DNase I hypersensitivity and expression of the Shrunken-1 gene of maize

The local chromatin structure of the Shrunken-1 (Sh) gene of maize was probed by analyzing DNase I hypersensitivity. Sh encodes the gene for sucrose synthetase, a major starch biosynthetic enzyme, which is maximally expressed in the endosperm during seed maturation. In addition to general DNase I sensitivity, specific DNase I hypersensitive sites were identified in endosperm chromatin that mapped near the 5 end of the Sh gene. The pattern of hypersensitive sites and their relative sensitivity were altered in other non-dormant tissues that produce little or no enzyme. However, some changes in chromatin structure appear to be independent of Sh gene expression and may reflect general alterations associated with plant development. The chromatin structure of several sh mutations, induced by Ds controlling element insertions, was also analyzed. Although the insertions perturbed expression of the gene, there were no notable effects on local chromatin structure.     

Three-dimensional structure of deoxycholate-treated purple membrane at 6 Å resolution and molecular averaging of three crystal forms of bacteriorhodopsin

The three-dimensional structure of the deoxycholate-treated form of purple membrane has been determined to a resolution of about 6 Å. Using low temperature electron diffraction data, room temperature electron microscope images and improved methods of data analysis, higher resolution has been reached than was obtained using native membranes of the same size. Statistical analysis of the data shows that the new map is considerably better than earlier maps. The map indicates the probable sites for the lipid molecules that remain in the deoxycholate-treated membranes; some of these sites differ from those suggested by the projection map of Glaeser et al. (1985). Comparison of the bacteriorhodopsin structures now determined independently from three crystal forms shows that the monomer structure is independent of the detailed contacts with lipid molecules. The average of the three structures gives a picture with very little noise showing seven similar rod-like features which are clearly best interpreted as -helices; there is no indication that part of the structure is -sheet as suggested by Jap et al. (1983). Phases from the averaged structure at 6 Å resolution will enable better refinement of the parameters that will be required in the analysis of higher resolution images from tilted specimens needed to extend the projection map at 3.5 Å resolution (Henderson et al. 1986) to produce a three-dimensional atomic resolution map.     

Methods for detecting non-randomness in species co-occurrences: a contribution

Summary Comparison of co-occurrences between species on a group of islands with those expected from a randombased null model could provide evidence on community structure. However, it is difficult to decide on the appropriate null model. Gilpin and Diamond proposed a model and a test for departure from it, but this test is shown to indicate significant structure even when applied to a matrix of random numbers. An alternative method is suggested, using the distribution of Gilpin and Diamond's deviation as test statistic, but determining the expected distribution by Monto Carlo simulation, and using many such simulations as a randomisation test of significance. The null model used accepts the observed totals of occurrences for islands and species; it therefore offers a somewhat conservative test. Applied to the Vanuatu bird data that Gilpin and Diamond used, significant departure from a null model is seen, but with an excess of extreme negative associations, the opposite result from that given by Gilpin and Diamond's method. It is not possible to tell whether the negative associations are due to autecology, biogeography, or to interactions between species.     

Effects of clonal variation of the host plant,interspecific competition,and climate on the population size of a folivorous thrips

Summary The effects of clonal variation, interspecific competition, and climate upon the population size of Apterothrips secticornis was assessed by a series of observations and experimental manipulations. Three clones of the host plant, Erigeron glaucus, consistently supported different numbers of thrips during monthly censuses. When rosettes of the three clones were transplanted to a common garden, relative numbers of thrips on the clones remained the same as those observed where the clones grew in situ. The presence or absence of other hervivores had no effect on thrips numbers in the common garden. Plume moth caterpillars and thrips were observed to co-occur less often than expected in the field but this was caused by differences in habitat selection by these two species rather than being the result of interspecific competition. Populations of thrips were affected by climate, but analyses suggest that the host clone was a more important factor.     

Structure and expression of the overlapping ND4L and ND5 genes of Neurospora crassa mitochondria

Summary Genes homologous to the mammalian mitochondrial NADH dehydrogenase subunit genes ND4L and ND5 were identified in the mitochondrial genome of the filamentous fungus Neurospora crassa, and the structure and expression of these genes was examined. The ND4L gene (interrupted by one intervening sequence) potentially encodes an 89 residue long hydrophobic protein that shares about 26% homology (or 41% homology if conservative amino acid substitutions are allowed) with the analogous human mitochondrial protein. The ND5 gene (which contains two introns) encodes a 715 residue polypeptide that shares 23% homology with the human analogue; a 300 amino acid long region is highly conserved (50% homology) in the two ND5 proteins. The stop codon of the ND4L gene overlaps the initiation codon of the downstream ND5 gene, and the two genes are contranscribed and probably cotranslated. A presumed mature dicistronic (ND4L plus ND5) RNA was detected. The postulated mRNA (about 3.2 kb) contains 5 and 3 non-coding regions of about 86 and 730 nucleotides, respectively; this species is generated from very large precursor RNAs by a complex processing pathway. The ND4L and ND5 introns are all stable after their excision from the precursor species.Abbreviations bp base pairs - rRNA ribosomal RNA - ND NADH dehydrogenase - URF unidentified reading frame - kDal kilodaltons; a.a., amino acid     

Effects of heavy metals on growth and ultrastructure ofChara vulgaris

Summary The toxicity of some heavy metals to the common macrophytic freshwater algaChara vulgaris was studied under laboratory conditions. For experiments, apical tips of algae containing two internodes were cultivated for fourteen days in the presence of various concentrations of cadmium, mercury or lead (as triethyl lead or lead nitrate). Fifty percent growth inhibition occurred with concentrations of 8.5×10^–8 M (9.5 ppb) cadmium, 7.5×10^–7M (150ppb) mercury, 1.6×10^–6 M (330ppb) organic lead or 4× 10^–5 M (8000 ppb) inorganic lead. Sublethal concentrations of these metals caused alterations in the fine structure of internodal cells which turned out to be at least partly metal-specific or in the case of lead, the effects depended on whether the lead was ionic or organically bound. Cadmium and inorganic lead induced disorders of cell wall microfibrils which resulted in local wall protuberances. Mercury affected the chloroplasts which mostly showed considerably increased grana stacks. In addition, mercury caused a dilation of the endoplasmic reticulum and of the mitochondrial tubuli. Organic lead damaged the membrane system of chloroplasts; sheet- or tubule-like thylakoids were disarranged and showed whorl-like structures. At higher concentrations of organic lead, tubular invaginations of the plasmalemma (charasomes) disappeared. The fine structure of nuclei was not altered by any of the metals.     

Cladocera in space and time: Analysis of lake sediments

Shells of Bosminidae and Chydoridae are quantitatively preserved in lake sediments. The chronological deposition of these remains provides the means for longterm observation of these Cladocera, both in terms of species and communities. Chydorid analysis, as based on subfossil assemblages, is an analysis of community and provides direct observation of community dynamics over extended periods of time. It has proved to be a valuable method to obtain information on the influence of environmental factors and time on community characteristics. Morphological variation inBosmina (Eubosmina) has been followed for some thousand years. This is of special interest for the evaluation of taxonomic rank (species, forms) if closely related taxa have co-existed. Bosmina successions, as well as shifts in the chydorid fauna, are related to environmental change. Thus, cladoceran analysis of lake sediments provides information on the developmental history of lakes and allows observation of the effects of longterm environmental changes, such as climatic changes and eutrophication.     

The possible origin ofDaphnia cucullata procurva Poppe 1887 in the lakes of the Pomeranian Lakeland by hybridization in the past

Besides the genusBosmina, the genusDaphnia offers considerable taxonomic difficulties due to the existence of a very great number of different morphotypes and their intergrades. Especially the morphotypes clustering aroundDaphnia galeata Sars, 1864,D. hyalina Leydig, 1860, andD. cucullata Sars, 1862 offer a bewildering picture. In the last years an attempt has been made to understand this phenomenon mainly as the result of hybridization and colonization of new biotopes by populations with hybridogenetic polymorphism and genotypic diversity (founder effect). Now it will be suggested on a morphological base thatD. cucullata procurva Poppe, 1887, a unique and aberrant formtype restricted to few lakes along the river Brda in Poland, is probably an old and stabilized hybrid originating from interspecific hybridization betweenD. galeata andD. cucullata.