Comparative karyological studies on the species of Eubothrium Nybelin, 1922 (Cestoda: Pseudophyllidea)

Karyotypes of Eubothrium salvelini, E. crassum and Eubothrium sp. were studied using conventional Giemsa staining and comparative karyometric analysis. The karyotypes, reported here for the first time, consist of eight chromosome pairs. The two first pairs of homologues are metacentric and markedly larger than the remaining elements. The obvious similarity in karyotype structure does not exclude the possibility of discriminating E. salvelini and E. crassum using karyotypic characters. The best cytogenetic marker is the last pair of chromosomes, which is acrocentric in the karyotype of E. salvelini and metacentric in that ofE. crassum. Karyological observations provide strong evidence for assigning Eubothrium sp. from Clupea harengus membras to E. crassum. Comments are made on the karyotypes of these and related species with respect to their phylogenetic links.     

The biology, specificity and habitat of the species of Eubothrium (Cestoda: Pseudophyllidea), with reference to their use as biological tags: a review

The literature pertaining to the distribution, habitat, specificity, life cycles and population biology of all the species of Eubothrium is reviewed. Records in which scolex morphology is used to identify species cannot be used as this character is too variable to be of value in specific recognition. Study of the valid records suggests that E. crassum comprises three races. There is a freshwater race, whose preferred host is non-migratory Salmo trutta fario, but which also infects parr, smolts and landlocked adult S. salar and parr of migratory S. trutta trutta. Its distribution is confined to Europe and Eurasia and is co-extensive with that of S. trutta: it does not occur in N. America or E. Asia. It may be carried to sea in migratory salmonids, where it dies out in S. salar but may survive in S. trutta. Its life cycle only takes place in fresh water, and requires a copepod as the only intermediate host. Other fish species may serve as paratenic or accidental hosts. The preferred host of the marine Atlantic race of E. crassum is S. salar, but S. trutta is also infected. Its distribution is co-extensive with that of S. salar on both sides of the Atlantic Ocean. It may be carried into fresh water by both hosts, when its numbers decline in S. salar but not in S. trutta. The life cycle is unknown, but infection probably takes place in marine coastal waters. The preferred hosts of the marine Pacific race are all species of Oncorhynchus, with which its distribttion is co-extensive on both sides of the Pacific Ocean. It may also be carried into fresh water, and its life cycle is also unknown. E. salvelini comprises two races. The European freshwater race is specific to Salvelinus alpinus, and does not infect Salmo spp. Its life cycle takes place in fresh water and involves only one intermediate host, a copepod. It may be carried to sea in migratory fish, and survive to return to fresh water. The American race, found throughout North America and East Asia, infects species of Salmo, Salvelinus, Oncorhynchus, Cristivomer and other genera. Its biology is otherwise similar to that of the European race, although its return from the sea has not yet been confirmed in America. The other species of Eubothrium are more local in their distribution, some being endemic; do not comprise different races, and infect marine and anadromous fish. Nothing is known of their biology or life cycle. Eubothrium is recognised as being a marine genus that has invaded fresh water with anadromous fish. The inability to distinguish the races of E. crassum and E. salvelini on morphological characters, their low rate of survival in the other medium and their wide distribution renders them unsuitable as biological tags.     

Deletion analysis and localization of SbPRP1, a soybean cell wall protein gene,in roots of transgenic tobacco and cowpea1

SbPRP1 is a member of the soybean (Glycine max L. Merr) proline-rich cell wall protein family and is expressed at high levels in root tissue. To characterize the sequences required for this expression, we have fused 1.1 kb of upstream flanking DNA sequence from an SbPRP1 genomic clone to a gene encoding -glucuronidase (GUS). This construct was introduced into tobacco using Agrobacterium tumefaciens-mediated transformation. Histochemical staining of GUS activity in transgenic tobacco indicated that SbPRP1 is expressed in the apical and elongating region of both primary and lateral roots, most strongly in the epidermis. A similar localization pattern was found in transformed hairy roots when this construct was introduced into cowpea (Vigna aconitifolia) using Agrobacterium rhizogenes-mediated transformation. Nested 5-deletion analysis of the SbPRP1 promoter indicated that a minimal promoter for SbPRP1 expression in roots is located within the first 262 bases of upstream flanking DNA and that the region between –1080 and –262 is required for maximal expression of this gene. Gel retardation assays showed that nuclear factors can be detected in soybean roots which specifically bind to sequences located between –1080 and –623, a region which is needed for maximal expression of the SbPRP1 promoter. Northern hybridization analysis was also used to show that little SbPRP1 mRNA was present in roots during the first 24 h after imbibition. These studies indicate that SbPRP1 expression is localized to the actively growing region of the root and that this expression is temporally regulated during very early stages of seedling growth.     

A comparison between the amino acid composition of an egg parasitoid wasp and some of its hosts

Amino acid compositions of the eggs of five lepidopteran hosts for Trichogramma minutum were compared with each other and with a non-host species, Rhodnius prolixus, in which T. minutum oviposits but does not develop. Host eggs are quite homogeneous, particularly when compared according to groupings of potentially interconvertible amino acids. Combined mole percent values for glycine, serine and alanine were higher in hosts (27.5–29.2 mole%) than in R. prolixus eggs (21.5 mole%), in bovine serum albumin (14.9%), which has been used as a protein source in artificial diets for T. minutum, or in many of the mixtures used in published diets for this species. Since these three amino acids make up 26.3 mole% of the adult amino acid content of T. minutum, their deficiency in diets could require metabolic compensation detrimental to development.Adult T. minutum arising from eggs of Manduca sexta, Choristoneura fumiferana, and Sitotroga cerealella are similar in amino acid composition to each other and, in general, to their hosts. Variability appears greater in hosts than in adult wasp composition, suggesting some interconversion of host amino acids to accommodate inflexible nutritional requirements of T. minutum.In the three host species tested, free amino acids constituted 15.8–19.3% by weight of the amino acid in egg contents. In M. sexta eggs, glycine, serine and alanine together make up 28.4% by weight of the total free amino acid, a much higher proportion than in many published diets. The four free amino acids (isoleucine, leucine, phenylalanine and histidine) reported to be oviposition stimulants in experiments on encapsulated diets are present in sufficient concentrations to induce oviposition in the host species tested and in R. prolixus. S. cerealella egg contents having approximately 1.8 g amino acid, yield one or rarely two adult T. minutum (1g amino acid/insect). In contrast, M. sexta eggs with 94 g amino acid each yield an average of 10–12 adults (8.2g amino acid/insect). This suggests that small hosts are allocated few eggs which can only develop into small adults because of nutrient supply (parasitoid size in metabolically restricted), whereas much larger hosts are allocated proportionately fewer eggs than the former resulting in larger, and presumably more viable and fecund, adults (parasitoid size is established behaviourally).     

Effects of light on nitrate-limited Oscillatoria agardhii in chemostat cultures

The effects of the average light irradiance (I) on growth and nitrate uptake kinetics of the cyanobacterium Oscillatoria agardhii, in nitrate-limited chemostat cultures, were studied. Light was nonsaturating for I <9.4 Wm^–2, for all growth rates () studied. However, was throughout limited by the availability of nitrate. Under light-saturating conditions the kinetics of nitrate-limited growth could be adequately described by both the Monod and Droop equations. Under light-non-saturating conditions the internal nitrogen content (Q) was a function of both and I, for which new formulas were derived. The high uptake capacity (V _max) of nitrate-limited cells was independent of , but was significantly increased for cells growing at I <9.4 Wm^–2. The half-saturation constant for nitrate uptake (K _s ^u ) increased with increasing , but was independent of the prevailing light conditions. The effects of light during nitrate-limited growth were associated with the regulation in the nitrogen-containing pigments.The results reported herein have important consequences for the use of Q, K _s ^u and V _max values as indicators of nutrient-deficiency of natural populations.     

Summer egg production rates of paracalanid copepods in subtropical waters adjacent to Australia's North West Cape

The biological oceanography of waters adjacent to Australia's North West Cape (21° 49 S, 114° 14 E) was studied during the austral summers of 1997/98 and 1998/99. We measured egg production rate (EPR) by the small paracalanid copepods that dominated the calanoid community. Bottle incubation experiments were conducted at a shallow (20 m) station in the mouth of Exmouth Gulf, and at a shelf-break station (80 m). In 1997/98, we measured EPR by Paracalanus aculeatus, P. indicus, Acrocalanus gracilis and Bestiolina similis, but in 1998/99, we concentrated on P. indicus. Maximal observed EPRs by Paracalanus and Acrocalanus species were 30 eggs female^–1 d^–1, but B. similis attained only 17 eggs female^–1 d^–1. Sporadic measurements of EPR by P. aculeatus minor (maximum 4 eggs female^–1 d^–1) and Parvocalanus crassirostris ( 9 eggs female^–1 d^–1) were also made. However, maximal EPRs were seldom achieved and were often less than 10 eggs female^–1 d^–1. There was no difference between EPR of either P. indicus or B. similis in 1997/98 and 1998/99, despite differences in temperature. Trophic resources severely limit copepod egg production in this area. We suggest that variability and skewness of egg production data derived from individual incubations may be used to judge the degree of food limitation of the population and the variability in feeding success between individuals. The dominance of small copepods and the invariance in their EPR suggest that pulses in physical forcing and subsequent primary production will be severely damped by trophodynamic processes before reaching larval fish.     

Distribution and biology of marine cladocerans in the coastal waters of southern China

Geographical and seasonal distributions of marine cladocerans in the coastal waters of southern China were studied. Penilia avirostris was the most common species, followed by Evadne tergestina and Podon schmackeri. P. avirostris and E. tergestina were most common during summer. P. schmackeri, found only in a small bay northeast of Hong Kong, showed no clear seasonal pattern of occurrence. P. avirostris and E. tergestina were found at temperatures ranging from 16–32°C and salinity ranging from 7.3–37.2. P. schmackeri was restricted to a temperature range of 17–29°C and a salinity range of 31.0–37.2. No significant relationships between marine cladoceran abundance and chlorophyll a concentration were found in samples taken from Tolo Harbour. Parthenogenetic brood size of P. avirostris and E. tergestina ranged from 1 to 14, while P. schmackeri was found to carry up to 19 embryos per brood. No geographical trend in fecundity patterns was observed. No correlation was found between body length and brood size. The occurrence of females with resting eggs was rare.     

Mixed oviposition in individual females of Gryllus firmus: Graded proportions of fast-developing and diapause eggs

Summary Eggs of field crickets (Gryllus spp.) held at 25±1°C hatch in 2–4 weeks (fast-developing eggs) or 5–28 weeks (diapause eggs). Most species lay but one type: at least 10 species lay only fast-developing eggs, and pennsylvanicus and ovisopis lay only diapause eggs. Gryllus firmus from Gainesville, Florida, lays both types, and individual females do so for as long as 8 weeks. The proportion of diapause eggs laid weekly by captive females exposed to outdoor photoperiods and temperatures varies seasonally from <5% (March–June) to ca. 50% (November–December). At outdoor temperatures in late fall some eggs that are presumptively fast-developing (at 25° C) enter diapause.Some firmus from Carolina Beach, North Carolina, lay both diapause and fast-developing eggs. Outdoor rearing experiments established that spring adults could result from fast-developing eggs of fall adults, refuting the hypothesis that spring and fall adults at that locality represent temporally isolated demes.High variance in hatching times for eggs laid by one female is appropriate to the unpredictable extremes of moisture and temperature that occur in the open, sandy habitats of G. firmus. Physiological mechanisms of the mixed oviposition and specific environmental determinants of the varying proportions are unknown.     

Effect of prey stage on life-table attributes of a genetically manipulated strain ofMetaseiulus occidentalis (Acari: Phytoseiidae)

Metaseiulus occidentalis females from the carbaryl-organophosphate-sulfur resistant strain (COS) lived longer (25.3 days versus 19.7 days), had a higher total fecundity (43.8 eggs female^–1 versus 33.6 eggs female^–1) and a higher daily fecundity rate (2.4 eggs female^–1 day^–1 versus 2.0 eggs female^–1 day^–1), and exhibited a higher intrinsic rate of increase (0.243 individuals female^–1 day^–1 versus 0.182 individuals female^–1 day^–1) and shorter generation time (13.9 days versus 17.0 days), at 24–28°C, 47–56%rh under continuous fluorescent light, when reared on a diet of 0–48-h-old eggs rather than a diet of mixed actives ofTetranychus pacificus McGregor on bean leaf disks. The sexratio of the progeny was female-biased for both diets, 2.1 females to 1 male forM. occidentalis reared on eggs and 2.0:1 : forM. occidentalis reared on mixed actives, suggesting that diet influences sex-ratio in some unknown way.There was no significant difference in oviposition rates for repeatedly-mated and once-matedM. occidentalis females reared on a diet of younger (0–24-h old) eggs compared to a diet of older (72–96-h old) eggs ofT. pacificus.The COS strain ofM. occidentalis exhibited life-table parameters comparable to the other strains reported in the literature, suggesting that the reproductive attributes of this acarine predator were not reduced as a result of artificial laboratory selection. Diet, a biotic factor, produced substantial differences in life-table parameters, suggesting that this factor can influence conclusions regarding the potential efficacy of biological control agents.     

Fecundity,reproductive effort,and pupal size in the profundal midgeChironomus cuccini (Diptera: Chironomidae)

Fecundity ofChironomus cucini increased linearly across a three-fold range of female pupal biomass. Females from a lake producing small pupae (Crystal Lake) had an average of 303 primary follicles, while larger pupae from Trout Lake had an average fecundity of 582. Pupae produced in Crystal Lake from larvae that received experimental food supplements were intermediate in size and fecundity. Pupal biomass explained 76% of the variation in fecundity. No difference in egg size was detected between pupae from the two lakes, and an average value of 2.1 g egg^–1 was used to calculate the total biomass allocated to eggs in each of 79 females dissected. This measure of reproductive effort scaled isometrically with pupal mass. On average, females allocated 48% of their biomass to eggs and 52% to somatic tissues. A comparison of average male biomass to female somatic biomass across 12 populations indicated that the biomass difference between the sexes is a biased predictor of fecundity.     

Limnological control of brine shrimp population dynamics and cyst production in the Great Salt Lake, Utah

In the Great Salt Lake of Utah, the brine shrimp Artemia franciscanaKellogg is an important food resource for birds and they produce dormant cysts that are harvested and used extensively in the aquaculture industry. We analyzed the limnological factors controlling Artemia growth and cyst production over 12 months in 1994 and 1995. Laboratory experiments showed that inter-brood intervals were highly dependent on temperature and slightly on food level. At optimal temperatures and nutritious food, juveniles reached reproductive size within 7 d in the laboratory. In winter when temperatures were less than 3 °C, Artemia were absent from the lake, phytoplankton abundance was high (13 Chl a g l^–1), and the dominant grazers were ciliated protozoans. In the spring, cysts hatched when phytoplankton was abundant (15–30 g Chl a l^–1), and the Artemia grew and produced large clutches of ovoviviparous eggs. Estimated naupliar production from these eggs was 80 l^–1 from April to May. Despite the high production of nauplii, Artemia densities declined to 8 l^–1by June and the growing shrimp population grazed down the phytoplankton resource to <1 g Chl a l^–1. With the depleted phytoplankton food resource during the summer, Artemia growth slowed, lipid indices decreased, clutch sizes declined, and females switched primarily to oviparous cyst production. During the summer, there was limited production of ovoviviparous eggs, and limited recruitment of juveniles, probably due to low food. Although oviparous reproduction began in June, more than 90% of the cysts were produced after July when female densities had declined to 1.5 l^–1, but nearly all of them were producing cysts. Estimated cyst production was 650000 m^–2, or 4.54 × 10⁶ kg dry weight for the entire lake. The reported commercial harvest took 21% of the 1994 cyst production. That harvest had little impact on the subsequent year's population, as Artemia densities were ultimately controlled by algal production in the lake.     

Intergeneric hybrids between Triticum crassum and Hordeum vulgare

Summary Intergeneric hybrids between Triticum crassum (2n=6x=42) and Hordeum vulgare cv. Bomi were obtained at a frequency of 15% of pollinated florets. Meiotic chromosome pairing in the hybrids was not different from that observed in a polyhaploid of T. crassum indicating negligible pairing between chromosomes of the two species and secondly that the genome of H. vulgare had no effect on intergenomic pairing in T. crassum.Contribution No. 646 Ottawa Research Station     

Weitere Untersuchungen zur phytochrominduzierten Akkumulation von Ascorbinsäure beim Senfkeimling (Sinapis alba L.)

Summary The accumulation of ascorbic acid (AS) in the young mustard seedling is greatly increased by the action of the active form of phytochrome (P₇₃₀) (see Schopfer, 1966). There is no photosynthesis in continuous far-red light, which was used throughout the experiments. The phytochrome-mediated increase in AS approximately parallels the synthesis of anthocyanin in the seedling, although the onset of AS-accumulation precedes the anthocyanin synthesis by 2–3 hours (Fig. 4 and 5).—The action of P₇₃₀ increases the amount of AS in every part of the seedling (cotyledons, hypocotyl, radicula) (Fig. 1–3). This increase in AS parallels the formation of P₇₃₀ rather than the different growth responses of these organs (enlargement of the cotyledons, inhibition of hypocotyl and radicula lengthening). The lag in AS-accumulation after onset of far-red irradiation is the same in all 3 parts of the seedling (about 1 hour under the experimental conditions; Fig. 4).—Actinomycin D (10 g/ml), which strongly inhibits anthocyanin synthesis (Fig. 9 and 10), has no corresponding effect on P₇₃₀-dependent increase in AS-accumulation (Fig. 7 and 8). This result support the hypothesis that already active genes are only slightly influenced by actinomycin D (see Lange and Mohr, 1965). It also shows that, in contrast to its role in anthocyanin synthesis, P₇₃₀ probably does not act by initiating potentially active genes in the case of AS-accumulation. — A dark synthesis of anthocyanin in the cotyledons can be obtained by application of AS to the seedlings (Fig. 11). Glucose and sucrose are ineffective in this respect (Table 2). The effect of AS-feeding on anthocyanin synthesis can be inhibited by actinomycin D in very much the same way as light induced anthocyanin synthesis is inhibited (Table 3). — Also the RNA content of the cotyledons is increased by feeding AS in the dark (Table 4).These results are in line with the earlier suggested hypothesis (see Schopfer, 1966) that increase in AS-accumulation is a very early event in the mediation of some positive photoresponses, e.g. anthocyanin synthesis. According to the hypothesis of Mohr (1966 a, b) it has been concluded that AS functions as a part of the signal chain of phytochrome-mediated photomorphogenesis. This signal chain is thought to start differential gene activation to bring about positive photoresponses.     

In vitro propagation and chromosome doubling of a Triticum crassum x Hordeum vulgare intergeneric hybrid

Summary In vitro culture of inflorescence tissue of a Triticum crassum (6x) x Hordeum vulgare cv. Bomi (2x) intergeneric hybrid resulted in the proliferation of totipotent callus from which plants were regenerated. Regeneration was also achieved from immature inflorescence callus of T. crassum but not from H. vulgare. T. crassum x H. vulgare regenerates had a somatic chromosome number of 28, identical to that of the original hybrid. Four chimeric plants with a partially doubled chromosome number were obtained by in vitro colchicine treatment of hybrid callus prior to induction of plant regeneration. All T. crassum regenerates had 35 chromosomes rather than the expected number of 42. Meiotic analysis of a 35-chromosome plant revealed an extremely abnormal meiosis which might be attributable to a complete disturbance in meiotic control system(s) including that of meiotic pairing.Dedicated to Professor Georg Melchers on the occasion of his 75th birthday.Contribution No. 624 Ottawa Research Station, Research Branch, Agriculture Canada, Ottawa, Ont. K1A OC6 (Canada)     

Electrogenic properties of the cloned Na+/glucose cotransporter: I. Voltage-clamp studies

Summary Cystic fibrosis (CF) is characterized by abnormal epithelial Cl^– conductance (G_Cl). In vitro studies that have shown that cAMP regulation is an intrinsic property of the CF-affected G_Cl(CF-G_Cl) have been carried out previously on cultured secretory cells and on nonepithelial cells. Even though G_Cl in absorption is defective in CF, a clear demonstration of cAMP regulation of CF-G_Cl in a purely absorptive tissue is lacking. We studied the cAMP regulation of CF-G_Cl in the microperfused intact human reabsorptive sweat duct. About 40% of the ducts responded to cAMP (responsive) while the remainder of the ducts did not. In responsive ducts, cAMP-elevating agents: -adrenergic agonist isoproterenol (IPR), CPT-cAMP, forskolin, theophylline or IBMX increased G _tby about 2.3-fold (n = no. of ducts = 8). Removal of media Cl^–, but not amiloride pretreatment (in the lumen), abolished the cAMP response, indicating exclusive activation of G_Cl. cAMP activated both apical and basolateral G_Cl. cAMP hyperpolarized gluconate: Cl^– (lumen: bath) transepithelial bionic potentials (V _t=–20.3±5.2 mV, mean ±se, n=9) and transepithelial 3 1 luminal NaCl dilution diffusion potentials (V _t=–8.8±2.9 mV, n=5). cAMP activated basolateral G_Cl as indicated by increased bi-ionic (gluconate: Cl^–, bath: lumen) diffusion potentials (by about 12 mV). The voltage divider ratio in symmetric NaCl solutions increased by 60%. Compared to responsive ducts, nonresponsive ducts were characterized by smaller spontaneous transepithelial potentials in symmetrical Ringer's solution (V _t=–6.9±0.8 mV, n=24, nonresponsive vs. –19.4±1.8 mV, n=22, responsive ducts) but larger bi-ionic potentials (–94±6 mV, n=35, nonresponsive vs. –65±5 mV, n=17, responsive ducts) and dilution diffusion potentials (–40±5 mV, n=11, nonresponsive vs. –29±3 mV, n=7, responsive ducts). These results are consistent with an inherently (prestimulus) maximal activation of G_Cl in nonresponsive ducts and submaximal activation of G_Cl in responsive ducts. We conclude that cAMP activates CF-G _Cl which is expressed and abnormal in both apical and basal membranes of this absorptive epithelium in CF.Abbreviations CF cystic fibrosis - G _t transepithelial conductance - V _b electrical potential across the basolateral membrane - V _a electrical potential across the apical membrane - V _t transepithelial potential - V _b transepithelial currentinduced voltage deflections across the basolateral membrane - V _a transepithelial current-induced voltage deflections across the apical membrane - V _t transepithelial current-induced voltage deflection across the epithelium - VDR voltage divider ratio - G_Cl transepithelial Cl^– conductance - CF-G_Cl cystic fibrosis-affected Cl^– conductance - EMF electromotive force - IPR isoproterenol - IBMX 3-isobutyl-1-methylxanthine - CPT-cAMP chlorophenylthio-adenosine 3-5 cyclic monophosphate - PGE₂ prostaglandin E₂     

Reproduction of the calanoid copepod Calanus propinquus in the southern Weddell Sea,Antarctica: observations in laboratory

Reproduction of the dominant Antarctic copepod Calanus propinquus was studied in February–April, 1989 aboard the R.V Dmitry Mendeleev during cruise N° 43 to the Weddell Sea. Single females were kept at 0 °C in the laboratory for 56 days with abundant food concentration (above 300 µg C l^–1 of Platymonas viridis). Females released clutches at night at 2–3 day intervals. Most clutches contained from 10 to 40 eggs, mean 37.3 eggs female^–1. Average carbon content of an egg was 0.37 ± 0.05 µg C. The maximum daily egg production rate of 30–50 eggs female^–1 d^–1 was observed for the first 3 days of the laboratory incubation, corresponding to 3.7–6.2% body C. The state of gonadal development of females showed the decline of the reproductive season in late February. The data suggest that egg laying in the region under study starts in December and lasts until March. The state of ovarian maturation, changes in vertical distribution and biochemical body composition of females suggest the possibility of two-year life cycle in C. propinquus in the southern Weddell Sea.     

CO2 Assimilation and Water Relations of Almond Tree (Prunus amygdalus Batsch) Cultivars Grown Under Field Conditions

Gas exchanges and leaf water potential (_w) of six-years-old trees of fourteen Prunus amygdalus cultivars, grafted on GF-677, were studied in May, when fruits were in active growing period, and in October, after harvesting. The trees were grown in the field under rain fed conditions. Predawn _w showed lower water availability in October compared with May. The lowest _w values at midday in May increased gradually afterwards, while in October they decreased progressively until night, suggesting a higher difficulty to compensate the water lost by transpiration. However, relative water content (RWC) measured in the morning was similar in both periods, most likely due to some rainfall that occurred in September and first days of October that could be enough to re-hydrate canopy without significantly increasing soil water availability. The highest net photosynthetic rate (P _N) was found in both periods early in the morning (08:00–11:00). Reductions in P _N from May to October occurred in most cultivars except in José Dias and Ferrastar. In all cultivars a decrease in stomatal conductance (g _s) was observed. Photosynthetic capacity (P _max) did not significantly change from spring to autumn in nine cultivars, revealing a high resistance of photosynthetic machinery of this species to environmental stresses, namely high temperature and drought. Osmotic adjustment was observed in some cultivars, which showed reductions of ca. 23 % (Duro d' Estrada, José Dias) and 15 % (Tuono) in leaf osmotic potential (). Such decreases were accompanied by soluble sugars accumulation. The Portuguese cultivar José Dias had a higher photosynthetic performance than the remaining genotypes.     

Population growth rate of the parasitic rotifer Proales gigantea,and susceptibility to parasitization in the snail Lymnaea acuminata at different stages of embryonic development

Developing eggs of the host snail Lymnaea acuminata were experimentally parasitized with the parasitic rotifer Proales gigantea to study the population growth rate of the parasite within the snail egg capsule and the susceptibility of the host eggs at different stages of embryonic development. The population growth rate of P. gigantea was 0.46 ± 0.07 individual^–1 day^–1 at the ambient temperature of 18–22 °C. Snail eggs were most susceptible to rotifer attack during the initial stages of development, becoming progressively more resistant after the hippo stage. Yet, regardless of the stage of development, the host embryo was doomed to die without hatching even if one individual rotifer gained entry inside the egg capsule. The presence of P. gigantea within the parasitized egg capsules or in the mucilage had no effect on the developmental rates and hatching success of non-parasitized eggs within the same egg mass.     

Cellular mechanism of HCO 3 − and Cl− transport in insect salt gland

Summary Active HCO ₃ ^t- secretion in the anterior rectal salt gland of the mosquito larva,Aedes dorsalis, is mediated by a 11 Cl^–/HCO ₃ ^– exchanger. The cellular mechanisms of HCO ₃ ^– and Cl^– transport are examined using ion- and voltage-sensitive microelectrodes in conjunction with a microperfused preparation which allowed rapid saline changes. Addition of DIDS or acetazolamide to, or removal of CO₂ and HCO ₃ ^– from, the serosal bath caused large (20 to 50 mV) hyperpolarizations of apical membrane potential (V _a) and had little effect on basolateral potential (V _bl). Changes in luminal Cl^– concentration alteredV _a in a repid, linear manner with a slope of 42.2 mV/decaloga _Cl ^l –. Intracellular Cl^– activity was 23.5mm and was approximately 10mm lower than that predicted for a passive distribution across the apical membrane. Changes in serosal Cl^– concentration had no effect onV _bl, indicating an electrically silent basolateral Cl^– exit step. Intracellular pH in anterior rectal cells was 7.67 and the calculated was 14.4mm. These results show that under control conditions HCO₃ enters the anterior rectal cell by an active mechanism against an electrochemical gradient of 77.1 mV and exits the cell at the apical membrane down a favorable electrochemical gradient of 27.6 mV. A tentative cellular model is proposed in which Cl enters the apical membrane of the anterior rectal cells by passive, electrodiffusive movement through a Cl^–-selective channel, and HCO ₃ ^– exits the cell by an active or passive electrogenic transport mechanism. The electrically silent nature of basolateral Cl^– exit and HCO₃ entry, and the effects of serosal addition of the Cl^–/HCO₃ exchange inhibitor, DIDS, on and transepithelial potential (V _ic) suggest strongly that the basolateral membrane is the site of a direct coupling between Cl^– and HCO ₃ ^– movements.     

Central projections of fibers in the auditory and tensor nerves of cicadas (Homoptera: Cicadidae)

Summary The auditory and tensor nerves of cicadas are mixed nerves containing both afferent and efferent elements. In 17-year cicadas, and in Okanagana rimosa, the auditory nerve contains afferents from body hairs, from the detensor tympani-chordotonal organ, and some 1300–1500 afferents from the hearing organ. Within the fused metathoracic-abdominal ganglionic complex the receptors from both the auditory and tensor nerves form a neuropilar structure that reveals the metameric organization of this complex. A few fibers run anteriorly, projecting into the meso and prothoracic ganglia. Within the ganglionic complex a division of auditory nerve afferents into a dense intermediate and a more diffuse ventral neuropile is observed. In addition, a dorsal motor neuropile is outlined by arborizations of the timbal motor neuron. This neuron is one of several efferent cell types associated with the auditory nerve, and there is an indication that several efferent fibers innervate the timbal muscle. There is anatomical evidence for a possible neuronal coupling between the bilaterally symmetrical large timbal motor neurons. In general, central projections from the auditory and tensor nerves support evidence of a structural layering within the CNS of insects.