Mictic patterns of the rotifer Brachionus plicatilis Müller in small ponds

Populations of the rotifer Brachionus plicatilis were monitored in three small ponds in a marsh on the Mediterranean coast. Samples were taken approximately every three weeks from July 1992 to November 1993. Salinity, temperature, conductivity, pH and oxygen concentration were measured in the field. Population density was determined from preserved quantitative samples. Individuals were classified as mictic females, amictic females, non-ovigerous females, and males, differentiating between two morphotypes (S and L). From these counts, a level of mixis was calculated. We also determined the proportion of mictic females in natural populations by culturing females isolated from fresh samples. From these data, mictic patterns over time and correlation between levels of mixis and environmental and population parameters were analyzed. From a previous study S and L morphotypes were known to correspond to genetically different clonal groups. Our data showed that reproduction was predominantly parthenogenetic in these clonal groups, but mictic females were found in most samples, the proportion of mictic females ranging from 0 to 29%. The clonal groups showed different patterns of mixis. L clonal group presented a continuous sexual reproductive pattern. In contrast, S clones showed a rather punctuated mictic pattern. A positive correlation between levels of sexual reproduction and population density was found for S and L groups. However, they differed in their density threshold for mictic reproduction. The adaptive meaning of these patterns and their implications in maintaining genetic diversity within and between populations are discussed.     

Mutagen sensitivity and mutability in lentil

Summary Seeds of two cultivars, each of macrosperma and microsperma varietal groups of lentil were mutagenised with gamma-rays and NMU to determine their mutagen sensitivity and mutability. The increasing doeses of gamma-rays and NMU decreased germination, root and shoot length, pollen fertility and plant survival, but increased the occurrence of leaf spots. The root system was found to be more sensitive to both mutagens than the shoot. The macrosperma varietal group was more sensitive to both the mutagens than microsperma group. In microsperma group, variety Pusa-1 was more sensitive to both the mutagens than L-259, while in the macrosperma group L-1491 showed more sensitivity to the mutagens than L-1492. Radio-sensitivity corresponded positively with chemosensitivity in both varietal groups. There was a positive relationship between radio- and chemo-sensitivity of the genotypes and their mutability. The results also revealed the existence of a parallelism between radiomutability and chemo-mutability. Due to saturation in the mutational events and vigour of both diplontic and haplontic selection in the biological material, the mutation frequency either decreased or remained constant at higher doses of the mutagens.     

Contrasting leaf and ‘ecosystem’ CO2 and H2O exchange in Avena fatua monoculture: Growth at ambient and elevated CO2

Elevated CO₂ (ambient + 35 Pa) increased shoot dry mass production in Avena fatua by 68% at maturity. This increase in shoot biomass was paralleled by an 81% increase in average net CO₂ uptake (A) per unit of leaf area and a 65% increase in average A at the ecosystem level per unit of ground area. Elevated CO₂ also increased ecosystem A per unit of biomass. However, the products of total leaf area and light-saturated leaf A divided by the ground surface area over time appeared to lie on a single response curve for both CO₂ treatments. The approximate slope of the response suggests that the integrated light saturated capacity for leaf photosynthesis is 10-fold greater than the ecosystem rate. Ecosystem respiration (night) per unit of ground area, which includes soil and plant respiration, ranged from-20 (at day 19) to-18 (at day 40) mol m^-2 s^-1 for both elevated and ambient CO₂ Avena. Ecosystem below-ground respiration at the time of seedling emergence was -10 mol m^-2 s^-1, while that occuring after shoot removal at the termination of the experiment ranged from -5 to-6 mol m^-2 s^-1. Hence, no significant differences between elevated and ambient CO₂ treatments were found in any respiration measure on a ground area basis, though ecosystem respiration on a shoot biomass basis was clearly reduced by elevated CO₂. Significant differences existed between leaf and ecosystem water flux. In general, leaf transpiration (E) decreased over the course of the experiment, possibly in response to leaf aging, while ecosystem rates of evapotranspiration (ET) remained constant, probably because falling leaf rates were offset by an increasing total leaf biomass. Transpiration was lower in plants grown at elevated CO₂, though variation was high because of variability in leaf age and ambient light conditions and differences were not significant. In contrast, ecosystem evapotranspiration (ET) was significantly decreased by elevated CO₂ on 5 out of 8 measurement dates. Photosynthetic water use efficiencies (A/E at the leaf level, A/ET at the ecosystem level) were increased by elevated CO₂. Increases were due to both increased A at leaf and ecosystem level and decreased leaf E and ecosystem ET.     

Induction of Somatic Embryogenesis and Plant Regeneration of ‘Ataulfo’ Mango (Mangifera indica)

Nucellar explants from the immature fruit of Ataulfo mango, 3–4 cm long, were used. The process had a very low efficiency (<10%); however, Ataulfo was more embryogenic than other cultivars such as Tommy Atkins or Haden in our hands. Overall, the process from nucellus to plantlet stage took 5 months. Twelve regenerated plants were obtained and are currently growing in the greenhouse. They appear to be normal and free of abnormalities. Some biochemical and molecular tests are currently being carried out.     

Linear differentiation of cereal chromosomes

Summary The BSG test was used in a comparative study of the linear chromosome differentiation and the idiograms of T. Macha ssp. tubalicum v. letschchumicum Dek. et Men., T. georgicum Dek., T. timopheevi. Zhuk., T. carthlicum Nevski, T. dicoccum Schrank, v. rufum, T. durum Desf. v. Arnautka were compiled.The karyotype of each polyploid wheat species consists of two groups of chromosomes. The first is formed by ten pairs of constant chromosomes occurring almost in all species and the second by all the rest of the variable chromosomes that are either fully specific for the species in question or occur only in a few species. T. timopheevi largely differs from other species of polyploid wheats in the high level and specific localization of structural heterochromatin on chromosomes. The rols of introgression in wheat evolution and the necessity of establishing a General Cytological Nomenclature of Cereal Chromosomes are discussed.     

Ultrastructural analysis of mineralized matrix from human osteoblastic cells: Effect of tumor necrosis factor-alpha

The study, addressed to understand whether or not human platelets possess a unique thiol-oxidase whose activity could be modulated by signalling pathway initiated upon the activation of Receptor-C_k revealed the existence of disulphide-dependent oxidation within these cells and this phenomenon was regulated by Receptor-C_k-dependent generation of second messengers especially phosphatidic acid (PA); cAMP and cGMP. Purification of this activity revealed the existence of 47 kDa protein having thiol-oxidase activity. Keeping in view these results we propose that the existence of this novel 47 kDa Thiol-oxidase within human platelets may provide a crucial switch for the regulation of Receptor-C_k-dependent mevalonate pathway in human platelets.     

Nitrogen mineralization in relation to C:N ratio and decomposability of organic materials

A desk study was made on N mineralization of various organic materials. Data were obtained from the literature containing information on mineralized organic N, C/N of the substrate and some index for decomposability. Per class of substrate decomposability, linear regression lines between N mineralization and substrate C/N were established, from which apparent initial age and humification coefficient were calculated to indicate decomposability. For quantitative grading, a resistance index was formulated comprising the concentrations of lignin and polyphenols. The results confirmed that the fraction of mineralized organic N is linearly related to substrate C/N for equally decomposable materials. The nature of the organic materials and the processes to which they had been subjected were reflected in the ranking by decomposability.     

Rna-mediated regulation of Receptor-Ck gene in human platelets

The study addressed to understand the regulation of Receptor-C_k gene atthe translational level revealed that exogenous cholesterol has the inherentcapacity to regulate the endogenous synthesis of Receptor-C_k by initiatingintracellular targeting of the Receptor-C_k to the mRNP pool within humanplatelets and this effect could be reversed when the platelets wereincubated with cholesterol coupled with either dB cAMP or dB cGMP. Basedupon these observations, we propose that Receptor-C_k initiated signalling,which involves second messengers like PA, cAMP and cGMP, may be responsiblefor the autoregulation of Receptor-C_k gene expression at the translationallevel.     

Chromosome and isoenzyme studies on cells derived from protoplast fusion of Nicotiana glauca with glycine max-Nicotiana glauca cell hybrids

Summary The somatic hybrids of Glycine max (L)Merr.-Nicotiana glauca Grah. exhibited a preferential loss of N. glauca chromosomes. When protoplasts from such hybrid cells were back fused twice to N. glauca protoplasts, a considerable increase in stability of the N. glauca chromosomes was observed. Gel electrophoresis studies of aspartate aminotransferase showed that the chromosome(s) responsible for this enzyme was stabilized in the back fused hybrid cell lines. The data suggest that the back fusion technique described in this study might aid in stabilizing somatic hybrids.NRCC No. 18040     

Restriction fragment analysis of ‘null’ forms at the Gli-1 loci of bread and durum wheats

Summary Wheat accessions lacking some of the - and -gliadin components encoded by the Gli-1 loci on the short arm of chromosome 1D in bread wheat and chromosome 1A in durum wheat were studied by two-dimensional polyacrylamide gel electrophoresis and restriction fragment analysis. Digested genomic DNAs of normal and null forms were probed with a cDNA clone related to -/-gliadins and with a genomic clone encoding an LMW subunit of glutenin. The hybridisation patterns with the -/-gliadin probe were similar to those of cvs Chinese Spring and Langdon used as standards for bread and durum wheats, respectively, but several restriction fragments located on the 1D chromosome of bread wheat and the 1A chromosome of durum wheat were absent in the null forms. In addition, specific LMW glutenin fragments encoded by the same chromosomes were also absent in the null forms, suggesting that simultaneous deletions of blocks of genes for both -/-gliadins and LMW glutenins had occurred. Comparisons of the protein and RFLP patterns enabled some proteins to be mapped to specific restriction fragments.     

Selection for rate of development and pupal weight in ‘Cnephasia’ jactatana: A genetic tool for quality improvement

Selection for fast and slow rate of pupation over three successive generations in Cnephasia jactatana (Walker) (Lepidoptera: Tortricidae) produced a fast strain that pupated 2 days earlier than the slow strain. Selection for pupal weight was asymmetrical with the light selection having more effect than the heavy selection. The larval critical weight (L_CW), the larval maximum weight (L_MW) and the latent feeding period were not affected by any of the selections. Slow and light selections resulted in longer pre-pupal periods than fast, heavy or the laboratory population. Fecundity was reduced in females from slow and light selections. Selection in insects is discussed as a possible genetic tool for overall quality improvement.Résumé La sélection pour la rapidité d'apparition des chrysalides de C. jactatana Walker produit en 3 générations une lignée rapide qui se nymphose 2 jours avant la lente. La sélection pour le poids des chrysalides est asymétrique, ayant plus d'effet sur la sélection développement lent que sur la sélection développement rapide. Le poids critique larvaire (L_CW), le poids larvaire maximal (L_MW) et la période latente d'alimentation ne sont pas modifiés par ces sélections. Les lignées lente et légère ont des périodes prénymphales plus longues que les lignées rapide et lourde, ou la souche de laboratoire. Les fécondités des lignées lente et légère sont réduites. Les sélections associées des insectes sont examinées comme outil génétique potentiel permettant d'améliorer les performances globales.     

Silver nitrate and aminoethoxyvinylglycine affect <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated apple transformation

In Fuji, the production of ethylene was increased with the addition of AgNO₃ and inhibited with the addition of 10 M aminoethoxyvinylglycine (AVG). The addition of 80 M AgNO₃ to transformed explants of Fuji cultured on selection medium resulted in increased ethylene production (20 l l^–1) at 3 weeks. Under examining the effect of AgNO₃ in Fuji, the 40 M AgNO₃ showed with higher 33.8% and 6.5% in the efficiency of regeneration and transformation. However, ethylene production in Gala explants treated with 10M AgNO₃ (3 l l^–1) decreased after 2 weeks compared with the control (5 l l^–1). Although the regeneration efficiency of Gala with 10 M AgNO₃ was higher (41.1%) than the control (20.1%), there was no significant difference in the transformation efficiency at the same concentration. Shoot regeneration of Fuji and Gala was completely inhibited with 10 M AVG. These results suggest that the addition of AgNO₃ affects the efficiency of Agrobacterium-mediated gene transfer in Fuji.Eun Soo Seong, Ill Min Chung- These two Authors Contributed equally to this work     

The origin of crop weed communities composed of summer annuals

Summary Evidence for the origin and dating of crop weed communities composed of summer annuals is to be found in palaeobotanical and archaeological data. There is archaeological evidence that around the middle of the first millennium BC fields were taken into permanent cultivation, even on the poorer soils.Fertilization with lime and manure and Plaggenwirtschaft were evidently involved in this early agriculture. In this paper the idea is put forward that Plaggenwirtschaft resulted in a sudden increase in the number of weed species brought together in cornfields and that this practise led to the very first beginning of our modern weed communities.Translated into English by Drs. C. van Driel-Murray.     

Are biodiversity ‘hotspots’ correlated with current ecoclimatic stability? A pilot study using the NOAA-AVHRR remote sensing data

The GAC (Global Area Coverage) by the NOAA-AVHRR satellites represents an excellent data set for studying global and regional patterns of variations in surface conditions driven in part by climatic variation. In this pilot study we examined whether biodiversity hotspots, defined from peak concentrations of neoendemics as well as geographically relict forms, differ in ecoclimatic stability from surrounding areas under present-day climatic conditions. Coefficients of variation of the ratio between brightness surface temperature (Ts) and the Normalized Difference Vegetation Index (NDVI) based upon 10 years' monthly composited scenes of tropical Africa revealed distinctive geographical patterns of interannual variability in surface conditions. Regions with a predominance of old species are characterized by spatial uniformity in the ecoclimatic variability, while regions where rapidly radiating groups dominate are spatially complex in this respect. However, the exact hotspots, with peak concentrations of endemic species, are characterized by a local reduction in ecoclimatic variability, or placement on the boundary to a stable region. This relationship was supported statistically by comparing ecoclimatic profiles across montane forests representing hotspots, and those of other montane forests. It is suggested that, because of interactions between prevailing atmospheric flows, topography and vegetation, the impact of extreme weather is moderated locally. The correlation between current stability and aggregates of neoendemics as well as old relics indicate that local moderation of climatic extremes persist through shifting climatic periods, permitting populations of unique species to survive in these places. The results are used to identify study sites for better ground truthing and for paleoclimatological studies which may be useful for more thorough studies of these relationships.     

Classification ofPythium ‘group F’ based on mycelial protein and isozyme patterns

Taxonomic characteristics were compared among 10 isolates ofPythium group F in tems of the electrophoretic patterns of their mycelial proteins and isozymes. These isolates were obtained from water of three ponds in different seasons and have an identical morphology of zoosporangia. Attempts to cross the isolates with each other themselves and with other isolates from the same group failed.Pythium group F is the most dominant of the pythia in the aquatic ecosystem and is difficult to identify because of the lack of sexual reproductive structures. Isozyme analysis proved useful in this respect. Comparisons of banding patterns of total soluble proteins and isozymes revealed five subgroups inPythium group F. Two isolates obtained from water of different ponds in different seasons showed the same protein and isozyme patterns. Our findings indicate that the use of total soluble protein and isozyme patterns for determining the variation withinPythium group F could become a valuable adjunct to the morphological and physiological criteria.     

The role of ‘Norin 10’ dwarfing genes in photosynthetic and respiratory activity of wheat leaves

Summary A comparative analysis of eight cultivars of spring wheat (Triticum aestivum) classified by height as tall (T), semi-dwarf (D₁), dwarf (D₂) and very dwarf (D₃) was conducted to study their efficiency of oxygen exchange during photosynthesis and dark respiration. Two cultivars were included in each height group.Cultivars carrying Norin 10 dwarfing genes (D₁, D₂ and D₃) were found to have a significantly higher photosynthetic rate per unit leaf area than talls (T) that lack these genes. Among the Norin gene carriers, dwarf group (D₂) was most efficient, followed by very dwarf (D₃) and semi-dwarf (D₁).Photosynthetic rate and respiratory rate were found to have a positive relationship.     

Carbon and nitrogen dynamics along the decay continuum: Plant litter to soil organic matter

Decay processes in an ecosystem can be thought of as a continuum beginning with the input of plant litter and leading to the formation of soil organic matter. As an example of this continuum, we review a 77-month study of the decay of red pine (Pinus resinosa Ait.) needle litter. We tracked the changes in C chemistry and the N pool in red pine (Pinus resinosa Ait.) needle litter during the 77-month period using standard chemical techniques and stable isotope, analyses of C and N.Mass loss is best described by a two-phase model: an initial phase of constant mass loss and a phase of very slow loss dominated by degradation of lignocellulose (acid soluble sugars plus acid insoluble C compounds). As the decaying litter enters the second phase, the ratio of lignin to lignin and cellulose (the lignocellulose index, LCI) approaches 0.7. Thereafter, the LCI increases only slightly throughout the decay continuum indicating that acid insoluble materials (lignin) dominate decay in the latter part of the continuum.Nitrogen dynamics are also best described by a two-phase model: a phase of N net immobilization followed by a phase of N net mineralization. Small changes in C and N isotopic composition were observed during litter decay. Larger changes were observed with depth in the soil profile.An understanding of factors that control lignin degradation is key to predicting the patterns of mass loss and N dynamics late in decay. The hypothesis that labile C is needed for lignin degradation must be evaluated and the sources of this C must be identified. Also, the hypothesis that the availability of inorganic N slows lignin decay must be evaluated in soil systems.     

Chydorus ‘mutilus’ Kreis, 1921 — a postephippial form of Chydorus sphaericus (O. F. Müller, 1785)

Since 1991 faunal collections have been made from the mountain lakes of NW Slovenia. These lakes are at altitudes of between 1250 and 2150 m a. s.l., and have rich biotas, both in terms of species-richness, and faunal abundance. Amongst the animals collected were hump-backed specimens of genus Chydorus. These are identical with Chydorus mutilus, a species described from Swiss mountain lakes by Kreis (1921). The abundance of specimen in the collections, coupled with the availability of data from four successive years of sampling, allowed the detailed analysis of these populations. This also includes an examination of chitinous remains preserved in subrecent sediments.The results show that C. mutilus Kreis, 1921 actually represents a postephippial form of C. sphaericus (O. F. Müller, 1785). From the data available, it appears that the hump-backed form only occurs under certain environmental conditions. Here I discuss environmental factors having the potential to trigger the formation of hump-backed Chydorus. These findings may prove significant in palaelimnological studies, and in the reconstruction of paleotemperatures.In addition, hump-backed animals, apparently identical to European C. mutilus, have also been found in a sample taken from Lake Titicaca (Peru) in 1954. This supports the hypothesis that the hump-backed morph is an environmentally-cued ecophenotype, and not an independent taxon.     

Afferent bursting activity of ruff lateral line induced by background noise stimulation

Summary Single unit resting activities were recorded from fibres innervating a neuromast of the supra-orbital canal of the lateral line system of the ruff (Acerina cernua). The interval histogram of 1 of the 4 types of resting activity had a bimodal distribution (bursting activity). The resting activity of these fibres was compared with the measured vibration of the experimental table. The conclusion that the bursting activity is not spontaneous but is caused by small background vibrations of the table was supported by recording of extracellular hair cell responses.Abbreviation ISI Interspike interval     

The wise use of wetlands: identifying development options for Ghana's coastal Ramsar sites

The Government of Ghana has recently declared five coastal wetlands to be Ramsar sites. This requires the wise use of wetlands of international importance for bird habitat, but does not preclude human habitation or ecologically friendly development. The sites are Muni-Pomadze, Densu Delta, Sakumo, Songor and Keta. An attempt was made to identify and assess a range of development options for initiation within the sites that would be compatible with the environmental concerns of Ramsar, while also being technically and economically viable and socially acceptable to the communities in the sites. The appraisal included developing a detailed understanding of the physical, biological, human and institutional resources of the areas, the land uses and prevailing livelihood systems of local people, and the pressures placed on the natural resources of the wetlands. Many of the developments nominated by stakeholders were rejected, but twenty topics passed the initial tests. These were considered in more detail using information collected for the study by national specialists. Most of the options were considered suitable for local level implementation by community groups or local entrepreneurs. Government assistance will be needed to ensure an enabling institutional framework for small-scale business development is provided.