Biophysical characterization of zebrafish connexin35 hemichannels

A subset of connexins can form unopposed hemichannels in expression systems, providing an opportunity for comparison of hemichannel gating properties with those of intact gap junction channels. Zebrafish connexin35 (Cx35) is a member of the Cx35/Cx36 subgroup of connexins highly expressed in the retina and brain. In the present study, we have shown that Cx35 expression in Xenopus oocytes and N2A cells produced large outward whole cell currents on cell depolarization. Using whole cell, cell-attached, and excised patch configurations, we obtained multichannel and single-channel current recordings attributable to the Cx35 hemichannels (I_hc) that were activated and increased by stepwise depolarization of membrane potential (V_m) and deactivated by hyperpolarization. The currents were not detected in untransfected N2A cells or in control oocytes injected with antisense Cx38. However, water-injected oocytes that were not treated with antisense showed activities attributable to Cx38 hemichannels that were easily distinguishable from Cx35 hemichannels by a significantly larger unitary conductance (_hc: 250–320 pS). The _hc of Cx35 hemichannels exhibited a pronounced V_m dependence; i.e., _hc increased/decreased with relative hyperpolarization/depolarization (_hc was 72 pS at V_m = –100 mV and 35 pS at V_m = 100 mV). Extrapolation to V_m = 0 mV predicted a _hc of 48 pS, suggesting a unitary conductance of intact Cx35 gap junction channels of 24 pS. Channel gating was also V_m dependent: open time declined with negative V_m and increased with positive V_m. The ability to break down the complex gating of intact intercellular channels into component hemichannels in vitro will help to evaluate putative physiological roles for hemichannels in vivo. connexin; gating; retina     

Delimitation of Epacridaceae: Preliminary Molecular Evidence

Comparative sequence data for the chloroplast encodedrbc L genehas been obtained for species representing the basal lineagesin the proposed phylogeny of Powellet al. (Annals of Botany77:305–315, 1996), with the aim of testing the delimitationof the family and the validity of the supra-generic taxa proposed,and estimating relationships within the family. Cladistic analysesindicate that EpacridaceaesensuPowellet al. (1996) is not monophyletic.Lebetanthus,a monotypic genus from South America commonly placed withinthe family, mostly near the Tasmanian endemicPrionotes, is shownto be closer toGaultheriaand other members of the ericaceoustribe Andromedeae. The hypothetical phylogeny of Powellet al.(1996) is evaluated in the light of this preliminary analysisof relationships within the family. The data do not supportthe recognition of the two subfamilies, Richeoideae and Epacridoideae,of Watson Epacridaceae; Ericales; molecular systematics; molecular systematics; rbc L     

Cloning and Functional Expression of a Novel Geranylgeranyl Pyrophosphate Synthase Gene from Arabidopsis thaliana in Escherichia coli

A gene encoding a novel geranylgeranyl pyrophosphate (GGPP)synthase from Arabidopsis thaliana has been identified and termedGGPS5. The gene has been sequenced and expressed in Escherichiacoli. The deduced amino acid sequence showed 64.5% and 57.5%identity with a putative GGPP synthase from Arabidopsis andCapsicum annuum, respectively. GGPP enzymatic activity was detectedin E. coli cells expressing the GGPS5 gene in two differentways. One was the direct measurement of GGPP synthase activityin cell extracts and the other was the yellow color productionof cells when the GGPS5 gene was co-expressed with crtB, crtI,crtX, crtY and crtZ genes derived from Erwinia uredovora. (Received May 20, 1996; Accepted December 14, 1996)     

The role of apical development around the time of leaf initiation in determining leaf width at maturity in wheat seedlings (Triticum aestivum L.) with impeded roots

High soil resistance to root penetration (measured as penetrometerresistance, R_s slows down leaf growth and reduces mature leafsize in wheat seedlings {Triticum aestivum L.). Underlying changesin the kinetics of cell partitioning and expansion and in thesize and organization of mature cells were reported in companionpapers (Beemster and Masle, 1996; Beemster et al., 1996). Inthe present study, the relationships between apex growth, primordiuminitiation and expansion were analysed for plants grown at contrastingR_s, focusing on a leaf whose whole development proceeded afterthe onset of root impedance (leaf 5). High R_s reduced the rates of apex and leaf development, butdid not appear to have immediate effects on the pattern of developmentof the newly initiated phytomers. During an initial short period,the rate of development of a leaf primordium and associatednode were related to plastochronic age, according to similarrelationships (slopes) at the two R_s. Effects on developmentalpatterns were first detected on phytomer radial expansion duringplastochron 2. The ontogenetic pattern of leaf elongation wasaffected later, during the next few plastochrons preceding leafemergence (‘post-primordial stage’). It is concludedthat a reduction in the number of formative divisions and inthe number of proliferative cells along the intercalary mer-istemreported earlier (Beemster and Masle, 1996; Beemster et al.,1996) is not related to the size of the apical dome at leafinitiation nor to the size and number of meristematic cellsinitially recruited to the leaf primordium, which were all unaffectedby R_s. Rather they are generated at the primordial and post-primordialstages. Key words: Wheat, apex development, leaf primodium development, mature leaf width, root impedance     

Nutrient-patch contrast in relation to clonal integration, with special reference to Glechoma longituba

Patch contrast, defined as the difference between patches, isamong the basic traits of environmental heterogeneity (Kolasa and Pickett 1991;Stuefer 1996). Clonal plants, especially those with long spacers,usually experience certain patches with different nutrient-patchcontrasts (de Kroon et al. 2005; Stuefer 1996). Clonal integrationhas been recognized as a basic strategy, by which clonal plantscan effectively cope with patchy resources and increase theirfitness in such habitats (de Kroon et al. 2005; Zhang et al. 2007).Glechoma longituba is distributed     

The Level of mRNA Transcribed from psaL, Which Encodes a Subunit of Photosystem I, Is Increased by Cytokinin in Darkness in Etiolated Cotyledons of Cucumber

A cDNA clone for an mRNA whose level increased within 2 h ofthe start of treatment with N⁶-benzyladenine in etiolated cotyledonsof cucumber was isolated by differential hybridization. ThecDNA was homologous to psaL, which encodes subunit XI (PSI-L)of photosystem I. The accumulation of psaL mRNA was specificallyinduced by cytokinins or light. (Received April 10, 1996; Accepted July 31, 1996)     

SYSTEMATIC REVISION OF THE EPIMENIIDAE (MOLLUSCA: SOLENOGASTRES)

The species of Epimeniidae (Solenogastres: Cavi-belonia) arecompared and revised according to available type material. Structuresof particular interest include the differentiation of the foregut,the pharyngo-buccal nervous system and the blood cells. Sevenspecies are recognized in the family. Of these, six are placedin the genus Epimenia: E. australis (Thiele) (synonym Dinomeniaverrucosa Nierstrasz), E. ohshimai Baba, E. arabica Salvini-Plawen& Benayahu, and the three new species E. babai from offKyushu, Japan (synonym E. verrucosa in Baba 1939–1951),E. allohaemata from off Korea and E.indica from the Maldives. E. vixinsignis Salvini-Plawen is transferred to Epiherpia gen.nov. (Received 2 February 1996; accepted 19 September 1996)     

Identification of Castasterone, 6-Deoxocastasterone, Typhasterol and 6-Deoxotyphasterol from the Shoots of Arabidopsis thaliana

Endogenous brassinosteroids in the shoots of Arabidopsis thalianawere investigated. Castasterone, 6-deoxocastasterone, typhasteroland 6-deoxotyphasterol were identified by GC-MS. The co-occurrenceof 6-deoxo-brassinosteroids and 6-oxo-brassinosteroids suggeststhat there are both early and late C6-oxidation pathways ofbrassinosteroids in A. thaliana. (Received September 17, 1996; Accepted October 11, 1996)     

A COMPARATIVE STUDY OF THE MATURE SPERMATOZOA OF BULINUS AFRICANUS (KRAUSS, 1848) AND B. GLOBOSUS (MORELET, 1866) (GASTROPODA: PLANORBIDAE)

The morphology of the mature spermatozoa of the closely-relatedfreshwater pulmonates, Bulinus africanus and Bulinus globosus,was examined using scanning and transmission electron microscopy.A comparison showed no useful differences that could be usedto distinguish the species though they did differ in one respectfrom Bulinus tropicus, the only other bulinid for which spermmorphology is known. (Received 12 August 1996; accepted 6 December 1996)     

Analysis of Concentration-response Relationship for Enhanced Sugar Responses of the Chorda Tympani Nerve in the Diabetic db/db Mouse

Chorda tympani responses to sugars were greater in diabetic(db/db) than in non-diabetic control mice. A kinetic analysissuggested that the greater sugar responses in db/db mice wereunlikely due to the increased number of sugar receptors. Chem.Senses 21: 59–63, 1996.     

Distribution of Calanus species in Kongsfjorden, a glacial fjord in Svalbard

The distribution of Calanus species was investigated in Kongsfjordenin summer of 1996 and 1997. In both years Calanus finmarchicusand Calanus glacialis dominated, although the boreal C. finmarchicuswas more abundant than the Arctic C. glacialis in 1997. Thiscoincided with a 2°C higher water temperature at 50 m in1997, indicating stronger influence of Atlantic origin waterthat year. Advected Calanus finmarchicus occurred in deep andsubsurface layers of the outer fjord in 1996 (200 ind. m^-3,mainly CIII). A less abundant local population aggregated insurface layers of the inner fjord (100 ind. m^-3). Similarly,advected C. finmarchicus occurred in subsurface layers in 1997(446 ind. m^-3, mainly CIII and CIV) and a local population insurface layers (183 ind. m^-3, mainly CI). Calanus glacialisin 1996 aggregated as CII and CIII in the deep layers of theouter fjord (272 ind. m^-3), whereas CIII–CV were abundant(216 ind. m^-3) in cold surface waters of the inner fjord. In1997 C. glacialis (mostly CIII–CV) was more abundant inthe outer than in the inner part of the fjord (40 and 192 ind.m^-3, respectively). Within Kongsfjorden, Calanus finmarchicusneeds one year to complete its life cycle, whereas Calanus glacialisneeds two. Calanus hyperboreus seems to be an expatriate inthe fjord system.     

Isolation, Properties and a Possible Function of a Water-Soluble Chlorophyll a/b-Protein from Brussels Sprouts

A water-soluble Chl a/b-protein (CP673) was isolated and purifiedfrom Brussels sprouts (Brassica oleracea L. var. gemmifera DC).The protein had a molecular mass of 78 kDa and an isoelectricpoint of 4.7, consisted of three or four subunits of 22 kDaand was extremely heat-stable. Although CP673 contained aboutone Chl a per protein, the blue and red absorption bands ofChl a that consisted of three or four Chl a forms with differentabsorption maxima suggested that there are several differentmodes or sites of binding for Chl a. Chl a/b ratio of largerthan 10 also indicated that Chl b is present only in a smallfraction of CP673. The heterogeneity of CP673 in terms of compositionand binding of Chl suggests that Chl is not an intrinsic componentof the Chl-protein. Homology search showed that the N-terminalamino acid sequence of CP673 is highly homologous with thatof a 22 kDa protein that accumulates in water-stressed leavesof two Brassicaceae plants, rapeseed and radish, but not withthose of the light-harvesting Chl a/b-proteins of photosynthesis.A possible function of the water-soluble Chl-protein was discussed. (Received September 17, 1996; Accepted November 18, 1996)     

Genetic Analysis of the Effects of Polar Auxin Transport Inhibitors on Root Growth in Arabidopsis thaliana

Polar auxin transport inhibitors, including N-1-naphthylphthalamicacid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), have variouseffects on physiological and developmental events, such as theelongation and tropism of roots and stems, in higher plants.We isolated NPA-resistant mutants of Arabidopsis thaliana, withmutations designated pir1 and pir2, that were also resistantto TIBA. The mutations specifically affected the root-elongationprocess, and they were shown ultimately to be allelic to aux1and ein2, respectively, which are known as mutations that affectresponses to phytohormones. The mechanism of action of auxintransport inhibitors was investigated with these mutants, inrelation to the effects of ethylene, auxin, and the polar transportof auxin. With respect to the inhibition of root elongationin A. thaliana, we demonstrated that (1) the background levelof ethylene intensifies the effects of auxin transport inhibitors,(2) auxin transport inhibitors might act also via an inhibitorypathway that does not involve ethylene, auxin, or the polartransport of auxin, (3) the hypothesis that the inhibitory effectof NPA on root elongation is due to high-level accumulationof auxin as a result of blockage of auxin transport is not applicableto A. thaliana, and (4) in contrast to NPA, TIBA itself hasa weak auxin-like inhibitory effect. (Received April 12, 1996; Accepted September 2, 1996)     

Efficient Conversion of L-Tryptophan to Indole-3-Acetic Acid and/or Tryptophol by Some Species of Rhizoctonia

In a study of various phytopathogenic fungi, we found that fungithat belong to the genus Rhizoctonia produce IAA efficientlyfrom tryptophan. R. solani Kühn MAFF-305219, in particular,produced large amounts of tryptophol (Tol), which was assumedto be a specific by-product of the indole-3-pyruvate (IPy) pathway,in addition to IAA. Therefore, this fungus seemed suitable foranalysis of the function and the regulation of the biosynthesisof auxin by a fungal pathogen. Under normal aerobic conditions,the ratio of IAA to Tol synthesized by this strain was higherthan that under less aerobic conditions. In metabolic studieswith various indole derivatives, R. solani converted L-tryptophanand indole-3-acetaldehyde to IAA and Tol, but other indole derivativeswere scarcely metabolized. These results suggest that both IAAand Tol are synthesized from tryptophan through the IPy pathwayin Rhizoctonia. (Received May 27, 1996; Accepted July 8, 1996)     

Pigment Composition of a Novel Oxygenic Photosynthetic Prokaryote Containing Chlorophyll d as the Major Chlorophyll

The principal pigment found in the majority of oxygenic photosyntheticorganisms is known to be chlorophyll a. However, we isolateda new oxygenic photosynthetic prokaryote that contained chlorophylld as a predominant pigment with chlorophyll a being a minorpigment. Chlorophyll d had previously been noted but its naturaloccurrence and function remained unclear. Cells of the new prokaryotehad an absorption maximum at red region of 714–718 nmdue to chlorophyll d absorption, but no characteristic absorptionpeak of chlorophyll a around 680 nm was observed. Chlorophylld of the new organism was identified spectrophotometricallyin several solvents and its chemical structure was confirmedby NMR and FABMS analysis. The cell also contained a chlorophyllc-like pigment, zeaxanthin and a-carotene but not chlorophyllb and ß-carotene. The content of chlorophyll d accountedfor more than 2% of the cell dry weight, while the content ofchlorophyll a was less than 0.1%. The chlorophyll a/d ratioremained between 0.03 and 0.09 under different culture conditions.The light absorption characteristics and the high content ofchlorophyll d along with the small content of chlorophyll aindicated the existence of a new light utilization mechanisminvolving chlorophyll d. (Received October 7, 1996; Accepted December 16, 1996)