Photo-oxidative Degradation of Chlorophyll-a and Unsaturated Lipids in Liposomal Dispersions at Low-Temperature

Liposomal dispersions in water were used as a tool to study photo-oxidation of chlorophyll-a and photo-oxidation of unsaturated lipids at 1 or 4°C. The presence of monogalactosyl diglyceride stimulated chlorophyll-a degradation. In addition the level of linolenic acid was decreased in liposomal dispersions containing chlorophyll-a, dipalmitoyl phosphatidyl choline, and monogalactosyl diglyceride, indicating that monogalactosyl diglyceride and chlorophyll-a were coupled in the preparations. In liposomal dispersions containing equal (molar) quantities of a-tocopherol, monogalactosyl diglyceride, and chlorophyll-a, a-tocopherol fully protected linolenic acid against photo-oxidative degradation, while chlorophyll-a degradation was only slightly reduced. In liposomal preparations containing a-tocopherol, chlorophyll-a and phosphatidyl choline, a-tocopherol catalyzed degradation of chlorophyll-a. Absorption spectra of the liposomal dispersions showed that the presence of a-tocopherol caused increased absorption in red light, which was attributed to structural changes in the liposomal preparations and thus could explain the noted effects. Tocopherol itself was rapidly degraded in chlorophyll-a containing liposomal preparations. Complex formation between chlorophyll-a and monogalactosyl diglyceride in chloroplasts is suggested and protection by a-tocopherol against photo-oxidation in chilling-sensitive plants; a suggestion which is founded on the similarities that exist between chloroplast preparations and liposomal preparations containing chlorophyll-a and monogalactosyl diglyceride as regards photo-oxidative degradation of chlorophyll-a, a-tocopherol and linolenic acid.     

Influence of ecdysterone, precocene and compounds with juvenile hormone activity on induction, termination and maintenance of diapause in the parasitoid wasp, Nasonia vitripennis

ABSTRACT. Using the Galleria bioassay, no difference could be found between the JH titre of diapausing and developing Nasonia larvae. Compared to the values found in some Lepidoptera, the JH titres in Nasonia larvae are low, c. 14 Galleria units/g live weight. Induction of diapause could not be brought about by topical application of JH I, JH analogues, precocene, or ecdysterone to the maternal generation, nor by treating eggs or larvae with compounds with JH activity. Diapause was easily terminated by topical application of ecdysterone, however. If ecdysterone treatment was preceded by JH-treatment, the percentage of larvae terminating diapause was reduced: JH II seems to be more potent than JH I or JH III in this effect if the interval between JH and ecdysterone treatment is 72 h.     

Evidence for the transfer of a soil‐borne contaminant from plants to ants via an aphid mediator

1. Uptake of environmental contaminants by lower trophic groups can have negative effects on higher trophic groups. This study tested the ability of selenium, an environmental contaminant found in high concentrations throughout the tissues of certain accumulating plants, to be transferred to ants via aphid tissue and honeydew. 2. Plants of the selenium accumulator, Raphanus sativus (wild radish), were watered with three different selenium treatments (0, 0.25 or 0.5 µg Se ml^?1). Aphids, Myzus persicae, and Argentine ant colonies, Linepithema humile, were added to each caged plant and allowed to interact freely. Ant colonies were supplemented with one of three different food options to encourage the consumption of aphids, aphid honeydew, or aphids and honeydew. 3. The accumulation of selenium by each trophic group and a trophic transfer factor (TTF) was calculated. The TTF for plants to aphids was > 1, indicating biomagnification, whereas the TTF for aphids to worker ants was < 1, indicating only biotransfer. Accumulated levels by worker ants did not statistically differ as a result of diet. 4. The amounts of selenium acquired by ants as a factor of diet and caste were compared. Plants, aphids and worker ants accumulated selenium in a dose‐dependent manner. Ant queens did not contain detectable amounts of selenium. Honeydew contained comparable amounts of selenium to plant selenium levels. 5. Access to toxic compounds via honeydew and insect protein may have negative effects on the range expansion of invasive species, such as the Argentine ant.     

The role of biofoam in shielding spittlebug nymphs (Insecta,Hemiptera, Cercopidae) against bright light

1. Biofoam in spittlebugs has traditionally been seen as a defence against predation and a microclimate that reduces the risks of overheating and drying out. This study addresses the possible role of the foam as a light attenuator. 2. Nymphs exhibit higher mortalities when reared under brighter light (1800–2000 lux) than under less bright light (600–800 lux). At all developmental stages, photoavoidance is strongest when the nymphs are depleted of foam covers. First‐ and second‐instar nymphs appear to be the most vulnerable to exposures by bright light. 3. Smaller bubbles are more effective as light attenuators than are larger ones. As younger instars possess smaller canals from which bubbles are released and, furthermore, exhibit higher concentrations of proteins in bubble liquid, they can produce smaller‐sized bubbles and their foams are more effective at reducing light than are those of older nymphs. 4. The findings of this study show that most of the visible and UV radiation is reflected by the foam: transmittance of visible light was 15% at 600 nm and 12% at 350 nm. 5. These results demonstrate that spittlebug foam also possesses properties that render it an effective barrier against potentially damaging solar radiation.     

Systematic revision of the subgenus Ceratitis MacLeay s.s. (Diptera, Tephritidae)

The fruit fly genus Ceratitis MacLeay (Diptera, Tephritidae) comprises several important pest species attacking a wide range of unrelated fruits. This is the third paper in a series revising the genus, and deals with representatives of the subgenus Ceratitis s.s . Eight species are recognized: Ceratitis brachychaeta Freidberg, C. caetrata Munro, C. capitata (Wiedemann), C. catoirii Guerin-Meneville, C. comuta (Bezzi), C. malgassa Munro, C. manjakatompo Hancock and C. pinax Munro. Lectotypes are designated for C. catoirii and C. pinax . A key for both sexes is provided, with illustrations of cephalic bristles, mesonotal and wing patterns, and shape of aculeus. All species are Afrotropical, except for 67. capitata , which has become widespread. The phylogeny and biogeography of Ceratitis s.s . are discussed, based on a cladistic analysis, and showing indications that the mediterranean fruit fly, C. capitata , may have its origins in eastern Africa. The relationship of this subgenus within the genus Ceratitis s.l . is also outlined.     

Community structure in temporary freshwater pools: disentangling the effects of habitat size and hydroregime

1. Hydroregime (duration, frequency and predictability of the aquatic phase) is a key feature of temporary aquatic habitats that not only moulds community structure and diversity (species sorting) but also life history characteristics of the inhabitants (natural selection). However, since hydroregime is a complex multidimensional entity that cannot be estimated from short term observations, morphometric variables are commonly used as proxies for hydroregime, making it impossible to separate effects of habitat size and hydroregime on biota.
2. We have used a simple hydrological model, validated with recent (average r ² = 96%) and historic water level observations (average r ² = 81%), to accurately reconstruct hydroregime based on historical rainfall and evaporation data in a cluster of 36 temporary rock pools in central South Africa.
3. Using the model output, we demonstrated that both hydroregime and habitat size had unique and shared effects on temporary pool biota and that these effects depended on the dispersal modes of the taxa. Model-generated hydrological data explained more variation in community patterns than short-term observations of hydroperiod. Hydroregime was more important for passive dispersers than for active dispersers that can migrate when pools dry up. Basin morphometry was a relatively poor predictor of pool hydroregime. We concluded that simple modelling may greatly improve the resolution of studies linking hydroregime to biological variables.
4. An accurate account of hydrological variation provides a firm foundation to understand community and population structure and dynamics in temporary aquatic habitats. Since many of these habitats have been destroyed or degraded in recent decades, our findings and tools may contribute to the development of reliable conservation guidelines.     

Intracellular distribution of 5' nucleotidase in rat liver

The intracellular distribution of 5' nucleotidase was investigated in rat liver by biochemical analysis of cell fractions obtained by differential centrifugation. The enzymatic activity was measured by determination of the inorganic phosphorus liberated from 5' nucleotides. The 5' nucleotidase activity was mainly found in the nuclear and microsomal fractions. An attempt to extract the enzyme from these fractions with Mg(++) ion solutions was unsuccessful. It is concluded that 5' nucleotidase is actually present in the nuclear and microsomal fractions of rat liver cells.