Acidity versus habitat structure as regulators of littoral microcrustacean assemblages

1. Emergence traps were set overnight on the sediment surface to sample the littoral microcrustaceans of 22 Canadian Shield lakes that ranged in pH from 4.56 to 6.92. Traps were randomly allocated in quintuplicate in both wave‐washed sandy habitats where pipewort (Eriocaulon septangulare) was the dominant macrophyte (termed pipewort habitats), and more protected habitats dominated by floating‐leaved macrophytes (termed floating‐leaved habitats). 2. In total, 50 cladoceran and 22 copepod species were found, with 16–45 species in each lake. Lakes that had never acidified exhibited a more diverse fauna than lakes that had acidified. 3. There were only minor differences between the numbers of species found in floating‐leaved versus pipewort habitats except for one lake. Non‐chydorid cladoceran, chydorids and copepods constituted 45%, 26% and 29% of the total number of individuals, respectively. 4. Based on presence/absence, dominance scores and frequency of occurrences of species, the microcrustacean faunal composition was similar in the two habitats. A detrended correspondence analysis confirmed that there was no separation between the two main types of habitat, and that pH was the parameter most strongly correlated with the dominant microcrustacean compositional gradient among lakes.     

Photochromic Pigments from Blue-Green Algae: Phycochromes a, b, and c

Aqueous extracts of blue-green algae were fractionated by electrofocusing. In all algae investigated, fractions with iso-electric points at or near 4.6 showed photochromic behaviour analogous to that of phytochrome, although they were sensitive to light of shorter wavelength. Three main types of photochromic pigments were found: Phycochrome a (in Tolypothrix distorta, Phormidium luridum, Nostoc muscorum 1453/12, and Anacystis nidulans) has one form absorbing maximally at about 590 nm (formed under red light) and one absorbing maximally at about 630 nm (formed under green light). Phycochrome b (in Tolypothrix distorta) has one form absorbing maximally near 510 nm and one form absorbing maximally at 570 nm (formed in yellow-green and blue-green light, respectively). Phycochrome c (in Nostoc muscorum A and probably in Tolypothrix tenuis) has one form absorbing maximally at 650 nm (formed under green light) and one absorbing very weakly in the green region (formed under red light). The conversion of Phormidium phycochrome a from its red-absorbing form to its green-absorbing form causes the same spectral change as if an f-chromophore of phycocyanin were transformed into an s-chromophore. The quantum yield for this conversion is estimated to be 0.1, while the quantum yield for the reversion is estimated to be 0.4 on the assumption that the absorption coefficients are those of f- and s-chromophores. Phycochrome c is less light-sensitive than phycochromes a and b.     

Light-Induced Absorption Changes in Etiolated Coleoptiles

Blue (or green) light induced reversible and irreversible absorption changes in etiolated wheat (Triticum aestivum) coleoptiles. Immediately after a 10 s pulse of blue light there was an absorbance increase at 440 nm and a decrease at 420 nm. The absorbance at 440 nm returned to the original level in a biphasic way, with first-order rate constants of 0.05 s^?1 and 0.006 s^?1 at 25°C. The change at 440 nm was partly, but not completely, inhibited by iodide. In the 500–600 nm region complex changes occurred, indicating the participation of at least two different cytochromes, one of which was oxidized during a 10 s light pulse and the other oxidized more slowly during the following dark period.     

Spermatozoa from the supertribes Lasiopteridi and Stomatosematidi (Insecta, Diptera, Cecidomyiidae): ultrastructure data and phylogeny of the subfamily Cecidomyiinae

Spermatozoa from seven gall-midge species, representing the supertribes Lasiopteridi and Stomatosematidi, have been examined by electron microscopy and compared to the spermatozoa of 30 previously examined gall-midge species of the subfamily Cecidomyiinae. Derived characteristics of all examined representatives of this subfamily are the lack of acrosome and the absence of accessory tubules in their axoneme. The sperm axoneme of Didactylomyia has a unique '9 + 5 pattern', i.e. with 9 outer doublets and 5 inner singlet microtubules. Unlike other members of Cecidomyiinae, Didactylomyia has retained some plesiomorphic traits, namely crystal containing mitochondria and a homogeneously condensed nucleus. Stomatosema has a 10 + 0 axoneme and an irregular nuclear condensation. Thus, Didactylomyia may serve as an useful outgroup for phylogenetic analysis within the subfamily Cecidomyiinae. The supertribe Stomatosematidi is a paraphyletic assemblage. Nearly all members of Lasiopteridi, Ozirhincus, Arnoldiola, Brachineura and Ledomyia , have a synapomorphic character in the great number of microtubules in parallel to the axoneme. A notable exception is Rhizomyia , which shares certain apomorphic traits with several genera that have previously been classified within the Cecidomyiidi, i.e. Contarinia, Allocontarinia, Lestodiplosis and Myricomyia. Moreover, these genera have a flat sperm tail and microtubular doublets located close to the cell membrane, both characteristics that differ markedly from the very peculiar sperm tail found in other members of Cecidomyiidi.
Cladistic analysis of sperm characters suggests that the supertribe Cecidomyiidi is a polyphyletic taxon and supports the existence of a sister-group relationship between the supertribe Lasiopteridi and the genera Rhizomyia, Contarinia, Allocontarinia, Lestodiplosis and Myricomyia.     

Factors Affecting Ethanol Induced Luminescence in Dark-Treated Chloroplasts

Dark-treated chloroplasts emit light when treated with a high ethanol concentration. The ethanol treatment causes chlorophyll solvation. The light is red and emanates from a singlet excited molecule, probably a chlorophyll peroxide. It is quenched by acetone, sodium dodecyl sulfate treatment of the chloroplasts before the addition of ethanol, boiling, reducing substances and low pH. It is enhanced by ferricyanide and high pH. This is interpreted as a requirement for an organized structure and for an energy transfer system for light emission to occur.     

THE INTRINSIC MECHANISM OF CHROMATIN DECONDENSATION AND ITS ACTIVATION IN HUMAN SPERMATOZOA*

In vitro decondensation of human sperm chromatin induced by the activation of an intrinsic mechanism was studied by light microscopy, scanning and transmission electron microscopy. Morphological evidence was provided to support the concept that this mechanism is essential for the chromatin decondensation occurring in vivo. Prostatic zinc is hypothesized to preserve this potential decondensation ability from oxidative destruction, by reversibly binding to free thiol-groups. The unique occurrence of disulphide-stabilized structures in eutherian spermatozoa may serve to protect the spermatozoon from structural degradation by its own proteolytic activity during the relatively slow passage through the eutherian egg investments.     

SEDIMENTARY STRUCTURES IN CAMBRIAN LIMESTONES STUDIED BY RADIOGRAPHY

The paper deals with radiographic studies of Middle Cambrian 'fragment limestone', and Upper Cambrian anthraconite concretions from Bornholm (Denmark). A very simple method provides good insight into the sedimentary structures of the rocks and hence a good foundation for interpretation of the lithogenesis.