Phase transitions in 1,2-and 1,3-diacyl-sn-glycerol-3-phosphocholine monolayers at the oil/water interface

Moving the phosphatidylcholine group from the 3-to the 2-position in monolayers of $\text{distearoyl}\text{-sn-}\text{glycero}\text{-3-}\text{phosphocholine}$ at the oil/water interface expands the surface pressure-area isotherm and markedly increases the surface pressure at which phase separation occurs with only a slight change in the monolayer surface density at the onset of the transition. This is interpreted in terms of a change in an ordering parameter in the solid-condensed state.     

Polyethylene glycol-mediated direct gene transfer in Nicotiana spp.

Direct gene transfer to protoplasts is a widespread experimental procedure. In this review, it is discussed in relation to the fate and expression of transforming DNA and its genetic transmission upon integration, and expression (in)stability during successive meiotic generations. The results suggest that the major differences between Nicotiana plumbaginifolia and N. tabacum were not in DNA uptake but rather in the specific fate of the transforming DNA. Differences between integrative transformation versus transient gene expression are discussed. Transient gene expression experiments with cotransformed independent constructs enable accurate assays of gene activity modulation, including both activation and repression. The study of the time of integration of foreign DNA using haploid mesophyll protoplasts showed that foreign DNA integration took place during the first two division cycles of the protoplasts. Most of the transfomants inherited the foreign genes as a monogenic trait: N. plumbaginifolia exhibited a higher proportion of multiple insertions compared with N. tabacum . Furthermore, gene integration occurs as a random process. Compared to 'simple' transformation, cotransformation with independent constructs showed a higher level of rearrangement of the inserted DNA. Foreign gene transmission, followed through different generations, indicated that inactivation of the inserted gene could happen through a variety of processes. These results open up a series of questions concerning the applied aspects of direct gene transfer to plants.     

Effect of temperature and surface potential on the electrogenic proton uptake in the QB site of the Rhodobacter sphaeroides photosynthetic reaction center: QA −. B −. → QAQBH2 transition

Direct electrometry was used to study the light-induced voltage changes in the Rhodobacter sphaeroides chromatophores adsorbed to a phospholipid-impregnated nitrocellulose film. After the second laser flash, a fast increase in the voltage associated with charge separation was followed by a slower increase attributed to the proton uptake in the Q_B site of the photosynthetic reaction centers. Kinetics and relative amplitudes of these voltage changes attributed to the Q_A ^–. _B ^–. Q_AQ_BH₂ transition, were measured as a function of pH and temperature between +4 and +40 °C. The kinetics can be approximated by a single exponent above +23 °C (100 µs at +25 °C, pH 7.2), whereas below this temperature, it was a good fit of two exponential approximation (65 µs and 360 µs with similar contributions at +10 °C, pH 7.2). The faster component diminished with an apparent pK 8.5, whereas the slower one was maintained at a constant level until pH 9.5 and then decreased. The calculated activation energy from the temperature dependence of the slower component (55 – 65 kJ/mol) was much higher than that of the faster component (< 10 kJ/mol). The two voltage components can be attributed to the transfer of the first (faster component) and the second (slower component) proton from the reaction center surface to Q_B. We suggested that higher activation energy of the slower component was due to a conformational change in the reaction center kinetically coupled to the second proton transfer to Q_BH^–.The faster component diminished in the presence of 1 M KCl, with an apparent pK 7.5. To explain this observation, we assume that: (i) the midpoint potential of the Q_A/Q_A ^–. redox pair was higher in 1 M KCl because of the reduced surface potential of chromatophores; (ii) the midpoint potential of the Q_B ^–./Q_BH^–. redox pair was insensitive to the surface potential change; (iii) the equilibrium constant of the reaction Q_A ^–.Q_B ^–. Q_AQ_BH^– decreased at high ionic strength.     

Abundance of Ticks (Acari: Ixodidae) Infesting the Western Fence Lizard, Sceloporus Occidentalis, in Relation to Environmental Factors

We examined the impact of environmental characteristics, such as habitat type, topographic exposure and presence of leaf litter, on the abundance of Ixodes pacificus ticks infesting the western fence lizard (Sceloporus occidentalis) at the University of California Hopland Research and Extension Center (HREC), Mendocino County, California. A total of 383 adult lizards were slip-noosed and examined for tick infestation in April and May 1998. At least 94% of the lizards were infested by ticks and at least 20% of the females and 33% of the males carried > 15 ticks. This intensive utilization of western fence lizards (which do not serve as natural reservoirs for Lyme disease spirochetes) by subadult ticks, is probably the primary reason for the low prevalence of infection with Borrelia burgdorferi in I. pacificus nymphs and adults previously recorded at the HREC. Tick loads were higher on male than female lizards. Also, male lizards were generally more heavily infested in late April than in late May. The prevalence of tick infestation exceeded 88% in all habitat types but males collected in woodland and grass/woodland edges had higher tick loads than those collected in open grassland. Male lizards captured in open, exposed grassland tended to carry heavier tick loads in northern/eastern, as compared to southern/western, exposures, and when leaf litter was present.     

Rationale for and Interpretation of Economy-Wide Materials Flow Analysis and Derived Indicators

Economy-wide material flow analysis (MFA) and derived indicators have been developed to monitor and assess the metabolic performance of economies, that is, with respect to the internal economic flows and the exchange of materials with the environment and with other economies. Indicators such as direct material input (DMI) and direct material consumption (DMC) measure material use related to either production or consumption. Domestic hidden flows (HF) account for unused domestic extraction, and foreign HF represent the upstream primary resource requirements of the imports. DMI and domestic and foreign HF account for the total material requirement (TMR) of an economy. Subtracting the exports and their HF provides the total material consumption (TMC).
DMI and TMR are used to measure the (de-) coupling of resource use and economic growth, providing the basis for resource efficiency indicators. Accounting for TMR allows detection of shifts from domestic to foreign resource requirements. Net addition to stock (NAS) measures the physical growth of an economy. It indicates the distance from flow equilibrium of inputs and outputs that may be regarded as a necessary condition of a sustainable mature metabolism.
We discuss the extent to which MFA-based indicators can also be used to assess the environmental performance. For that purpose we consider different impacts of material flows, and different scales and perspectives of the analysis, and distinguish between turnover-based indicators of generic environmental pressure and impact-based indicators of specific environmental pressure. Indicators such as TMR and TMC are regarded as generic pressure indicators that may not be used to indicate specific environmental impacts. The TMR of industrial countries is discussed with respect to the question of whether volume and composition may be regarded as unsustainable.     

Mistletoe (Tapinanthus bangwensis Reichenbach) infestation of indigenous and non‐indigenous trees at Amani Nature Reserve,Tanzania

A survey of Tapinanthus bangwensis was carried out in a plantation in the botanic garden at Amani Nature Reserve, which forms part of the East Usambara Mountain, located in the north‐east of Tanzania. A total of 169 trees were examined on four transects of 100 × 50 m (5000 m²) each, located about 700 m apart. Three treatment transects were established in open woodland with a control transect in the closed canopy. Out of 101 trees (81 non‐indigenous and 20 indigenous) examined in the open canopy, T. bangwensis was present on 24; eighteen non‐indigenous and six indigenous. Of all the infested trees, a non‐indigenous species, silky oak (Grevillea robusta) was the most common (37.4%), followed by an indigenous species, mzindanguruwe (Blighia unijugata) with 16.6%. Chi‐squared tests showed that there was no significant difference in frequency of infestation between non‐indigenous and indigenous species (χ² = 0.715, P = 0.5826). t‐Testing showed that T. bangwensis preferred taller and larger trees (t = ? 3.930, P = 0.0002 and t = ? 2.416, P = 0.0175, respectively). No T. bangwensis was found on the 68 trees examined in the closed canopy.     

Factors Affecting Survival of Clavibacter michiganensis subsp. sepedonicus in Water

The survival of Clavibacter michiganensis subsp. sepedonicus (Cms), the causal organism of bacterial ring rot in potato, was studied in water, to assess the risks for dissemination of Cms via surface water and infection of potato crops by irrigation. Cms was able to survive for a maximum period of 7 days in non‐sterile surface water at 10°C, a period during which Cms can be transported over long distances, but will also be strongly diluted. It is concluded that contamination of surface water with Cms can pose a threat on potato production only if aquatic host plants can multiply Cms in high densities. Survival of a fluidal and non‐mucoid strain was also studied in sterile ditch water and simulated ‘drainage water’, in sterile MilliQ water, in tap water, in physiological salt and in artificial xylem fluid. In addition, the influence of temperature and low oxygen conditions on persistence of Cms in some of these diluents was studied. A maximum survival period of 35 days was found for Cms in sterile tap water at 20°C, independent of the strain used. In the other diluents survival periods ranged between 0 and 21 days. Relatively poor survival was found in MilliQ water and artificial xylem fluid. Low temperatures of 4°C do not favour survival as it does in soil. Oxygen depletion affected survival detrimentally. Survival periods determined by agar dilution plating and a direct viable counting method, based on the use of indicators for esterase activity and membrane integrity were similar. Therefore, it was concluded that under the experimental conditions studied, Cms did not form cells in a viable but non‐culturable state.     

In-vitro culture of fertilized embryo sacs of maize: Zygotes and two-celled proembryos can develop into plants

Fertilized embryo sacs of Zea mays L. surrounded by a few layers of nucellar cells were cultured in vitro. Primary expiants contained zygotes or twocelled proembryos. Embryos of various sizes and shapes were isolated from 12–48% of explants after two weeks of culture in hormone-free media supplemented with 6–12% of sucrose. Many embryos were at the transition or proembryo stages whilst the rest were either differentiated, with a scutellum, a coleoptile and a shoot apex, or had a deformed apical part. Organogenesis started in 36–89% of embryos cultured on a semisolid medium supplemented with coconut water. Most of the embryos formed only roots but up to 9% of embryos regenerated into plants. This simple method leads the way to plant regeneration from in-vitro-manipulated zygotes or proembryos of maize.Abbreviation NBM medium composed of N6 macronutrients, B5 micronutrients and MS vitamins This research was supported by an I.N.R.A. post-doctoral fellowship. The authors thank R. Blanc for donor plant culture, Dr. M. Cock (Reconnaissance Cellulaire et Amélioration des Plantes, Université Lyon 1) for correction of the English and P. Audenis for micrograph development.