Morphological Analysis of Leaf and Tiller Number Dynamics of Wheat (Triticum aestivumL.): Responses to Temperature and Light Intensity

In recent literature on Gramineae species, leaf and tiller numberdynamics have been studied by analysing site filling and thephyllochron of the mainstem. However, site filling is influencedby three components: (1) the phyllochron of the mainstem anddaughter tillers; (2) specific site usage (i.e. fraction ofbuds that ultimately develop into a visible tiller at a specificsite); and (3) HS-delay (i.e. difference in Haun Stage (HS)between the parent tiller and daughter tiller above the pointwhere the daughter tiller appears). These three morphologicalcomponents affecting site filling were studied under differentenvironmental conditions in a growth chamber experiment withspring and winter wheat (Triticum aestivumL.). Treatments weretemperature (daily average 10.5, 15.5 or 20.5 °C) and lightintensity (111, 191 or 286 µmol m^-2s^-1). Effects of temperatureand light intensity on phyllochron were well described by equationsalready reported in the literature. Specific site usage washigher at cooler temperatures and greater light intensitiesand was related to tiller position. It is proposed that theseeffects on specific site usage reflect differences in availabilityof local assimilate for tiller appearance. HS-delay of a tillerwas shorter if the expected tiller appearance was later andwas only slightly affected by light intensity or temperature.This new concept, combining HS-delay and specific site usage,can be useful in constructing more general models of the effectsof environmental factors on the dynamics of leaf number andleaf area ofGramineaespecies.Copyright 1998 Annals of BotanyCompany Triticum aestivum; wheat; phyllochron; temperature; light intensity; leaf number; tillering; site filling; site usage.     

The Effects of Temperature and Light Intensity on Embryo Numbers in Wheat Doubled Haploid Production through WheatxMaize Crosses

Triticum aestivumxZea mayscrosses are now widely used in theproduction of wheat doubled haploids to produce homozygous lines.Seasonal effects are known to influence the number of haploidembryos produced through wheatxmaize crosses, but the effectsof temperature and light have not been quantified. This studyinvestigated the effect of temperature and light intensity onhaploid embryo production. New Zealand wheat cultivars weregrown in a glasshouse until booting when they were transferredto growth cabinets at three temperatures (day/night; 17/12,22/17 or 27/22 °C at an irradiance of 250 µmol m^-2s^-1PAR).In another experiment, wheat lines were transferred to a growthcabinet at one of three light intensities (300, 500 or 1000µmol m^-2s^-1PAR at 22/17 °C day/night, with a photoperiodof 16 h). The temperature and light intensity at which pollinationswere made and subsequent fertilisation and embryo developmentoccurred, significantly (P<0.01) influenced the frequencyof haploid embryo production. The optimal temperature for embryorecovery was 22/17 °C. The greatest number of embryos wasproduced at a light intensity of 1000 µmol m^-2s^-1. Thesefindings will result in improvements in the overall efficiencyof the wheatxmaize system for wheat doubled haploid production.Copyright1998 Annals of Botany Company Intergeneric crossing, temperature, light intensity,Triticum aestivum,wheat,Zea mays,maize.     

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; )     

Properties of Chlamydomonas Photosystem II Core Complex with a His-Tag at the C-Terminus of the D2 Protein

A His-tagged PSII core complex was purified from recombinantChlamydomonas reinhardtii D2-H thylakoids by single-step Ni²⁺-affinitycolumn chromatography and its properties were partially characterizedin terms of their PSII functions and chemical compositions.The PSII core complex that has a His-tag extension at the C-terminusof the D2 protein evolved oxygen at a high rate of 2,400 µmol(mg Chl)^–1h^–1 at the optimum pH of 6.5 with ferricyanideand 2,6-dichlorobenzoquinone as electron acceptors in the presenceof Ca²⁺ as an essential cofactor, and approximately 90% of theactivity was blocked by 10 µM DCMU. The core complex exhibitedthe thermoluminescence Q-band but not the B-band regardlessof the presence or absence of DCMU, although both bands wereobserved in the His-tagged thylakoids. The core complex wasfree from PSI and contained one Y_D, Tyr 160 of the D2 protein,four Mn atoms, two cytochrome b-559, about 46 Chl a molecules,and probably one Q_A, the primary acceptor quinone of PSII. Itwas inferred from these results that His-tagging at the C-terminusof the D2 protein does not affect the functional and structuralintegrity of the PSII core complex, and that the ‘His-tagstrategy’ is highly useful for biochemical, physicochemical,and structural studies of Chlamydomonas PSII. (Received October 22, 1998; Accepted December 25, 1998)     

Elicitor Activity of a Fungal Product Assessed at the Single-Cell Level by a Novel Gel-Bead Method

Elicitor from Erysiphe pisi was incorporated into gel beads.Individual beads were placed on single cells from barley coleoptiles.The elicitor induced unusual cytoplasmic responses and temporaryresistance to infection in coleoptile cells. The technique isapplicable to assessment of elicitor activity at the single-celllevel. ¹Contribution no. 118 from the Laboratory of Plant Pathology,Mie University. ²Present address: Laboratory of Plant Pathology & GeneticEngineering, College of Agriculture, Okayama University, Okayama,700 Japan     

Presence of the Photoactive Reaction-Center Chlorophyll of PSI (P700) in Dark-Grown Cells of a Chlorophyll-Deficient Mutant of Chlorella kessleri

Compositions of pigments and polypeptides of pale green membranesthat had been isolated from dark-grown cells of a chlorophyll-deficientmutant of Chlorella kessleri were investigated. They containedChl a in a level corresponding to about 1% of that present inthe thylakoid membranes isolated from autotrophically grownwild-type cells and a trace amount of chlorophyllide a, butneither Chl b nor carotenoids. The polypeptide profile of themutant membranes was similar to that of membranes isolated fromwild-type cells that were grown in the dark. Neither the chlorophyll-bindingsubunits of PSI nor the apoproteins of LHCP were detected bySDS-PAGE and immunoblot analysis. However, the light-minus-darkdifference spectrum of the mutant membranes revealed the presenceof the reaction-center chlorophyll of PSI (P700) at a molarratio of 190 chlorophyll (Chl a plus Chlide a) per P700. P700was more stable than Chl a and Chlide a in the light so thatprolonged illumination led to a decline in the Chl/P700 ratioto 24. The initial rate of P700 photooxidation in the mutantmembranes was comparable to that in CP1 isolated from the dark-grownwild-type cells. Under illumination with strong light, the initialrate was decreased in parallel to the decrease in Chl/P700 ratio.The results suggest that most of Chi present in the mutant membranescan transfer excitation energy to P700. (Received March 13, 1998; Accepted August 7, 1998)     

Mutagenesis of the N-glycosylation site of hNaSi-1 reduces transport activity

The human Na⁺-sulfate cotransporter (hNaSi-1) belongs to the SLC13 gene family, which also includes the high-affinity Na⁺-sulfate cotransporter (hSUT-1) and the Na⁺-dicarboxylate cotransporters (NaDC). In this study, the location and functional role of the N-glycosylation site of hNaSi-1 were studied using antifusion protein antibodies. Polyclonal antibodies against a glutathione S-transferase fusion protein containing a 65-amino acid peptide of hNaSi-1 (GST-Si65) were raised in rabbits, purified, and then used in Western blotting and immunofluorescence experiments. The antibodies recognized native NaSi-1 proteins in pig and rat brush-border membrane vesicles as well as the recombinant proteins expressed in Xenopus oocytes. Wild-type hNaSi-1 and two N-glycosylation site mutant proteins, N591Y and N591A, were functionally expressed and studied in Xenopus oocytes. The apparent mass of N591Y was not affected by treatment with peptide-N-glycosylase F, in contrast to the mass of wild-type hNaSi-1, which was reduced by up to 15 kDa, indicating that Asn⁵⁹¹ is the N-glycosylation site. Although the cell surface abundance of the two glycosylation site mutants, N591Y and N591A, was greater than that of wild-type hNaSi-1, both mutants had greatly reduced V_max, with no change in K_m. These results suggest that Asn⁵⁹¹ and/or N-glycosylation is critical for transport activity in NaSi-1. antifusion protein antibodies; Xenopus oocytes; sulfate; immunofluorescence     

Mutations in the SGR4, SGR5 and SGR6 Loci of Arabidopsis thaliana Alter the Shoot Gravitropism

Shoots of higher plants grow upward in response to gravity.To elucidate the molecular mechanism of this response, we haveisolated shoot gravitropism (sgr) mutants in Arabidopsis thaliana.In this report, we describe three novel mutants, sgr4-1, sgr5-1and sgr6-1 whose inflorescence stems showed abnormal gravitropicresponses as previously reported for sgr1, sgr2 and sgr3. Thesenew sgr mutations were recessive and occurred at three independentgenetic loci. The sgr4-1 mutant showed severe defect in gravitropismof both inflorescence stem and hypocotyl but were normal inroot gravitropism as were sgr1 and sgr2. The sgr5-1 and sgr6-1mutants showed reduced gravitropism only in inflorescence stemsbut normal in both hypocotyls and roots as sgr3. These resultssupport the hypothesis that some mechanisms of gravitropismare genetically different in these three organs in A. thaliana.In addition, these mutants showed normal phototropic responses,suggesting that SGR4, SGR5 and SGR6 genes are specifically involvedin gravity perception and/or gravity signal transduction forthe shoot gravitropic response. (Received November 21, 1996; Accepted February 17, 1997)     

Genetic Engineering of the Processing Site of D1 Precursor Protein of Photosystem II Reaction Center in Chlamydomonas reinhardtii

The D1 protein (D1) of photosystem II (PSII) reaction centeris synthesized as a precursor (pD1) and then processed at itscarboxyl terminus to establish the function of water cleavage.The amino acid sequence of the carboxyl terminal extension excisedby this process is poorly conserved except for a residue afterthe cleavage site at position of 345. We have constructed avector for site-directed mutagenesis of the chloroplast psbAgene encoding D1 of the green alga, Chlamydomonas reinhardtii.The vector enables one to transform the chloroplasts of a psbAdeletion mutant (Fud7) and directly select transformants forresistance to spectinomycin. Using this transforming vector,we have substituted Ser345 to Gly, Cys, Val and Phe in orderto investigate effects of the amino acid side chain at thisposition on the processing rate. All of the resulting transformantsexhibited the PSII activity as wild type and grew normally underphotoautotrophic conditions even under strong light where rapidturnover of Dl protein is expected to occur. Western blottinganalysis demonstrated that mature D1 accumulates in these transformantsat wild type level. Pulse and chase labeling of chloroplast-encodedproteins using [³⁵S]sulfate revealed that the processing ofD1 precursor protein occurs in all four transformants as efficientlyas in wild type, at least under the experimental conditionsexamined. The results suggest that either the amino acid sidechain at position of 345 (+1 position) is not crucial to theenzymatic cleavage of pD1 in vivo or the apparent rate of processingin vivo is not limited by the enzymatic cleavage. (Received September 22, 1995; Accepted December 25, 1995)     

Flexible Leaf Orientations ofArisaema heterophyllumMaximize Light Capture in a Forest Understorey and Avoid Excess Irradiance at a Deforested Site

Effects of flexible leaflet orientations on light capture andphotosynthesis were investigated forArisaema heterophyllumBlume,a perennial herb with a single palmately compound leaf, in twocontrasting light environments: a riparian forest understoreyand an adjacent deforested open site. Leaf orientations aredetermined by inclination of leaflet midvein and folding ofleaflet blade. Leaves were flatter and had smaller angles ofinclination at the forest site than at the deforested site.Directions (angular altitude and azimuth) of leaf surfaces ofthe forest site plants were close to those predicted to maximizediffuse light capture at each microsite, as determined by theanalysis of a hemispherical canopy photograph. Mean light captureefficiency (the ratio of actual diffuse light capture by a leafto maximal receivable light) reached 98%. In contrast, markedleaflet folding occurred only at the deforested site. The degreeof folding varied diurnally with the maximum around noon. Computersimulations showed that PPFDs (photosynthetically active photonflux density) over the photosynthetic saturation level ofA.heterophyllumcan be effectively reduced by increasing the slopeof leaflet surfaces. The importance of decreasing excess irradianceto avoid photoinhibition and to maintain high rates of photosynthesiswas confirmed by artificially constraining leaves horizontally.Copyright1998 Annals of Botany Company Arisaema heterophyllumBlume, forest understorey, hemispherical canopy photograph, high light stress, leaf orientation, light capture efficiency, microsite light availability, midday depression, photoinhibition, photosynthesis.     

Quantal Response of Fruit and Seed Germination Rate in Quercus robur L. and Castanea sativa Mill, to Constant Temperatures and Photon Dose

A linear relationship between constant temperatures in the sub-optimaltemperature range and germination rate is shown in both Quercusrobur L and Castanea sativa Mill germinated under nominal darkconditions. The mean base temperature was interpolated for Qrobur as 0 8 ? or 2-4 ?, depending on seed lot provenance, andfor C. sativa as 1 -4? The optimum temperature for germinationin Q. robur was about 20? compared with around 28 ? in C. sativaOver the sub-optimal temperature range the distribution of thermaltimes was log-normal for each population studied their spreadvarying both between Q robur seed lots and between species However,in C. sativa germinated close to the mean base temperature,the distribution in thermal times was reduced Thermal timesto germination were decreased in Q. robur and C sativa by approximately0 3 and 0-5 log-units, respectively, when the pericarp was removed,i.e in the seeds, but the sensitivity of the response remainedrelatively unaltered In both species the germination rate was the same when nominaldark or safe green light conditions were employed during thegermination test. However, at 21 ? Q robur exhibited the highirradiance reaction (HIR) at photon doses above 30mmol m^–2d^–1. HIR first affected the germination rate by an inhibitionof radicle extension The sensitivity of the response to thermaltime was reduced as photon dose increased. This photo-inhibitionwas exacerbated at supra-optimal temperatures. In contrast,C. sativa germination rate at 26 ? was little influenced bylight at a photon dose of 752 mmol m^–2 d^–1 Key words: Seed germination rate, temperature, thermal time, light, photon dose     

Isolation and Characterization of Double-Stranded RNAs from the Pea Pathogen, Mycosphaerella pinodes

Studies on the structure of the extrachromosomal nucleic acidsin the plant pathogenic fungus, Mycosphaerella pinodes, OMP-1,isolated from Okayama, Japan, indicate that at least three double-stranded(ds) RNAs are present in the cytoplasm, while a strongly pathogenicisolate from England, MP-3, does not contain any of the dsRNAs.The sizes of these dsRNAs are 6.0 kb (L), 4.0 kb (M), and 2.6kb (S), respectively. Weakly pathogenic mutants selected fromUV-irradiated OMP-1 contain considerably higher copy numberof S than does the parental strain, while one of the mutants,OMP-X62, contains no detectable M. OMP-1 was cured of detectabledsRNAs by treatment with cycloheximide. Curing was accompaniedby an increase in virulence and by partial recovery of a colonymorphology similar to that of MP-3. The presence of these dsRNAsapparently results in a reduction in mycelial growth, in thestimulation of sporulation and possibly in the promotion ofhypovirulence. (Received February 19, 1990; Accepted October 30, 1990)     

The Interactive Effects of Atmospheric Carbon Dioxide and Light on Stem Elongation in Seedlings of Four Species

Four species,Sinapis albaL.,Medicago sativaL.,Gypsophila paniculataL.andPicea abies(L.) Karsten, were grown in three light regimes:darkness, low light (25 µmol m^-2s^-1for 10 min d^-1) andhigh light (120 µmol m^-2s^-1for 12 h  d^-1) and fourlevels of carbon dioxide: 0, 350, 700 and 1400±50 µll^-1. Germination was not affected by any of the treatments.The effects of carbon dioxide on stem elongation were identicalin low and high light: stem length increased at a decreasingrate with level of carbon dioxide in all species. Level of carbondioxide also affected stem elongation in complete darkness,but the pattern was more complex and varied among species. Totalweight did not vary with level of carbon dioxide to any significantextent in either darkness or low light, but increased with levelof carbon dioxide at high light in all four species. Due tothe absence of any effect of carbon dioxide on growth in darknessand low light, we suggest the effects of carbon dioxide on stemelongation are independent of effects on growth and may be dueto a direct interaction with developmental processes. In contrast,level of carbon dioxide had little effect on allocation patternsin the dark and low light experiments, but had marked effectsin high light. Therefore, the effect of carbon dioxide on allocationwas probably due to the effects of carbon dioxide on growthrather than to any direct interaction between carbon dioxideand development. An understanding of the mechanisms by whichcarbon dioxide affects development may help us understand theoften variable effects of carbon dioxide upon plants.Copyright1998 Annals of Botany Company Sinapis albaL.;Medicago sativaL.;Gypsophila paniculataL. andPicea abies(L.) Karsten; elevated carbon dioxide; stem elongation; germination; allocation; phytochrome.     

Photoinhibition and light-induced cyclic electron transport in ndhB(-) and psaE(-) mutants of Synechocystis sp. PCC 6803

The ndhB^– and psaE^– mutants of the cyanobacteriumSynechocystis sp. PCC 6803 are partly deficient in PSI-drivencyclic electron transport. We compared photoinhibition in thesemutants to the wild type to test the hypothesis that PSI cyclicelectron transport protects against photoinhibition. Photoinhibitorytreatment greatly accelerated PSI cyclic electron transportin the wild type and also in both the mutants. The psaE^–mutant showed rates of PSI cyclic electron transport similarto the wild type under all conditions tested. The ndhB^–mutant showed much lower rates of PSI cyclic electron transportthan the wild type following brief dark adaptation but exceededwild type rates after exposure to photoinhibitory light. Thewild type and both mutants showed similar rates of photoinhibitiondamage and photoinhibition repair at PSII. Photoinhibition atPSI was much slower than at PSII and was also similar betweenthe wild type and both mutants, despite the known instabilityof PSI in the psaE^– mutant. We conclude that photoinhibitorylight induces sufficient PSI-driven cyclic electron transportin both the ndhB^– and psaE^– mutants to fulfill anyrole that cyclic electron transport plays in protection againstphotoinhibition. ⁴ Corresponding author: E-mail, sherbert@uwyo.edu; Fax, +1-307-766-2851;Phone, +1-307-766-4353.     

Time Lapse Analysis of Root Elongation Rates of Rice and Sorghum During the Day and Night

This paper describes a technique to monitor the root elongationrate (RER) per hour for several days, and variation in RER duringthe day and night. Rice (Oryza sativaL.) and sorghum (SorghumbicolorMoench) were grown in root boxes placed inside a growthchamber set at 25 °C with a 12 h photoperiod. Seminal rootaxes were sandwiched between a transparent acrylic board andfilter paper placed on a loamy sand soil. The roots were photographedunder dim green light using a CCD camera connected to a timelapse video recorder. The environment of the root, includingtemperature, light, nutrient, water and air supply, was controlledprecisely and maintained constant. RER fluctuated hourly insorghum and to a greater extent in rice. Maximum RERs were 1.4to 4.4 times faster than minimum rates. RERs during the dayand night did not differ statistically when temperatures werethe same.Copyright 1998 Annals of Botany Company Oryza sativaL., periodicity, root elongation,Sorghum bicolorMoench, time lapse.     

AGR,an Agravitropic Locus of Arabidopsis thaliana, Encodes a Novel Membrane-Protein Family Member

Mutations in the Agr locus of Arabidopsis thaliana impair theroot gravitropic response. Root growth of agr mutants is moderatelyresistant to ethylene and to an auxin transport inhibitor. Verticallyplaced agr roots grow into agar medium containing IAA or naphthalene-1-aceticacid, but not into medium containing 2,4-D. Positional cloningshowed that AGR encodes a root-specific member of a novel membrane-proteinfamily with limited homology to bacterial transporters. (Received September 4, 1998; Accepted September 21, 1998)     

Ferric chelate reduction by sunflower (Helianthus annuus L.) leaves: influence of light, oxygen, iron-deficiency and leaf age

The presence of ferric chelate reducing activity in sunflower[Helianthus annuus L.) leaves has been studied by submergingleaf discs in a solution with Fe(III)-ethylenediaminetetra-acetate(FeEDTA), batho-phenanthroline disulphonate (BPDS) and vacuuminfiltration. The effect of different factors on the Fe(III)reduction rate was studied. Ferric reduction rate was about10-fold higher in the light than in darkness. The light effectwas greatly inhibited by 3-(3,4-dichloro-phenyl)-1,1-dimethylurea(DCMU), a photosystem II inhibitor. Several inhibitors of redoxsystems [cis-platinum (II) diamine dichloride (cis-platin),p-nitro-phenylacetate (p-NPA) and p-hydroxymercuribenzoic acid(pHMB)] decreased the FeEDTA reduction rate. The greatest inhibitionwas produced by the - SH group reagent pHMB (17% of control,in light). The FeEDTA reduction rate was much higher in theabsence of O₂ than with air or 100% O₂. Superoxide dismutase(SOD) decreased FeEDTA reduction with air in the light. Youngleaves reduced Fe(III)-chelate at a higher rate than did olderleaves. In iron-deficient plants, leaves did not exhibit enhancedferric chelate-reducing activity as was observed in roots. Itis suggested that at least two different redox systems or twostates of the same redox system work in the light and in darkness. Key words: Iron, leaves, plasma membrane-redox, light, oxygen level     

Light Quality and Vernalization Interact in Controlling Late Flowering in Arabidopsis Ecotypes and Mutants

The late flowering ecotypes of Arabidopsis thaliana L. (Heyn.)Eifel, Pitztal and Innsbruck responded to 10 d vernalization(cold treatment) by flowering earlier with less with less thanhalf the number of leaves of non-induced plants. The vernalizationresponse was cumulative: increased numbers of days of vernalizationinduced earlier flowering up to an apparent saturation in responseafter 30 to 40 d. The ratio of red:far-red (R:FR) light alsoaffected non-vernalized time-to-flower. When grown under fluorescentplus incandescent lamps (R:FR = 1·0), time-to-flowerwas approximately half that required by plants grown under fluorescentlamps (R:FR = 5·8) at the same photon flux density andphotoperiod. Leaf production rate was unaffected by either vernalizationor light quality changes and time-to-flower and leaf numberwere highly correlated (r² = 0·973). The late flowering mutants of Landsberg erecta were grown underlighting which displayed a gradient of R:FR. Some mutants likeco, flowered at the same time in all R:FR treatment, while otherlike fca took nearly twice as long to flower, with double thenumber of leaves at R:FR ratio of 5·8 compared with theR:FR = 1 treatment. The ranking of the response from least tomost responsive was co, fe, gi, WT, fd, fwa, ft, fha, fpa, fy,fve and fca. Vernalization of these Landsberg mutants always resulted inearlier flowering, although only fca, fve, fy and fpa were significantlymore sensitive to thermoinduction than the wild type parent.There was a high correlation (r² = 0·89 between the responseto thermoinduction and to R:FR ratio. Vernalization of fca for24 d largely eliminated the R:FR time-to-flower response. Vernalizationand photoinduction similarly affect late flowering and can substitutefor each another.Copyright 1993, 1999 Academic Press Light quality, vernalization, flowering, Arabidopsis thaliana, phytochrome, thermoinduction, photoperiod, photoinduction, growth conditions, photon flux density, daylength, spectral quality, far-red light     

Mytilus edulis chilensis infested with Coccomyxa parasitica (Chlorococcales, Coccomyxaceae)

The association between the green alga Coccomyxa parasitica (Chlorococcales)and the mussel Mytilus edulis chilensis at Goose Green, Falkland Islandsis reported. C. parasitica occurred within the soft tissueswith an overall infestation rate of 16%. The highest levelsof infestation (23%) occurred in individuals from the middleof the main mussel bed, with considerably lower levels of infestation inthe upper and lower regions (<1% and 5% respectively). Noconsistent seasonal pattern in infestation rate was detectedbetween September 1993 and February 1996. C. parasitica wasmost commonly observed in tissues located in the posterior territoryof the host, in areas most directly exposed to light. Tissuesof infested mussels were rather watery and translucent and theadductor muscle appeared weak and stringy. During the summermonths when Falkland mussels are in peak reproductive condition,dry flesh weight of infested mussels was significantly lowerthan non–infected mussels of comparable size suggestingthat infestation by C. parasitica may reduce reproductive output.However it is uncertain whether poor condition of the host isdue to the presence of the parasitic alga or whether C. parasiticainfests only those mussels that are already in poor condition. ¹ Present address: 3, St Marys Walk, PO Box 530, Stanley, Falkland Islands (Received 10 June 1998; accepted 8 September 1998)     

Demonstration of Two Sites of Inhibition of Electron Transport by Protein Phosphorylation in Wheat Thylakoids

The effect of protein phosphorylation on electron transportactivities of thylakoids isolated from wheat leaves was investigated.Protein phosphorylation resulted in a reduction in the apparentquantum yield of whole chain and photosystem II (PSII) electrontransport but had no effect on photosystem I (PSI) activity.The affinity of the D1 reaction centre polypeptide of PSII tobind atrazine was diminished upon phosphorylation, however,this did not reduce the light-saturated rate of PSII electrontransport. Phosphorylation also produced an inhibition of thelight-saturated rate of electron transport from water or durohydroquinoneto methyl viologen with no similar effect being observed onthe light-saturated rate of either PSII or PSI alone. This suggeststhat phosphorylation produces an inhibition of electron transportat a site, possibly the cytochrome b₆/f complex, between PSIIand PSI. This inhibition of whole-chain electron transport wasalso observed for thylakoids isolated from leaves grown underintermittent light which were deficient in polypeptides belongingto the light-harvesting chlorophyll-protein complex associatedwith photosystem II (LHCII). Consequently, this phenomenon isnot associated with phosphorylation of LCHII polypeptides. Apossible role for cytochrome b₆/f complexes in the phosphorylation-inducedinhibition of whole chain electron transport is discussed. Key words: Electron transport, light harvesting, photosystem 2, protein phosphorylation, thylakoid membranes, wheat (Triticum aestivum)