Ion channel formation by zervamicin-IIB

Zervamicin-IIB (Zrv-IIB) is a 16 residue peptaibol which forms voltage-activated, multiple conductance level channels in planar lipid bilayers. A molecular model of Zrv-IIB channels is presented. The structure of monomerc Zrv-II3 is based upon the crystal structure of Zervamicin-Leu. The helical backbone is kinked by a hydroxyproline residue at position 10. Zrv-IIB channels are modelled as helix bundles of from 4 to 8 parallel helices surrounding a central pore. The monomers are packed with their C-terminal helical segments in close contact, and the bundles are stabilized by hydrogen bonds between glutamine 11 and hydroxyproline 10 of adjacent helices. Interaction energy profiles for movement of three different probes species (K⁺, Cl^– and water) through the central pore are analyzed. The conformations of: (a) the sidechain of glutamine 3; (b) the hydroxyl group of hydroxyproline 10; and (c) the C-terminal hydroxyl group are optimized in order to maximize favourable interactions between the channel and the probes, resulting in favourable interaction energy profiles for all three. This suggests that conformational flexibility of polar sidechains enables the channel lining to mimic an aqueous environment.     

Pioneer and late stage tropical rainforest tree species (French Guiana) growing under common conditions differ in leaf gas exchange regulation,carbon isotope discrimination and leaf water potential

Leaf gas exchange rates, predawn _wp and daily minimum _wm leaf water potentials were measured during a wet-to-dry season transition in pioneer (Jacaranda copaia, Goupia glabra andCarapa guianensis) and late stage rainforest tree species (Dicorynia guianensis andEperua falcata) growing in common conditions in artificial stands in French Guiana. Carbon isotope discrimination () was assessed by measuring the stable carbon isotope composition of the cellulose fraction of wood cores. The values were 2.7 higher in the pioneer species than in the late stage species. The calculated time integratedC _i values derived from the values averaged 281 mol mol^–1 in the pioneers and 240 mol mol^–1 in the late stage species. The corresponding time-integrated values of intrinsinc water-use efficiency [ratio CO₂ assimilation rate (A)/leaf conductance (g)] ranged from 37 to 47 mmol mol^–1 in the pioneers and the values were 64 and 74 mmol mol^–1 for the two late stage species. The high values were associated—at least inJ. copaia—with high maximumg values and with high plant intrinsinc specific hydraulic conductance [Cg/(_wm–_wp], which could reflect a high competitive ability for water and nutrient uptake in the absence of soil drought in the pioneers. A further clear discriminating trait of the pioneer species was the very sensitive stomatal response to drought in the soil, which might be associated with a high vulnerability to cavitation in these species. From a methodological point of view, the results show the relevance of for distinguishing ecophysiological functional types among rainforest trees.     

Microsatellite markers in the hexaploid Prunus domestica species and parentage lineage of three European plum cultivars using nuclear and chloroplast simple-sequence repeats

In a previous study, cDNA microsatellite markers were described in apricot (Prunus armeniaca L.). Specific PCR primers were designed to amplify the microsatellite-containing regions from genomic DNA in different Prunus species. In the present work, cDNA microsatellite markers were developed in the hexaploid Prunus domestica L. species and polymorphism was ascertained in a segregating plum population. Co-dominant mendelian segregation of alleles was demonstrated and microsatellite polymorphism displayed up to 6 alleles per SSR locus per individual. Parentage lineage of three full-sib European plum cultivars (cv. Cacanska najbolja, Cacanska rana and Cacanska lepotica) was reconstructed by the analysis of the above nuclear SSR markers, completed by four chloroplastic microsatellite loci. The six most informative nuclear loci enabled discrimination between the three Cacak cultivars and unrelated individuals as well as the previously proposed parents, Wangenheim and Pozegaca. Data obtained support previous evidence that these cultivars originated from the Stanley cultivar. However, SSR analysis finally excluded Wangenheim as the other possible parent. Based on the results obtained with nuclear and chloroplast SSR loci, we propose the origin of those three Cacak cultivars in a cross between Stanley as the mother plant and Ruth gerstetter as the pollinator. Furthermore, we demonstrate the utility of these apricot SSR markers for genotype fingerprinting of the hexaploid plum cultivars.     

Cloning and sequencing of a ligninase gene from a lignindegrading basidiomycete,Phanerochaete chrysosporium

Summary A ligninase gene has been cloned from a Phanerochaete chrysosporium genomic DNA library. Nucleotide sequencing of the gene has revealed that the ligninase structural gene contains 1116 bp of the protein-encoding sequence, of which 84 bp encode the signal peptide. The protein-encoding sequence is interrupted by eight introns which conform to the universal G-T/A-G splicing rule observed for the 3 and 5 intron boundaries. The putative eukaryotic regulatory sequences, i.e. CAAT and TATA box-like sequences, are present in the 5 flanking region.     

The cytology of phytophthora infestans

Summary Phytophthora infestans has three kinds of somatic nuclei: an oval shaped nucleus (approx. 3.1×2.7 ) which stains diffusely except for a crescent shaped Feulgen positive cap which stains intensely; a granular nucleus whose contents are organized into a fairly constant number of stained bodies, and, a deeply staining condensed nucleus. The capped nucleus is thought to be metabolic or resting and the granular nucleus is thought to be dividing as it is most commonly found in hyphal tips. Attenuated forms of all three kinds of nuclei are found.Nuclear division is mitotic and intranuclear. Eight—ten chromosomes are seen at metaphase.Sporangia have a mean of 6.3 nuclei which is constant for age and strain of culture. Sporangia become multinucleate as a result of nuclear migration and not by division in the developing sporangium. Zoospores are usually uninucleate.The nuclear cap is persistent throughout nuclear division when it also divides. It is associated with flagella production and nuclear migration and has some of the properties of a blepharoplast.     

Alamethicin and related peptaibols — model ion channels

Peptaibols are considered as models of those ion channels which consist of a bundle of transbilayer helices surrounding a central pore. X-Ray diffraction and NMR studies have yielded high resolution structures for several peptaibols. In conjunction with other spectroscopic investigations and molecular dynamics simulations, these studies suggest that peptaibols form proline-kinked -helices, and that there may be hinge-bending movement of the helix in the region of the central proline residue. The amphipathicity of peptaibol helices is analyzed in relation to their channel-forming properties. Studies of the interactions of peptaibols with lipid bilayers suggest that they are helical when in a membrane-like environment, and that the helix orientation relative to the bilayer is sensitive to the peptaibol: lipid ratio, and to the degree of hydration of the bilayer. Electrical studies reveal that many peptaibols form multiple-conductance level channels in a voltage-dependent fashion. Analysis of conductance levels provides support for the barrel stave model of channel formation, whereby different conductance levels correspond to different numbers of monomers in a helix bundle. Alternative models for voltage-activation are discussed, and the roles of molecular dipoles and of hinge-bending in this process are considered. Two molecular models for an N = 6 bundle of alamethicin helices are presented and their electrostatic properties analyzed. The relevance of studies of peptaibols to channel and transport proteins in general is considered.Abbreviations Aib -amino-isobutyric acid - Alm alamethicin - ATR-FTIR attenuated total reflection Fourier transform infrared - CD circular dichroism - CFP channel-forming peptide - Chol cholesterol - diPhyPC diphytanoyl phosphatidylcholine - DMPC dimyristoyl phosphatidylcholine - DOPC dioleoyl phosphatidylcholine - DOPE dioleoyl phosphatidylethanolamine - DPPS dipahnitoyl phosphatidylserine - DTPC ditetradecyl phosphatidylcholine - HSM hydrophilic surface map - I-V current-voltage - MLV multilamellar vesicle - nAChR nicotinic acetylcholine receptor - P:L protein-to-lipid ratio - POPC palmitoyloleoyl phosphatidylcholine - SUV small unilamellar vesicle - Zrv zervamicin     

Regulation of adenosine 5′-phosphosulfate sulfotransferase activity by H2S and cyst(e)ine in primary leaves of Phaseolus vulgaris L.

During chloroplast development in the primary leaves of Phaseolus vulgaris, the extractable activity of adenosine 5-phosphosulfate sulfotransferase increased ten-fold. When chloroplast development took place in air enriched with 3.5 l H₂S·l^-1 there was a decrease in adenosine 5-phosphosulfate sulfotransferase activity. Cyst(e)ine in concentrations up to 1 mM (in the external medium) did not affect the increase in adenosine 5-phosphosulfate sulfotransferase activity in intact plants. In plants with excised roots, 0.75 mM cyst(e)ine inhibited this increase. In green primary leaves, H₂S or cyst(e)ine treatment resulted in a decrease of extractable adenosine 5-phosphosulfate sulfotransferase activity. In intact plants, this effect of cyst(e)ine was observed at a concentration of 1 mM, and in plants with excised roots, 0.25 mM had a comparable effect.In developing plants, the extractable activities of O-acetyl-L-serine sulfhydrylase (EC 4.2.99.9) and ribulosebisphosphate carboxylase (EC 4.1.1.39.) were not affected by H₂S or cyst(e)ine.Abbreviations APS adenosine 5-phosphosulfate - APSSTase adenosine 5phosphosulfate sulfotransferase - BSA bovine serum albumin - DTE dithioerythritol - EDTA ethylenediaminetetra-acetic acid - OASSase O-acetyl-L-serine sulfhydrylase - PAPS adenosine 3-phosphate 5-phosphosulfate - POPOP 1,4 Di 2-(5-phenyloxazolyl)-benzene - PPO 2,5-diphenyloxazol - RubP ribulose-bisphosphate - RubPCase ribulosebiphosphate carboxylase This is no. 8 in the series Regulation of Sulfate Assimilation in Plants. The term cysteine is used when it is clear that cystine is not involved; cyst(e)ine is used for an undefined mixture of cysteine and cystine. The concentrations are expressed in all cases relative to cysteine     

The reliability of parasitic water-mites (Hydracarina) as indicators of physiological age in mosquitoes (Diptera: Culicidae)

The reliability of parasitic water-mites as criteria of a nulliparous condition has been investigated in ten species of mosquito in Uganda. Larvae of two kinds of hygrobatid-type mites, when alive, were found only on nulliparous mosquitoes; but living larvae of two other hygrobatids occurred on a small proportion of pars also. Larvae of thyasid-type mites occurred at least as often on pars as on nullipars. Different types of scars caused by mites can provide information concerning the original infestation rate of a population and also the likelihood that an individual female is parous.In the species of mosquito studied, the infestation rate of nullipars sometimes exceeded 80%, but was usually less than 20%.

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Zusammenfassung An 10 Mückenarten von Uganda wurde untersucht, inwieweit schmarotzende Wassermilben zuverlässig sind zur Unterscheidung alter Mücken (d.h. solcher, die Eier gelegt haben) von jungen Mücken (d.h. solchen, die noch keine Eier gelegt haben). Untersuchung der Ovarien ermöglichte es, weibliche Mücken in alte und junge Individuen einzuteilen. Zu diesem Zweck wurden mehr als 20.000 Mücken seziert.Der Lebenszyklus der an Mücken schmarotzenden Wassermilben wird besprochen. Die Larven zweier Arten von hygrobatischen Wassermilben wurden lebend nur an jungen Mücken gefunden; lebende Larven von zwei anderen hygrobatischen Milbenarten kamen auch an einem kleinen Teil von alten Mücken vor. Larven von thyasischen Milben wurden mindestens ebenso oft an alten wie an jungen Mücken gefunden. Deshalb war es wichtig, den Milbentypus festzustellen und zu erkennen, ob die Milben lebendig oder tot waren.Die Infektion der Mücken durch fünf der gewöhnlichen Wassermilben-Species wird beschrieben. Es hängt von der Milben- und von der Wirts-Art ab, welche Stelle die Milben zum Anheften wählen. Verschiedene Typen der durch die Milben verursachten Narben informieren über die ursprüngliche Befallsrate einer Bevölkerung und auch über die Wahrscheinlichkeit, dass die Mücke alt ist. Die Stärke der Infektion ändert sich bei einer einzigen Mückenart von Monat zu Monat beträchtlich. Manchmal sind über 80% der jungen Mücken befallen, im allgemeinen aber weniger als 20%.Bei Culex annulioris, bei dem die hygrobatischen Larven sich auf die jungen Mücken beschränken, ist der Stechzyklus eines befallenen Weibchens derselbe wie dem aller jungen Weibchen. Deshalb kann der Stechzyklus der jungen Mücken, nicht aber der der alten, direkt von den untersuchten milbentragenden Weibchen abgeleitet werden.Es wird gefolgert, dass bestimmte Wassermilben des hygrobatischen Typus für eine schnelle Diagnose von jungen Mücken nützlich sind; vorher muss jedoch in ausgedehnten Versuchen der Grad ihrer Zuverlässigkeit für jede Wirtsart festgelegt werden.

     

Cation permeation at the amphibian motor end-plate

Summary Measurements of acetylcholine-induced single-channel conductance and null potentials at the amphibian motor end-plate in solutions containing Na, K, Li and Cs ions (Gage & Van Helden, 1979;J. Physiol. (London) (in press) were analyzed in terms of three models. Two of these models, the neutral site channel model and the charged site channel model were developed to cater for three cations. Both were shown to be able to explain the dependence of single-channel conductance on membrane potential and gave the following sequences of equilibrium constants and mobilities.K _Li/K _Na/K _K/K _Cs=71.710.9 andu _Cs/u _K/u _Na/u _Li=1.410.580.13 at 8 °C. Similar sequences were obtained at 20 °C. Although the neutral model fitted the data for relative conductances in Li-, Cs-and Na-solutions slightly better than the charged model, experiments done in normal [NaCl] and [NaCl]/2 solutions could only be fitted by the neutral model. In contrast, the third model, the Constant Field Equation, was unable to fit the conductance data in any of the above situations. The data available suggests that permeation is through long neutral channels, lined with high field-strength negative polar groups and including one or possibly more high resistance barriers for anions.     

Size fractionation of trace metal species in freshwaters: implications for understanding their behaviour and fate

Data on both the colloid size distributionpresent in freshwaters and the extent to whichtrace metal ions associate with the differentsize fractions within the so-called dissolved phasein these systems are examined. Several keyfeatures are identified: (i) division of totalmetal into particulate and dissolved fractions via a single ca. 450 nm filtrationprocedure provides no useful information, (ii)within the dissolved fraction, a continuum ofparticle sizes exists in the colloidal sizerange in freshwaters, (iii) for the tracemetals Cu, Cd, Zn, Cr, Co, and Ni, the greatestproportion of dissolved trace metals are in the low molecular mass fraction, together withthe largest proportion of DOC, (iv) in allrivers, and in lakes with a low DOC content,the predominant determiner of the sizedistribution of trace metals is the lowermolecular size, more strongly complexing,pedogenic organic matter fraction.     

Modulation of inner mitochondrial membrane channel activity

Three classes of inner mitochondrial membrane (IMM) channel activities have been defined by direct measurement of conductance levels in membranes with patch clamp techniques in 150 mM K Cl. The 107 pS activity is slightly anion selective and voltage dependent (open with matrix positive potentials). Multiple conductance channel (MCC) activity includes several levels from about 40 to over 1000 pS and can be activated by voltage or Ca²⁺. MCC may be responsible for the Ca²⁺-induced permeability transition observed with mitochondrial suspensions. A low conductance channel (LCC) is activated by alkaline pH and inhibited by Mg²⁺. LCC has a unit conductance of about 15 pS and may correspond to the inner membrane anion channel, IMAC, which was proposed from results obtained from suspension studies. All of the IMM channels defined thus far appear to be highly regulated and have a low open probability under physiological conditions. A summary of what is known about IMM channel regulation and pharmacology is presented and possible physiological roles of these channels are discussed.     

Low conductance states of a single ion channel are not ‘closed’

We have used a polymer-exclusion method to estimate the sizes of the high and low-conductance states of Staphylococcus aureus -toxin channels across planar lipid bilayers. Despite a >10-fold difference in conductance between high and low-conductance states, the size differs by <2-fold. We conclude that factors other than the dimensions have a strong influence on the conductance of -toxin channels. We also show that the high conductance state is destabilized by the presence of high molecular weight polymers outside the channel, compatible with the removal of channel water as the high conductance state shrinks to the low conductance state.We are grateful to Drs. D.T. Edmonds, A.A. Lev and V.A. Parsegian for fruitful discussion and to the Cell Surface Research Fund, the Science and Engineering Research Council, The Wellcome Trust, UNESCO (Molecular and Cellular Biology Network) and the National Academy of Sciences/National Research Council for financial support.     

Ion permeation through single channels activated by acetylcholine in denervated toad sartorius skeletal muscle fibers: Effects of alkali cations

Summary The gigaohm seal technique was used to study ion permeation through acetylcholine-activated channels in cell-attached patches of the extrajunctional membrane of chronically denervated, enzyme-treated cells from the sartorius muscle of the toadBufo marinus. The most frequently occurring channel type (>95% of channel openings), provisionally classified as extrajunctional, had a chord conductance of approximately 25 pS under normal conditions (–70 mV, 11°C, Normal Toad Ringer's). The less frequently observed channel type (<5% of channel openings), classified as a junctional type, had a conductance of 35 pS under the same conditions, and a similar null potential. In many patches, a small percentage (usually <2%) of openings of the extrajunctional channel displayed a lower conductance state. The shape of theI–V curves obtained for the extrajunctional channel dependend on the predominant extracellular cation. For Cs and K, theI–V curves were essentially linear over the voltage range +50 to –150 mV across the patch, suggesting that the potential independent component of the energy profile within the channel was symmetrical. For Li, theI–V curve was very nonlinear, displaying a significant sublinearity at hyperpolarized potentials. Both an electrodiffusion and a symmetrical uniform four-barrier, three-site rate-theory model provided reasonable fits to the data, whereas symmetrical two-barrier, single-site rate-theory models did not. For the alkali cations examined, the relative permeability sequence wasP _Cs>P _K>P _Na>P _Li—a proportional selectivity sequence. This was different from the single channel conductance sequence which was found to be _K> _Cs> _Na> _Li implying that ions do not move independently through the channel. The relative binding constant sequence for the channel sites was found to be a polarizability sequence, i.e.,K _Li>K _Cs>K _Na>K _K There was an inverse relationship for the cations examined. Under conditions when the single-channel conductance was relatively high, the conductance at depolarized potentials was lower than that predicted by both electrodiffusion and rate theory models, suggesting that there was a rate-limiting access step for ions, from the intracellular compartment into the channel.     

Studies on Tn951 (lac+) expression in Agrobacterium

Summary None of the Agrobacterium tumefaciens and A. rubi strains tested produces detectable amounts of -galactosidase although they are capable of utilizing lactose as sole source of carbon. This opportunity was taken to investigate the expression of lac transposon Tn951 (Cornelis et al. 1978) in Agrobacterium with the ultimate goal of using this system to investigate alien gene expression. When the transposon was introduced with the help of a broad-host range plasmid, RP1, the transconjugants produced significant quantities of -galactosidase which was inducible by isopropyl--D-thiogalactopyranoside. Tn951 was capable of restoring the Lac⁺ phenotype to an A. tumefaciens mutant not capable of using lactose. Cellobiose, a known inducer of aldohexopyranoside: cytochrome c oxidoreductase which regulates the characteristic 3-ketolactose production in Agrobacterium: van Beeumen and De Ley (1968), had no effect on -galactosidase activity.Abbreviations NCPPB National Collection of Plant Pathogenic Bacteria, Harpenden - km kanamycin resistance - str streptomycin resistance - rif ^r rifampicin resistance     

A frequency-time domain 3D COSY-J technique for measurement of1H−31P coupling constants in oligonucleotides

Summary A frequency-time domain 3D NMR technique has been developed for measurement of heteronuclear coupling constants in oligonucleotides employing a combination of COSY andJ-resolved techniques. The method employs frequency-selective excitation to generate the ₁ axis and 2D FT to generate the ₂ and ₃ axes. The procedure yields high resolution, especially along the ₁ axis. The technique is demonstrated on a dinucleotide.     

The meiotic pairing of nine wheat chromosomes

Summary The meiotic identification of nine pairs of chromosomes at metaphase I of meiosis of Triticum aestivum (B genome, 4A and 7A) has been achieved using a Giemsa C-banding technique. As a result, the analysis of the pairing of each chromosome arm in disomic and monosomic intervarietal hybrids between Chinese Spring and the Spanish cultivar Pané 247 could be carried out. Differences in the chiasmata frequencies per chromosome arm cannot be explained on the basis of relative arm lengths only. Possible effects of arm-to-arm heterochromatic differences on meiotic pairing are discussed.     

Zur Histochemie von Hydrolasen im Hoden des Hundes und der Katze

Zusammenfassung Wir untersuchten das Verteilungsmuster von unspezifischer Esterase, alkalischer Phosphatase, Adenosintriphosphatase, 5-Nucleotidase und -D-Glucuronidase im Hoden von Hund und Katze. Besonders hervorzuheben sind eine starke Aktivität der unspezifischen Esterase in den Sertolizellen der Katze, der Reichtum der Membrana propria aller Hodentubuli an alkalischer Phosphatase und Adenosintriphosphatase sowie die kräftige Reaktion auf -D-Glucuronidase in den Leydigzellen beider Tierarten.Die Befunde werden diskutiert.

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Summary The localization of unspecific esterase, alkaline phosphatase, adenosine triphosphatase, 5-nucleotidase, and -D-glucuronidase in the testes of cat and dog was demonstrated by histochemical means. We observed a strong esterase activity in the Sertoli cells of the cat and high amounts of alkaline phosphatase and adenosine triphosphatase in the membrana propria of all seminiferous tubules. In both species the principal site of -D-glucuronidase was in the Leydig cells. Our findings obtained being discussed.

     

Inactivation of the Reconstituted Oxoglutarate Carrier from Bovine Heart Mitochondria by Pyridoxal 5′-Phosphate

The effect of pyridoxal 5-phosphate and some other lysine reagents on the purified,reconstituted mitochondrial oxoglutarate transport protein has been investigated. The inhibition ofoxoglutarate/oxoglutarate exchange by pyridoxal 5-phosphate can be reversed by passing theproteoliposomes through a Sephadex column but the reduction of the Schiff's base by sodiumborohydride yielded an irreversible inactivation of the oxoglutarate carrier protein. Pyridoxal5-phosphate, which caused a time- and concentration-dependent inactivation of oxoglutaratetransport with an IC₅₀ of 0.5 mM, competed with the substrate for binding to the oxoglutaratecarrier (K _i = 0.4 mM). Kinetic analysis of oxoglutarate transport inhibition by pyridoxal5-phosphate indicated that modification of a single amino acid residue/carrier molecule wassufficient for complete inhibition of oxoglutarate transport. After reduction with sodiumborohydride [³H]pyridoxal 5-phosphate bound covalently to the oxoglutarate carrier. Incubation ofthe proteoliposomes with oxoglutarate or L-malate protected the carrier against inactivationand no radioactivity was found associated with the carrier protein. In contrast, glutarate andsubstrates of other mitochondrial carrier proteins were unable to protect the carrier. Mersalyl,which is a known sulfhydryl reagent, also failed to protect the oxoglutarate carrier againstinhibition by pyridoxal 5-phosphate. These results indicate that pyridoxal 5-phosphateinteracts with the oxoglutarate carrier at a site(s) (i.e., a lysine residue(s) and/or the amino-terminalglycine residue) which is essential for substrate translocation and may be localized at or nearthe substrate-binding site.     

Activation kinetics of single high-threshold calcium channels in the membrane of sensory neurons from mouse embryos

Summary Activation kinetics of single high-threshold inactivating (HTI orN-type) calcium channels of cultured dorsal root ganglion cells from mouse embryos was studied using a patchclamp method. Calcium channels displayed bursting activity. The open-time histogram was single exponential with an almost potential-independent mean open time _op. The closed-time histogram was multicomponent; at least three of the components were associated with the activation process. The fast exponential component with the potential-independent time constant _cl ^f included all intraburst gaps, while two slower ones with potential-dependent time constants _cl ^vs described shut times between bursts and between clusters of bursts. The burst length histogram was biexponential. The fast component with a relatively potential-independent time constant _bur ^f described short, isolated channel openings while the slow component characterized real bursts with a potential-dependent mean life time. The waiting-time histogram could be fitted by a difference of two exponentials with time constants being the same as _cl ^s and _cl ^vs . The data obtained were described in the frame of a 4-state sequential model of calcium channel activation, in which the first two stages are formally attributed to potential-dependent transmembrane transfer of two charged gating particles accompanying the channel transitions between three closed states, and the third one to fast conformational changes in channel protein leading to the opening of the channel. The rate constants for all transitions were defined. The validity of the proposed model for both low-threshold inactivating (LTI orT-type) and high-threshold noninactivating (HTN orL-type) calcium channels is discussed.     

Effect of hydration,photoperiod and temperature on diapause termination in eggs ofPetrobia (Tetranychina) harti (Acari: Tetranychidae)

Petrobia harti (Ewing) displays a facultative summer diapause in the egg stage. An adult female will lay only either diapause or non-diapause eggs throughout her life. In the laboratory, diapause eggs are laid by females which develop on detachedOxalis articulata leaves under long-day photoperiods and a relatively low temperature of 19±1°C.Diapause occurs in a stage of advanced embryonic development, in which the embryo appears U-shaped when observed from the egg's ventral side. Embryonic development ceased at this stage, and no further growth occurred when the eggs were kept under a relative humidity of about 70% in various photoperiod and temperature conditions. However, when the eggs were hydrated by placing them on wet cotton wool, development in some embryos (apparently in those which had completed their diapause development) proceeded beyond the U-stage at a rate similar to that in non-diapause embryos and the eggs hatched.Under LD 168 and 19±1°C or 26±1°C, the later from oviposition the period of egg hydration started, the higher the percentage of diapause termination. Under LD 168 and 26±1°C, diapause termination occurred mostly during the first week of hydration, while at 19±1°C mostly during the second and third week.At 26±1°C, in eggs hydrated 15 days but not 30 days from oviposition, the percentage of diapause termination was higher under a long-day than under a short-day photoperiod.Under LD 168, when the eggs were hydrated continuously from oviposition or starting 15, 30 and 45 days from it, the percentage of diapause termination was higher at 26±1°C than at 19±1°C.The percentage of diapause-laying adult females and the intensity of egg diapause were higher when the pre-imaginal mites grew at LD 1212 and 19±1°C, than when they grew at LD 168 and 26±1°C. This maternal effect on egg diapause intensity was expressed when the eggs were maintained at LD 1212 and 19±1°C but not at LD 168 and 26±1°C.