The copy number of chloroplast gene minicircles changes dramatically with growth phase in the dinoflagellate Amphidinium operculatum

The chloroplast genome of algae and plants typically comprises a circular DNA molecule of 100-200kb, which harbours approximately 120 genes, and is present in 50-100 copies per chloroplast. However, in peridinin dinoflagellates, an ecologically important group of unicellular algae, the chloroplast genome is fragmented into plasmid-like 'minicircles', each of 2-3kb. Furthermore, the chloroplast gene content of dinoflagellates is dramatically reduced. Only 14 genes have been found on dinoflagellate minicircles, and recent evidence from EST studies suggests that most of the genes typically located in the chloroplast in other algae and plants are located in the nucleus. In this study, Southern blot analysis was used to estimate the copy number per cell of a variety of minicircles during different growth stages in the dinoflagellate Amphidinium operculatum. It was found that minicircle copy number is low during the exponential growth stage but increases during the later growth phase to resemble the situation seen in other plants and algae. The control of minicircle replication is discussed in the light of these findings.     

Molecular diversity of bacterial production of the climate-changing gas, dimethyl sulphide, a molecule that impinges on local and global symbioses

This paper describes the ddd genes that are involved in theproduction of the gas dimethyl sulphide from the substrate dimethylsulphoniopropionate(DMSP), an abundant molecule that is a stress protectant inmany marine algae and a few genera of angiosperms. What is knownof the arrangement of the ddd genes in different bacteria thatcan undertake this reaction is reviewed here, stressing thefact that these genes are probably subject to horizontal genetransfer and that the same functions (e.g. DMSP transport) maybe accomplished by very different mechanisms. A surprising numberof DMS-emitting bacteria are associated with the roots of higherplants, these including strains of Rhizobium and some rhizospherebacteria in the genus Burkholderia. One newly identified strainthat is predicted to make DMS is B. phymatum which is a highlyunusual β-proteobacterium that forms N₂-fixing noduleson some tropical legumes, in this case, the tree Machaeriumlunatum, which inhabits mangroves. The importance of DMSP catabolismand DMS production is discussed, not only in terms of nutritionalacquisition by the bacteria but also in a speculative scheme(the ‘messy eater’ model) in which the bacteriamay make DMS as an info-chemical to attract other organisms,including invertebrates and other plankton. Key words: Acyl CoA transferase, Burkholderia, CLAW hypothesis, dimethyl sulphide, dimethylsulphoniopropionate, Marinomonas, nitrogen fixation, Rhizobium, rhizosphere, root nodules, Spartina Received 30 May 2007; Revised 27 September 2007 Accepted 1 October 2007     

Relative Sensitivity and Tolerance of some Gladiolus Cultivars to Sulphur Dioxide

Five Gladiolus cultivars, namely ‘Aldebaran’, ‘BrightEye’, ‘Illusion’, ‘Manisha’ and‘Manmohan’, were exposed to 1 and 2 µg l^–1sulphur dioxide to test their relative-sensitivity toleranceto the pollutant Plants were fumigated experimentally for 2h daily Foliar injury symptoms were observed first in ‘Manisha’followed by ‘Aldebaran’ and ‘Illusion’at the higher dose Photosynthetic pigments and leaf extractpH were significantly decreased, particularly in ‘Manisha’and ‘Illusion’ Overall disturbances in the plantmetabolism due to SO₂ treatment led to retarded growth of plants,as evident from decreased shoot length and phytomass valuesThe order of sensitivity of the five Gladiolus cultivars toSO₂ was as follows, with the greatest first Manisha, Illusion,Aldebaran, Bright Eye, Manmohan Cultivars, Gladiolus, sensitivity, sulphur dioxide, tolerance     

ERRATA

On page 235, Table I: Equation (1) for Node 4 should read ‘A/A_c=0·840+0·0006A_c’;Equation (2) for Node 4 should read ‘A=0·89A_c’and Equation (2) for Node 5–10 should read ‘A=0·813A_c’.     

Effects of Photoperiod and Maturity Genes on Plant Growth, Partitioning, Radiation Use Efficiency, and Yield in Soyabean [Glycine max(L.) Merrill] 'Clark'

Plants of four isolines of soyabean [Glycine max(L.) Merrill]‘Clark’, viz‘L71-920’ (maturity genecomplemente₁e₂e₃ ), ‘L80-5914’ (E₁e₂e₃), ‘Clark’(e₁E₂E₃), and ‘L65-3366’ (E₁E₂E₃), were grown inshort (12.25 h d ^{- 1}natural light) and long days (12.25 h d^{- 1}natural light supplemented with 2.75 h d ^{- 1}low-irradianceartificial light) from first flowering to maturity in a polythenetunnel maintained at 30/24°C (day/night). Whereas therewere few differences among the isolines grown in short days,in long days the dominant alleles increased crop duration, biomassand seed yield substantially. Increases in biological and economicyield were not solely a consequence of longer crop duration:the dominant alleles also increased crop growth rate and radiationuse efficiency in long days (from 1.3 g MJ ^{- 1}total radiationine₁e₂e₃ to 2.8 g MJ ^{- 1}inE₁E₂E₃ ). Greater radiation use efficiencyresulted from a relatively longer leaf area duration, betterdistribution and orientation of a larger mass of leaves withinthe canopy, and smaller partitioning of assimilates to reproductivestructures. The work reveals the substantial effects of thethree lociE₁ / e₁, E₂/ e₂and E₃/e₃ on the response of plantgrowth, as well as development, to environment. Their relevanceto crop adaptation is discussed. Copyright 2000 Annals of BotanyCompany Glycine max(L.) Merrill, soyabean, maturity genes, flowering, phenology, growth, yield     

The Sensitivity of Net Photosynthesis in Several Plant Species to Short-term Fumigation with Sulphur Dioxide

The effects of exposure of up to 2 h with sulphur dioxide ona range of plant species was observed by measuring changes inthe rate of net photosynthesis under closely controlled environmentalconditions. Ryegrass, Lolium perenne ‘S23’ was thespecies most sensitive to SO₂; significant inhibition was detectedat 200 nl l^–1. Fumigations at 300 nl l^–1 also inhibitedphotosynthesis in field bean (Vicia faba cv. ‘Three FoldWhite’ and ‘Blaze’) and in barley (Hordeumvulgare cv. ‘Sonja’). No effect was detected inwheat (Triticum aestivum cv. ‘Virtue’) at concentrationsup to 600 nl l^–1 SO₂, or in oil-seed rape (Brassica napuscv. ‘Rafal’) except at 800 nl l^–1 SO₂). Recoverycommenced immediately after the fumigation was terminated andwas complete within 2 h when inhibition had not exceeded 20%during the SO₂ treatment. Key words: Sulphur dioxide, short-term fumigation, photosynthesis     

Plastid-derived single gene minicircles of the dinoflagellate Ceratium horridum are localized in the nucleus

Recent reports show that numerous chloroplast-specific proteins of peridinin-containing dinoflagellates are encoded on minicircles-small plasmidlike molecules containing one or two polypeptide genes each. The genes for these polypeptides are chloroplast specific because their homologs from other photosynthetic eukaryotes are exclusively encoded in the chloroplast genome. Here, we report the isolation, sequencing, and subcellular localization of minicircles from the peridinin-containing dinoflagellate Ceratium horridum. The C. horridum minicircles are organized in the same manner as in other peridinin-containing dinoflagellates and encode the same kinds of plastid-specific proteins, as previous studies reported. However, intact plastids isolated from C. horridum do not contain minicircles, nor do they contain DNA that hybridizes to minicircle-specific probes. Rather, C. horridum minicircles are localized in the nucleus as shown by cell fractionation, Southern hybridization, and in situ hybridization with minicircle-specific probes. A high-molecular-weight DNA was detected in purified C. horridum plastids, but it is apparently not minicircular in organization, as hybridization with a cloned probe from the plastid-localized DNA suggests. The distinction between C. horridum and other peridinin-containing dinoflagellates at the level of their minicircle localization is paralleled by C. horridum thylakoid organization, which also differs from that of other peridinin-containing dinoflagellates, indicating that a hitherto underestimated diversity of minicircle DNA localization and thylakoid organization exists across various dinoflagellate groups.     

ERRATA

Effects of coupled solute and water flow in plant roots withspecial reference to Brouwer's experiment. Edwin L. Fiscus. p. 71 Abstract: Line 3 delete ‘interval’ insert‘internal’. p. 73 Materials and Methods: line 6: delete ‘diversion’ insert ‘division’ line 9 equation should read J_v=L_p P–RT(C⁰–C¹). 74 Last line of figure legend: 10^–1 should read 10^–11. 75 Line 11: delete ‘seems’ insert ‘seem’. le 1 column heading—10⁶ should read 10¹¹. 77 delete ‘...membrane in series of...’ insert ‘membranein series or...’ Delete final paragraph.     

The Permeability of the Guard Cell Plasma Membrane and Tonoplast

Uptake experiments and efflux compartmental analysis of planthormones, osmotica and toxins using ‘isolated’ guardcells of Valerianella locusta and guard cell protoplasts (GCP)of Vicia faba were performed in order to study the permeabilityproperties of guard cell plasma membrane and tonoplast. Theplasma membrane of guard cells exhibits a higher permeabilitythan plasma membranes of mesophyll cells for most solutes investigated.The permeability coefficients (P_s calculated for the guard cellplasma membranes are also significantly higher than the P_s valuesfor the guard cell tonoplast. This applies also for protonatedABA. We suppose that the high permeability for ABAH could bepart of the target cell properties. A Collander analysis demonstratesa linear correlation between P_s, values and the ratio K_r/M_r^1,5for both plasma membrane (r = 0.87) and for the tonoplast (r=0.93). Because of deviations from the observed correlations,the permeation of some solutes (ABA, GA, IAA through the tonoplast;methylamine through the plasma membrane) seems to be facilitatedby an additional transport mechanism. The Collander analysisof the plasma membrane of GCP shows very similar results tothe analysis of the plasma membrane of ‘isolated’guard cells, indicating that isolation of protoplasts does notalter the permeability of the guard cell plasma membrane. Key words: Permeability coefficient, guard cells, plasma membrane, tonoplast     

'Empty' minicircles and petB/atpA and psbD/psbE (cytb559 alpha) genes in tandem in Amphidinium carterae plastid DNA

Amphidinium carterae minicircle chloroplast DNA was separated from total DNA by centrifugation through a sucrose/NaCl gradient. Sequences of minicircles with psbA and 23S rRNA contained a common region of 67 bp. Primers designed from this generated numerous polymerase chain reaction products of 1.5-2.6 kb. These contained psaA and psaB as one gene/circle, and petB/atpA and psbD/psbE as two genes/circle. 'Empty' minicircles of 1.7-2.5 kb containing no identifiable genes or parts of genes were more abundant than gene-containing circles. From 15 minicircles a minimum common region of 48 bp was identified, with little identity to that from other dinoflagellate minicircles.     

Evidence for horizontal gene transfer from bacteroidetes bacteria to dinoflagellate minicircles

Dinoflagellate protists harbor a characteristic peridinin-containing plastid that evolved from a red or haptophyte alga. In contrast to typical plastids that have ～100-200 kb circular genomes, the dinoflagellate plastid genome is composed of minicircles that each encode 0-5 genes. It is commonly assumed that dinoflagellate minicircles are derived from a standard plastid genome through drastic reduction and fragmentation. However, we demonstrate that the ycf16 and ycf24 genes (encoded on the Ceratium AF490364 minicircle), as well as rpl28 and rpl33 (encoded on the Pyrocystis AF490367 minicircle), are related to sequences from Algoriphagus and/or Cytophaga bacteria belonging to the Bacteroidetes clade. Moreover, we identified a new open reading frame on the Pyrocystis minicircle encoding a SRP54 N domain, which is typical of FtsY proteins. Because neither of these minicircles share sequence similarity with any other dinoflagellate minicircles, and their genes resemble bacterial operons, we propose that these Ceratium and Pyrocystis minicircles resulted from a horizontal gene transfer (HGT) from a Bacteroidetes donor. Our findings are the first indication of HGT to dinoflagellate minicircles, highlighting yet another peculiar aspect of this plastid genome.     

Influence of Flooding on Net CO2Assimilation, Growth and Stem Anatomy of Annona Species

A series of experiments was conducted to assess net CO₂assimilationand growth responses to waterlogging of grafted and seedlingtrees in the genus Annona. Seedlings of A. glabra, A. muricataandA. squamosa L., and scions of ‘Gefner’ atemoya(A. squamosaxA. cherimola Mill.), ‘49-11’ (‘Gefner’atemoyaxA. reticulata L.), ‘4-5’ (‘Priestley’atemoyaxA. reticulata), A. reticulata grafted onto either A.glabra, A. reticulata orA. squamosa rootstocks were floodedfor up to 60 d. Soil anaerobiosis occurred on the third dayof flooding. Seedlings ofA. glabra and A. muricata, and thescions ‘49-11’, ‘Gefner’ atemoya, andA. reticulata grafted onto A. glabra rootstock were consideredflood tolerant based on their ability to survive and grow inflooded conditions. Scions of the normally flood-sensitive A.reticulata, ‘Gefner’ atemoya, and ‘49-11’tolerated root waterlogging when grafted onto the flood-tolerantspecies, A. glabra. In contrast, flooding of A. squamosa seedlingsand rootstocks, and A. reticulata rootstocks greatly reducedgrowth and net CO₂assimilation rates, and resulted in 20–80%tree mortality. Stem anatomical responses to long-term flooding(12 continuous months) were assessed in seedlings of A. glabraand A. muricata, and trees of ‘49-11’ grafted ontoA. glabra. Flooded trees developed hypertrophied stem lenticels,particularly in A. glabra, and enlarged xylem cells resultingin thicker stems with reduced xylem density. Flooding did notincrease air spaces in pre-existing xylem near the pith or inxylem tissue that was formed during flooding. Thus, flood tolerancedid not involve aerenchyma formation in the stem. Copyright1999 Annals of Botany Company Flood tolerance, net CO₂assimilation, photosynthesis, stem anatomy, shoot growth, anaerobiosis, Annonaceae.     

The Apparent Induction of Nitrate Uptake by Chara corallina Cells following Pretreatment with or without Nitrate and Chlorate

Nitrate provision has been found to regulate the capacity forChara corallina cells to take up nitrate. When nitrate was suppliedto N sufficient cells maximum nitrate uptake was reached after8 h. Prolonged treatment of the cells in the absence of N alsoresulted in the apparent ability of these cells to take up nitrate.Chlorate was found to substitute partially for nitrate in the‘induction’ step. The effects on nitrate reductionwere separated from those on nitrate uptake by experiments usingtungstate. Tungstate pretreatment had no effect on NO^–₃uptake ‘induced’ by N starvation, but inhibitedNO^–₃ uptake associated with NO^–₃ pretreatment. Chloridepretreatment similarly had no effect on NO^–₃ uptake ‘induced’by N deprivation, but inhibited NO^–₃ uptake followingNO^–₃ pretreatment. The data suggest that there are atleast two mechanisms responsible for the ‘induction’of nitrate uptake by Chara cells, one associated with NO^–₃reduction and ‘induced’ by CIO^–₃ or NO^–₃and one associated with N deprivation. Key words: Nitrate, Chlorate, Chara corallina, Induction     

The Presence of Gibberellins in Excised Tomato Roots

Substances having similar physiological properties to the gibberellins(located by the ‘Meteor’ dwarf pea bio-assay) havebeen detected in extracts from excised tomato root. The chromatographicbehaviour of the most active zone is similar to that of gibberellinA₁. Experiments using the d-1 and d-5 mutants of mazie did not indicatethe presence of substances with differential effects on thesetwo mutants.     

Temperature-dependent development in marine copepods: comments on choices of models

Guerrero et al (1994) promote Tauti's equation, rate = a exp(b temp), as simple to fit by log conversion (which may be formallyinappropriate), empirically adequate, and having ‘appropriatebiological characteristics’. No function is justifiablefrom reductionist theories, but Belehrádek's, rate =a (temp – T₀)^b, with b fixed for the taxon of interest,fits equally well, and singularly distinguishes differencesattributable to temperature adaptation (T₀, often misunderstoodas ‘biological zero’), and to size or other species-dependentproperties (a).     

Developmental control of xylem hydraulic resistances and vulnerability to embolism in Fraxinus excelsior L.: impacts on water relations

The freezing tolerance of many plants, such as pea (Pisum sativum),is increased by exposure to low temperature or abscisic acidtreatment, although the physiological basis of this phenomenonis poorly understood. The freezing tolerance of pea shoot tips,root tips, and epicotyl tissue was tested after cold acclimationat 2C, dehydration/rehydration, applications of 10^–4M abscisic acid (ABA), and deacclimation at 25C. Tests wereconducted using the cultivar ‘Alaska’, an ABA-deficientmutant ‘wil’, and its ‘wildtype’. Freezinginjury was determined graphically as the temperature that caused50% injury (T₅₀) from electrical conductivity. Endogenous ABAwas measured using an indirect enzyme-linked immunosorbant assay,and novel proteins were detected using 2-dimensional polyacrylamidegel electrophoresis. The maximum decrease in T₅₀ for root tissuewas 1C for all genotypes, regardless of treatment. For ‘Alaska’shoot tips and epicotyl tissue, exogenous ABA increased thefreezing tolerance by –1.5 to –4.0C, while coldtreatment increased the freezing tolerance by –7.5 to–14.8C. Cold treatment increased the freezing toleranceof shoot tips by –9 and –15C for ‘wil’and ‘wild-type’, respectively. Cold acclimationincreased endogenous ABA concentrations in ‘Alaska’shoot tips and epicotyls 3- to 4-fold. Immunogold labeling increasednoticeably in the nucleus and cytoplasm of the epicotyl after7 d at 2C and was greatest after 30 d at the time of maximumfreezing tolerance and soluble ABA concentration. Cold treatmentinduced the production of seven, three, and two proteins inshoot, epicotyl, and root tissue of ‘Alaska’, respectively.In ‘Alaska’ shoot tissue, five out of seven novelproteins accumulated in response to both ABA and cold treatment.However, only a 24 kDa protein was produced in ‘wil’and ‘wild-type’ shoot and epicotyl tissues aftercold treatment. Abscisic acid and cold treatment additivelyincreased the freezing tolerance of pea epicotyl and shoot tissuesthrough apparently independent mechanisms that both resultedin the production of a 24 kDa protein. Key words: Pisum sativum, cold acclimation, immuno-localization