Species-specific cell mobility of bacteria-feeding myxamoebae in plasmodial slime molds

On decaying wood or litter in forests, plasmodial slime molds (myxomycetes) represent a large fraction of eukaryotic protists that feed on bacteria. In his seminal book Experimental Physiology of Plants (1865), Julius Sachs referred to the multinucleate plasmodium of myxomycetes, which were considered at that time as primitive plants (or fungi). Today it is well established that myxomycetes are members of the Amoebozoa (Protista). In this study we compare the mobility of myxamoebae of 3 European species, Lycogala epidendrum (order Liceales), Tubulifera arachnoidea, and Trichia decipiens (order Trichiales). Using agar plates, on which 3 separate bacterial species were cultivated as prey organisms (Methylobacterium mesophilicum, Escherichia coli, Agrobacterium tumefaciens), we document large differences in cell motility between the myxomycetes investigated. In addition, we show that the 3 species of myxamoebae can be distinguished based on their average cell size. These data shed light on the mode of co-occurrence via differential substrate utilization in these members of the Amoebozoa.     

Seedling development in buckwheat and the discovery of the photomorphogenic shade‐avoidance response

Numerous botanists of the early 19th century investigated the effect of sunlight on plant development, but no clear picture developed. One hundred and fifty years ago, Julius Sachs (1863) systematically analysed the light–plant relationships, using developing garden nasturtium (Tropaeolum majus) and seedlings of buckwheat (Fagopyron esculentum) as experimental material. From these studies, Sachs elucidated the phenomenon of photomorphogenesis (plant development under the influence of daylight) and the associated ‘shade‐avoidance response’. We have reproduced the classical buckwheat experiments of Sachs (1863) and document the original shade‐avoidance syndrome with reference to hypocotyl elongation and cotyledon development in darkness (skotomorphogenesis), white light and shade induced by a canopy of green leaves. In subsequent publications, Sachs elaborated his concepts of 1863 and postulated the occurrence of ‘flower‐inducing substances’. In addition, he argued that the shade‐avoidance response in cereals, such as wheat and maize, is responsible for lodging in crowded plant communities. We discuss these processes with respect to the red‐ to far‐red light/phytochrome B relationships. Finally, we summarise the phytochrome B–phytohormone (auxin, brassinosteroids) connection within the cells of shaded Arabidopsis plants, and present a simple model to illustrate the shade‐avoidance syndrome. In addition, we address the relationship between plant density and health of the corresponding population, a topic that was raised for the first time by Sachs (1863) in his seminal paper and elaborated in his textbooks.     

Ontogenetic changes in the scaling of cellular respiration with respect to size among sunflower seedlings

The respiration rates R (oxygen uptake per min) and body mass M (mg per individual) of sunflower (Helianthus annuus L.) seedlings were measured for populations raised in the dark (scotomorphogenesis) and for plants subsequently grown in white light (photomorphogenesis) to determine the allometric (scaling) relationship for R vs. M. Based on ordinary least squares and reduced major axis regression protocols, cellular respiration rates were found to increase non-linearly as a ‘broken-stick’ curve of increasing M. During germination, the scaling was ca. 7.5-fold higher than after the emergence of the cotyledons from the seed coat, which can be attributed to the hypoxic conditions of the enclosed embryo. During seedling development, R was found to scale roughly as the 3/7 power of body mass (i.e., R ∼ M^−3/7), regardless of whether plants were grown in the dark or subsequently in white light. The numerical value of 3/7 statistically significantly differs from that reported across small field- or laboratory-grown plants (i.e., R ∼ M^−1.0). It also differs from the expectations of recent allometric theory (i.e., R ∼ M^−0.75 to M^−1.0). This difference is interpreted to be the result of species-specific tissue-compositions that affect the volume fractions of metabolically active and less active cells. These findings, which are supported by cytological and ultrastructural observations (i.e., scanning- and transmission electron micrographs), draw attention to the need to measure R of developing plants in a tissue- or organ-specific context.Key words: dark respiration, metabolic scaling, photomorphogenesis, oxygen uptake, skotomorphogenesis     

Alfred Russel Wallace

Alfred Russel Wallace The British naturalist Alfred Russel Wallace (1823–1913), well known as co‐discoverer of the “Darwinian” principle of natural selection, came from an ordinary background. Wallace left school aged 14 and never attended University. He became a land surveyor and studied, in his spare time, the works of the most famous naturalists of his age. After extensive expeditions (Amazon, 1848–1852; Southeast Asia, 1854–1862), Wallace spent the rest of his life in England as a free‐lance science writer. His contributions to systematics (he discovered/described many new species), evolutionary biology, zoogeography, anthropology and other branches of the live sciences are summarized in his 22 books and ca. 700 papers. Since Wallace became an adherent of spiritualism and mixed up supernatural phenomena with scientific facts in some of his later books, he remains a controversial figure in the history of the life sciences.     

Characterization of the Arion vulgaris pedal gland system

The most common European gastropod species, Arion vulgaris, is one of the most troublesome pests for private garden owners and commercial agriculturists. The sticky and hard to remove secretion produced by these animals allows them to overcome most artificial and natural barriers. However, this highly adherent biopolymer has recently shown great potential for novel wound-healing applications in medicine. Nevertheless, our knowledge of the underlying gland system is still limited and few studies on the ventral gland system are available. We studied the lateral and ventral pedal glands in Arion vulgaris to determine their secretory content histochemically and through lectin assays. Using these histological and histochemical methods we differentiate five gland types with different mucus composition in the lateral pedal region of the foot of Arion vulgaris. These contain sulphated and carboxylated mucosubstances (positive Alcian blue staining) but lack hexose-containing mucosubstances (negative PAS staining). In the ventral pedal region, four gland types can be differentiated producing sulphated and carboxylated mucosubstances. Within the ventral mucus, a high affinity for the lectins PNA and WGA is observed. While the lateral glands are histochemically negative for PAS, a positive staining with the lectin JAC is observed. Arion vulgaris shows clear morphological differences from other arionid species. This raises the question whether the variation in the chemistry of the secretory material and mucus composition is the result of different functions and/or is related to the animals' different environmental conditions. A comparison of some glands of Arion vulgaris with those of the helicid species Helix pomatia and Cepaea hortensis indicates morphological similarities.     

The Feeding Strategies of the Leech Erpobdella octoculata (L.): A Laboratory Study

The feeding behaviour of the freshwater leech Erpobdella octoculata was analysed by exposing potential invertebrate and vertebrate prey organisms (alive, wounded or dead) to leech attack in dishes, in the laboratory. The fact that E. octoculata is a macrophagous feeder that swallows living prey organisms whole (preferentially Chironomus larvae) is documented. However, it was repeatedly observed that adult leeches sucked the body fluids from wounded larvae. Likewise, cut pieces of earthworms, dead crustaceans and crushed water snails were attacked and the soft parts sucked in with the aid of the unarmed pharynx. Adult leeches sucked the body fluids from dead, decaying bodies of vertebrates (fish, newt larvae). Newly hatched young are blood suckers that rapidly attacked the wounded regions of Chironomus larvae and other invertebrates such as crushed water snails. It is concluded that the common leech E. octoculata is not only a predator, but also a fluid sucker and a scavenger. The ecological implications of this finding are discussed.     

Current status of technical protein refolding

The expression of heterologous proteins in microbial hosts frequently leads to the formation of insoluble aggregates. To fully exploit the production capacity of the cells, efficient strategies for further processing have to be developed. While in lab scale matrix assisted refolding techniques, especially of histidine-tagged proteins have become very popular, in production scale refolding by dilution is still predominant due to its simplicity. However scaling up dilution processes leads to large volumes and low protein concentration. This is a heavy burden both for liquid handling and for subsequent downstream processing steps. Process development aims to operate at uniform, reproducible conditions, to reduce costs to a minimum and to guarantee the required quality of the product. The general refolding kinetics, exploration of appropriate refolding conditions are reviewed. The major refolding operations such as dilution, matrix assisted refolding, pressure driven refolding or continuous refolding applications are discussed in view of industrial applicability.