Chlorophyll-Protein Complexes and other Thylakoid Components at the Low Intensity Threshold in Euglena Chloroplast Development

The plastids of dark-grown resting cells of Euglena gracilisKlebs var. bacillaris Cori undergo only limited developmentwhen illuminated at the developmental threshold for light intensity7 foot-candles (ft-c) (27 µW/cm²). In the present work,we have found that these low intensity cells have substantialamounts of electron transport components such as ferredoxin-NADPreductase and Cyt c-552 but only trace amounts of the majorantenna components such as the light-harvesting Chl-proteincomplex (LHCP), the LHCP oligomer, CP la, Chi b and the 26.5kDa apo-LHCP; CP I and CPa are at levels comparable to the electrontransport components. Exposure of the low intensity cells tonormal light intensity causes large increases in major antennacomponents and small increases in electron transport components.The kinetics of accumulation of the antenna components Chi band apo-LHCP during greening of dark-grown resting cells atnormal intensities are the same as for Chi a. The low intensitywild-type cells strongly resemble mutants of Euglena low inChi b grown at normal intensities in lacking major antenna components. (Received April 7, 1987; Accepted June 19, 1987)     

Changes in the Levels of Chlorophyll and Light-Harvesting Chlorophyll a/b Protein of PS II in Rice Leaves Aged under Different Irradiances from Full Expansion through Senescence

Effects of irradiance on changes in the amounts of chlorophyll(Chl) and light-harvesting chlorophyll a/b protein of PS II(LHCII) were examined in senescing leaves of rice (Oryza sativaL.). Results of treatments at two irradiances (100% and 20%natural sunlight) were examined after the full expansion ofthe 13th leaf throughout the course of senescence. With 20%sunlight, the Chl content decreased only a little during leafsenescence, while with 100% sunlight it decreased appreciably.Similarly, the amount of LHCII protein during treatment with20% sunlight remained almost constant. However, the ratio ofChl a/b during the shade treatment decreased significantly andthe rate of decrease was greater than during the full-sunlighttreatment. The ratio of Chl a/b for Chl a and b bound to LHCIIwas about 1.2, irrespective of leaf age or irradiance treatment.When the amounts of Chl bound to LHCII were calculated fromthe total leaf content of Chl and the ratio of Chl a/b, assuminga ratio of Chl a/b bound to LHCII of 1.2, they were well correlatedwith the amounts of LHCII protein. Changes in the amounts of LHCII synthesized during the two irradiancetreatments were examined using an ¹⁵ tracer. Incorporation of¹⁵N into LHCII declined dramatically during both treatmentsfrom full expansion through senescence, suggesting that therewas little synthesis of LHCII protein during that time. In addition,the amount of LHCII synthesized during senescence was lowerduring the shade treatment than during the 100% sunlight treatment.These results indicate that the absence of an apparent changein levels of LHCII with shade treatment during senescence wascaused by the very low rate of turnover of LHCII protein. (Received June 17, 1992; Accepted September 28, 1992)     

The Presence of Two Types of Gene That Encode the Chlorophyll a/b-Binding Protein (LHCPII) and Their Light-Independent Expression in Pine (Pinus thunbergii)

A cDNA clone (pPDLHC3117) for LHCPII of pine (Pinus thunbergii)was isolated and sequenced. From a comparison of the deducedamino acid sequence with those of proteins from other seed plants,pPDLHC3117 was identified as encoding a type I LHCPII. Specificprobes for genes for type I and type II LHCPII were made frompPDLHC3117 and a type II cDNA (pPDLHC2176), respectively. Northernblotting with the specific probes showed that both types ofLHCPII were expressed in dark-grown seedlings of pine. ¹This work was supported by a Grant-in-Aid from the Ministryof Agriculture, Forestry and Fisheries of Japan (IntegratedResearch Program for the Use of Biotechnological Proceduresfor Plant Breeding).     

Events surrounding the early development of Euglena chloroplasts 13. Photocontrol of protein synthesis

Protein synthesis measured as leucine incorporation was followedduring the early hours of light exposure of dark-grown cellsof wild type cells of Euglena gratilis var. bacillaris and ofbleached mutants W₃BUL and W₁₀SmL which lack detectable plastidDNA. In all strains, linear rates of leucine incorporation wereobserved in dark-grown resting cells and on exposure to light,this rate increased. After about 3 hr light exposure in wildtype cells and somewhat later in the mutants, the rate of proteinsynthesis sharply declined below that of the dark-grown anddark-incubated cells. Experiments in wild type cells showedthat leucine uptake was not rate limiting for protein synthesisalthough light exposure decreased the rate of uptake. The changesin rate found during continuous labeling of wild type cellswere verified by pulse-labeling experiments in continuous light.Exposure of dark-grown wild type cells to a two hour pulse oflight produced a transient increase in the rate of leucine incorporationwhich subsequently returned in darkness to the level of thedark-grown cells which received no light; thus the changes inrate of leucine incorporation are light-dependent. Since theeffects of light on leucine incorporation can be reproducedin mutants lacking detectable plastid DNA, the photoreceptormachinery involved cannot be coded in plastid DNA, and probablyoriginates in nuclear DNA. The role of light in programmingprotein synthesis and turnover in early chloroplast developmentis discussed. ¹Supported by Grant Number GM-14595 from the National Institutesof Health. ²Microbiology trainee of the National Institutes of Health,Grant Number GM1586. Portions of the material in this paperwere taken from a dissertation submitted by S. D. S. to theGraduate Faculty of Brandeis University in partial fulfillmentof the requirements for the Ph.D. degree. Present address: Schoolof Life Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska68588, U. S. A. ³Abraham and Etta Goodman Professor of Biology and Director,Institute for Photobiology of Cells and Organdies, BrandeisUniversity, Waltham, MA, U. S. A. 02154, to whom reprint requestsshould be sent. (Received February 8, 1979; )     

Purification and properties of the photoactive particle corresponding to photosystem II

1. 1) Purification of the photoactive particle corresponding tophotosystem II (particle II) was achieved using a combinationof procedures including digitonin- and Triton X-100-treatments,sonication, and differential- and density-gradient centrifugations.
2. 2) The "purified" particle II preparation showed only oxygenevolution activity and showed no NADP⁺ photoreduction activityeven when an electron donor couple was added.
3. 3) The chemicalcompositions of this particle and of the particlecorrespondingto photosystem I (particle I) were compared withrespect tothe composition and contents of their chlorophylls,carotenoids,cytochromes, plastoquinones, protein and lipid.Marked differenceswere found.
4. 4) Using the two photoactive particles I and IIlacking therespective counterpart activity, a partial successwas attainedin reconstituting a system, in which photoinducedelectron flowfrom water to NADP⁺ was observed, provided thatsuitable intermediateelectron carriers, e. g. plastoquinoneand plastocyanin, wereadded.
5. 5) The nature of the two photoactiveparticles obtained andtheir relationship to particles so farreported are discussed.

¹This study was aided by grants from the Ministry of Education(407160-1965, 91402-1966, 1967). Financial support from SanyoBroadcasting Scientific Foundation is also acknowledged withcordial thanks. (Received October 23, 1968; )     

A Comparative Study of the Biological Activities of Two Molecular Species of Chloroplast-type Ferredoxins

Pairs of two molecular species of soluble chloroplast-type ferredoxins(Fd I and Fd II) from Nostoc muscorum and Aphanothece sacrumwere used to examine and compare the abilities of ferredoxinto substitute for spinach ferredoxin in the photoreduction ofNADP⁺ by spinach chloroplasts or N. muscorum membrane fragmentsand to link the reducing power of illuminated spinach chloroplaststo the Bacillus polymyxa nitrogenase system. Ferredoxins II of Nostoc and Aphanothece showed rather low activitiesin NADP⁺ photoreduction and nitrogenase system with spinachchloroplasts as the photosensitizer, compared to other ferredoxins.However, there was no difference between two ferredoxins (FdI and Fd II) from Nostoc in NADP⁺ photoreduction by photosyntheticmembrane fragments prepared from the same organism, N. muscorum. The biological significance of two molecular species of ferredoxinsin one organism could be ascribed to the different contributionof each ferredoxin to certain biological reactions in whichferredoxin functioned as an electron carrier. (Received November 4, 1980; Accepted January 9, 1981)     

Leaf Development in Lolium temulentum: Photosynthesis and Photosynthetic Proteins in Leaves Senescing under Different Irradiances

Changes in carbon fixation rate and the levels of photosyntheticproteins were measured in fourth leaves of Lolium temulentumgrown until full expansion at 360 µmol quanta m^–2s^–1 and subsequently at the same irradiance or shadedto 90 µmol m^–2 s^–1. Ribulose-1,5-bisphosphatecarboxylase/oxygenase (Rubisco), light-harvesting chlorophylla/b protein of photosystem II (LHCII), 65 kDa protein of photosystemI (PSI), cytochrome f (Cytf) and coupling factor 1 (CF₁) declinedsteadily in amount throughout senescence in unshaded leaves.In shaded leaves, however, the decrease in LHCII and the 65kDa protein was delayed until later in senescence whereas theamount of Cyt f protein decreased rapidly following transferto shade and was lower than that of unshaded leaves at the earlyand middle stages of senescence. Decreases in the Rubisco andCF₁ of shaded leaves occurred at slightly reduced rates comparedwith unshaded leaves. These results indicate that chloroplastproteins in fully-expanded leaves are controlled individually,in a direction appropriate to acclimate photosynthesis to agiven irradiance during senescence. (Received August 20, 1992; Accepted January 5, 1993)     

An electrophysiological study of the membrane in aplanospore-like cell of Boergesenia forbesii

Membrane potential and resistance, each of which was the sumof those of the plasmalemma and tonoplast, measured in the coenocyticthallus of Boergesenia forbesii were 6.7 mv inside positiveand 2.8 k.cm², respectively. Protoplasm squeezed from the thallus into artificial sea water(ASW) formed numerous spherical bodies, which are termed aplanospore-likecells (simply "spores"). The following electrical propertiesof the "spores" 20–40 hr after squeezing were obtained:potential difference (p.d.) across plasmalemma (E_co) was –66mv (– means inside negative), plasmalemma resistance 665cm², p.d. across the tonoplast (E_vc) +73 mv, and tonoplast resistance2.6 k.cm². Tenfold increase in external [K⁺] caused +45 mv changein E_co and +17 mv in E_vc. The plasmalemma was entirely depolarizedin Ca⁺⁺-free ASW or ASW containing Triton X-100. When the "spore" was immersed in potassium-rich (277 mil) ASW,E_co was almost zero and the tonoplast showed two states (I andII, E_ve about +70 mv and +20 mv, respectively). E_vc went backand forth between the two states spontaneously or when a smallcurrent was applied. In most cases oscillatory changes in E^vcoccurred after the lapse of a long time in the K+-rich sea water.Membrane resistances in states I and II were 5 and 9 k.cm²,respectively. (Received July 11, 1977; )     

Photoconversion of a Water-Soluble Chlorophyll Protein from Chenopodium Album: Resonance Raman and Fourier Transform Infrared Study of Protein and Pigment Structures

A water-soluble Chl a/b-protein complex, CP668, from Chenopodiumalbum converts to another form of protein complex, CP743, uponlight illumination. Structural changes of pigments and proteinsupon photoconversion were studied using resonance Raman (RR)and Fourier transform infrared (FTIR) spectroscopies. RR spectraof CP668 and CP743 and a light-induced FTIR difference spectrumshowed that the macrocyle C=C bands of Chl a in CP668 considerablychanged upon conversion to the pigment (not chemically identifiedyet) in CP743. The C=C band pattern of the RR spectrum of CP743was similar to that of bacteriochlorophyll a, suggesting thatthe conjugated system of the CP743 pigment resembles a bacteriochlorinring. Judging from the C=O frequencies, the 13¹-keto C=O groupsof Chl a and b in CP668 are free from hydrogen bonding, whereasthe 13²-ester C=O groups of both Chl a and b and the 7-formylC=O of Chl b in CP668 are hydrogen bonded. Upon conversion toCP743, interactions of the 13¹-keto and 13²-ester C=O groupswere basically unaffected, demonstrating no drastic changesaround these C=O groups. FTIR spectra in the amide I' regionof CP668 and CP743 in D₂O buffer showed a peak at 1,633 cm^–1,which represents a major component of ß-sheet conformation.Second-derivative spectra of the amide I' bands as well as alight-induced FTIR difference spectrum suggested that drasticchange in the protein conformation does not occur upon photoconversion. (Received November 1, 1998; Accepted December 24, 1998)     

苔藓新老组织及其根际土壤的碳氮元素含量和同位素组成(δ13C和δ15N)对比

 对细叶小羽藓(Haplocladium microphyllum)新老组织及其根际土壤的碳氮含量和同位素组成进行了分析,探讨了苔藓衰老过程控制元素和同位 素变化的机制以及苔藓对土壤的贡献。同种组织碳氮含量之间的相关性反映了苔藓固碳能力和氮需求的相互联系。新生组织碳氮含量明显高于 衰老组织且存在相关性,反映了苔藓衰老过程体内碳氮物质向新生组织迁移的生理特征。两种组织之间同位素组成(δ¹³C和δ¹⁵N)没有明显差 异,说明组织间的物质迁移没有产生明显的同位素分馏,其原因可能在于细叶小羽藓形态结构简单,体内物质迁移对碳氮同位素组成的影响较 小。相反,苔藓组织与根际土壤之间的有机碳/ 氮信息没有相关性,这可能与苔藓植物长期滞留营养物质、缓慢的分解和成土速度有关,反映了 该研究区苔藓层对土壤碳氮累积的贡献较小。     

DNA Levels in Dividing and Developing Plastids in Expanding Primary Leaves of Avena sativa

The amounts of plastid DNA in the primary leaves of 4-d-oldlight- and dark-grown seedlings of Avena sativa were measuredby microspectrofluorometry using the DNA-fluorochrome DAPI (4',6-diamidino-2-phenylindole). In the light-grown primary leaves (40–45 mm long) therewas a marked increase in DNA level per plastid from 10.2 to18.5 ? 10^–15 g between 2.0 mm and 10 mm from the leafbase, resulting from the rate of plastid DNA synthesis beinghigher than the rate of plastid division. Beyond 30 mm the plastidDNA level was reduced to 14 ? 10^–15g due to chloroplastdivision rates being higher than the rate of plastid DNA synthesis,while from 20 mm plastid DNA levels were constant at 2.2 ? 10^–12g per cell, which corresponds to 16000 plastome copies per cell. Observations of dark-grown leaves establish that, in Avena,light is not necessary for plastid division and the dark-grownleaf cells accumulate higher amounts of plastid DNA than light-grownleaf cells. Plastid nucleoids showed a change of distribution after completionof plastid DNA synthesis in light-grown leaves. A change inthe distribution of plastid nucleoids was also observed duringthe greening of etioplasts of dark-grown leaves while plastidDNA level remained constant. Such changes in plastid nucleoiddistribution appear to be independent of plastid DNA synthesisand correlate with the formation of grana stacks. Key words: Avena sativa, microspectrofluorometry, plastid DNA     

Effect of Continous Light on CO2 Fixation and Chloroplast Structure of the Mosses Pleurozium schreberi and Ceratodon purpureus

When the mosses Pleurozium schreberi (Brid.) Mitt, and Ceratodon purpureus (Hedw) Brid. were exposed for 4 week to either continuous or rhythmie light of 75 or 150 μE m^?2 s^?1, the photosynthetic rate, calculated on the basis of chlorophyll and of dry weight, was lower in the moss plants exposed to continuous light. RUBP-carboxylase activity was lower in these plants, too. On the other hand more starch was accumulated in the chloroplasts in continuous than in rhythmic light. Neither moss species showed any differences in the dark respiration rates. The chlorophyll content was lower in continuous light, especially at the higher intensity; but Chi a/Chl b ratio showed little change compared with that in rhythmic light. The reduction of chlorophyll did not affect the two chlorophyll protein complexes equally; the percentage of chlorophyll associated with CP I decreased, while that associated with CP II showed liltle change. The decrease in CP I chlorophyll appeared to be due to the partial destruction of stroma thylakoids: the size or the grana increased in continuous light. Many of the effects of continuous light in these mosses resembled those observed in higher plants in the early phases of senescence.     

Photosynthetic and Photorespiratory Enzymes in Widely Divergent Plant Species with Special Reference to the Moss Ceratodon purpureus: Properties of Ribulose Bisphosphate Carboxylase/ Oxygenase, Phosphoenolpyruvate Carboxylase and Glycolate Oxidase

Rintamäki, E. and Aro, E.-M. 1985. Photosynthetic and photorespiratoryenzymes in widely divergent plant species with special referenceto the moss Ceratodon purpureus: Properties of ribulose bisphosphatecarboxylase/oxygenase, phosphoenolpyruvate carboxylase and glycolateoxidase.—J. exp. Bot. 36: 1677–1684. Km(CO₂) values and maximal velocities of ribulose bisphosphatecarboxylase/oxygenase (E.C. 4.1.1.39 [EC] ) were determined for sixplant species growing in the wild, consisting of a moss, a fernand four angiosperms. The maximum velocities of the RuBP carboxylasesvaried from 0.13 to 0.;62 µmol CO₂ fixed min^–1 mg^–1soluble protein and the Km(CO₂) values from 15 to 22 mmol m^–3CO₂. The highest Km(CO₂) values found were for the moss, Ceratodonpurpureus, and the grass, Deschampsia flexuosa. These plantsalso had the highest ratios of the activities of RuBP carboxylaseto RuBP oxygenase. Glycolate oxidase (E.C. 1.1.3.1 [EC] ) activitieswere slightly lower in D.flexuosa, but not in C. purpureus,than for typical C₃ species. Phosphoenolpyruvate carboxylase(E.C. 4.1.1.31 [EC] ) was not involved in the photosynthetic carboxylationby these two plants. However, another grass, Phragmites australis,was intermediate in PEP carboxylase activity between C₃ andC₄ plants The properties of RuBP carboxylase/oxygenase are discussedin relation to the activities of PEP carboxylase and glycolateoxidase and to the internal CO₂ concentration. Key words: RuBP carboxylase, oxygenase, Km(CO₂), moss     

The Fate of Sulphate within the Capsular Polysaccharide of the Unicellular Red Alga Rhodella maculata

³⁵SO^2–₄ was used in pulse-chase experiments to study themetabolism of sulphate in the capsular polysaccharides of R.maculata. Radioactivity reached an equilibrium between the chiefintracellular pools during an 8 h pulse and there was no lossof radioactivity from the cells during an extended chase ofup to 14 d, until cultures reached stationary growth phase.Any loss then found was due to dissociation of sulphated capsularmaterial from the cells. The failure of biochemical assays todetect extracellular sulphatase or sulphotransferase activitiessupports the conclusion from pulse-chase experiments that thereis no turnover of sulphate in the capsular polysaccharide ofR. maculata. Key words: sulphated polysaccharides, sulphate turnover, Rhodella     

Inhibition of the Chloroplast Photochemical Reactions by Treatment of Wheat Seedlings with Low Concentrations of Cadmium: Analysis of Electron Transport Activities and Changes in Fluorescence Yield

The effect of treatment of wheat plants with Cd²⁺ ions on thephotochemical activity of the primary leaves was examined. Threeday-old etiolated seedlings were treated with Cd²⁺ ions for24 h in dark, and after this treatment the plants were grownin the light until the primary leaves were fully developed.Cd²⁺ ions (30–120 µM) induced a significant decreasein activities of both photosystem II and photosystem I. Theextent of the decrease in PS II activity was much greater thanthat in the PS I activity. Analysis of changes in the fluorescenceyield of chlorophyll also indicated that Cd²⁺ ions drasticallyaffect the photochemistry of photosystem II. Cd²⁺ ions induceddecrease in the rates of photoreduction of 2,6-dichlorophenolindophenol even in the presence of the exogenous electron donor,hydroxylamine, both in Tris-treated and untreated chloroplasts.This result suggests that the site of inhibition is near thesite of donation of electrons by hydroxylamine. Treatment withCd²⁺ ions impairs the electron transport system on the reducingside of PS II. The decrease in the fluorescence yield of Chi is less than that in the evolution of O₂ mediated by oxidizedphenylenediamine. This difference may be a result of inhibitionon the reducing side of PS II. In addition to inhibition onthe reducing side, Cd²⁺ ions may affect the oxidizing side ofPS II. A comparative study of the rates of evolution of O₂ withp-benzoquinone and dichloro-p-benzoquinone as electron acceptorswas performed since the halogenated benzoquinones have beenshown to accept electrons from both active and inactive centersof photosystem II while some of the benzoquinones accept electronsonly from active centers. The results suggest that Cd²⁺ ionsinduced a marginal increase in the number of inactive reactioncenters in PS II. Analysis of light-saturation-kinetics of theevolution of O₂ catalysed by PS II indicates a reduction inthe size of the antennae as well as in the concentration ofthe active (-type) reaction centers of PS II. Thus, the Cd²⁺-inducedeffects on the photochemistry of PS II involve changes on thereducing side of PS II as well as possible changes in the sizesof the populations of active and inactive centers. Thus, short-termexposure to Cd²⁺ ions during establishment of seedlings hasa severely detrimental effect on photochemical activities inchloroplasts. (Received October 17, 1990; Accepted July 3, 1991)     

Division of Rhizobitoxine-Producing and Hydrogen-Uptake Positive Strains of Bradyrhizobium japonicum by nifDKE Sequence Divergence

Genomic digests from 25 strains of Bradyrhizobium japonicum,for which the phenotypes have been determined with respect toproduction of rhizobitoxine, hydrogen uptake (Hup) and compositionof extracellular polysaccharide (EPS), were hybridized withprobe DNAs of the nifDK and nifE genes of B. japonicum USDA110. The degree of the estimated base substitution in and aroundnifDKE clearly divided the strains of B. japonicum into twomarkedly divergent groups, which were designated as genotypeI and II. Moreover, a strict correlation was observed betweenthese genotypes, production of rhizobitoxine and EPS composition.The genotype I strains produced no rhizobitoxine and an EPScomposed of glucose, mannose, galactose, 4-O-methyl galactoseand galacturonic acid, whereas the genotype II strains producedrhizobitoxine and an EPS composed of rhamnose and 4-O-methylglucuronic acid. Hup⁺ strains were confined exclusively to thegenotype I. Hind III digests of genomic DNAs from the 25 strainswere hybridized with probe DNA of structural genes for the uptakehydrogenase from B. japonicum. In 23 wild-type strains, Hup⁺strains generated a 5.9-kb band that hybridized to the probeunder high-stringency conditions, while Hup^– strains didnot generate the band. These results suggest that the genotypesI and II are two highly divergent evolutionary lines that definea marked division of various phenotypes, such as productionof rhizobitoxine, EPS composition and hydrogen uptake. (Received July 10, 1989; Accepted November 4, 1989)     

The Extent of Starch Turnover in Mature Pepper Leaves in the Light

The extent of starch turnover in pepper leaves in the lighthas been estimated. After leaves were labelled with ¹⁴CO₂ atconstant specific activity for 4–7 h, the irradiance wasreduced to a level which caused no net change in the starchcontent of the leaf, and the supply of ¹⁴CO₂ was removed. Therewas no significant change in specific activity of starch overthe following 6–10 h, thus there was no exchange of ¹⁴C-starchwith ¹²C-assimilates entering the chloroplasts. Starch, turnover, ¹⁴C-labelling, pepper, Capsicum annuum L.     

Drought Tolerance in Two Mosses: Correlated with Enzymatic Defence Against Lipid Peroxidation

Drought-induced changes in the activities of superoxide dismutase(SOD) and catalase, level of lipid peroxidation, and membranepermeability (solute leakage) have been studied in two mosses,the drought-tolerant Tortula ruralis and the drought-sensitiveCratoneuron filicinum. In T. ruralis the activities of SOD andcatalase increase during slow drying. The level of lipid peroxidationconsequently declines. On subsequent rehydration the enzymeactivities decline and the level of lipid peroxidation risesgradually to normal levels. The leakage of preloaded ⁸⁶Rb onrehydration of slowly dried T. ruralis is similar to that inturgid moss, i.e. leakage of about 20% of tissue ⁸⁶Rb. WhenT. ruralis is subjected to rapid drying there is no change inthe enzyme activities or in lipid peroxidation. However, whenthis moss is rehydrated there is a large immediate increasein lipid peroxidation. Half of the tissue ⁸⁶Rb is leaked intothe bathing medium during the first hour of rehydration. Butwithin the next hour, when SOD and catalase activities haveincreased to high levels, lipid peroxidation quickly declinesto a level lower than that in the turgid control moss, and the⁸⁶Rb leaked earlier is partly reabsorbed indicating that membranerepair is well underway. On prolonged rehydration the enzymeactivities decline and the level of lipid peroxidation risesgradually to reach normal levels found in control turgid moss.In the case of drought-sensitive C. filicinum the activitiesof SOD and catalase decline during drying as well as duringsubsequent rehydration. There is a rapid increase in lipid peroxidationduring rehydration and most of the preloaded ⁸⁶Rb leaks intothe bathing medium irreversibly. The changes in lipid peroxidationduring drying and subsequent rehydration of both the mossesappear to coincide in time with the reported changes in O₂ uptake,indicating that the drought-induced membrane damage may be dueto free radical-induced lipid peroxidation which is known torequire active O₂ uptake. Furthermore, there appears to be agood correlation between an ability of the tissue to controllipid peroxidation and its ability to retain solutes. It issuggested that ability of plant tissues to mobilize enzymaticdefence against uncontrolled lipid peroxidation may be an importantfacet of their drought tolerance.     

Homonojirimycin and N-methyl-homonojirimycin inhibit N-Iinked oligosaccharide processing

Homonojirimycin (HNJ) and N-methylhomonojirimycin (MHNJ) weretested as inhibitors of the purified glycopro-tein processingenzymes, glucosidase I and glucosidase II. MHNJ was a reasonablygood inhibitor of glucosidase I (K₁ = 1 x 10^–6 M) andwas about three times as effective on this enzyme as was HNJ.On the other hand, HNJ inhibited glucosidase II with a K₁ ofabout 1 x 10^x6 M, whereas MHNJ was three times less effective(K₁ = 3 x 10^–5 M). However, the butyl derivative of HNJhad very low activity toward these two processing glucosidases.HNJ and its methyl derivative were also tested in vivo usinginfluenza virus-infected MDCK cells, and measuring the inhibitionof N-linked oligosaccharide processing of the viral envelopeglycoproteins. With 100 µg/ml of MHNJ in the medium, essentiallyall of the N-linked oligosaccharide chains of the virus wereof the "high-mannose" type with the major structure being characterizedas Glc₃Man₉(GlcNAc)₂. Similar results were obtained with HNJalthough this compound was less effective in vivo as well asin vitro. These results are in keeping with these inhibitorsbeing effective at the glucosidase I step. Both inhibitors werealso tested in MDCK cell cultures to determine whether theyaffected the in vivo synthesis of proteins, or of lipid-linkedsaccharides. In contrast to deoxynojirimycin, which has beenreported to inhibit the formation of lipid-linked saccharides,no effects were seen on either the incorporation of mannoseinto lipid-linked saccharides or the incorporation of leucineinto protein. glucosidase lipid influenza virus oligosaccharide