Water and ion permeability of a native collagen membrane

With the help of a ribonucleoprotein it is possible to precipitate collagen in a layer of fibers with a 700 Å period. As collagen is a constituent of many membrane systems in the body, it seemed interesting to investigate the permeability of ions and water through a native collagen membrane.The experiments were carried out with the help of an acryl glass apparatus, where an osmotic pressure, a hydrostatic pressure difference or both can be maintained between the two bulk phases separated by the membrane. The diffusion coefficients for NaCl and KCl were found to be comparable with those in other biological membranes (D_s = 9 · 10⁻⁷cm² · s⁻¹) whereas there is difference of more than three orders of magnitude in the hydraulic permeability (L_p = 6 cm⁴ · J⁻¹ · s⁻¹).Volume flow measurements caused by an osmotic gradient indicated that the reflection coefficient for NaCl and KCl is very small. In hydrostatic pressure experiments, the membrane shows a preferred direction for volume flows which seems to have something to do with the mode of preparation of the membrane.     

Restriction fragment length polymorphism (RFLP) analysis of bovine nuclear protein genes

Summary We have recently cloned both the bovine protamine (Krawetz et al. 1987, DNA 6: 47–57) and high mobility group (HMG-1) cDNAs (Pentecost and Dixon 1984, Bioscience Reports 4: 49–57). They have been used as probes for Restriction Fragment Length Polymorphism analysis of male-female pairs of different species and breeds, within the genus Bos. Utilizing this approach we have studied inheritance, chromosomal location and gene copy number of the bovine protamine and HMG-1 genes. This revealed that these nuclear protein genes are highly conserved suggesting that selective pressure has maintained their gene structures during evolution. A polymorphic Taq 1 restriction fragment was identified that was shown to be a heritable marker. These genes are not sex-linked and are present in a single copy for protamine and at least two copies for the HMG-1.     

Sperm ultrastructure of five species of the Neotropical ant genus Pseudomyrmex (Hymenoptera: Formicidae)

The seminal vesicles of adult males of five species of Pseudomyrmex were prepared for light and transmission electron microscopy. The Pseudomyrmex spermatozoa are long and slender with similar morphology. The head region has an acrosome and a nucleus. In all the studied species, two morphologically distinct types of acrosomal vesicles were observed, a long structure, as observed in all known ants, and a pear‐shaped one, never before observed in ants. The nucleus is elongated and both condensed and loose chromatin are present. The flagellum has an axoneme, a centriolar adjunct, two mitochondrial derivatives and two accessory bodies. The centriolar, the mitochondrial derivatives and the accessory bodies are similar to observations in most ant species that have been studied. The axoneme presents an uncommon 9 + 9 + 1 microtubule arrangement and the central microtubule has 13 protofilaments. The acrosomal dimorphism and the different levels of chromatin organization are exclusive characteristics of Pseudomyrmex. Furthermore, the 9 + 9 + 1 microtubule arrangement is different from all Hymenoptera, as well as from most insects, which present a 9 + 9 + 2 arrangement. These new morphological characters that are specific to Pseudomyrmex, are valuable synapomorphies of the genus and can be used in taxonomic characterization of the Pseudomyrmecinae subfamily and in phylogenetic analyses in Formicidae family.     

Honeydew amino acids in relation to sugars and their role in the establishment of ant-attendance hierarchy in eight species of aphids feeding on tansy (Tanacetum vulgare)

Abstract. The ratio of the concentration of honeydew total amino acids to total sugars in the honeydew of eight species of aphids, all feeding on tansy, Tanacetum vulgare (L.), was determined and correlated with honeydew production and ant‐attendance. The honeydew of the five ant‐attended aphid species [Metopeurum fuscoviride (Stroyan), Trama troglodytes (v. Hayd), Aphis vandergooti (Börner), Brachycardus cardui (L.), Aphis fabae (Scopoli)] was rich in total amino acids, ranging from 12.9 to 20.8 nmol µL^?1 compared with the unattended aphid Macrosiphoniella tanacetaria (Kalt.) with only 3 nmol µL^?1. Asparagine, glutamine, glutamic acid and serine (all nonessential amino acids) were the predominant amino acids in the honeydew of all species. The total concentration of amino acids in the phloem sap of tansy was much higher (78.7 nmol µL^?1) then in the honeydew samples, and the predominant amino acids were glutamate (34.3%) and threonine (17.7%). A somewhat unexpected result was the finding that those aphid species with the highest total amino acid concentration in the honeydew always had the highest concentration of sugars. The lowest amino acid–sugar combined value was 104–28.8 nmol µL^?1 in the non ant‐attended species M. tanacetaria, and the highest value was an average of 270–89.9 nmol µL^?1 for the three most intensely attended aphid species M. fuscoviride, A. vandergooti and T. troglodytes. There is no evidence that any single amino acid or group of amino acids in the honeydew acted as an attractant for ant‐attendance in these eight aphid species. The richness of the honeydew (rate of secretion × total concentration of sugars), along with the presence of the attractant sugar melezitose, comprised the critical factors determining the extent of ant‐attendance of the aphids feeding on T. vulgare. The high total amino acid concentration in sugar‐rich honeydews can be explained by the high flow‐through of nutrients in aphids that are particularly well attended by ants.     

Pre‐copulation intervals,copulation frequencies,and initial progeny sex ratios in two biotypes of whitefly,Bemisia tabaci

The whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) is a species complex, and its systematic classification requires controlled crossing experiments among its genetic groups. Accurate information on pre‐copulation intervals, copulation frequencies, and initial frequency of egg fertilization of newly emerged adults is critical for designing procedures for collecting the virgin adults necessary for these experiments. In the literature, considerable variation is reported between B. tabaci populations, with respect to the length of the pre‐copulation interval and the initial frequency of egg fertilization. Here, we used a video‐recording method to observe continuously the copulation behaviour of the Mediterranean/Asia Minor/Africa (B biotype) and the Asia II (ZHJ1 biotype) groups of B. tabaci. We also recorded the initial frequency of egg fertilization, as determined by the sex of the progeny. When adults were caged in female–male pairs on leaves of cotton plants, the earliest copulation events occurred 2–6 h after emergence; at 12 h after emergence 56–84% of the females had copulated at least once, and nearly all (92–100%) had copulated at least once by 36 h after emergence. Both females and males copulated repeatedly. Approximately 80 and 20% of copulation events occurred during the photophase and scotophase, respectively. By 72 h post‐emergence, the females of the B and ZHJ1 biotypes had copulated on average 6.1 and 3.9 times, respectively. When adults were caged in groups on plants 1–13 h after emergence, 30–35% of the eggs deposited during this period were fertilized, and approximately 90% of females were fertilized by the end of the 13 h. Although timing of copulation differed in detail between the two genetic groups, the results demonstrate that B. tabaci adults can start to copulate as early as 2–6 h post‐emergence and the majority of females can become fertilized on the day that they emerge.     

Changes in hydraulic conductance of citrus trees following a reduction in wetted soil volume

Abstract The effcct of the transition from fully to partially wetted soil voluine on transpiration rate and hydraulic conductance of mature citrus trees was examined in a 23-year-old, coninicrcial, sprinklerirrigated, Shanio u t i orange orchard. I rriga t i on frequency was determined by the rate of water loss from the soil, a s measured by neutron probes. The hydraulic conductance of tlic tree was coniputed from the rclationship between sap flow i n the trunk and leaf water potential. The diurnal valucs of leaf water potential and sap flow shifted towards lower levels as tlie water stored in the root zone was depleted. In the fully wetted soil volume the tree hydraulic conductance remained constant throughout the irrigation period, from June to Novcniber. However, partial wetting of the soil volume (40%) caused a reduction in the hydraulic conductance of the tree. Tlie decreased hydraulic conductance is attributed to tlie permanent interruption of water transport in part of tlie root system. Tlie rcsults of tlie experiment suggest that despite tlie increase of irrigation frequency, partial wetting intensifies water stress in tlie trees.     

Polyploidy and habitat differentiation in Dactylis glomerata L. from Galicia (Spain)

Summary The microdistribution of diploid and tetraploid plants of Dactylis glomerata L. was examined and related to their immediate environment in several sites in central Galicia, where morphologically indistinguishable individuals of both ploidies grow in sympatry. The two related cytotypes differed in habitat preference. Diploids were mainly confined to the low-density forest-floor habitat in woodlands of mostly ancient origin, whereas tetraploids were widespread in varied habitats but clearly predominant in open areas, particularly in disturbed anthropic sites. The in situ comparison of plant performance showed that where plants of each ploidy were more common they produced more tillers, panicles and seeds. This habitat preference closely reflected differences in life-history characteristics. The tetraploids had an early and short flowering time almost always completed before the aestival drought, whereas the diploids began to flower several weeks later and flowered throughout the drought. Comparisons along artificial gradients of soil water availability and light transmittance indicated that the cytotypes had distinct physiological requirements which probably originated in metabolic and more general genetic differentiation and could be directly attributable to ploidy. Habitat differentiation increases the species' colonizing ability. It also amplifies divergence in reproductive strategy between diploids and tetraploids, which reduces ineffective crossing between cytotypes and thereby permits them to coexist in sympatry. The effect of hybridization at the polyploid level on the differentiation between cytotypes was assessed from the recent introduction of a foreign tetraploid entity into the study area. Hybridization between the two distinct tetraploids was found to increase habitat differentiation between the diploids and the tetraploids, but the major part of this differentiation is probably attributable to ploidy itself.     

Activation of fatty acids by non-glyoxysomal peroxisomes

Ethylene treatment (approx. 20 l ·1^-1 in air for 2 d) of tobacco (Nicotiana tabacum L. cv. Havana 425) plants markedly increases the endo--1,3-glucanase (EC 3.2.1.39) content of leaves. The antigenic form of the enzyme induced is the same one whose production is blocked by treating cultured cells with combinations of auxin (1.1 · 10^-5 M -naphthaleneacetic acid) and cytokinin (1.4 · 10^-6 M kinetin). Evidence is presented that cultured tobacco cells require ethylene for -1,3-glucanase accumulation: i) ethylene treatment increased the accumulation of \-1,3-glucanase in callus tissues >10 d after subculturing and in cell-suspension cultures; ii) callus tissues can produce ethylene; iii) conditions known to inhibit ethylene production (1 mM CoCl₂; 33° C treatment) or ethylene action (approx. 1.6 mmol · 1^-1 norbornadiene in air) inhibited -1,3-glucanase accumulation by callus tissues treated for 4 d following subculturing; and, these inhibitory effects were prevented by exogenous ethylene. Combinations of auxin and cytokinin blocked ethylene-induced accumulation of -1,3-glucanase by cell-suspension cultures. The results favor a model in which ethylene induces results favor a model in which ethylene induces 1,3-glucanase accumulation, and auxin and cytokinin inhibit this induction process.Abbreviations NAA -naphthaleneacetic acid - NDE norbornadiene