Multiple gene control of plastome-genome incompatibility and plastid DNA inheritance in interspecific hybrids of Zantedeschia

From interspecific hybridisation in the genus Zantedeschia, we have previously produced albino, variegated and virescent hybrids. The inhibition of chloroplast development in these hybrids is due to plastome-genome incompatibility. The albino hybrids did not develop prolamellar bodies in their etioplasts in darkness and formed only distended membranes, but no grana in light. This indicates that the block to chloroplast development occurs before or during the development of etioplasts. In albino leaf sectors of variegated hybrids, chlorophyll and carotenoid contents were only 2–4% of those in green plants. The mRNA levels for five plastid-development-related genes were also severely reduced, but they were still readily detectable using Northern hybridisation techniques. In the green sectors of variegated hybrids, chlorophyll content and mRNA levels of the fives genes were slightly reduced. We have earlier shown that F₁ hybrids between Z. aethiopica and Z. odorata were albino when Z. odorata plastids were present but virescent when Z. aethiopica plastids were present. When the F₁ hybrids with Z. aethiopica plastids were backcrossed to Z. odorata, the progeny were albino, virescent or green. Z. odorata plastids were inherited only from maternal parents in the F₁ progenies but inherited from either maternal or paternal parents in the backcross. The increased compatibility with, and inheritance of Z. odorata plastids in the backcross suggests that multiple genes play a major role in the plastome-genome incompatibility. An increase in the number of genes from the parent contributing the plastids improves chloroplast development in the hybrids of the genus Zantedeschia. Received: 29 November 1999 / Accepted: 2 December 1999     

Chlorophyll Deficiency Caused by a Specific Blockage of the C5-Pathway in Seedlings of Virescent Mutant Rice

Temperature-sensitive mutants of rice, designated virescent(v₁, v₂ and v₃), develop chlorophyll-deficient leaves at a restrictivetemperature (20°C) but develop nearly normal green leavesat a permissive temperature (30°C). Analysis of the chlorophyllbiosynthetic pathway in the virescent mutants indicated thatthe chlorophyll deficiency at the restrictive temperature wasdue to specific blockage of the C₅-pathway. Northern analysissuggested that the chlorophyll deficiency in the virescent mutantswas caused by specific inhibition of the expression of chloroplasttRNA^Glu. (Received October 22, 1993; Accepted January 25, 1994)     

Chromosome elimination in trisomics of Coix aquatica Roxb.

Summary Somatic chromosome elimination was identified and its patterns studied in a trisomic (2n=11) with marker genes in Coix aquatica Roxb. In a cross between a recessive trisomic with green base and white style (ccc ii ss) and a dominant disomic having purple base and purple style (CC II SS), all the F₁ seedling progeny were purple based because of the presence of C, I and S. For C. to be expressed in seedling base, either I should be absent or S should be present with I. In style colour, however, irrespective of the presence of I and S, C produces purple phenotype.In one trisomic (Ccc ii ss) plant (designated as 4–15) of the F₁ progeny, a part of the seedling base was green. All the tillers coming up from the green side of the main tiller also had green base, and those arising on the purple side were purple based. Similarly, the pistillate spikelets on the green side of the main culm and on the tillers with green base were white styled, and the male spikes showed 10 chromosomes. Female spikelets on the purple side of the main tiller and on the tillers with purple base were mostly purple styled and the male spikes had 11 chromosomes. In some of the purple based tillers, however, there were both 11 and 10 chromosomes in different regions or different inflorescence clusters on the tiller. In these tillers, where the chromosome number was 11, style colour was purple, and white style occurred when there were 10 chromosomes. In one tiller, the style colour was purple but the chromosome number was 10.The recessive phenotype of the style in the trisomic conceivably resulted from an elimination of the extra chromosome carrying the dominant allele C. On the basis of the morphological features of the extra chromosome, such as length, centromere position and distribution pattern of the hetero and eupycnotic regions, it was identified as chromosome No. 2 in the complement. It was therefore possible to place with certainty the gene c on this chromosome. Sometimes, however, the extra chromosome carrying c also was eliminated giving 10 chromosomes and purple style.In the other trisomic plants of the F₁ progeny, one plant showed 11 chromosomes but in a tiller there were only 10 chromosomes and white styles. In two other plants, although the chromosome number was 11 throughout, white style was present in a single cluster of inflorescences in one plant, and in one pistillate spikelet in the other. In the latter two cases, white style was believed to have arisen as a result of a mutation from C to c or somatic crossing over, giving the genotype ccc in the affected regions. In a single plant, chromosome elimination was observed in only one cell.Apparently the 10-chromosome sectors arose from the 11-chromosome condition by selective elimination of the extra chromosome during mitosis in the primordium giving rise to these sectors. In the affected plants, elimination did not obviously occur at the same stage but at different times in their ontogeny. Instability is probably governed by one or a few major genes, associated with a number of modifiers, exhibiting incomplete penetrance and variable expression. Chromosome elimination did not apparently follow any particular pattern but was erratic. Probably some intracellular environment is necessary to trigger the mechanism governing the elimination into action. The unstable system, occurring in combination with other favourable features like the functional nature of the aneuploid gametes, sexual reproduction, monoecious condition favouring cross pollination and tolerance of extra chromosomes by the sporophyte, could be an important factor in the cytogenetic evolution of the species.     

Characteristics of a virescent cotton mutant

The virescent cotton (Gossypium hirsutum) mutant described here differs from normal cultivated cotton by a single mutation in the nucleus. The mutant exhibits nuclear control of chlorophyll and carotenoid development. Young leaves are distinctly yellow and become green with age. There is no unusual photometabolism of ¹⁴CO₂ or ¹⁴C-acetate in this mutant. It is probable that the nuclear virescent mutation is in a locus concerned with making structural units. The yellow leaves do show a high photosynthetic capacity on a chlorophyll basis. At saturating light intensity the rate of CO₂ fixation is 8 fold higher than the green control leaves. Thus, impaired pigment synthesis which could be lethal is offset by a high photosynthetic capacity in the virescent leaves.     

Anther culture of an interspecific rice hybrid and selection of fine grain type with submergence tolerance

Improvement of rice with respect to resistance to biotic and abiotic stresses through introgression of alien genetic variation is an important breeding objective of wide hybridization. Anther culture of an interspecific hybrid between Oryza sativa L. cv. pankaj x O. rufipogon Griff. (both of them having "AA" genome) was done to obtain submergence tolerant high yielding recombinant type. Inoculation of anthers in five basal media viz. N6, modified N6, R3, He2 and He5 each one supplemented sith NAA (2 mg l^-1), kinetin (0.5 mg l^-1) and sucrose (5%) showed that the rate of callusing was highest (8.3%) in He2 medium. Calluses initiated in all the above five media when transferred to regeneration medium [MS medium containing NAA (0.5 mg l^-1), kinetin (2 mg l^-1) and sucrose (3%)], percentage of green plant regeneration was also high (13%) in calluses initiated in He2 medium. Androgenic doubled haploid plants, showed 1:1 segregation of the traits for most of the morphological characters studied whereas, different segregating ratios were found in F₂ population. Wider range of variation for different agronomic characters were noted in androgenic population as compared to F₂>. Of the 533 field grown doubled haploid plants, five plants were O. sativa type parental forms with fine grains and submergence tolerant (tested at ten days old seedling stage). Further screening has helped to select only one awnless, fine grain, submergence tolerant line tested at seedling stage and six weeks old plant age. This revised version was published online in June 2006 with corrections to the Cover Date.     

Evolution of Chilean colonizing populations of <Emphasis Type="Italic">Drosophila subobscura</Emphasis>: lethal genes and chromosomal arrangements

Knowledge of the frequency, distribution, and fate of lethal genes in chromosomal inversions helps to illuminate the evolution of recently founded populations. We analyze the relationship between lethal genes and inversions in two colonizing populations of D. subobscura in Chile. In the ancestral Palearctic populations of this species, lethal genes seem distributed at random on chromosomes. But in colonizing American populations, some lethal genes are associated with specific chromosomal arrangements. Some of these associated lethals were detected only during the first stages of the colonization (O ₃₊₄₊₂ ), and never thereafter, whereas others have persisted (O ₃₊₄₊₇ and O₅). However, most lethal genes in American populations have been observed only once: they have arisen by novel mutation and soon disappear. Finally, recombination between different inversions has been observed in America. However, the persistence of lethal genes associated with the heterotic inversions O ₃₊₄₊₇ and O₅ could indicate that recombination inside these inversions is rare. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of “skeleton” photoperiods and high frequency light-dark cycles on the rhythm of cell division in synchronized cultures of Euglena

Summary Two further lines of evidence support the contention (Edmunds, 1966) that the cell cycle in autotrophically grown Euglena can be coupled to an endogenous, circadian biological clock under certain conditions. So-called skeleton photoperiods (LD: 3,6,3:12 and LD: 4,4,4:12) following a complete photoperiod regime entrain the cell division rhythm in the population to a precise 24 hr period, although the step-sizes of the successive fission bursts are always less than 2.00, indicating that not all cells divide in any one 24 hr interval. These findings imply that the continuous action of light is not required for synchronization and suggest that the putative oscillation underlying the rhythm can be phased by discrete light (or dark) pulses or signals.The effects of high frequency LD cycles whose periods were integral submultiples of 24 hr were also investigated. In most regimes (LD:1/4,1/2; LD:1/2,1; LD: 1,2; LD: 1,3; LD: 2,4; LD: 2,6; LD: 4,4) synchronous cell division iccurred in the culture with an average period of 26–27 hr, although only a fraction of the cells divided during any one burst. Similar results were obtained if (i) a synchronized culture was exposed to certain high frequency cycles whose periods were not integral submultiples of 24 hr (e.g., LD: 5,5 or LD: 8,8); (ii) an asynchronous culture (grown in LL) was subsequently exposed to a high frequency cycle; or (iii) a synchronized culture was subjected to a random LD cycle. The synchrony does not break down as long as the given LD regime is imposed and shows some indications of persistence in certain ensuing conditions of continuous illumination.A general formula was derived which predicts the time of division, t _D , for an individual cell: t _D =k+n, where k is the initial phase delay, n is an integer, and is the free-running period of the rhythm observed in the population. These results are interpreted as indicating that the high frequency cycles employed were unable to entrain the circadian oscillation(s) hypothesized to underly and gate cell division, with the result that the rhythm reverted to its free-running period. Exposure to such cycles, however, apparently either initiates a rhythm or synchronizes the phases of the individual oscillations in the populations of cells. The possible direct interaction between energy supply and the observed somewhat variable period lengths is discussed; also, the relevance of stochastic models for the decay of division synchrony in the absence of a recurrent synchronizing procedure is considered.Some of these results were initially reported at the 5th International Congress on Photobiology, Hanover, N.H., U.S.A., August 26–31, 1968.This work was supported by NSF research grants #GB-4140 and #GB-6892 to L. Edmunds.     

Proteome analysis on lethal effect of <Emphasis Type="Italic">l</Emphasis><Subscript>2</Subscript> in the sex-linked balanced lethal strains of silkworm, <Emphasis Type="Italic">Bombyx mori</Emphasis>

The sex-linked balanced lethal (SLBL) strains of silkworm serve as an effective system for sex-control in silkworm. To gain comprehensive insight into the effect of one sex-linked balanced lethal gene l ₂, comparative proteomic analysis was carried out between the survival embryos ( W ^{+ l₁} Z^{l₁ + l₂} )\left( {W^{ + l_1 } Z^{l_1 + l_2 } } \right) and lethal embryos ( W ^{+ l₁} Z ^{+ l₁ l₂} )\left( {W^{ + l_1 } Z^{ + l_1 l_2 } } \right) before the lethal stage. The lethal stage of l ₂ was confirmed by observing the typical dead embryo morphology. The two genotype embryos before lethal stage were distinguished using polymorphic simple sequence repeats (SSR) markers closely linked to l ₂ on the sex chromosome. Finally, 11 differentially expressed protein spots were successfully identified by MALDI-TOF/TOF mass spectrometry (MS). Among them, only 1 protein identified as heat shock protein 20.4 (HSP20.4) was up-regulated in the lethal embryos, while the other 10 were down-regulated. The up-regulation of HSP20.4 suggests that there may be abnormal polypeptides produced in the lethal embryos. The gene ontology (GO) annotation indicated those down-regulated proteins are involved in important biological processes including embryo development, nucleoside metabolism, tRNA splicing, translation and protein folding. The biological pathway analysis showed that those down-regulated proteins are mainly involved in spindle assemblage and morphogenesis. Based on our results, we suggest that the l ₂ may be the mutant expressing abnormal polypeptides. Its expression has a negative effect on mitosis and morphogenesis processes. The death of the embryos may be caused by the accumulation of abnormal polypeptides and the handicap of cell proliferation and morphogenesis.     

Detection of epistatic interactions of three QTLs for heading date in rice using single segment substitution lines

A library consisting of 1123 single segment substitution lines (SSSLs) in the same genetic back-ground of an elite rice variety Huajingxian74 (HJX74) was evaluated for heading date. From this library, two SSSLs, W23-03-8-9-1 and W15-03-1-31, with substitution segments on chromosome 3 and 2, respectively, were found to have significantly different heading date from the recipient HJX74. For genetic dissection and epistatic interaction of quantitative trait loci (QTLs) for heading date in two SSSLs, three secondary SSSLs with smaller substitution segments and genic pyramiding lines (GPLs) were developed from an F₂ segregating population of a cross between the two donor SSSLs, W23-03-8-9-1 and W15-03-1-31, using marker-assisted selection (MAS). The QTL analysis revealed that QTL for heading date detected in SSSL W23-03-08-9-1 was genetically dissected into two QTLs, qHD3-1 and qHD3-2, by overlapping mapping. At the same time, one QTL, qHD2-1 in the donor SSSL W15-03-1-31 was also identified. Analysis of GPLs for heading date showed epistatic interactions between qHD3-1 and qHD3-2, between qHD3-1 and qHD2-1, and between qHD3-2 and qHD2-1. These QTLs and epistatic interactions were confirmed in three cropping seasons under different natural daylength conditions, and their physiological functions for heading date were performed.     

Comparative studies on the structural gene for the ribosomal protein S1 in ten bacterial species

Summary Callus protoplasts of a plastome chlorophyll-deficient mutant of tobacco, Nicotiana tabacum, were fused with mesophyll protoplasts from one of the following five sources: cms-analogs of tobacco bearing the cytoplasms of N. suaveolens, N. undulata, N. repanda, and N. plumbaginifolia, respectively, and the wild species N. glauca. In the sixth experiment, callus cells of the tobacco chlorophyll-deficient genome mutant, homozygous for the Su gene, were hybridized with mesophyll protoplasts of the plastome chlorophyll-deficient mutant of tobacco. Individual dividing heteroplasmic fusion products were isolated mechanically and cloned in microdroplets of nutrient medium. Among the regenerants in all parental combinations, though not in all clones, besides pure green and pure chlorophyll-deficient plants, numerous variegated plant forms were obtained. The variegation of cybrid and hybrid plants was connected with their heterozygocity for chloroplast DNA composition, as demonstrated by restriction analysis. In analytical crosses, the variegation was inherited maternally by part of the sexual progeny, and variegated F₁ progeny were also heterozygous for chloroplast DNA composition. As demonstrated by electron microscopic studies, the variegation is connected with the presence of mixed, i.e., heteroplastidic cells in leaves. The results obtained demonstrate that (1) upon somatic cell fusion, plastome genes are inherited biparentally in most fusion products, and (2) despite an evident mitotic segregation process, heterozygosity for plastome genes is a relatively durable state and can be revealed in cell hybrids of different specific combinations of plasmons after a great number of cell generations. In this regard the plastome cytogetes obtained by somatic cell fusion do not differ qualitatively from the cytoplasmic heterozygotes that arise as a result of the mutation process.     

Effect of K223E and K226E amino acid substitutions in PsbO protein of photosystem 2 on stability and functional activity of the water-oxidizing complex in Chlamydomonas reinhardtii

Site-directed mutations were introduced into PsbO protein of photosystem 2 to study the role of two lysine residues, 223 and 226 (LGAKPPK), in the green alga Chlamydomonas reinhardtii. Lysines 223 and 226 homologous to His228 and His231 from cyanobacteria are located on the protein side facing the lumen and can participate in formation of a channel connecting the Mn cluster with the intrathylakoid space. The K223E and K226E mutants were generated on the basis of the ΔpsbO strain of C. reinhardtii with the substitution of glutamic acid for the lysine residues. The K226E mutation leads to a decrease in stability of the protein and development of the ΔpsbO phenotype (the absence of both photosynthetic activity of photosystem 2 and photoautotrophic growth), with substantially decreased PsbO content in the cells. In the case of K223E, the mutant strain accumulated the normal level of PsbO protein and was able to grow photoautotrophically and to evolve oxygen. However, the rate of oxygen evolution and the F _v/F _m ratio were reduced by 15–20% compared to the control. Also, the time of the dark decay of F _v in the presence of DCMU in the cells of the K223E mutant was increased, indicating impairment in the water-oxidizing complex. In general, our study shows the importance of amino acids K223 and K226 located at the lumenal surface of PsbO protein for the activity of the water-oxidizing complex.     

Latitudinal and altitudinal growth patterns of brown trout Salmo trutta at different spatial scales

Spatial variation in growth of stream‐dwelling brown trout Salmo trutta was explored in 13 populations using a long‐term study (1993–2004) in the Bay of Biscay drainage, northern Spain. The high variability in fork length (L_F) of S. trutta in the study area was similar to the body‐size range found in the entire European distribution of the species. Mean L_F at age varied: 0+ years, 57·4–100·7 mm; 1+ years, 111·6–176·0 mm; 2+ years, 155·6–248·4 mm and 3+ years, 194·3–290·9 mm. Average L_F at age was higher in main courses and lower reaches compared with small tributaries and upper reaches. Annual specific growth rates (G_L) were: 0+ to 1+ years, 0·634–0·825 mm mm⁻¹ year⁻¹; 1+ to 2+ years, 0·243–0·342 mm mm⁻¹ year⁻¹; 2+ to 3+ years, 0·166–0·222 mm mm⁻¹ year⁻¹, showing a great homogeneity. Regression models showed that water temperature and altitude were the major determinants of L_F at age variability within the study area. A broader spatial analysis using available data from stream‐dwelling S. trutta populations throughout Europe indicated a negative relationship between latitude and L_F of individuals and a negative interaction between latitude and altitude. These findings support previous evidence of the pervasive role of water temperature on the L_F of this species. Altitude appeared as the overall factor that includes the local variation of other variables, such as water temperature or food availability. At a larger scale, latitude was the factor that encompassed these environmental gradients and explained the differences in L_F of S. trutta. In summary, L_F at age in stream‐dwelling S. trutta decreases with latitude in Europe, the converse of Bergmann's rule.     

Genetic mapping of Eutr1, a locus controlling E2-induced pyometritis in the Brown Norway rat, to RNO5

In certain rat strains, chronic estrogen administration can lead to pyometritis, an inflammation of the uterus accompanied by infection and the accumulation of intraluminal pus. In this article, we report that the Brown Norway (BN) rat is highly susceptible to pyometritis induced by 17β-estradiol (E2). The susceptibility of the BN rat to E2-induced pyometritis appears to segregate as a recessive trait in crosses to the resistant August × Copenhagen Irish (ACI) strain. In a (BN × ACI)F₂ population, we find strong evidence for a major genetic determinant of susceptibility to E2-induced pyometritis on rat chromosome 5 (RNO5). Our data are most consistent with a model in which the BN allele of this locus, designated Eutr1 (Estrogen-induced uterine response 1), acts in an incompletely dominant manner to control E2-induced pyometritis. Furthermore, we have confirmed the contribution of Eutr1 to E2-induced uterine pyometritis using an RNO5 congenic rat strain. In addition to Eutr1, we obtained evidence suggestive of linkage for five additional loci on RNO2, 4, 11, 17, and X that control susceptibility to E2-induced pyometritis in the (BN × ACI)F₂ population.     

Estimation of the position and effect of a lethal factor locus on a molecular marker linkage map

In the mapping of DNA markers the distortion of segregation of marker genotypes is often observed, which may be caused by a lethal factor acting in filial generations derived from distant crosses. A method is presented for estimating the recombination values between a lethal factor locus and neighboring molecular markers, and the relative viability or fertilization ability of gametes or zygotes affected by the lethal factor in an F₂ population using the maximum likelihood method and the expectation conditional maximization (ECM) algorithm. Three selection models of gamete or zygote were considered, and the most likely one was determined by goodness of fit of the observed frequency of the phenotypes to the expected ones under the models. The method was applied to segregation data of molecular markers of an F₂ population consisting of 144 individuals derived from a cross between an Indica and a Japonica rice variety. The presence of a lethal factor locus (L) located on chromosome III that caused partial gametic selection in both the male and female sides was suggested. The locus L was tightly linked to RFLP marker number 23 of the RFLP linkage map of Saito et al. (1991a), and the fertilization chance of a male or female gamete possessing the lethal factor was, on average, 41.5% of that of the normal gamete.     

The Discovery of Intramolecular Stereoelectronic Forces That Drive The Sugar Conformation in Nucleosides and Nucleotides

Abstract

This report summarizes our results⁸ on how the determination of the thermodynamics of the two-state North (N, C2′-exo-C3′-endo) ? South (S,C2′-endo-C3′-exo) pseudorotational equilibrium in aqueous solution (pD 0.6 - 12.0) basing on vicinal ³J_HH extracted from ¹H-NMR spectra measured at 500 MHz from 278K to 358K yields an experimental energy inventory of the unique stereoelectronic forces that dictate the conformation of the sugar moiety in β-D-ribonucleosides (rNs), β-D-nucleotides, in the mirror-image β-D- versus β-L-2′-deoxynucleosides (dNs) as well as in α-D- or L- versus β-D- or L-2′-dNs. Our work shows for the first time that the free-energies of the inherent internal flexibilities of β-D- versus β-L-2′-dNs and α-D- versus α-L-2′-dNs are identical, whereas the aglycone promoted tunability of the constituent sugar conformation is grossly affected in the α-nucleosides compared to the β-counterparts.     

Physiological responses of carbon-sequestering microalgae to elevated carbon regimes

In order to identify a high carbon-sequestering microalgal strain, the physiological effect of different concentrations of carbon sources on microalgae growth was investigated. Five indigenous strains (I-1, I-2, I-3, I-4 and I-5) and a reference strain (I-0: Coccolithus pelagicus 913/3) were subjected to CO₂ concentrations of 0.03–15% and NaHCO₃ of 0.05–2 g CO₂ l^–1. The logistic model was applied for data fitting, as well as for estimation of the maximum growth rate (μ_max) and the biomass carrying capacity (B_max). Amongst the five indigenous strains, I-3 was similar to the reference strain with regards to biomass production values. The B_max of I-3 significantly increased from 214 to 828 mg l^–1 when CO₂ concentration was increased from 0.03 to 15% (r = 0.955, P = 0.012). Additionally, the B_max of I-3 increased with increasing NaHCO₃ (r = 0.885, P = 0.046) and was recorded at 153 mg l^–1 (at 0.05 g CO₂ l^–1) and 774 mg l^–1 at (2 g CO₂ l^–1). Relative electron transport rate (rETR) and maximum quantum yield (F_v/F_m) were also applied to assess the impact of elevated carbon sources on the microalgal cells at the physiological level. Isolate I-3 displayed the highest rETR confirming its tolerance to higher quantities of carbon. Additionally, the decline in F_v/F_m with increasing carbon was similar for strains I-3 and the reference strain. Based on partial 28s ribosomal RNA gene sequencing, strain I-3 was homologous to the ribosomal genes of Chlorella sp.     

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature‐controlled, Brett‐type swimming‐tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L_F), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U_crit) was 102·5 ± 13·7 cm s^?1 or 4·6 ± 0·9 L_F s^?1. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U_max,c) was 99·4 ± 14·4 cm s^?1 or 4·5 ± 0·9 L_F s^?1. Oxygen consumption rate (M in mg O₂ min^?1) increased with swimming speed and with fish mass, but mass‐specific M (mg O₂ kg^?1 h^?1) as a function of relative speed (L_F s^?1) did not vary significantly with fish size. Mean standard metabolic rate (R_S) was 170 ± 38 mg O₂ kg^?1 h^?1, and the mean ratio of M at U_max,c to R_S, an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U_opt), at which the gross cost of transport was a minimum of 2·14 J kg^?1 m^?1, was 3·8 L_F s^?1. In a subset of the fish studied (19·7–22·7 cm L_F, 106–164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L_F. The mean propulsive wavelength was 86·7 ± 5·6 %L_F or 73·7 ± 5·2 %L_T. Mean ±s.d . yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L_F; 23·4, 25·3 and 26·4 cm L_T), were 4·6 ± 0·1 and 17·1 ± 2·2 %L_T, respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.     

Intracellular pH regulation by the plasma membrane V-ATPase in Malpighian tubules of Drosophila larvae

The functional significance of the apical vacuolar-type proton pump (V-ATPase) in Drosophila Malpighian tubules was studied by measuring the intracellular pH (pH_i) and luminal pH (pH_lu) with double-barrelled pH-microelectrodes in proximal segments of the larval anterior tubule immersed in nominally bicarbonate-free solutions (pH_o 6.9). In proximal segments both pH_i (7.43±0.20) and pH_lu (7.10±0.24) were significantly lower than in distal segments (pH_i 7.70±0.29, pH_lu 8.09±0.15). Steady-state pH_i of proximal segments was much less sensitive to changes in pH_o than pH of the luminal fluid (pH_lu/pH_o was 0.49 while pH_i/pH_o was 0.18; pH_o 6.50–7.20). Re-alkaliniziation from an NH₄Cl-induced intracellular acid load (initial pH_i recovery rate 0.55±0.34 pH·min^-1) was nearly totally inhibited by 1 mmol·l^-1 KCN (96% inhibition) and to a large degree (79%) by 1 mol·l^-1 bafilomycin A₁. In contrast, both vanadate (1 mmol·l^-1) and amiloride (1 mmol·l^-1) inhibited pH_i recovery by 38% and 33%, respectively. Unlike amiloride, removal of Na⁺ from the bathing saline had no effect on pH_i recovery, indicating that a Na⁺/H⁺ exchange is not significantly involved in pH_i regulation. Instead pH_i regulation apparently depended largely on the availability of ATP and on the activity of the bafilomycin-sensitive proton pump.Abbreviations DMSO dimethylsulphoxide - DNP 2,4-dinitrophenol - NMDG N-methyl-D-glucamine - pH_i intracellular pH - pH_lu pH of the luminal fluid - pH_o pH of the superfusion medium - _I intrinsic intracellular buffer capacity     

Effects of copper sulphate on Tisbe holothuriae Humes (Copepoda) and development of tolerance to copper

A study was made of the toxicity of copper to the marine copepod Tisbe holothuriae Humes and the development of increased tolerance due to acclimation. In sublethal concentrations, copper causes a prolongation of maturation time and a reduction in offspring production. These effects increased proportionally to the copper concentration used, while the respiratory rate (measured at the highest concentration used: 0.008 mg l^–1 Cu) increased. A tendency for higher tolerance due to acclimation was also observed. The copper induced delay in maturation time observed in the F₂ generation, became less pronounced from F₃ onwards. In animals exposed at 0.008 mg l^–1 Cu the maturation time of F₃ was not statistically different from that of untreated animals. The LC50 48 h also presented an increase due to acclimation in animals exposed at 0.004 (F₅) and 0.008 mg l^–1 Cu (F₃ and F₅ generations), but this increase was not statistically significant.