Ultrastructure of spermiogenesis in <Emphasis Type="Italic">Cristatella mucedo</Emphasis> Cuvier (Bryozoa: Phylactolaemata: Cristatellidae)

In Cristatella mucedo spermiogenesis occurs in a morula consisting of a large number of spermatids connected with a central cytophore. The mature sperm cell is filiform and consists of a head, a midpiece and a tail region, the latter two separated by a deep circular constriction. The comparatively short head contains a drop-shaped, bilaterally symmetrical and pointed nucleus capped by a minute acrosome. The single centriole is placed in a deep posterior invagination of the nucleus followed by the axoneme with the typical 9 + 2 pattern. The elongated midpiece is 0.9–1.1 μm thick and contains several helices of mitochondria surrounding the axoneme. The tail is thicker (1.3 μm) and richer in cytoplasm with many compact accumulations of an electron-dense substance lying peripherally and another less dense material wrapped around the axoneme. The course of the spermiogenesis and the fine structure of the sperm are very similar to that of Plumatella fungosa. Comparison with other species shows that the same sperm type is recognizable in four of the five families of Phylactolaemata and, provided it occurs also in the fifth family, the Stephanellidae, is a synapomorphy of the entire class.     

Morpho-histogenic studies on tendrils of Passiflora

The ontogenetic development of the tendril and its associatedorgans is investigated in 17 species of Passiflora. The shootapex shows a single tunica layer though the second layer simulatestunica. The cytohistological zonation is not a constant feature.In P. caerulea Linn., it is distinct at leaf initiation butin P. pruinosa Mast., P. vespertilio Linn., and P. watsonianaMast., it is indistinct. The main axillary bud differentiatesfrom the peripheral meristem of the shoot apex. The differentiationof this bud into floral and tendril menstems occurs at a nodeimmediately below the shoot apex in P. minima Blanco. and Pracemosa Brot. In other species this differentiation generallyoccurs at the lower nodes. The floral meristem is initiatedas an accessory bud from this bud, thus forming a bud complex.The residuum of the bud complex develops as a tendril. The thirdaccessory bud which does not originate from this bud complex,develops into a vegetative branch. The fundamental nature ofthe vascular relationship between the flower, tendril, accessorybud, subtending leaf, and the axis is similar in most of theinvestigated species.     

Optimal Control of Gas Exchange during Drought: Theoretical Analysis

An optimal strategy of stomatal control during a drought period,in plants adapted to a humid climate, is derived by maximizingthe photosynthetic production during the expected duration ofdrought. The expected duration of drought is calculated fromthe probability that rain occurs during a certain period, whichis assumed constant. The underlying plant model describes photosyntheticproduction and the consumption of water from the soil, witha given initial soil water content. Water is consumed throughtranspiration at a rate dependent on water vapour deficit, temperatureand stomatal conductance and carbon is assimilated at a ratedependent on light intensity and stomatal conductance. The optimizationproblem is solved with driving variables and the probabilityof rain corresponding to a Fenno-Scandian climate. The resultingoptimal stomatal control consists of two processes with differenttime constants: (1) daily variation depending on the drivingvariables, and (2) a declining trend as a function of the initialsoil water content and the probability of rain. The result allowsfor a physical interpretation of the so-called ‘cost ofwater’ used in similar optimization studies. An approximatemodel is derived from the optimal solution, such that the ‘costof water’ is a function of the soil water content. Photosynthesis; transpiration; stomatal conductance; soil water content; probability of rain; optimal control; drought; model     

The anatomy of Addisonia (Mollusca,Gastropoda)

Summary The organization of Addisonia lateralis (Requien, 1848) and A. brophyi McLean, 1985 is described. Addisonia species have a thin, asymmetrical, cup-like shell and a very simple shell muscle. Eyes, oral lappets and epipodial tentacles are absent and the right cephalic tentacle is also used as a copulatory organ. Most characteristic is the enormously developed gill which is enlarged into the right subpallial cavity. It is composed of about 30 leaflets with skeletal rods and its epithelia are uniquely arranged. The heart is large and the single auricle is situated anteriorly left. There are two kidneys: the left is small, while the right forms large coelomic cavities and has no connection with the pericardium or the hermaphroditic genital system. Testis and ovary are separate: both have a simple duct proper (vas deferens, oviduct). They are connected to the copulatory organ by an open seminal groove; a small receptaculum is present. The mouth opening is typically triangular, with no jaws or subradular sense organs. Addisonia possesses tuft-like salivary glands, a radula diverticulum and distinct, tubular oesophageal glands. The oesophagus itself is simple. The radula and the posterior alimentary tract are unique; the stomach is completely reduced and the intestine forms a pseudostomach. The streptoneurous, hyoathroid nervous system has pedal cords with three commissures. The visceral loop is also cord-like. A single (left) osphradium is present and the small statocysts have several statocones.The peculiarities and unique combination of primitive and advanced characters in Addisonia reflect a highly enigmatic organization among the Archaeogastropoda. Possible relationships to other archaeogastropod groups are discussed.     

MORPHOLOGY AND ECOLOGY OF THE MARINE BENTHIC DINOFLAGELLATE SCRIPPSIELLA SUBSALSA (DINOPHYCEAE)1

The thecal surface morphology of Scrippsiella subsalsa (Ostenfeld) Steidinger et Balech was examined using the scanning electron microscope. This species is distinguished by a number of morphological characteristics. Apical plate 1′ is wide, asymmetric, and pentagonal, and it ends at the anterior margin of the cingulum. Intercalary plates 2a and 3a are separated by apical plate 3′. The apical pore complex includes a large P_o plate with a raised dome at the center and a deep canal plate with thickened margins at plates 2′, 3′, and 4′. The intercalary bands are wide and deeply striated. The cingulum is deep, formed by six cingular plates; its surface is transversely striated and aligned with a row of minute pores. The cingular list continues around postcingular plate 1′” to form a sulcal list. The sulcal list is a flexible ribbon with a rounded tip that protrudes posteriorly, partially covering the sulcal plates. The hypotheca is lobed, and the antapical plates are irregularly shaped and wide in antapical view. The thecal surface is vermiculate to reticulate. A comparison in morphology and ecology is presented between S. subsalsa and other known Scrippsiella species.     

The regulation of urease activity in Aspergillus nidulans

Aspergillus nidulans can utilize urea as a sole source of nitrogen but not as a carbon source. Urea is degraded by a urease. Mutation at any one of three genes, ureB, ureC, and ureD, may result in deficient urease activity. The ureB gene is closely linked to ureA, the structural gene for the urea transport protein. The heat lability of a ureB ^– revertant strain, intragenic complementation tests, and the linkage of ureB to ureA suggest that ureB is the urease structural gene. The ureD gene is probably involved in the synthesis or incorporation of a nickel cofactor essential for urease activity. The function of the ureC gene is not known. Urease is not induced but is subject to nitrogen regulation. The urease activities of ammonium-derepressed mutants show that the effector of nitrogen regulation is more likely to be glutamine than ammonium. When glutamine is present in the medium, urease appears to be inactivated by some means which does not involve a newly synthesized protease or a direct interaction between glutamine and urease.     

Meloidogyne microcephala n. sp. (Meloidogynidae), a Root-knot Nematode from Thailand

Meloidogyne microcephala n. sp. is described and illustrated from specimens obtained from tobacco (Nicotiana tabacum L.) in Thailand. The female perineal pattern usually has a low dorsal arch, coarse striae, and a series of small cuticular flaps around the tail terminus. The stylet of the female is 14.4 μm long, with large, square to rectangular stylet knobs, The distinctive male head region is narrow, small, and truncate with a low, flattened head cap. The stylet length is 20.6 μm, and the knobs are small, angular, and set off from the shaft. Mean length of second-stage juveniles is 457.5 μm, and stylet length is 9.3 μm. The tail tip in the juveniles is set off from the rest of the tail as a small finger-like projection. M. microcephala reproduces by mitotic parthenogenesis, and has a chromosome number of 2n = 36.     

Place du scanner dans l’imagerie de l’hyperparathyroïdie primaire

Primary hyperparathyroidism is a biological diagnosis. The reference treatment is surgery. When minimally invasive surgery is considered, it is recommended to perform a cervical ultrasound and a scintigraphic examination to localize the hypertrophied parathyroid glands. The multiphasic scanner (4D CT) is a very effective examination to detect and locate precisely the parathyroid adenomas. The study of densities makes it possible to differentiate the adenoma from the thyroid and the lymph nodes that are the differential diagnoses. Without injection, the adenoma is more hypodense than the thyroid with a threshold set at 75 UH. On the early phase after injection, the adenoma appears very hypervascularized with a density > 114 UH. The ganglion appears hypovascularized with a density < 114 UH. In the late phase, there is a decrease in the density within the adenoma, while density within the ganglion increases. The parathyroid scan is indicated in case of negativity or discordance of the couple ultrasound scintigraphy. It is also strongly recommended, in case of persistence or recurrence of hyperparathyroidism after surgery, as well as to better study a parathyroid ectopy.     

The morphology of the cerebellar nuclei of Galago and Tupaia

The cerebellar nuclei of the lesser bushbaby (Galago senegalensis) and the tree shrew (Tupaia glis) were studied. The cerebellar nuclear grey of Galago is divisible into a medial nucleus, a nucleus interpositus anterior, a nucleus interpositus posterior, and a lateral nucleus. The lateral nucleus is slightly concave medially suggestive of a primitive hilus. The interpositus nucleus is divided into anterior and posterior portions by a delicate lamina of fibers. The medial cerebellar nucleus is an irregular mass of cells located dorsal to the fourth ventricle. The cerebellar nuclear grey of Tupaia is also divisible into a medial nucleus, a nucleus interpositus anterior, a nucleus interpositus posterior, and a lateral cerebellar nucleus. The medial cerebellar nucleus is located dorsal to the fourth ventricle. The nucleus interpositus anterior and nucleus interpositus posterior are joined together and with the lateral nucleus in the caudo-ventral region. The NIA and NIP have an anterior-posterior relationship to each other and the lateral nucleus has no apparent undulations suggestive of early sacculations. The configuration of the cerebellar nuclei of Tupaia more closely resembles the more primitive patterns of the rat, hedgehog, and mole than those of Galago or other primates.     

Description of Non-Type Seinura winchesi from Mushroom Compost (Nematoda: Seinuridae)

Non-type material identified as Seinura winchesi, and deposited in the collection of the Nematology Department, Rothamsted Experimental Station, England, is described. The material was collected from mushroom compost in Leeds, England, in 1957. Females of this population are characterized by a set-off head, knobless stylet (20-21 µm), two rows of oogonia-oocytes, and absence of a postuterine sac. The median bulb is oblong and, at times, is constricted in the middle. The body is 565 to 675 µm long and tapers posteriorly to a pointed terminus. The cuticle is finely annulated, and there are three incisures in the lateral field. The ovary is outstretched and overlaps the esophageal gland lobes. A spermatheca is present, and spermatozoa are visible. The vulva is posteriorly located (V = 77-80), and a flap is absent. Males are 550 to 680 µm long with a spicate tail that bears three pairs of subventral papillae. The spike is short (14-18 µm), about one-half the tail length. The testis is 360 to 412 µm long, not reflexed, and at times overlaps the esophageal gland lobes. Spermatogonia-spermatocytes are in two rows. Spicules are 14 to 15 µm long with a prominent apex, and small rostrum. A bursa and gubernaculum are absent.     

The steppes and deserts of the Xizang Plateau (Tibet)

The Xizang Plateau (Tibet) covers a vast area over 4 000 m with a severe environment. Steppes and deserts are widely distributed on the plateau to the west of 91.5°E. Poaceae, Asteraceae, Fabaceae and Cyperaceae are the most important families in the composition of steppe communities. The steppe can be divided into high-cold steppe and montane steppe. The former one is characterized by the Stipa purpurea community, which occupies a vast area with a cold, dry climate: annual mean temperature 0 to –6°C, annual rainfall is 150–300 mm; The latter one is distributed in some limited regions, where the climate is less severe: annual mean temperature 0–7°C, annual rainfall is 150–400 mm. The representative communities here are the Stipa glareosa and S. bungeana communities. Chenopodiaceae and Asteraceae play a principal role in both high-cold and montane deserts. The high-cold desert is unique. Its major representative is the Ceratoides compacta community, which is found at about 5 000 m, in an extremely cold and very dry climate. The Ceratoides latens and Ajania fruticulosa communities are the common ones of the montane desert which mainly appears below 4 600 m in elevation, where the annual temperature is about 0°C and the rainfall is less than 100 mm. The distribution of the steppe and the desert communities shows a clear regional differentiation, and an equally clear vertical distribution pattern.     

GALEIDINIIUM RUGATUM GEN. ET SP. NOV. (DINOPHYCEAE), A NEW COCCOID DINOFLAGELLATE WITH A DIATOM ENDOSYMBIONT1

A new sand‐dwelling dinoflagellate from Palau, Galeidinium rugatum Tamura et Horiguchi gen. et sp. nov., is described. The life cycle of this new alga consists of a dominant nonmotile phase and a brief motile phase. The motile cell transforms itself directly into the nonmotile cell after swimming for a short period, and cell division takes place in the nonmotile phase. The nonmotile cell possesses a dome‐like cell covering, which is wrinkled and equipped with a transverse groove on the surface. The cell has 10–20 chloroplasts and a distinct eyespot. The motile cell is Gymnodinium‐like in shape. The dinoflagellate possesses an endosymbiotic alga to which the chloroplasts belong and which is separated from the host (dinoflagellate) cytoplasm by a unit membrane. The endosymbiont cytoplasm also possesses its own eukaryotic nucleus and mitochondria. The eyespot is surrounded by triple membranes and is located in the host cytoplasm. Photosynthetic pigment analysis, using HPLC, revealed that G. rugatum possesses fucoxanthin as the principal accessory pigment instead of peridinin. The rbcL tree showed that G. rugatum is monophyletic with Durinskia baltica (Levander) Carty et Cox and Kryptoperidinium foliaceum (Stein) Lindemann and that this clade is closely related to the pennate diatom, Cylindrotheca sp. The endosymbiont of G. rugatum is therefore shown to be a diatom. Phylogenetic analysis based on small subunit rDNA sequences demonstrated that G. rugatum, D. baltica, and K. foliaceum, all of which are known to harbor an endosymbiont of diatom origin, are closely related.     

Life Cycle and Morphology of Bryopsidella ostreobiformis spec. nov. (Bryopsidaceae,Chlorophyta) from the Mediterranean,under Culture Conditions,with Comments on the Phylogeny of the Bryopsis/Derbesia Complex

Bryopsidella ostreobiformis sp. nov. is presented as the second species of the genus. The latter is amended to accomodate this new species. The derbesioid sporophyte is capable of producing three- to eight-rayed stellate propagules. The dioecious gametophyte is a heterotrichous thallus with branched, prostrate filaments and unbranched, erect ones, and does not resemble Bryopsis. The life cycle is distinctly diplohaplontic, with a diploid sporophyte and a haploid gametophyte. B. ostreobiformis is postulated as the starting point of a hypothetical evolutionary sequence of life histories in the Derbesia/Bryopsis complex.     

Embryology of Clitoria ternatea (Fabaceae)

ABSTRACT

The embryology of Clitoria ternatea was studied. Anthers contain four sporangia. The anther wall comprises an epidermis, an endothecium, a middle layer and a glandular tapetum. Microspore tetrads are tetrahedral and pollen grains are shed at the 2-cell stage. The ovule is campylotropous, bitegmic and crassinucellate. The micropyle is formed by both the integuments. The megaspore tetrad is linear or T-shaped. The chalazal megaspore is functional and embryo sac development follows the monosporic Polygonum type. Endosperm development is of the nuclear type. The chalazal part of the endosperm forms a haustorium. Embryo development follows the Onagrad type.     

Ultrastructure of the spermatozoon of Myrmecocichla formicivora (Vieillot, 1881) and Philetairus socius (Latham, 1790) (Aves; Passeriformes), with a new interpretation of the passeridan acrosome

Passerine spermatozoa exhibit apomorphies that distinguish them from non‐passerine neognaths and palaeognaths. The acrosome is longer than the nucleus (excepting the suboscines, most Corvida, and a few Passerida). A perforatorium and endonuclear canals are absent. The proximal centriole is absent (except in the suboscines). The distal centriole is secondarily short, contrasting with its elongate condition in palaeognaths and Galloanserae. In the Passerida a single mitochondrial strand winds extensively along the axoneme (restricted to the anterior axoneme in suboscines and Corvida). A fibrous, or amorphous, periaxonemal sheath, seen in palaeognaths and many non‐passerines, respectively, is absent. The acrosome in Myrmecocichla formicivora and Philetairus socius is bipartite: an acrosome core is surmounted by an acrosome crest; the core is ensheathed by a layer which is a posterior extension of the crest. The acrosome helix is a lateral extension of the crest and the crest layer with (Myrmecocichla) or without (Philetairus) protrusion of material of the acrosome core into it. In M. formicivora, as in other muscicapoids, a fibrous helix is intertwined with at least the more proximal region of the mitochondrial helix. The fibrous helix is absent at maturity in Philetairus and other described passeroid spermatozoa with the possible exception of Passer italiae. In Philetairus a granular helix precedes the mitochondrial helix.     

Acidification: its impact on the environment and mitigation strategies

The effect of acidification on ecosystems is reviewed. About 30% of the world land area is acidified mostly by natural processes. Only a small part of it is acidified from pollution which leads to extensive forest and surface water deterioration in Europe and North America. The damage is especially visible in areas of poor soil quality. The acid deposition pattern is characterized, with a special emphasis on Poland. It was shown that strategies for mitigation of ecosystem acidification lead to a decrease of SO₂ emissions due to the use of lower sulphur content fuels and application of desulphurisation methods. Also, a decrease in NO_x emissions is observed due to use of catalysts and application of NO_x removal technologies. However, since about 50% of NO_x emission is from vehicles, this improvement is offset by a continuously increasing vehicle population. The application of liming, forest fertilisation and suitable land use for mitigation of ecosystem acidification is also reviewed.     

A biresonant plasma source based on a gapped linear microwave vibrator

The operating principle of a novel microwave plasma source—a linear microwave vibrator with a gap—is discussed. The source is placed on a microwave-transparent window of a chamber filled with a plasma-forming gas (argon or methane). The device operation is based on the combination of two resonances—geometric and plasma ones. The results of experimental tests of the source are presented. For a microwave frequency of 2.45 GHz, microwave power of ≤1 kW, and plasma-forming gas pressure in the range 5 × 10⁻²–10⁻¹ Torr, the source is capable of filling the reactor volume with a plasma having an electron density of about 10¹² cm⁻³ and electron temperature of a few electronvolts.     

THREE NEW BENTHIC SPECIES OF PROROCENTRUM (DINOPHYCEAE) FROM BELIZE: P. NORRISIANUM SP. NOV., P. TROPICALIS SP. NOV., and P. RETICULATUM SP. NOV.1

Three new benthic, photosynthetic dinoflagellate species, Prorocentrum norrisianum, Prorocentrum tropicalis, and Prorocentrum reticulatum, from floating detritus and coral rubble of Central America are described from scanning electron micrographs. Species were identified based on shape, size, surface micromorphology, thecal plate ornamentation, and architecture of the periflagellar area and intercalary band. Cells of P. norrisianum are ovate with a cell size of 20–25 μm long and 13–16 μm wide. The theca is delicate, its surface smooth, pores species specific with 95 to 105 pores per valve. Pores are round with a diameter of about 0.1 μm. The periflagellar area is V-shaped, located on the right valve in a shallow depression. It has no ornamentation. The flagellar and auxiliary pores are unequal in size. The intercalary band is smooth. Prorocentrum tropicalis cells are ovoid, 50–55 μm long and 40–45 μm wide in valve view with maximum width behind the middle region, narrow at the anterior end. The periflagellar area, situated in the right valve, is a V-shaped wide triangle with a deeply indented depression; the left valve exhibits a flat ridge. The periflagellar area is unornamented, and the flagellar and auxiliary pores are unequal in size. The valve surface is rugose with evenly distributed valve poroids. Each poroid appears to have a small dome in the center. The intercalary band is rimlike around the cell margin, granulated, and horizontally striated. Prorocentrum reticulatum cells are oblong in valve view; cells are 55–60 μm long and 40–45 μm wide. Thecal surface is reticulated; it is composed of a labyrinth of ridges with alternating depressions that vary in size and shape. Each depression has a narrow, oblong-kidney-shaped opening about 0.6 μm long. The periflagellar area is a deep, V-shaped triangle. The right valve of P. reticulatum is excavated, and contains a large flagellar pore and a smaller auxiliary pore surrounded by a narrow apical collar. The left valve margin exhibits a curved flat ridge. The intercalary band is smooth.     

The Q-cycle reviewed: How well does a monomeric mechanism of the bc1 complex account for the function of a dimeric complex?

Recent progress in understanding the Q-cycle mechanism of the bc₁ complex is reviewed. The data strongly support a mechanism in which the Q_o-site operates through a reaction in which the first electron transfer from ubiquinol to the oxidized iron–sulfur protein is the rate-determining step for the overall process. The reaction involves a proton-coupled electron transfer down a hydrogen bond between the ubiquinol and a histidine ligand of the [2Fe–2S] cluster, in which the unfavorable protonic configuration contributes a substantial part of the activation barrier. The reaction is endergonic, and the products are an unstable ubisemiquinone at the Q_o-site, and the reduced iron–sulfur protein, the extrinsic mobile domain of which is now free to dissociate and move away from the site to deliver an electron to cyt c₁ and liberate the H⁺. When oxidation of the semiquinone is prevented, it participates in bypass reactions, including superoxide generation if O₂ is available. When the b-heme chain is available as an acceptor, the semiquinone is oxidized in a process in which the proton is passed to the glutamate of the conserved -PEWY- sequence, and the semiquinone anion passes its electron to heme b_L to form the product ubiquinone. The rate is rapid compared to the limiting reaction, and would require movement of the semiquinone closer to heme b_L to enhance the rate constant. The acceptor reactions at the Q_i-site are still controversial, but likely involve a “two-electron gate” in which a stable semiquinone stores an electron. Possible mechanisms to explain the cyt b₁₅₀ phenomenon are discussed, and the information from pulsed-EPR studies about the structure of the intermediate state is reviewed.The mechanism discussed is applicable to a monomeric bc₁ complex. We discuss evidence in the literature that has been interpreted as shown that the dimeric structure participates in a more complicated mechanism involving electron transfer across the dimer interface. We show from myxothiazol titrations and mutational analysis of Tyr-199, which is at the interface between monomers, that no such inter-monomer electron transfer is detected at the level of the b_L hemes. We show from analysis of strains with mutations at Asn-221 that there are coulombic interactions between the b-hemes in a monomer. The data can also be interpreted as showing similar coulombic interaction across the dimer interface, and we discuss mechanistic implications.