When colour patterns reflect phylogeography: New species of Dasypeltis (Serpentes: Colubridae: Boigini) from West Africa

Six colour phases are currently known in the genus Dasypeltis in West Africa, three in the D. scabra complex and three in the D. fasciata complex. Molecular phylogenetic analysis reveals that all correspond to distinct species. D. parascabra sp. nov. is described from wet savannah areas of Guinea and Ivory Coast. D. latericia is given full specific rank. The validity of D. sahelensis, D. gansi and D. confusa – three species recently described on the basis of colour pattern and biogeography – is confirmed. D. fasciata is confined to rain forest areas of West and Central Africa. D. scabra is absent from West Africa.     

Developmental phase-dependent photosynthetic responses to ultraviolet-B radiation: damage, defence, and adaptation of primary leaves of wheat seedlings

Alterations in photosynthetic capacity of primary leaves of wheat seedlings in response to ultraviolet-B (UV-B; 280–320 nm; 60 μmol m⁻² s⁻¹) exposure alone and in combination with photosynthetically active radiation (PAR; 400–800 nm; 200 μmol m⁻² s⁻¹) during different phases of leaf growth and development were assessed. UV-B exposure resulted in a phase-dependent differential loss in photosynthetic pigments, photochemical potential, photosystem 2 (PS2) quantum yield, and in vivo O₂ evolution. UV-B exposure induced maximum damage to the photosynthetic apparatus during senescence phase of development. The damages were partially alleviated when UV-B exposure was accompanied by PAR. UV-B induced an enhancement in accumulation of flavonoids during all phases of development while it caused a decline in anthocyanin content during senescence. The differential changes in these parameters demonstrated the adaptation ability of leaves to UV-B stress during all phases of development and the ability was modified in UV-B+ PAR exposed samples.     

Delayed luminescence of Prorocentrum minimum under controlled conditions

Delayed luminescence (DL), also termed delayed fluorescence or delayed light emission, is the phenomenon of long-lived light emission by plants and cyanobacteria after being illuminated with light and put into darkness. Culture growth of three Prorocentrum minimum strains was studied with DL measurements. DL decay kinetics was measured from 1–60 s after a pulse of white light. The strains used were from the Adriatic Sea (PmK), from Chesapeake Bay, USA (D5), and from the Baltic Sea (BAL), cultured at salinity of 32, 16, and 8 (practical salinity scale), respectively. The strains differed in cell size and chlorophyll a content (PmK > D5 > BAL), as well as in DL parameters. The DL results were compared to standard measurements of culture density and carbon content (calculated from biovolumes). DL decay curves had a specific peak, which changed with culture growth and showed more similarities between the strains PmK and D5. The DL intensity increased with cell density and carbon content in a two-stage process, corresponding to the lag and exponential phases of growth. DL intensity was best correlated with carbon content irrespective of strain and is proposed as an estimate of biomass and for differentiating between lag and exponential phases of growth.     

Physiological interaction model of sunflower plant with its nutrient medium during ontogenesis

A study was conducted with sunflower plants (Helianthus annuus, L.) cv. Peredovik in field experiments, one of which included 9 NPK-fertilizer treatments. The intensity of uptake,i.e. the quantity (mg) of nutrient taken up for the accumulation of 1 g dry matter/day, the concentrations of all essential elements in the plant organ tissues and their distribution among above-ground organs, by stages of development, were investigated. The results have revealed the inherent physiological system responsible for the uptake intensity of individual elements, as well as the simultaneous uptake and distribution of all essential elements of the root nutrition by the shoots, throughout the life cycle of the plant.     

Influence of the nature of the sterol on the behavior of palmitic acid/sterol mixtures and their derived liposomes

The phase behavior of mixtures formed with palmitic acid (PA) and one of the following sterols (dihydrocholesterol, ergosterol, 7-dehydrocholesterol, stigmasterol and stigmastanol), in a PA/sterol molar ratio of 3/7, has been characterized by IR and ²H NMR spectroscopy at different pH. Our study shows that it is possible to form liquid-ordered (lo) lamellar phases with these binary non-phospholipid mixtures. The characterization of alkyl chain dynamics of PA in these systems revealed the large ordering effect of the sterols. It was possible to extrude these systems, using standard extrusion techniques, to form large unilamellar vesicles (LUVs), except in the case of ergosterol-containing mixture. The resulting LUVs displayed a very limited passive permeability consistent with the high sterol concentration. In addition, the stability of these PA/sterol self-assembled bilayers was also found to be pH-sensitive, therefore, potentially useful as nanovectors. By examining different sterols, we could establish some correlations between the structure of these bilayers and their permeability properties. The structure of the side chain at C17 of the sterol appears to play a prime role in the mixing properties with fatty acid.     

Interpenetrating Triphase Cobalt‐Based Nanocomposites as Efficient Bifunctional Oxygen Electrocatalysts for Long‐Lasting Rechargeable Zn–Air Batteries

Rational construction of atomic‐scale interfaces in multiphase nanocomposites is an intriguing and challenging approach to developing advanced catalysts for both oxygen reduction (ORR) and evolution reactions (OER). Herein, a hybrid of interpenetrating metallic Co and spinel Co₃O₄ “Janus” nanoparticles stitched in porous graphitized shells (Co/Co₃O₄@PGS) is synthesized via ionic exchange and redox between Co²⁺ and 2D metal–organic‐framework nanosheets. This strategy is proven to effectively establish highways for the transfer of electrons and reactants within the hybrid through interfacial engineering. Specifically, the phase interpenetration of mixed Co species and encapsulating porous graphitized shells provides an optimal charge/mass transport environment. Furthermore, the defect‐rich interfaces act as atomic‐traps to achieve exceptional adsorption capability for oxygen reactants. Finally, robust coupling between Co and N through intimate covalent bonds prohibits the detachment of nanoparticles. As a result, Co/Co₃O₄@PGS outperforms state‐of‐the‐art noble‐metal catalysts with a positive half‐wave potential of 0.89 V for ORR and a low potential of 1.58 V at 10 mA cm^?2 for OER. In a practical demonstration, ultrastable cyclability with a record lifetime of over 800 h at 10 mA cm^?2 is achieved by Zn–air batteries with Co/Co₃O₄@PGS within the rechargeable air electrode.     

GENETICS OF GRACILARIA TIKVAHIAE (RHODOPHYCEAE). XI. FURTHER CHARACTERIZATION OF A BISEXUAL MUTANT1,2

A spontaneous bisexual mutant of Gracilaria tikvahiae McLachlan has been further characterized. Female plants that are carriers for the mutation, but do not themselves express bisexuality, have been identified among progeny derived from the original bisexual male plant. In crosses to normal males these carrier females yielded normal tetrasporophytes which in the subsequent gametophyte generation produced a 2 female: 1 male: 1 bisexual segregation. In crosses to bisexual males the carrier females produced unusual tetrasporophytes that formed cystocarps in addition to tetraspores. The gametophyte generation obtained from the tetraspores of these tetrasporophytes included only females and bisexuals, these being present in a 1:1 ratio. Other crosses, using bisexual male progeny, indicated that these have the same characteristics as the original bisexual mutant. All of the results are consistent with the genetic interpretation made previously that bisexuality results from a single recessive mutation, designated bi, in a gene distinct from the mt locus controlling male vs. female differentiation. From the phenotypes that have been observed it appears that the mutation does not cause bisexuality per se but rather results in unregulated female expression in males and tetrasporophytes where female-specific genes are normally repressed. It is suggested that the normal bi⁺ allele plays an important role in that repression process. The origin of the bisexual mutation has been re-examined by studying the progenitor stock of the mutation and stocks related to it. It appears that the bisexual mutation arose in a two-step process, first to a low level of expression that is found in the progenitor stocks and then to the high level of expression found in mutant clone 1045(bi) and its descendants.     

Memory dynamics in the honeybee

Reward learning in honeybees initiates a sequence of events which leads to long-lasting memory passing through multiple phases of transient memories. The study of memory dynamics is performed at the behavioral (both natural foraging behavior and appetitive conditioning), neural circuit and molecular levels. The results of these combined efforts lead to a model which assumes five kinds of sequential memories, each characterized by a set of behavioral and mechanistic properties. It is argued that these properties, although reflecting general characteristics of step-wise memory formation, are adapted to the species-specific adaptations in natural behavior, here to foraging at scattered and unreliable food sources. Accepted: 12 May 1999     

Minutes-Fast Production of Vacancy-Enriched MXenes as an Efficient Platform for Single-Atom Electrocatalysts

Although MXenes have been synthesized by liquid phase and molten salt etching approaches, it still suffers from sluggish reaction kinetics of removing A species from MAX phases associated with an overlong production time (5–48 h). Here, a minute-level production approach is developed to produce MXenes (Ti₂CCl_x) by selectively etching MAX phases (Ti₂AlC) under metal chloride (ZnCl₂) vapor. In this synthetic protocol, metal chloride vapor possesses a very high chemical activity to the interlaminar A metal layers of MAX phases owing to negative Gibbs free energies, accompanied with the fast removal of gaseous A-containing chlorides in the reaction system. Moreover, some M species can be controllably etched off from the lattice of MX slabs to generate metal vacancies, which have a high reducing ability to implant single-atom Zn from ZnCl₂ vapor. Finally, vacancy-enriched MXenes are produced after the volatilization of Zn. In this manner, the etching time is less than one-sixtieth those of liquid phase and molten salt etching approaches. The resultant MXenes can be employed as an efficient platform for implanting single-atom Pt, showing a low overpotential of 41 mV at a current density of 10 mA cm⁻² and a good long-term stability up to 5000 cycles.