FORMATION OF PHYCOERYTHRIN IN PRE-ILLUMINATED CELLS OF TOLYPOTHRIX TENUIS WITH SPECIAL REFERENCE TO NITROGEN METABOLISM

1. The formation, in the dark, of phycoerythrin in the preilluminatedcells of a blue-green alga, Tolypothrix tenuis, was investigatedwith special reference to its nitrogen metabolism.
2. On incubatingthe pre-illuminated algal cells under a darkaerobiccondition,and with nitrate as N-source, the formation of phycoerythrinoccurs after an induction period of about 5 hours. No time-lagis observed in the nitrate-uptake by the organism. Similar resultsare obtained with nitrite, ammonia, urea and arginine as N-sources.
3. The above stated formation of phycoerythrin is suppressedbysubstances such as chloramphenicol and p-fluorophenylalanine,substances known to be potent inhibitors of protein-synthesis.
4. On the basis of these findings, it was inferred that therearetwo consecutive processes involved in the dark-formationofphycoerythrin in the pre-illuminated cells: (i) uptake andconversionof exogenous nitrogen sources into some intermediarynitrogenouscell substances, and (ii) synthesis of the pigment-proteinfromthese substances.

(Received June 27, 1960; )     

ZmXTH1, a new xyloglucan endotransglucosylase/hydrolase in maize, affects cell wall structure and composition in Arabidopsis thaliana

Xyloglucan endotransglucosylase/hydrolases (XTHs; EC 2.4.1.207and/or EC 3.2.1.15 [EC] 1) are enzymes involved in the modificationof cell wall structure by cleaving and, often, also re-joiningxyloglucan molecules in primary plant cell walls. Using a poolof antibodies raised against an enriched cell wall protein fraction,a new XTH cDNA in maize, ZmXTH1, has been isolated from a cDNAexpression library obtained from the elongation zone of themaize root. The predicted protein has a putative N-terminalsignal peptide and possesses the typical domains of this enzymefamily, such as a catalytic domain that is homologous to thatof Bacillus macerans β-glucanase, a putative N-glycosylationmotif, and four cysteine residues in the central and C terminalregions of the ZmXTH1 protein. Phylogenetic analysis of ZmXTH1reveals that it belongs to subgroup 4, so far only reportedfrom Poaceae monocot species. ZmXTH1 has been expressed in Pichiapastoris (a methylotrophic yeast) and the recombinant enzymeshowed xyloglucan endotransglucosylase but not xyloglucan endohydrolaseactivity, representing the first enzyme belonging to subgroup4 characterized in maize so far. Expression data indicate thatZmXTH1 is expressed in elongating tissues, modulated by cultureconditions, and induced by gibberellins. Transient expressionassays in onion cells reveal that ZmXTH1 is directed to thecell wall, although weakly bound. Finally, Arabidopsis thalianaplants expressing ZmXTH1 show slightly increased xyloglucanendohydrolase activity and alterations in the cell wall structureand composition. Key words: Cell elongation, cell wall, plant transformation, XEH, XET, XTH, Zea mays     

Ultrastructural and Cytochemical Studies of 'Air Blisters' in Pilea cadierei Gagnep. and Guillaumin

Cells from the sub-epidermal layer of Pilea cadierei preparedfor electron microscopy using standard fixation and embeddingprocedures appear extremely osmiophilic, with the organellesstanding out in negative relief. However, when tissues werefixed in glutaraldehyde supplemented with either procaine orcaffeine (substances known to complex with phenols) the osmiophilicmaterial was generally limited to the vacuole. After procaineor caffeine fixation the surrounding cytoplasm appeared as inadjacent, nonphenolic cells. Some small aggregates of phenolicmaterial appear in the cisternae of the endoplasmic reticular,indicating these organelles may be involved in either the synthesisor transport of phenolics in Pilea. Since one of the major functionsof phenolics is in light-screening, air blisters may serve toscreen out damaging radiation from the underlying tissue. Thepresence of typical shade-type plastids in Pilea air blistersis a further indication of this light-screening role. Pilea cadierei, aluminium plant, air blister, cytochemistry, ultrastructure, light screening, phenolics     

Embryo and Endosperm Function and Failure inSolanumSpecies and Hybrids

Although the importance of the endosperm as a food store inmany angiosperm seeds is well known, its significance duringearly embryogenesis has been neglected. In many interspecifichybrids, and in some other situations, embryos do not developfully and abort. It has often been stated that this is causedby the endosperm failing to conduct sufficient nutrients tothe embryo, but seldom has it been suggested that the endospermactively controls most of the early stages of morphogenesisof the embryo. Information gleaned from a broad survey of theliterature, combined with additional evidence presented here,obtained fromSolanum incanumand interspecific hybrids, indicatethat the endosperm is dynamic and very active in regulatingearly embryo development. This requires highly integrated geneticcontrol of rapidly changing metabolism in the endosperm. Ininterspecific hybrids, lack of coordination may cause unbalancedproduction of growth regulating substances by the endospermand hence abortion of the embryo, or even unregulated productionof nucleases and proteases resulting firstly in autolysis ofthe endosperm and then digestion of the embryo. The endospermmay thus serve to detect inappropriate hybridization of speciesor ploidy levels and so prevent waste of resources by producingseeds that would result in sterile hybrids or unthrifty subsequentgenerations. This discriminatory function of the endosperm hasdiminished during evolution and domestication of the crop plantSolanummelongenaL.Copyright 1998 Annals of Botany Company Solanum, embryo morphogenesis, endosperm, hybrid, seed development.     

The Olfactory System as a Model for the Analysis of the Contribution of Gene Expression to Programmed Cell Death

The process of programmed cell death is frequently attenuatedby inhibitors of protein and RNA synthesis. This implies thatgene expression is necessary for the active elimination of somecell types. Genes such as bcl-2 and bax have been implicatedin the direct control of cell death, while cellular immediate-earlygenes (clEGs), such as c-fos and c-jun have been repeatedlyassociated with neuronal degeneration. We are using the olfactoryneuroepithelium as a model system to investigate the role thatexpression of such genes might play in cell death. The advantagesof this system is that even in the adult, there is spontaneousdegeneration of olfactory receptor neurons followed by theirreplacement by the division and differentiation of precursors.Futhermore, the receptor neurons can be induced to die synchronouslyby removal of the olfactory bulb or intranasal administrationof toxic agents. We have generated fos-lacZ and jun-lacZ transgenicmice that can be used to assess expression of c-fos and c-junfollowing these various manipulations. In addition, a line oftransgenic mice has been derived that express Bcl-2 under thecontrol of the olfactory receptor protein promoter. These micehave high levels of Bcl-2 selectively in receptor neurons ofthe primary neuro-epithelium and vomeronasal organ. Since insome circumstances, Bcl-2 can protect against programmed celldeath these mice are being assessed for neuronal turnover underbasal conditions and following olfactory bulbectomy.     

Water Distribution in Foliose Lichen Species: Interactions between Method of Hydration, Lichen Substances and Thallus Anatomy

Three lichens (Neofuscelia pokornyi, N. pulla and Xanthoriaparietina) from a semi-arid habitat were examined using low-temperaturescanning electron microscopy to evaluate the effects of hydrationmethod, lichen substances and thallus anatomy on the water distributionof hydrated thalli. In theNeofuscelia species, extracellularwater within the thallus was observed in association with cracksin its otherwise impervious upper cortex, while X. parietinashowed abundant extracellular water between medullary hyphae.Spraying the thalli followed by maintenance for 14–20h in a water-saturated atmosphere led to the disappearance ofthe external water film in X. parietina but not in the Neofusceliaspecies. Surface water was abundant in specimens of all speciesimmediately after spraying for 15 min. No extracellular waterwas observed inside the thallus 14–20 h after spraying,but after rinsing with acetone its presence was detected inall three species. Hydric strategy correlated with cortex hygroscopicity:X. parietina, an aero-hygrophytic species, had a more hygroscopicupper cortex than theNeofuscelia species, which are substrate-hygrophytic.The hygroscopicity of the upper cortex was linked with the amountof extracellular water in the thalline interior. Differencesbetween X. parietina and Neofuscelia in the polarity and distributionof their lichen substances agreed with species differences inthe presence and distribution of free water both as a film overthe surface and inside the thallus. Lichen substances appearto play a role in the maintenance of air-filled intrathallinespaces in species whose anatomy, habitat, or both, favour water-loggedconditions. Copyright 2000 Annals of Botany Company Lichen, water relations, semi-arid, lichen substances, LTSEM, thallus anatomy, extracellular water, Neofuscelia pokornyi(Körb.) Essl., Neofuscelia pulla(Ach.) Essl., Xanthoria parietina(L.) Th. Fr     

REVIEW ARTICLE: Zygotic embryogenesis versus somatic embryogenesis

This review will summarize molecular and genetic analyses aimedat identifying the mechanisms underlying the sequence of eventsduring plant zygotic embryogenesis. These events are being studiedin parallel with the histotogical and morphological analysesof somatic embryogenesis. The strength and limitations of somaticembryogenesis as a model system will be discussed briefly. Theformation of the zygotic embryo has been described in some detail,but the molecular mechanisms controlling the differentiationof the various cell types are not understood. In recent yearsplant molecular and genetic studies have led to the identificationand characterization of genes controlling the establishmentof polarity, tissue differentiation and elaboration of patternsduring embryo development. An investigation of the developmentalbasis of a number of mutant phenotypes has enabled the identificationof gene activities promoting (1) asymmetric cell division andpolarization leading to heterogeneous partitioning of the cytoplasmicdeterminants necessary for the initiation of embryogenesis (e.g.GNOM),(2) the determination of the apical-basal organization whichis established independently of the differentiation of the tissuesof the radial pattern elements (e.g.KNOLLE, FACKEL, ZWILLE),(3) the differentiation of meristems (e.g.SHOOT-MERISTEMLESS),and (4) the formation of a mature embryo characterized by theaccumulation of LEA and storage proteins. The accumulation ofthese two types of proteins is controlled by ABA-dependent regulatorymechanisms as shown using both ABA-deficient and ABA-insensitivemutants (e.g.ABA, ABI3). Both types of embryogenesis have beenstudied by different techniques and common features have beenidentified between them. In spite of the relative difficultyof identifying the original cells involved in the developmentalprocesses of somatic embryogenesis, common regulatory mechanismsare probably involved in the first stages up to the globularform. Signal molecules, such as growth regulators, have beenshown to play a role during development of both types of embryos.The most promising method for identifying regulatory mechanismsresponsible for the key events of embryogenesis willcome frommolecular and genetic analyses. The mutations already identifiedwill shed light on the nature of the genes that affect developmentalprocesses as well as elucidating the role of the various regulatorygenes that control plant embryogenesis. Key words: Development, marker, mutant, somatic embryogenesis, zygotic embryogenesis     

Xenopus laevis L-14 lectin is expressed in a typical pattern in the adult, but is absent from embryonic tissues

Soluble, dimeric, lactose-binding lectins with subunit Mr ofñ 14–16 x 10³, here called L-14s, are expressedin multiple tissues in all vertebrates that have been examined.L-14s have particular affinity for polylactosamine chains onlaminin, co-localize with laminin in some basement membranes,and influence adhesion to laminin and proliferation for somecultured cells. In previous studies of mammals and chickens,L-14s have been found at high levels in a variety of adult tissues,such as muscle and peripheral nerve, but at much higher levelsin many embryonic tissues, suggesting a special role in development.To further explore possible roles of L-14 in embryogenesis,we have studied the expression of L-14 in embryonic and adultXenopus laevis tissues. Except for the abundant L-14 in poisonglands in adult Xenopus skin, we find that Xenopus L-14 is expressedin the same general distribution as its mammalian homologues.However, we could detect no expression of L-14 in Xenopus embryosusing either a sensitive immunoassay for the protein or a sensitiveRNase protection assay for its mRNA. Furthermore, use of affinitychromatography to identify other lactose-binding lectins inembryonic tissue revealed only scarce proteins with higher subunitmolecular weights. These results suggest that in X.laevis L-14functions in adult tissues and is not involved in embryogenesis. ß-galactoside-binding lectin L-14 lectin Xenopus laevis.     

Ultrastructure of Angiosperm Haustoria--A Review

It has been clear for many years that the evolution of parasitismin the angiosperms has taken place independently in a numberof unrelated groups (Kuijt, 1969). In other words, the parasiticorgans (haustoria) which both structurally and physiologicallyjoin host and parasite are remarkable instances of convergentevolution in these different groups. The main thread which canbe followed throughout the many anatomical studies which inthe past have been carried out on haustoria is the search forcommon denominators between various groups; that is, as to howmuch the haustoria of unrelated taxa have come to resemble eachother. When Solms-Laubach (1867–1868) more than a century agoreviewed the structure of angiosperm haustoria it required wellover one hundred pages to do so. Needless to say the bulk ofour present knowledge has been obtained since that time, andlight microscopy continues to unearth significant new information.In a recent review of haustorial anatomy (Kuijt, 1969), severalstructural parallelisms are noted. The advent of electron microscopyhas, since the latter review, resulted in a great deal of additionalinformation which has enabled certain comparisons between groupsto be made. Ultrastructural studies have quite naturally concentratedon the most readily available which, of course, are also thosewhich have been most i ntensively studied with the light microscopein the past. The haustoria of several families, such as Rafflesiaceae,Balanophoraceae, Hydnoraceae, and Lennoaceae, have scarcelybeen studied even with the light microscope. The purpose of the present paper is to give a general reviewof present knowledge of the ultrastructure of haustoria. Todo so we must of necessity ignore most recent purely anatomicalwork, except where relevant to the topics under discussion.Ultrastructural observations have been made on mistletoes (Arceuthobiumand Phthirusa, Loranthaceae), Santalaceae (several genera),Scrophulariaceae(Castilleja), Orobanchaceae (Orobanche) andConvolvulaccae (Cuscuta), in which order the discussion willproceed.     

Anaesthetic Enhancement of Echinochloa crus-galli (L.) Beauv. Seed Germination: Possible Membrane Involvement

Taylorson, R. B. 1988. Anaesthetic enhancement of Echinochloacrus-galli (L.) Beauv. seed germination: possible membrane involvement.—J.exp. Bot 39: 50–58. Dormant E. crus-galli seeds can be stimulated to germinate bycontact with solutions of several anaesthetic-like substances.The order of activity was n-pentanol > benzyl alcohol >n-butanol > n-propanol > ethanol. 2-propanol is nearlyinactive. The relative activity of the substances as germinationstimulants is closely related to their membrane-buffer partitioncoefficients in a manner similar to their effectiveness as anaestheticsin animals. Thus, n-pentanol is a more active stimulant of germinationthan ethanol and its increased effectiveness is correlated witha higher membrane-buffer partition coefficient Similarly, ananaesthetic that stimulated germination (n-propanol) causedgreater leakage of electrolytes, U.V. absorbing substances andamino acids from E. crus-galli seeds than a substance that wasnot active as a germination stimulant (2-propanol). In animals,action of anaesthetics can be prevented by application of externalpressure, an argument for membrane action. Action of n-propanolin stimulating germination can be similarly prevented by pressurein E. crus-galli seeds. The several lines of evidence supporta membrane action for anaesthetic-like substances in seeds and,accordingly, a membrane site as the locus of seed dormancy. Key words: Anaesthetics, germination, membranes     

Paternal Care in Canids

Paternal care has never been reported as absent in any canidspecies, and some form of care has been seen in 18 of the 36species in the family. Food provisioning, active defense ofthe young, and protecting young by remaining at the den as thefemale forages appear to be the commonest forms of male care.In addition males may groom, retrieve, play and rest with young.Male canids are rarely involved in den selection or construction.The effect on the fitness of the young of indirect forms ofmale care such as provisioning the female and territory defenseare hard to assess. Quantitative studies of male provisioningin seven species offer few generalizations. In two species (Canisaureus, C mesomelas) females provided more food to the youngthan males; in one species (Alopex lagopus) the pair contributedequally to feeding young, and in four species (Canis lupus,Vulpes vulpes, Chrysocyon brachyurus, and Lycaon pictus), malesprovided more food than females. Much more data are required,particularly from field studies, before patterns of variationcan be interpreted.     

NaCl-induced Senescence in Leaves of Rice (Oryza sativa L.) Cultivars Differing in Salinity Resistance

The influence of NaCl on senescence-related parameters (proteinand chlorophyll concentrations, membrane permeability and chlorophyllfluorescence) was investigated in young and old leaves of fiverice cultivars differing in salt resistance. NaCl hastened thenaturally-occurring senescence of rice leaves which normallyappears during leaf ontogeny: it decreased chlorophyll and proteinconcentrations and increased membrane permeability and malondialdehydesynthesis. Such an acceleration of deteriorative processes affectedall leaves in salt-sensitive cultivars while it was more markedin oldest than in youngest leaves of salt-resistant genotypes.NaCl-induced senescence also involved specific modifications,such as an increase in basal non-variable chlorophyll fluorescence(F ₀) recorded in all cultivars or a transient increase in solubleprotein concentration recorded in salt-resistant genotypes only.Alteration of membrane permeability appeared as one of the firstsymptoms of senescence in rice leaves and allowed discriminationamong cultivars after only 7 d of stress. In contrast, F _v/F _mratio (variable fluorescence/maximal fluorescence) was thesame for all cultivars during the first 18 d of stress and thuscould not be used for identifying salt-resistant rice exposedto normal light conditions. Relationships between parametersinvolved in leaf senescence are discussed in relation to salinityresistance of rice cultivars. Chlorophyll concentration; chlorophyll fluorescence; electrolyte leakage; magnesium; malondialdehyde; membrane permeability; NaCl; Oryza sativa L.; protein; rice; salinity resistance; senescence; UV absorbing substances     

Hormonal regulation of oligopeptide transporter Pept-1 in a human intestinal cell line

The intestinal oligopeptide transporter (cloned as Pept-1) hasmajor roles in protein nutrition and drug therapy. A key unstudied question is whether expression of Pept-1 is hormonally regulated. Inthis experiment, we investigated whether insulin has such a role. Weused a human intestinal cell monolayer (Caco-2) as the in vitro modelof human small intestine and glycylglutamine (Gly-Gln) as the modelsubstrate for Pept-1. Results showed that addition of insulin at aphysiological concentration (5 nM) to incubation medium greatlystimulates Gly-Gln uptake by Caco-2 cells. This stimulation was blockedwhen genistein, an inhibitor of tyrosine kinase, was added toincubation medium. Studies of the mechanism of insulin stimulationshowed the following. 1) Stimulationoccurred promptly (30-60 min) after exposure to insulin.2) There was no significant changein the Michaelis-Menten constant of Gly-Gln transport, but there was anearly twofold increase in its maximal velocity.3) Insulin effect persisted evenwhen Golgi apparatus, which is involved in trafficking of newlysynthesized Pept-1, was dismantled.4) However, there was completeelimination of insulin effect by disruption of microtubules involved intrafficking of preformed Pept-1. 5)Finally, with insulin treatment, there was no change in Pept-1 geneexpression, but the amount of Pept-1 protein in the apical membrane wasincreased. In conclusion, the results show that insulin, when it bindsto its receptor, stimulates Gly-Gln uptake by Caco-2 cells byincreasing the membrane population of Pept-1. The mechanism appears tobe increased translocation of this transporter from a preformedcytoplasmic pool.     

Bcl-2 family members and apoptosis, taken to heart

Loss of myocardial cells via apoptosis has been observed in many cardiovascular diseases and has been shown to contribute to the initiation and progression of heart failure. The Bcl-2 family members are important regulators of the mitochondrial pathway of apoptosis. These proteins decide whether the mitochondria should initiate the cell death program and release proapoptotic factors such as cytochrome c. The Bcl-2 proteins consist of anti- and proapoptotic members and play a key role in regulating apoptosis in the myocardium. The antiapoptotic proteins have been demonstrated to protect against various cardiac pathologies, whereas the antiapoptotic proteins have been reported to contribute to heart disease. This review summarizes the current understanding of the role of Bcl-2 proteins in the heart. cardiovascular disease; cytochrome c; protein; mitochondria     

Cellular Neuronal Control of Molluscan Heart

Bivalve and gastropod molluscs undergo large changes in externalenvironmental conditions, as well as in internal state. Cardiacresponses to these changing conditions have been recorded ina variety of species. There is a general tendency for heartrate, and presumably cardiac output, to increase in responseto situations that would increase the load on respiratory andexcretory systems. Changes in molluscan heart function in manycases appear not to be mediated directly by cardiac nerves,but rather by such indirect mechanisms as changes in blood constituentsor mechanical, hemodynamic effects on heart muscle. Three typesof cardiac response in Aplysia have been shown to be mediated,at least in part, by the heart regulator nerves. The neural circuits that regulate heart rate in Aplysia andin Helix have been partially described in cellular detail. InMercenaria, Aplysia and other molluscan species there is evidencethat cyclic adenosine monophosphate has a role in mediatingthe excitatory effects of serotonin on heart muscle. There appearsto be, in fact, a general tendency in the Aplysia nervous systemfor neurons that exert tonic, modulatory effects within neuralnetworks that control a variety of behaviors to use serotoninfor a transmitter. In each case there is evidence to suggestthat changes in cyclic adenosine monophosphate levels may mediatesome of the modulatory effects of serotonin.     

Haustorial Role of Pollen Tubes

In angiosperms, the pollen tube is siphonogamous and its mainfunction is to carry the male gametes for double fertilization.In some taxa, as in Cucurbitaceae, the tube branches after enteringthe ovule, prior to fertilization. The tube may even swell andform a bulla. During post-fertilization development of the ovule,a portion of the tube may persist in the micropyle, or in theembryo sac, or in both, sometimes even in the micropyle of themature seed. Haustorial function has been presumed in a numberof taxa. In Grevillea, following fertilization, the pollen tube branchesat the micropyle, and the branches grow intercellularly intothe ovarian tissue where further branching occurs. A haustorialrole of the pollen tube is presumed from circumstantial evidence.In gymnosperms (for example, Cycas, Zamia and Ginkgo) the pollentube is nonsiphonogamous, arises from the distal (upper) poleof pollen grain, and grows laterally in the apical region ofthe nucellus. The tube branches in Cycas and Ginkgo but remainsunbranched in Zamia. These pollen tube branches are enucleate,and are not concerned with the transport of male gametes forfertilization. However, the haustorial role has been well documented.In Podocarpus, the pollen tube is siphonogamous and arises fromthe proximal (lower) pole of pollen grain. After traversingthe nucellus, the tube forms a bulla at the point of contactwith the female gametophyte, and several branches originatefrom the bulla. The pollen tube branches grow along the innersurface of the nucellus and the outer surface of the femalegametophyte. The haustorial role of the pollen tube branchesis uncertain. Procedures for convincingly demonstrating thehaustorial role of pollen tubes are discussed. Angiosperms, gymnosperms, pollen tube, bulla, fertilization, haustorial role     

Studies on Mature Seeds of Cuscuta pedicellata and C. campestris by Electron Microscopy

The seeds of Cuscuta pedicellata have been investigated by transmissionand scanning electron microscopy. Additional observations havebeen made on seeds of C. campestris by SEM only. The seed coatconsists of an outer single epidermis, two different palisadelayers, and an inner multiparenchyma layer. The outer epidermalwall in C. pedicellata has a thick cuticle and zones rich inpectic substances. The thicker ‘U-shaped’ cell wallsin the outer palisade layer are strengthened by a wall layerof hemicellulose. The inner palisade layer has thick walledcells with a ‘light line’. The inner cell wall ofthe compressed multiparenchyma layer has a thin cuticle. A fairlythick cuticle is positioned directly on the endosperm surface.The aleurone cell walls are different from the remaining endospermwalls. The latter are thick and believed to be of galactomannans.There is a ‘clear’ zone between the plasmalemmaand the cell wall in the aleurone cells. The embryo cells arepacked with lipids and proteins. In Cuscuta campestris mostendosperm has been absorbed during the seed development. Theembryo apex has two minute leaf primordia. The features of theCuscuta seeds are discussed in relation to functional and environmentalconditions. Cuscuta pedicellata, Cuscuta campestris, seed, seed coat, cuticle, cell walls, endosperm, aleurone cells, galactomannan, embryo, TEM, SEM