentration of KCN to the cytochromeb₅₆₁ produced a change in the absorption spectrum, evidencethat KCN interacts with the heme moiety of cytochrome b₅₆₁.Results of this and preceeding studies show that the cytochromeoxidase (cytochrome "o") described earlier (Sasaki et al. 1970)is cytochrome b₅₆₁. (Received May 16, 1983; Accepted September 8, 1983)     

Inhibition of an aa3-Type Two-Subunit Cytochrome c Oxidase from Nitrobacter agilis by N,N'-Dicyclohexylcarbodiimide

The electron transfer activity of an aa₃-type two-subunit cytochromec oxidase of Nitrobacter agilis was inhibited by DCCD. Althoughthe activity of the purified cytochrome c oxidase dissolvedin 1% Triton X- 100 was not affected by DCCD even at a ratioof 1,000 mol DCCD per mol cytochrome aa₃, the activity of theenzyme dissolved in 0.02% Tween 20 or 0.02% Triton X-100 wasinhibited by 60% or more at a ratio of 1,000 mol DCCD per molcytochrome aa₃. The results of SDS polyacrylamide gel electrophoresisof the enzyme incubated with DCCD suggested that subunit IImight be a binding site for DCCD. (Received February 23, 1985; Accepted April 23, 1985)     

Chloroplast development in 4-thiouridine-cultured radish seedlings III. Photochemical activities in isolated plastids

Accumulation of chlorophyll, development of photosystem I andII activities and contents of chloroplastic components wereinvestigated in greening radish seedlings germinated and grownwith 4-thiouridine (4SU). The development of photosystem I activityprior to that of photosystem II was observed also in the 4SU-culturedgreening radish cotyledons in which chlorophyll accumulationwas inhibited up to 60–80% of that of the control. Photochemicalactivities expressed on a plastid protein basis decreased withthe increase of 4SU in the culture medium. In contrast to ferredoxinand ferredoxin-NADP reductase, which were present in significantamounts in the treated cotyledons, chloroplastic cytochromes(f, b₅₅₉ and b₆ decreased in the plastids from 4SU-culturedcotyledons. These results suggest that 4SU interferes in partwith protein synthesis in plastids and thereby with chloroplastdevelopment. (Received December 4, 1979; )     

Exposure of the Cyanobacterium Synechocystis PCC6803 to Salt Stress Induces Concerted Changes in Respiration and Photosynthesis

In order to survive and to grow in the presence of a high salinity(550 mM NaCl) Synechocystis PCC6803 increases its energeticcapacity. The salt-induced increase of electron transport ratesinvolves both cytochrome c oxidase and photosystem I. In contrast,electron transport rates measured through complexes I plus IIIof the respiratory chain, or through the photosystem II pluscytochrome b₆f complexes of the photosynthetic chain, do notshow appreciable changes. The time at which changes in electrontransport rates occur in the photosystem I and cytochrome coxidase complexes after the onset of salt stress indicates similaritiesin the adaptation of dark respiration and (cyclic) photosyntheticelectron flow. Given an increase of whole cell respiration andof PSI cyclic electron flow larger than the neosynthesis ofcytochrome aa3 and PSI reaction centers would predict, it appearsthat both adaptations require more than just synthesis of thesetwo complexes. (Received April 12, 1993; Accepted August 10, 1993)     

aa3-Type Cytochrome c Oxidase Occurs in Halobacterium halobium and Its Activity is Inhibited by Higher Concentrations of Salts

Cytochrome aa₃ was found to occur in Halobacterium halobiumat an early exponential phase of growth. Some of its spectralproperties were determined with a solubilized membrane fractionof the bacterium. Cytochrome c oxidizing activity of the cytochromeaa₃ was not dependent on salt concentration, but decreased steeplywith increasing buffer concentration of the reaction mixture,just as the activity of cytochrome aa₃ from non-halophilic bacteria. (Received July 4, 1986; Accepted October 17, 1986)     

Changes in Levels of Heme a, Protoheme and Protochlorophyll(ide) in Submerged Rice Seedlings after Exposure to Air

Rice (Oryza sativa L. cv. Yamabiko) seedlings germinated underwater for 5 days contained small amounts of heme a and protohemebut no protochlorophyll(ide) [Pchl(ide)]. Levels of hemes andPchl(ide) increased rapidly upon transfer to air. When expressedin terms of fresh weight of tissue, hemes reached the levelsin aerobic controls after 24 h of contact with air, but Pchl(ide)did not. A comparison of the increases during 24-h adaptationto air in levels of heme a and Pchl(ide), which are specificto mitochondria and plastids, respectively, suggested that thedevelopment of mitochondria preceded that of plastids. The rateof synthesis of 5-aminolevulinic acid (ALA) was low in submergedseedlings, as compared to the rate in aerobic controls, butit increased during air adaptation. The sum of the amounts ofheme a, protoheme and Pchl(ide) increased in parallel with theamount of porphyrins, equivalent to the amount of ALA synthesizedduring the experimental period. When submerged seedlings thathad been pretreated with levulinic acid were exposed to air,no Pchl(ide) was formed. In contrast, Pchl(ide) accumulatedunder water when submerged seedlings were fed with ALA. Theseresults indicate that the synthesis of ALA, the limiting stepin the synthesis of Pchl(ide), is repressed under hypoxic conditions. ¹ Present address: KRI International, Inc., Kyoto Research Park17, Chudoji Minami-machi, Shimogyo-ku, Kyoto, 600 Japan. ² Present address: Research Institute for Bioresources, OkayamaUniversity, Kurashiki, 710 Japan.