Indirect Immunofluorescence Microscopy of Microtubular Structures in Male Germ Cells of Wildtype and l(3)pl (lethal-polyploid) Drosophila hydei

Tubulin-containing structures of the male germ cells of Drosophila hydei crossreact in indirect immu-nofluorescence microscopy with antibody directed against homogeneous porcine brain tubulin. There is no detectable difference in reactivity between germ cells of wildtype flies and the mutant l(3)pl (lethal-polyploid) which is characterized by microtubular abnormalities. However, the technique of indirect immunofluorescence microscopy allows the direct visualization of several abnormalities in the arrangement of the microtubular system of the mutant, particularly in the axonemal complex.     

Temperature-dependent changes in circadian patterns of cricket premating behaviour

ABSTRACT. Male-calling and female-walking in Teleogryllus commodus (Walker) is mainly performed during the night (in LD 12:12 at constant temperature). Cold nights of 1–7°C switched both activities from night to daytime. After cold exposure it took several transient cycles until the original phase angle difference to lights-out was re-established. The involvement of a circadian clock in these processes was revealed by observing the free-running rhythm in constant light after a cold night. The rhythm was delayed, evidently due to the resetting of the biological clock by the cold exposure. This temporal alteration of premating behaviour in males and females is discussed in relation to intraspecific consequences, its adaptive value in natural conditions, and with respect to the potential parallel effects in parasites and predators.     

Degradation, Recycling, and Shedding of Trypanosoma brucei Variant Surface Glycoprotein

ABSTRACT. Trypanosoma brucei bloodstream forms express a densely packed surface coat consisting of identical variant surface glycoprotein (VSG) molecules. This surface coat is subject to antigenic variation by sequential expression of different VSG genes and thus enables the cells to escape the mammalian host's specific immune response. VSG turnover was investigated and compared with the antigen switching rate. Living cells were radiochemically labeled with either ¹²⁵I-Bolton-Hunter reagent or ³⁵S-methionine, and immunogold-surface labeled for electron microscopy studies. The fate of labeled VSG was studied during subsequent incubation or cultivation of labeled trypanosomes. Our data show that living cells slowly released VSG into the medium with a shedding rate of 2.2 ± 0.6% h⁻¹ (t_1/2= 33 ± 9 h). In contrast, VSG degradation accounted for only 0.3 ± 0.06% h⁻¹ (t_1/2= 237 ± 45 h) and followed the classical lysosomal pathway as judged by electron microscopy. Since VSG uptake by endocytosis was rather high, our data suggest that most of the endocytosed VSG was recycled to the surface membrane. These results indicate that shedding of VSG at a regular turnover rate is sufficient to remove the old VSG coat within one week, and no increase of the VSG turnover rate seems to be necessary during antigenic variation.     

Characteristics of Zinc Uptake by Barley Roots

The linear uptake of zinc by excised barley roots (Hordeum distichon L.) in the time range from 20–120 min is not continued over periods of 20–28 h. In concentration dependent uptake experiments with intact barley roots three phases in the range up to 1.38 mM zinc could be detected independent of the tested uptake period. The kinetic constants increased with higher phases and the transition points were lowered with increasing time. The presence of copper did not inhibit the uptake of zinc competitively. On the contrary a slight stimulation in the uptake rates was observed indicating an interaction with the transition site. It is concluded that zinc and copper are taken up by separate mechanisms.     

Seed quality effects in bulb onions (Allium cepa L.)

The nature and persistence of seed quality effects produced by a range of seed production treatments was investigated in the autumn-sown onion crop. Genotypically equivalent seed lots raised in different glasshouses within the same year were found to germinate at significantly different rates. The seed lot which emerged earlier produced larger seedlings and this difference in size persisted throughout the growing period. In a comparison between the effects of hand crossing and self-pollination techniques the hand crossing method produced a much lower total seed yield but heavier seeds and larger plants. The induced effects persisted throughout the year but were not significant in the mature bulb characters. The implications of these results upon the control of seed production for plant breeding and genetical experiments is discussed.     

Elevated volatile concentrations in high‐nutrient plants: do insect herbivores pay a high price for good food?

1. A tritrophic perspective is fundamental for understanding the drivers of insect–plant interactions. While host plant traits can directly affect insect herbivore performance by either inhibiting or altering the nutritional benefits of consumption, they can also have an indirect effect on herbivores by influencing rates of predation or parasitism. 2. Enhancing soil nutrients available to trees of the genus Eucalyptus consistently modifies plant traits, typically improving the nutritional quality of the foliage for insect herbivores. We hypothesised that resulting increases in volatile essential oils could have an indirect negative effect on eucalypt‐feeding herbivores by providing their natural enemies with stronger host/prey location cues. 3. Eucalyptus tereticornis Smith seedlings were grown under low‐ and high‐nutrient conditions and the consequences for the release of volatile cues from damaged plants were examined. The influence of 1,8‐cineole (the major volatile terpene in many Eucalyptus species) on rates of predation on model caterpillars in the field was then examined. 4. It was found that the emission of cineole increased significantly after damage (artificial or herbivore), but continued only when damage was sustained by herbivore feeding. Importantly, more cineole was emitted from high‐ than low‐nutrient seedlings given an equivalent amount of damage. In the field, predation was significantly greater on model caterpillars baited with cineole than on unbaited models. 5. These findings are consistent with the hypothesis that any performance benefits insect herbivores derive from feeding on high‐nutrient eucalypt foliage could be at least partially offset by an increased risk of predation or parasitism via increased emission of attractive volatiles.     

Foliar application of nitrate or ammonium as sole nitrogen supply in Ricinus communis. II. The flows of cations, chloride and abscisic acid

Following a precultivation with pedospheric nitrogen nutrition, Ricinus plants were supplied with nitrogen solely by spraying nitrate or ammonium solution onto the leaves during the experimental period. The chemical composition of tissues, xylem and phloem exudates was determined and on the basis of the previously determined nitrogen flows (Peuke et al., New Phytologist (1998), 138 , 657–687) the flows of potassium, sodium, magnesium, calcium, chloride and ABA were modelled. These data, which permit quantification of net-uptake, transport in xylem and phloem, and utilization in shoot and root, were compared with results obtained in plants with pedospherically-supplied nitrate or ammonium and data in the literature. Although the overall effects on the chemical composition of supplying ammonium to the leaves were not as pronounced as in pedospherically supplied plants, there were some typical responses of plants fed with ammonium (ammonium syndrome). In particular, in ammonium-sprayed plants uptake and transport of magnesium decreased and chloride uptake was increased compared with nitrate-sprayed plants. Furthermore, acropetal ABA transport in the xylem in ammonium-sprayed Ricinus was threefold higher than in nitrate-sprayed plants. Additionally, concentrations of anions were more or less increased in tissues, particularly in the roots, and transport fluids. The overall signal from ammonium-sprayed leaves without a direct effect of ammonium ions on uptake and transport systems in the root is discussed.