Shoot multiplication in cultures of mature <Emphasis Type="Italic">Alnus glutinosa</Emphasis>

Shoot cultures were initiated from mature trees of Alnus glutinosa. On medium containing 1–5 μM 6-benzylamino purine (BAP), the shoots elongated without branching, formed heavy callus at the base of the stems and readily formed roots. The possibility that these characteristics could be attributed to the strong influence of endogenous auxin was tested on media that contained two auxin transport inhibitors, 1-N- naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), at concentrations of 0.1–3 μM, in combination with 2 μM BAP. On these media, shoots produced numerous branches, less callus and no roots. After 30 weeks (five subcultures) on this medium, leaves were smaller and showed signs of vitrification. These problems were resolved without detriment to shoot proliferation, by reverting to medium without NPA or TIBA. Shoots rooted readily after transfer to medium without growth regulators and were successfully acclimatised after transfer to soil.     

Coevolutionary arms races: increased host immune defense promotes specialization by avian fleas

We investigated the relationship between host defense and specialization by parasites in comparative analyses of bird fleas and T-cell mediated immune response of their avian hosts, showing that fleas with few main host species exploited hosts with weak or strong immune defenses, whereas flea species that parasitized a large number of host species only exploited hosts with weak immune responses. Hosts with strong immune responses were exploited by a larger number of flea species than hosts with weak responses. A path analysis model with an effect of T-cell response on the number of host species, or a model with host coloniality directly affecting host T-cell response, which in turn affected the number of host species used by fleas, best explained the data. Therefore, parasite specialization may have evolved in response to strong host defenses.     

Effects of water stress and nitrogen supply on leaf gas exchange and fluorescence parameters of <Emphasis Type="Italic">Sophora davidii</Emphasis> seedlings

Two-month-old seedlings of Sophora davidii were subjected to a randomized complete block design with three water (80, 40, and 20 % of water field capacity, i.e. FC₈₀, FC₄₀, and FC₂₀) and three N supply [N0: 0, Nl: 92 and Nh: 184 mg(N) kg⁻¹(soil)] regimes. Water stress produced decreased leaf area (LA) and photosynthetic pigment contents, inhibited photosynthetic efficiency, and induced photodamage in photosystem 2 (PS2), but increased specific leaf area (SLA). The decreased net photosynthetic rate (P _N) under medium water stress (FC₄₀) compared to control (FC₈₀) might result from stomatal limitations, but the decreased P _N under severe water deficit (FC₂₀) might be attributed to non-stomatal limitations. On the other hand, N supply could improve photosynthetic capacity by increasing LA and photosynthetic pigment contents, and enhancing photosynthetic efficiency under water deficit. Moreover, N supply did a little in alleviating photodamages to PS2 caused by water stress. Hence water stress was the primary limitation in photosynthetic processes of S. davidii seedlings, while the photosynthetic characters of seedlings exhibited positive responses to N supply. Appropriate N supply is recommended to improve photosynthetic efficiency and alleviate photodamage under water stress.     

Histochemistry of proteases in ependyma, choroid plexus and leptomeninges

Aminopeptidase M (APM), aminopeptidase A (APA), dipeptidyl peptidase IV (DPP IV) and gamma-glutamyl transferase (GGT) were demonstrated histochemically in cryostat sections of the rat brain to show the reaction pattern of ependyma, choroid plexus and leptomeninges. GGT was only demonstrable in the cell membranes of ependymal cells and in the leptomeninges; however, APA, APM and DAP IV showed a variable degree of activity in the capillary endothelium of the choroid plexus as well as in the leptomeninges. On the basis of these results, it is postulated that peptides in the cerebrospinal fluid can be cleaved extraventricularly by the enzymes demonstrated in the leptomeninges.     

Levels of organization in biology: on the nature and nomenclature of ecology's fourth level

Viewing the universe as being composed of hierarchically arranged systems is widely accepted as a useful model of reality. In ecology, three levels of organization are generally recognized: organisms, populations, and communities (biocoenoses). For half a century increasing numbers of ecologists have concluded that recognition of a fourth level would facilitate increased understanding of ecological phenomena. Sometimes the word "ecosystem" is used for this level, but this is arguably inappropriate. Since 1986, I and others have argued that the term "landscape" would be a suitable term for a level of organization defined as an ecological system containing more than one community type. However, "landscape" and "landscape level" continue to be used extensively by ecologists in the popular sense of a large expanse of space. I therefore now propose that the term "ecoscape" be used instead for this fourth level of organization. A clearly defined fourth level for ecology would focus attention on the emergent properties of this level, and maintain the spatial and temporal scale-free nature inherent in this hierarchy of organizational levels for living entities.     

Sulphur-oxidizing extracellular bacteria in the gills of Mytilidae associated with wood falls

Six morphotypes of small mussels (Bivalvia: Mytilidae) were found attached to naturally sunken wood collected in the Bohol Sea (Philippines). These specimens are related to the large Bathymodiolus mussels that are found worldwide at cold seeps and hydrothermal vents. In these habitats, the mytilids harbour sulphur- and methane-oxidizing endosymbionts in their gills and depend on the energy and carbon provided by the symbionts. In this study, bacteria associated with the gills of wood-associated mussels are characterized using molecular and microscopic techniques. The existence of bacteria in the lateral zone of gill filaments in all specimens is demonstrated. Comparative analyses of 16S rRNA gene and adenosine 5'-phosphosulphate (APS) reductase gene sequences indicate that the bacteria are closely related to sulphur-oxidizing endosymbionts of Bathymodiolus. FISHs using specific probes confirm that sulphur oxidizers are by far the most abundant, if not the only bacteria present. Electron micrographs displayed mostly extracellular bacteria located between microvilli at the apical surface of host gill epithelial cells all along the lateral zone of each gill filament. In some specimens, occasional occurrence of intracellular bacteria with similar morphology was noted. This study provides the first molecular evidence for the presence of possible thiotrophic symbiosis in sunken wood ecosystems. With their epibiotic bacteria, wood-associated mussels display a less integrated type of interaction than described in their seep, vent and whale fall relatives.     

Formation of 15alpha-hydroxyestriol and 15alpha-hydroxyestradiol from C19 15alpha-hydroxylated precursors in human pregnancy.

A mixture of 3H-15alpha-hydroxyandrostenedione and 14C-15alpha-hydroxydehydroisoandrosterone was injected intravenously into two subjects in the third trimester of pregnancy and, in a second study, directly into two fetuses in utero during transfusion for erythroblastosis fetalis. The urine was collected for 4-5 days and steroid conjugates in the urine were hydrolyzed into sulfate and glucosiduronate fractions. From the glucosiduronate fraction 15alpha-hydroxyestriol, 15alpha-hydroxyestradiol, 15alpha-hydroxyandrostenedione and 15alpha-hydroxydehydroisoandrosterone were isolated. No metabolites were identified in the sulfate fraction of the urine. A marked difference was observed in the metabolism of 15alpha-hydroxyandrostenedione and 15alpha-hydroxydehydroisoandrosterone which is dependent on the route of administration of the substrates. Both substrates were converted to 15alpha-hydroxyestriol and 15alpha-hydroxyestradiol, and the 3H/14C ratios and percentage conversions suggest that 15alpha-hydroxyandrostenedione seems to be a better precursor of the urinary 15alpha-hydroxylated estrogens than 15alpha-hydroxydehydroisoandrosterone. The 3H/14C ratios also suggest that 15alpha-hydroxydehydroisoandrosterone was converted to 15alpha-hydroxyestriol via 15alpha-hydroxyandrostenedione, and that the formation of 15alpha-hydroxyestradiol from 15alpha-hydroxydehydroisoandrosterone via 15alpha-hydroxyandrostenedione is a pathway of minor importance. Finally, 15alpha-hydroxydehydroisoandrosterone was recovered from the urine only when the precursors were injected into the maternal circulation. Also, an unknown metabolite containing only 14C was detected in the glucosiduronate fraction of the urine of each subject.     

Distribution of Assimilates from Various Source Leaves During the Development of Gladiolus grandiflorus

The distribution pattern of the products of photosynthesis wasstudied in gladiolus plants (Gladiolus grandiflorus cv Eurovision)in four stages of development I, plants having a very younginflorescence still enclosed between the leaves; II, plantswith a young inflorescence just emerged from the leaves, III,plants at full bloom, IV, plants with young fruits. The first,third or sixth foliage leaf was labelled with ¹⁴CO₂, and subsequentdistribution in the plant was determined Results were expressedas a percentage of translocated ¹⁴C accumulated by each partof the plant which gives a measure of its ‘sink strength’,or as ‘relative sink activity’ (RSA) which is independentof the size of the indicated organ. There are two competing sinks in the developing gladiolus—theinflorescence and the new corm. When RSA is the criterton theinflorescence constitutes the main sink irrespective of thesource leaf from the first stage until flowering. With the subsequentwilting of the flowers and fruit set RSA of the inflorescencedeclines rapidly and the new corm becomes the main sink When‘sink strength’ is the criterton it appears thatthe inflorescence acts as a very weak sink when it is youngand becomes increasingly stronger until flowering and then declinessteeply. Sink strength of the corm declines during the developmentof the inflorescence and then increases again steeply with wiltingof the flowers and fruit set. There are small differences betweenthe various source leaves. The young new corm acts as a strongsink for the lower foliage leaf and progressively weaker forupper leaves. Gladiolus grandiflorus, flower development, corm, assimilates distribution, sink strength, relative sink activity