Polysaccharides from the red seaweed Gracilaria dura (Gracilariales, Rhodophyta)

The yield and physical and chemical properties of agars from Gracilaria dura (C. Agardh) J. Agardh, harvested in Thau lagoon (Mediterranean sea, France), were investigated. The agar yield ranged from 32% to 35%. Gel strength of agar ranged from 263 to 600 g cm(-2), with the maximum observed in October. A positive correlation was found between agar yield and gel strength (r = 0.82; P < 0.01). The gelling temperature followed the same pattern of gel strength and also showed higher value in October (43 degrees C). The nitrogen content varied from 1.04+/-0.60% (June) to 4.70+/-0.01% (October). A positive correlation was noted between nitrogen content and gel strength (r = 0.77; P < 0.05). The 3,6-anhydrogalactose content ranged from 0.70 to 0.84 and showed monthly significant differences (P < 0.05). There was a positive correlation between 3,6-anhydrogalactose content and gel strength. The values of sulfate content were relatively constant during the studied period and no significant differences were observed. The relative high gel strength indicates that this species may be considered as source of agar for commercial use.     

Seasonal variation in the chemical composition of two tropical seaweeds

The chemical composition of red seaweed Gracilaria cervicornis and brown seaweed Sargassum vulgare from Brazil was investigated. In this study, the relationship between the nutritive components of each species and the environment was established. Protein content varied from 23.05+/-3.04% to 15.97+/-3.04%. The highest value was found in G. cervicornis. The protein levels were positively correlated with nitrogen content and negatively with water temperature and salinity. Carbohydrate contents of both species varied significantly (p<0.01) and the values observed were superior to others chemical constituents. Contrary to carbohydrates, the lipid concentrations were the lowest recorded chemical component and varied slightly between the two species. Ash content was greater in S. vulgare (14.20+/-3.86) than in G. cervicornis (7.74+/-1.15). In general the variation in chemical composition was related to environment.     

Northern distribution boundaries and thermal requirements of Gracilaria and Gracilariopsis (Gracilariales, Rhodophyta) in Atlantic Europe and Scandinavia

Using verified records from 1970 onwards, northern distribution boundaries in Atlantic Europe and Scandinavia are established for Gracilaria bursa-pastoris, G. multipartita, G. gracilis and Gracilariopsis longissima , the last two species being distinguished for the first time in Northern Ireland, Scotland, Denmark, Germany and The Netherlands. Boundaries are shown to exist as zones (rather than lines) fluctuating in location and in time. Thermal requirements for survival and growth in G. gracilis have been determined, and the requirements for all four species are related to their geographical boundary zones.     

五种丛生状棕榈植物叶热值的月变化研究

对5种丛生状棕榈植物一欧洲棕、细叶棕竹、小箬棕、玲珑椰子、缨络椰子的叶片热值和灰分含量的月变化进行了研究,结果表明,5种植物具有较高的灰分含量,但灰分含量的月变化趋势各不相同;欧洲棕、细叶棕竹、小箬棕3种植物干重热值的月变化趋势有些差异,同属的缨络椰子、玲珑椰子干重热值的月变化趋势基本相似;缨络椰子、小箬棕的干重热值与灰分含量具有显著的线性相关(P<0．05),而其余3种植物的干重热值与灰分含量相关性不显著(P>0．05);从去灰分热值的月变化来看,细叶棕竹与小箬棕,缨络椰子与玲珑椰子的月变化趋势相似。     

Relationship of testicular growth and size to age, body weight and onset of puberty in Menz ram lambs

Scrotal circumference as an index of testes size, along with body weight, wither height, heart girth and body condition score were measured fortnightly for 114 Menz ram lambs from weaning (91+/-7 SD days) until puberty, which was defined as age at first collection of an ejaculate with 50 x 10(6) spermatozoa and 10% motility. The animals were maintained on poor (n=28), low (n=29), medium (n=29) or high (n=28) levels of nutrition through grazing and supplementation. Further, half the lambs in each group were drenched for endoparasites. Daily gains in live weight, wither height, heart girth and scrotal circumference were 48.5+/-1.6 g, 0.05+/-0.01 cm, 0.07+/-0.01 cm and 0.07+/-0.03 cm, respectively for the period from weaning to puberty and varied with level of nutrition (P<0.05 to 0.001) but not with drenching or its interaction with nutrition level (P>0.10). Scrotal circumference increased linearly and was strongly correlated with age, body weight, wither height, and heart girth (r = 0.83 to 0.85, P<0.001), and lamb weight could be predicted by the equation: 6.35 + 0.53 scrotal circumference (R(2) = 0.73). Mean age, body weight and condition score at puberty were 288+/-6 days, 19.3+/-0.4 kg and 2.6+/-0.06, respectively, and varied due to season of birth, level of nutrition and weaning weight (P<0.01 to 0.001). The nutrition level also influenced (P<0.001) scrotal circumference at puberty, averaging 21.5+/-0.3 cm. It was concluded that postweaning nutrition management had a strong influence on lamb weight gain, which in turn was related to testicular growth and puberty onset in Menz ram lambs. The suitability of scrotal size measurement as a criterion for early selection of tropical ram lambs is emphasised.     

Physical properties of the agar of Gracilariopsis tenuifrons (Gracilariacea) from Sucre, Venezuela

The yield, gel strength, gelling and melting temperatures of Gracilariopsis tenuifrons agar from Guayacán, Araya Peninsula, Sucre State, Venezuela were determined. Yield values with and without alkali treatment ranged from 23.22 to 39.57% and from 16.29 to 22.42% respectively, while gel strength with alkali treatment fluctuated betwen 699.31 and 1231.69 g/cm2 and without treatment varied from 278.0 to 691.06 g/cm2. Gelling and melting temperatures were in the range reported for other agarophytes. Considering gel strength, the agar quality of G. tenuifrons was higher than in other species and its exploitation in economically feasible.     

3,6 anhydrogalactose, sulfate and methoxyl contents of commercial agarophytes from different geographical origins

The chemical composition of agars extracted from six economically important species of Gracilaria from different geographical sources (Argentina, Brazil, Indonesia, China and Turkey) and one species of Gracilariopsis (G. lemaneiformis) collected from two different Japanese localities was investigated. Agar was extracted by pretreatment with various concentrations of NaOH (3%, 5%, 7%, 10%) for 2 h at 80°C. The sulfate, 3,6-anhyd, rogalactose and methoxyl contents of each agar extract were analyzed. High sulfate and 3,6 anhydrogalactose contents were found in non-alkali treated agar from Turkish Gracilaria gracilis (3.4%) and from Chilean G. chilensis (54.3%) after alkali treatment concentration of 5% NaOH, respectively. High methoxyl contents (4.9%) were obtained from non-alkali treated agar from Chinese G. tenuistipitata. This revised version was published online in August 2006 with corrections to the Cover Date.     

Gonadal and extragonadal sperm reserves in Boran and Boran x Friesian bulls raised on two planes of nutrition in the Highlands of Ethiopia

Gonadal and extragonadal sperm reserves were determined in testicular and epididymal tissues obtained from Boran (n=10) and Boran x Friesian (n=12) bulls fed either a high or low plane nutrition diet for a 1-year period. The bulls were 32 months of age at castration. Mean (+/-SEM) daily body weight gains over a 1-year period were 776+/-34 and 264+/-34 g/day (P<0.001) for bulls on high and low nutrition, and their respective body weights at castration were 458+/-17 and 276+/-17 kg (P<0.01). Mean body weights did not differ between Boran and Boran x Friesian bulls. Mean scrotal circumference measurements were 32.1+/-0.6 and 28.8+/-0.6 cm for the high and low planes of nutrition (P<0.01) and 31.8+/-0.7 and 29.2+/-0.6 cm for the Boran and the Boran x Friesian bulls (P<0.05). Paired testes and epididymal weights averaged 432+/-22 and 313+/-22 g (P<0.01) and 46.3+/-2.0 and 32.5+/-2.0 g (P<0.001) for bulls on the high and low planes of nutrition, respectively. Boran x Friesian bulls had significantly heavier (P<0.05) testes, but epididymal weithts did not differ between breeds. Although daily sperm production per gram was not influenced by either plane of nutrition or breed, daily sperm production differed between high (5.3 x 10(9)) and low nutrition (2.9 x 10(9)) bulls (P<0.001) and between Boran (4.6 x 10(9)) and Boran x Friesian (3.5 x 10(9)) bulls (P<0.01). Extragonadal sperm reserves were significantly higher in high than in low nutrition bulls (13.1 x 10(9) vs 6.9 x 10(9); P<0.001) and in Boran than Boran x Friesian bulls (12.9 x 10(9) vs 7.1 x 10(9); P<0.01). The cauda epididymis contributed 50 to 54% to the total epididymal sperm reserves. It was concluded that the plane of nutrition influenced growth rates and testes and epididymal weights, and it improved gonadal and extragonadal sperm reserves in young Boran and Boran x Friesian bulls.     

Agar quality of commercial agarophytes from different geographical origins: 1. Physical and rheological properties

Six economically important species ofGracilaria, from a number of commercial sources around the world, andGracilariopsis lemaneiformis, collected from two Japanese localities, were used as the sources of raw material for the evaluation of agar quality. Agar-agar was extracted by pretreatment with various concentratrions of NaOH (0%, 3%, 5%, 7%, 10%) incubated at 80 °C for 2 h. Agar yield, viscosity, dynamic gelling and melting temperature and gel texture were determined for 1.5% agar gels. The highest agar yield was obtained fromG. gracilis from Argentina (39.5%), while the lowest was from BrazilianG. gracilis (13.37%). Dynamic gelling temperature was highest in the agar fromG. gracilis from Turkey (59 °C) and lowest in the non-alkali treated agar isolated fromG. edulis from Indonesia (46 °C). Melting temperature ranged from 96 °C in the agars from the JapaneseGracilariopsis andG. chilensis from Chile to 69 °C in the non-alkali treated agar fromG. edulis from Indonesia. In general, all species produced an agar with high gel strength after treatment with 5% NaOH, except forG. chilensis and the twoGracilariopsis species, which produced an agar with high gel strength after treatment with 3, 7 and 10% NaOH. The highest gel strength (2056 ± 13.6 cm^–2) and hardest gel (261 ± 19.89 g mm^–2) were obtained fromG. lemaneiformis from Japan (Oita Prefecture) after treatment with 7 and 10% NaOH respectively. The lowest gel strength (351 ± 93 cm^–2) was obtained fromG. gracilis from Brazil after treatment with 3% NaOH. The softest gel (66.31 ± 9.63 g mm^–2) was isolated fromG. tenuistipitata from China, after treatment with 3% NaOH. The most flexible gel (11.62 ± 0.31 g mm^–2 × 10²) was obtained fromG. chilensis from Chile after treatment with 3% NaOH.Author for correspondence     

Fine-scale phylogenetic structure and major events in the history of the current wild soybean (Glycine soja) and taxonomic assignment of semi-wild type (Glycine gracilis Skvortz.) within the Chinese subgenus Soja

Wild and cultivated species of soybeans have coexisted for 5000 years in China. Despite this long history, there is very little information on the genetic relationship of Glycine soja and G. max. To gain insight into the major events in the history of the subgenus Soja, we examined 20 simple sequence repeat (SSR) markers of a large number of accessions (910). The results showed no significant differences between wild and semi-wild soybeans in genetic diversity but significant differences between G. soja and G. max. Ancestry and cluster analyses revealed that semi-wild soybeans should belong to the wild category and not to G. max. Our results also showed that differentiation had occurred not only among G. soja, G. gracilis, and G. max but also within G. soja and within G. gracilis. Glycine soja had 3 clear genetic categories: typical small-seeded (≤2.0 g 100-seed weight), dual-origin middle-seeded (2.0-2.5 g), and large-seeded plants (2.51-3.0 g). These last were genetically close to G. gracilis, their defining some traits having been acquired mainly by introgression from soybeans. Small-seeded G. gracilis (3.01-3.5 g) were genetically different from larger seeded ones (from 3.51 to 4.0 to over 10 g). Seed size predominated over seed coat color in evolutionary degree. Typical and large-seeded G. soja were found to have 0.7% and 12% introgressive cultivar genes, respectively. The genetic boundary of G. gracilis was at the range of 2.51-3.0 g of G. soja. In the great majority of wild accessions, traits such as white flowers, gray pubescences, no-seed bloom, and colored seed coats were likely introgressive from domesticated soybeans.     

Freezing tolerance of the European water frogs: the good, the bad, and the ugly

Survival and some physiological responses to freezing were investigated in three European water frogs (Rana lessonae, Rana ridibunda, and their hybridogen Rana esculenta). The three species exhibited different survival times during freezing (from 10 h for R. lessonae to 20 h for R. ridibunda). The time courses of percent water frozen were similar; however, because of the huge differences in body mass among species (from 10 g for Rana lessonae to nearly 100 g for Rana ridibunda), the ice mass accumulation rate varied markedly (from 0.75 +/- 0.12 to 1.43 +/- 0.11 g ice/h, respectively) and was lowest in the terrestrial hibernator Rana lessonae. The hybrid Rana esculenta exhibited an intermediate response between the two parental species; furthermore, within-species correlation existed between body mass and ice mass accumulation rates, suggesting the occurrence of subpopulations in this species (0.84 +/- 0.08 g ice/h for small R. esculenta and 1.78 +/- 0.09 g ice/h for large ones). Biochemical analyses showed accumulation of blood glucose and lactate, liver glucose (originating from glycogen), and liver alanine in Rana lessonae and Rana esculenta but not in Rana ridibunda in response to freezing. The variation of freeze tolerance between these three closely related species could bring understanding to the physiological processes involved in the evolution of freeze tolerance in vertebrates.     

Seasonal variation of the agar quality and chemical composition of Gracilaria veleroae and Gracilaria vermiculophylla (Rhodophyceae,Gracilariaceae) from Baja California Sur,Mexico

Yield and physico‐chemical properties of agar from Gracilaria veleroae E.Y. Dawson and Gracilaria vermiculophylla (Ohmi) Papenfuss were studied and the chemical composition of the two seaweeds was determined. Samples were collected seasonally from summer 2003 to spring 2005. The agar yield did not vary significantly between seasons for both species. The lowest agar gel strength was obtained from G. veleroae (207.5 g cm^–2) in summer 2003 and the highest from G. vermiculophylla (793.1 g cm^–2) in winter 2004. Melting temperatures and hysteresis were higher in G. vermiculophylla, whereas gelling temperatures and 3,6‐anhydrogalactose content were higher for G. veleroae. Moisture, ash, crude fiber, and ether extract showed no significant seasonal variation for G. veleroae. The chemical composition of G. vermiculophylla showed significant seasonal variation. G. vermiculophylla possesses a better agar quality than G. veleroae and is a species that could be considered as a source of agar for commercial use.     

Components of litter size in gilts with different prolactin receptor genotypes

Behavioral estrus and components of litter size at Day 35/36 of pregnancy were studied in gilts with prolactin receptor (PRLR) genotype AA (n=9), AB (n=25), and BB (n=22). This PRLR polymorphism (two alleles, A and B) has been associated with litter size, although it is not known whether the polymorphism itself causes differences in litter size or whether it is a marker for a closely linked causative gene. Estrus length in three successive estrous cycles was not affected by genotype, but estrous cycle length tended (P<0.1) to be longer for AA gilts compared to AB and BB gilts. AA gilts had a significantly (P<0.05) higher ovulation rate (21.5+/-0.9) than BB gilts (18.7+/-0.6), resulting in a numerically higher number of embryos at Day 35/36 (17.0+/-1.3, 15.6+/-0.8, and 13.7+/-0.9 for AA, AB, and BB gilts, respectively) which may lead to a subsequent difference in litter size. Ovulation rate of AB gilts (20.0+/-0.5) was intermediate. Genotype affected the total weight of the ovaries (P<0.05). Even after subtraction of the total weight of corpora lutea, ovarian weight in AA gilts was highest (16.6+/-1.0 g), in BB lowest (13.4+/-0.6g), and in AB gilts intermediate (15.0+/-0.6g; P<0.05). Unlike AB gilts, in AA and BB gilts uterine length was adapted to litter size, which led to longer (P<0.05) uteri for AA gilts (669+/-28 cm) compared to BB gilts (566+/-18 cm). Furthermore, embryos of AA gilts had heavier placentae (52.5+/-3.4 g) and larger implantation surface areas (309+/-19 cm(2)) than embryos of BB (42.0+/-2.3g, P<0.05; 256+/-12 cm(2), P<0.1) or AB (43.2+/-2.0 g, P<0.1; 257+/-11 cm(2), P<0.05) gilts. Results of this experiment show that the PRLR gene or a very closely linked gene affects porcine ovaries, uterus, and placenta in a way that might lead to differences in litter size. Since other genes and also environmental factors, however, might change the effect within the 112 days to parturition, it is preferable to state that the PRLR gene is a candidate gene for ovulation rate rather than for litter size.     

The yield,physical and chemical properties of agar gel from Gracilaria species (Gracilariales,Rhodophyta) of the Kenya coast

Six species of Gracilaria, G. corticata J. Agardh, G. crassa Harvey, G. millardetii J. Agardh, G. salicornia (J. Ag.) Dawson, G. verrucosa (Huds.) Papenfuss and Gracilaria sp, collected from different stations along the Kenya coast were studied. The yield of hot water native agar extract ranges from 8.1–30% of dry weight, with G. verrucosa and G. salicornia having the greatest and the least yield, respectively. The gel-strength of 1.5% agar solution was highest in G. verrucosa (220 g cm^–2) and lowest in G. corticata (< 60 g cm – 2) whereas the highest gelling temperature was recorded for Gracilaria sp. (40.4 °C) and the lowest in G. verrucosa (28.9 °C). 3,6 anhydrogalactose content was the highest in G. verrucosa and the lowest in G. corticata while sulphate content was higher in the latter.     

Determination of the diterpenoid,kaurenoic acid,in Annona glabra by HPLC

The isolation of ent-kaur-16-en-19-oic acid (1) from the leaves and bark of Annona glabra and its determination by reversed-phase HPLC with a photodiode array detector is described. The results indicate that 1 accumulates in the bark of the plant with only very low concentrations in the leaves. Levels of 1 varied throughout the year being highest for bark and leaves in the autumn (5.29 +/- 0.23 and 0.27 +/- 0.01 mg/g dry weight, respectively) and lowest in the spring for bark and in the winter for leaves (4.00 +/- 0.25 and 0.11 +/- 0.01 mg/g dry weight, respectively).     

The growth and phosphorus utilisation of plants in sterile media when supplied with inositol hexaphosphate, glucose 1-phosphate or inorganic phosphate

Seedlings of six temperate pasture species, three grasses and three legumes, were grown for 19–24 days in sterile agar or sand-vermiculite media, in the presence of inorganic phosphate (P_i), glucose 1-phosphate (G1P) or inositol hexaphosphate (IHP). Agar (pH 5.0) had a low IHP-sorbing capacity while IHP was almost completely sorbed in sand-vermiculite. P_i and G1P were relatively available in both media. Growth of each species was measured in relation to phosphorus (P) supply and levels of P_i supply at which shoot yields reached 90% of maximum yield (P_crit) were determined. P_crit values were generally higher for the legume species than for the grasses, and were six-fold higher for Trifolium subterraneum L. seedlings when grown in sand-vermiculite relative to agar. When supplied with G1P, seedlings of the six species grew as well as plants supplied with P_i. By contrast, IHP was a poor source of P for plant growth, even when supplied in agar at levels up to 40-fold greater than P_crit. Using the growth of T. subterraneum in the presence of IHP, it was calculated that roots released approximately 0.09 nkat phytase g^-1 root dry wt per day, over 20 days of growth. By supplementing agar containing IHP with phytase from Aspergillus niger (E.C. 3.1.3.8; 0.012 nkat plant^-1, or _∼1.3 nkat g^-1 root dry wt), sufficient P became available to enable T. subterraneum seedlings to grow as well as P_i-supplied plants. These results indicate that while pasture plants can quite effectively use P from some organic P sources (e.g. G1P), the acquisition of phytate-P is limited both by availability of substrate and the capacity of plant roots to hydrolyse available IHP. This revised version was published online in June 2006 with corrections to the Cover Date.     

Localization of horseradish peroxidase (HRP)-anti-HRP complexes in cryostat sections: Influence of endotoxin on trapping of immune complexes in the spleen of the rat

Substance P-like immunoreactivity (SPLI) was studied by immunocytochemistry and radioimmunoassay in the cerebral arteries, choroid plexus and dura mater of the guinea-pig, rabbit, cat and man. The highest concentrations were found in cerebral blood vessels: 6.1 +/- 2.3 pmol/g (guinea-pig), 9.0 +/- 1.1 pmol/g (rabbit), 7.1 +/- 0.4 pmol/g (cat), and 2.4 +/- 0.9 pmol/g (man). Lower levels were obtained in the choroid plexus and dura mater. The distribution of substance P (SP)-immunoreactive nerve fibres found in various regions of the guinea-pig correlated well with the amount of SPLI measured. Sympathectomy did not alter the concentration of SPLI in the dura mater or in cerebral blood vessels. Electrical field stimulation or 124 mM potassium enhanced the spontaneous efflux of SPLI by 10 and 20%, respectively, from superfused pial arteries in vitro. These data are in support of a functional role of perivascular SP within the cranial circulation.     

Seasonal variation in the biomass, quantity and quality of agar from Gelidiella acerosa (Forsskal) Feldmann et Hamel (Gelidiales, Rhodophyta) from the Gulf of Mannar Marine Biosphere Reserve, India

The Gulf of Mannar on the southeast coast of India, which has recently been declared as biosphere reserve, is the main harvesting place of Gelidiella acerosa for the Indian agar industry. The biomass harvested from natural stocks was estimated to be over 10 000 tonnes dry weight (DW) in the last two decades and is a serious cause of concern on long term sustainability of this valuable resource from this region. The present study reports the seasonal variation in the biomass and agar yield and quality from G. acerosa in four different habitats such as Rameswaram (rocky intertidal), Ervadi (lower intertidal), Sethukarai (subtidal) and Krusadai Island (lagoon reef area). A maximum biomass of 260 ± 26 g DW m^?2 was recorded from Ervadi, whereas Sethukarai showed the highest percentage cover (69.83 ± 4.83%) and density (208.20 ± 30.16 plants m^?2). Biomass, percentage cover and density were lowest in Rameswaram and significantly lower (P < 0.001) than the other three stations. A single peak in biomass was observed with autumn maxima in Ervadi and Rameswaram and southwest monsoon maxima in Sethukarai and Krusaidai Island. Length of G. acerosa was maximum (9.65 ± 0.25 cm) in Ervadi and the branch index value was maximum (24.70 ± 4.01 br^?1 g^?1 DW) for Rameswaram. Agar yield (37.24 ± 7.59%) and gel strength (448.66 ± 6.50 g/cm²) were higher in Sethukarai plants. The agar yields attained a peak in the northeast monsoon and decreased in summer, whereas a reverse trend was observed for gel strength. Evidently, agar yield showed a strong negative correlation with gel strength (P < 0.0001) and gelling (P < 0.0001) and melting temperatures (P < 0.01). The single annual peak in biomass observed in the present study, as compared with two peaks reported earlier, are attributed to the continuous overharvesting that would have had an effect on the overall annual biomass production. The findings of this study reveal that a single harvest during the autumn months (January to March) could yield optimum biomass with moderate agar and that would be the best for sustainable usage and conservation of this resource from this region.     

The Euglena gracilis chloroplast genome: analysis by restriction enzymes.

1. Chloroplast DNA was isolated from autotrophically and mixotrophically grown Euglena gracilis cells. 2. Aliquots of chloroplast DNA were mechanically degraded to an average molecular weight of 4-7 X 10(6) and G+C-rich DNA fragments (density 1.701 g/cm3) were separated from the bulk DNA (density 1.685 g/cm3) using preparative CsCl density gradients. 3. Total chloroplast DNA and its DNA subfractions, which first were characterized with respect to average G+C content and hybridization capacity for chloroplast rRNA, were hydrolysed with restriction endonucleases (endo R-EcoRI, end R-HindII, endoR-HindIII, endo R-HindII+III, endoR-Hpal, endo R-HpaII and endoR-HaeIII). The fragments were separated on gels under a variety of electrophoretic conditions. 4. With each enzyme tested, a rather large number of bands was obtained. In all cases, different banding patterns were obtained for total DNA, and the DNA subfractions. 5. Chloroplast DNA from autotrophically and mixotrophically grown cells gave identical banding patterns. 6. Digestion of total DNA with the endoR-HaeIII yielded 51-52 fragments separated in the gels in a total of 36 bands of which 11-12 bands were composed of 2-3 fragments as estimated by densitometry. The molecular weights of all fragments combined was 87 X 10(6) or 95% of the genome (92 X 10(6)). 7. Chloroplast RNA hybridized to 5.1% with total chloroplast DNA, equal to three RNA cistrons per genome (Mr92 X 10(6)). These cistrons are located on seven different types of endo R-HaeIII fragments. The hybridising fragments are preferentially found in the G+C-rich subfraction and in bands which are composed of 2-3 fragments.     

The isolated anterior stomach of larval mosquitoes (Aedes aegypti): voltage-clamp measurements with a tubular epithelium

The anterior stomach of larval Aedes aegypti was isolated and perfused via two pipettes. For transepithelial voltage (V(te)) measurement, the inflow pipette and the bath were connected via agar bridges to calomel electrodes. For voltage-clamping, the lumen of the tissue contained an Ag/AgCl wire held by the outflow pipette, and the preparation was placed in a bath within a spiral of Ag/AgCl wire. After equilibrating the tissue in mosquito saline on both sides, a V(te) of -8+/-1 mV was measured (+/-S.E.M., N=32). Current-voltage curves (+/-100 mV) demonstrated ohmic behaviour of the epithelium. Short-circuiting resulted in a current (I(sc)) of 103+/-16 microA cm(-2) and a mean transepithelial conductance (G(te)) of 11.8+/-1.3 mS cm(-2) (+/-S.E.M., N=32). A Yonath-Civan plot of G(te) of individual preparations over the corresponding I(sc) resulted in a straight line (r(2)=0.8422), indicating that the difference in I(sc) of individual preparations is mainly based on different transcellular conductances (G(c)). This analysis allowed to estimate the mean leak conductance (G(l) approximately 3.9 mS cm(-2)) and the mean transcellular electromotive force (E(c) approximately 13 mV). After administering 0.2 micromol L(-1) serotonin, I(sc) and G(te) significantly increased, to 457+/-49 microA cm(-2) and to 21.3+/-2.3 mS cm(-2) (+/-S.E.M., N=31, P<0.05), respectively. The Yonath-Civan plot after serotonin resulted again in a straight line (r(2)=0.8219), indicating a mean G(l) of about 1 mS cm(-2) and a mean E(c) of about 22 mV. Dinitrophenol (2.5 mmol L(-1)) almost abolished I(sc) and significantly reduced G(te) (N=6). Concanamycin A (100 micromol L(-1)) reduced I(sc) by more than 90% without significantly affecting G(te).