Shallows of the lower Danube as additional sources of potamoplankton

This paper presents studies on the algal flora of the Bulgarian Danube section during three summer periods (1980–1982) and during the four seasons of 1987/1988. The following variables were investigated: 1) species composition of the river phytoplankton and the phytobenthos; 2) frequency quotients of the species; 3) number of species at the investigated sites; 4) phytoplankton numbers and biomass; 5) floristic similarity between the sites. The data show the existence of a dynamic connection between phytoplankton and phytobenthos. The shallows in the midstream and river arms play an important role as potamoplankton sources during the periods of low waters. It is comparable with the role of the adjacent wetlands to which previously priority was given. This is especially so below 597th river kilometer.Academia Naturalis Heidelberg     

The potamoplankton of the Middle Loire and the role of the ’moving littoral‘ in downstream transfer of algae and rotifers

The seasonal succession of the potamoplankton of the Middel Loire was studied fortnightly from June to October 1995, a period of low water flow. The increase in dissolved oxygen, suspended matter, BOD₅ and chlorophyll a, associated with the decrease in nutrients downstream, are typical of eutrophic rivers. Algae were the principal components of the suspended matter flux in the river. Their density increased from the upper site of Dampierre-en-Burly to the lower site of Saint-Laurent des Eaux, with respective maxima of 68 ×10⁶ cells l^-1 and 106 × 10⁶cells l^-1. A large rotifer community developed in association with the algal growth, with densities up to 3700 ind l^-1 at Dampierre-en-Burly and up to 5800 ind l^-1 at Saint-Laurent des Eaux. They had a high Shannon-Weaver diversity, while grazing appeared to control the algae. As the year progressed to the warmer season, the biomass of the β and β α mesosaprobic rotifer species increased parallel with algae. The water theoretically transported potamoplankton at 0.2 ms^-1 during mid-summer, which meant that the biomass of the algae doubled in minimum 17 km and that of the rotifers in 34 km. From these values and the distances between sampling stations, we deduce that inoculation points were located in areas which could be as short as a hundred meters. Not only algae, but also rotifers are capable of restoring an inoculum of organisms from place to place. Summer hydrodynamics, close to localised lentic areas, were responsible for an increase in plankton abundance in the stream. These movements had an ecotone effect at the boundary between standing and running water, creating pulses. The lower regions were progressively enriched by successive inoculates, dilution and seeding inputs, which did not prevent the growth of algae and of parthenogenetic species in the river. Such processes, which occur in years of low flow, are responsible for the large variations in plankton density observed between years. This revised version was published online in August 2006 with corrections to the Cover Date.     

Structure-function relationships in insulin

A new interpretation of structure-function relationships in the insulin molecule is presented. Negative cooperativity is postulated to arise from a dimerization event occurring between two receptor-bound molecules. The receptor-binding surface of insulin can necessarily not involve residues involved in dimerization as has been generally accepted. Support for this interpretation is based on published data.     

Scale-dependence in species-area relationships

Species-area relationships (SARs) are among the most studied phenomena in ecology, and are important both to our basic understanding of biodiversity and to improving our ability to conserve it. But despite many advances to date, our knowledge of how various factors contribute to SARs is limited, searches for single causal factors are often inconclusive, and true predictive power remains elusive. We believe that progress in these areas has been impeded by 1) an emphasis on single-factor approaches and thinking of factors underlying SARs as mutually exclusive hypotheses rather than potentially interacting processes, and 2) failure to place SAR-generating factors in a scale-dependent framework. We here review mathematical, ecological, and evolutionary factors contributing to species-area relationships, synthesizing major hypotheses from the literature in a scale-dependent context. We then highlight new research directions and unanswered questions raised by this scale-dependent synthesis.     

Structure-activity relationships in nitrothiophenes

The structure and electronic properties of a series of biologically active 2-nitrothiophenes (1) have been calculated using both semi-empirical and ab initio molecular orbital methods. Multi-linear regression analysis suggests that there is a reasonable correlation between the experimental activity of the derivatives against either Escherichia coli or Micrococcus luteus and calculated properties such as the HOMO energies, the total atomic charges and ring angles at the heterocyclic sulfur atom, but there is no correlation with the calculated solvation energies or dipole moments. The presence or absence of an additional nitro group at the 3-position of the ring also has a significant effect on the activity. From the derived QSAR equations, the 2-chloro- or 2-bromo-3,5-dinitrothiophenes (1a and 1c) are predicted to show the highest activity against both bacteria, while 2-nitrothiophene (1n) is predicted to be the least active, in line with the experimental results.     

Structure-function relationships in heme-proteins

Biological systems rely on heme-proteins to carry out a number of basic functions essential for their survival. Hemes, or iron-porphyrin complexes, are the versatile and ubiquitous active centers of these proteins. In the past decade, discovery of new heme-proteins, together with functional and structural research, provided a wealth of information on these diverse and biologically important molecules. Structure determination work has shown that nature has used a variety of different scaffolds and architectures to bind heme and modulate functions such as redox properties. Structural data have also provided insights into the heme-linked protein conformational changes required in many regulatory heme-proteins. Remarkable efforts have been made towards the understanding of factors governing redox potentials. Site-directed mutagenesis studies and theoretical calculations on heme environments investigated the roles of hydrophobic and electrostatic residues, and analyzed the effect of heme solvent accessibility. This review focuses on the structure-function relationships underlying the association of heme in signaling and iron metabolism proteins. In addition, an account is given about molecular features affecting heme's redox properties; this briefly revisits previous conclusions in the light of some more recent reports.     

Parent-child relationships

Parents and doctors have an obligation to supply children with an emotional diet leading to their eventual maturity. This is as important to the child as is his physical guidance. The proteins, carbohydrates, fats, minerals and vitamins of a child's emotional diet are: (1) the need for security; (2) the need to achieve social adaptability; (3) the need for success; and (4) the need for independence. In helping parents provide their children with these major guideposts along the road of character development toward maturity, physicians have a challenge and opportunity for real service to the humanities-a field of endeavor far behind science in human progress.     

Mycoparasitic relationships

The mode of attack and the infection structures of the necrotrophic mycoparasite, Pythium acanthicum, as well as the responses of various fungal hosts to parasitism were studied using both electron and light microscopy. Many taxonomically distinct fungal hosts were used, though Phycomyces blakesleeanus, Pythium aphanidermatum, Rhizoctonia solani and a basidiomycete identified as Corticium sensu lato were studied in greatest detail. Parasitism was by direct penetration of the fungal host without appressorium formation by the parasite. The host's cells responded to contact by P. acanthicum by forming papillae. The morphological features of the papillae varied with the particular host. In P. blakesleeanus they were comprised of vesicles and segments of cytoplasm entrapped in a fibrillo-granular matrix, while in R. solani and the Corticium basidiomycete they contained considerable amounts of electron-opaque and electron-translucent material. Evidence for both mechanical and enzymatic penetration of the host fungi by the parasite are presented. Details of host wall and septum penetration by the parasite are presented using time-lapse light microscopy with in vivo systems. Many of these stages of parasitism were examined ultrastructurally. Some comparisons of these mycoparasitic relationships are discussed in relation to what is known from the literature about phytoparasitic interactions.