Carbonic anhydrase subunits of the mitochondrial NADH dehydrogenase complex (complex I) in plants

The mitochondrial nicotinamide adenine dinucleotide, reduced (NADH) dehydrogenase complex (complex I) of plants has a molecular mass of about 1000 kDa and is composed of more than 40 distinct protein subunits. About three quarter of these subunits are homologous to complex I subunits of heterotrophic eukaryotes, whereas the remaining subunits are unique to plants. Among them are three to five structurally related proteins that resemble an archaebacterial γ-type carbonic anhydrase (γCA). The γCA subunits are attached to the membrane arm of complex I on the matrix-exposed side and form an extra spherical domain. At the same time, they span the inner mitochondrial membrane and are essential for assembly of the protein complex. Expression of the genes encoding γCA subunits is reduced if plants are cultivated in the presence of elevated CO₂ concentration. The functional role of these subunits within plant mitochondria is currently unknown but might be related to photorespiration. We propose that the complex I–integrated γCAs are involved in mitochondrial HCO₃⁻ formation to allow efficient recycling of inorganic carbon for CO₂ fixation in chloroplasts under high light conditions.     

Orthocoelium serpenticaecum (Paramphistomidae: Orthocoeliinae), a new species from the swamp buffalo (Bubalus bubalis Linnaeus) in the Philippines

Orthocoelium serpenticaecum n. sp. is described and illustrated from specimens collected from the swamp buffalo (Bubalus bubalis Linnaeus) in the Philippines. It is readily distinguished from all species of the genus by the tortuous dorso-ventral bends of the caeca and the different types of pharynx and terminal genitalium which are described as ‘serpenticaecum types’ (new types). Supported by a research grant (No. 8301 Ag) from the National Science and Technology Authority (NSTA) Assisted University of the Philippines System (UPS) Integrated Research Program.     

Copepods of the Juréia ecological reserve,state of São Paulo,Brazil. II. The genera Hesperocyclops,Muscocyclops, and Bryocyclops (Cyclopoida,Cyclopidae)

Cyclopid copepods collected mainly in aquatic microcosms and semiterrestrial habitats in the Juréia Ecological Reserve are studied. Hesperocyclops herbsti and Bryocyclops campaneri are described as new species and their taxonomical relationships discussed. Females of Muscocyclops operculatus (Chappuis) are redescribed and the males described for the first time. An emended diagnosis for Muscocyclops is proposed.     

Ultrastructure and division behaviour of dinoflagellate chromosomes

Chromosomes of Prorocentrum triestinum and P. micans have similar substructural and morphometrical values as revealed by electron microscopy of thin sections. However, differences were found between the species in mean length, volume and numerical density of chromosomes, and the volume of the chromosome complement, the nuclear volume and the chromosome number. When examined by a whole-mount procedure both Prorocentrum species have left-handed screw-like chromosomes which end in differentiated telomeres. The chromosomes divide sequentially from one telomere towards the other, presenting a Y and finally a V configuration. At the region where each chromosome divides nascent sister chromatids are connected by two bridges. Sister chromatids have similar quantitative values when compared with each other and with the still undivided chromosome, which suggests that both replication and division take place as coupled events.Supported by CAICYT, grant 2409/83     

Behavioral analysis of the choice of oviposition site by single females ofDrosophila Melanogaster (Diptera: Drosophilidae)

The oviposition behavior of single females of Drosophila melanogasterwas studied in population cages over 24 h. Each female shows a different behavior, but they can be arbitrarily separated into those which concentrate their egg laying in only one tube and those which spread it over more than two tubes. A comparison is made between females extracted from the Valdivian population and flies from lines selected for high and low aggregation. When one-tube females were grouped and compared with more-than-one-tube females, the aggregation indices between these groups were significantly different.     

Organisation and functions of the actV A region of the actinorhodin biosynthetic gene cluster of Streptomyces coelicolor

Summary Sequence analysis of the actVA region of the actinorhodin biosynthetic gene cluster of Streptomyces coelicolor revealed a succession of six open reading frames (ORFs), all running in the same direction and extending over 5.32 kb. The protein product of actVA-ORF1 strongly resembles that of another gene, elsewhere in the act cluster (actII-ORF2), which codes for a trans-membrane protein previously implicated in actinorhodin export from the mycelium. This suggests that the two gene products may co-operate in actinorhodin export, perhaps being sufficient for self-protection of the organism against suicide. At least four of the other five ORFs are implicated in the control of the C-6 and C-8 ring-hydroxylation reactions, lacking in actVA mutants, that occur at middle to late stages in the actinorhodin biosynthetic pathway. This conclusion was reached by genetic mapping of actVA mutants to actVA-ORF3 and-ORF5 (and perhaps -ORF4), and by the finding of strong resemblances between the protein products of actVA-ORF2 and -ORF6 and the products of genes of the oxytetracycline or tetracenomycin gene clusters that have been implicated in ring-hydroxylation reactions in the biosynthesis of these other aromatic polyketide antibiotics.     

Phosphorylation of K+ channels in the squid giant axon. A mechanistic analysis

Protein phosphorylation is an important mechanism in the modulation of voltage-dependent ionic channels. In squid giant axons, the potassium delayed rectifier channel is modulated by an ATP-mediated phosphorylation mechanism, producing important changes in amplitude and kinetics of the outward current. The characteristics and biophysical basis for the phosphorylation effects have been extensively studied in this preparation using macroscopic, single-channel and gating current experiments. Phosphorylation produces a shift in the voltage dependence of all voltage-dependent parameters including open probability, slow inactivation, first latency, and gating charge transferred. The locus of the effect seems to be located in a fast 20 pS channel, with characteristics of delayed rectifier, but at least another channel is phosphorylated under our experimental conditions. These results are interpreted quantitatively with a mechanistic model that explains all the data. In this model the shift in voltage dependence is produced by electrostatic interactions between the transferred phosphate and the voltage sensor of the channel.     

Principles of environmental physics

Book Review

Principles of environmental physicsJ.L. Monteith and M.H. Unsworth Second edition. London: Edward Arnold, 1990. xii + 291 pages. £30.00 (hardback), £14.95 (paperback). ISBN 0-7131-2931-X     

Screening of white-rot fungi on (14C)lignin-labelled and (14C)whole-labelled wheat straw

Summary 74 Basidiomycetes have been tested for ligninolytic capability on (¹⁴C)lignin-labelled wheat straw. Fifteen strains were selected and rested more accurately for ligninolytic activity and the capacity to degrade wheat straw. The asymptote, inflexion point and degradation rate were determined using a model approach. The fungi exhibited very different responses with respect to lignin biodegradation: high asymptote for Pleurotus ostreatus (77%), low inflexion points for Sporotrichum pulverulentum Nov. (6.1 days) and Pycnoporus spp. (2.7 to 4.7 days) with high and slow degradation rates, respectively (0.91% and 0.45% of ¹⁴CO₂ release/day). Degradation values for (¹⁴C)whole-labelled wheat straw exhibited less variation. Finally, the strains Pleurotus ostreatus, Dichomitus squalens and Bjerkandera adusta showed the highest selectivity of lignin removal.