Sources of the lipids in the bottom sediments of an English oligo-mesotrophic lake

SUMMARY. 1. The organic geochemistry of Coniston Water, a low productivity lake, has been investigated.
2. The relative inputs of the various known sources to different compound classes suggest terrestrial higher plants as the major source of sedimentary organic matter.
3. Early lipid diagenesis, proceeding in the bottom sediments as a result of microbial activity, produces relatively rapid changes, with shorter chain and unsaturated compounds being preferentially degraded.
4. Free and bound (acid liberated) lipids exhibit significant differences in composition, related to their respective sources and stability towards degradation.
5. The lipid composition of an aquatic higher plant, growing in the margins of the lake, has been determined; comparison with the sedimentary lipids reveal it not to be a significant source.     

How robust are Palearctic migrants to habitat loss and degradation in the Sahel?

The Sahel region of West Africa is an important wintering ground for Palearctic migrants. It is, however, undergoing significant anthropogenic degradation that is likely to reduce its value in this regard. Despite there being evidence that the populations of several Palearctic species may be determined by conditions on their Sahelian wintering grounds, there are almost no baseline data on their habitat use there and so the effects that habitat change might have on their future density and distribution cannot be determined. This study measured which habitat variables were associated with the presence of Common Whitethroat Sylvia communis, Lesser Whitethroat S. curruca and Subalpine Warbler S. cantillans by carrying out point counts and habitat measurements at 1861 points at 16 sites in northern Nigeria during the winters of 2001 and 2002. Common Whitethroats were most common at intermediate tree heights and densities of Salvadora persica (with this effect strongest in the pre‐migratory period), and increased as Balanites aegyptiaca density increased initially, although this effect levelled off at higher Balanites densities. Subalpine Warblers were most common at intermediate tree heights and Balanites densities, increased as Acacia and Salvadora density increased, decreased with tree density and were least common at intermediate shrub densities. Lesser Whitethroats were most common at intermediate tree heights, Acacia and Salvadora densities, increased with Balanites density, and decreased with tree density and diversity. The shallow slopes of the significant relationships found between Palearctic warbler species and habitat parameters suggest that the group may be robust to habitat degradation, with densities remaining relatively constant across a wide range of habitat types. Common Whitethroats, in particular, appear to be able to survive in extremely degraded habitats, yet may be vulnerable to the disappearance of Salvadora, the fruit of which may allow pre‐migratory fattening.     

Modifications to the photosynthetic apparatus of higher plants in response to changes in the light environment

A brief review of the photosynthetic apparatus of higher plants is given, followed by a consideration of the modifications induced in this apparatus by changes in light intensity and light quality. Possible strategies by which plants may optimize photosynthetic activity by both long- and short-term modifications of their photosynthetic apparatus in response to changing light regimes are discussed.     

The Effect of Inhibitors of Photosynthetic and Respiratory Electron Transport on Nitrate Reduction and Nitrite Accumulation in Excised Z. mays L. Leaves

The assimilation of nitrate and nitrite under dark and lightconditions in Zea mays L. leaves was investigated. Nitrate wasassimilated under dark-aerobic conditions. Anaerobiosis stimulatednitrate reduction and nitrite accumulation under dark conditions.Vacuum infiltration of inhibitors of respiratory electron transport,antimycin A and rotenone, stimulated nitrate reduction and nitriteaccumulation under dark-aerobic conditions. Vacuum infiltrationof low concentrations of PCP, DNP and mCCCP depressed nitratereduction and nitrite accumulation under dark-aerobic conditions,whereas, infiltration of higher concentrations stimulated nitratereduction and nitrite accumulation. The greatest level of nitrateand nitrite reduction occurred under light conditions. The inhibitorof photosynthetic electron transport, DCMU, stimulated the accumulationof nitrite in the light, but decreased nitrate reduction. Whenthe inhibitors of respiratory electron transport antimycin Aand rotenone, were supplied together with DCMU in the light,nitrite accumulation was enhanced. Low concentrations of mCCCPdecreased both nitrate reduction and nitrite accumulation underlight conditions when supplied with DCMU. Key words: Nitrate reduction, Nitrite accumulation, Leaves     

Evidence for a Calcium/Calmodulin Involvement in Density-Dependent Melanogenesis in Murine B16 Melanoma Cells

Previous work from our laboratory has shown that both cyclic AMP and calcium/calmodulin appear to be involved in the regulation of melanogenesis in murine B16 melanoma cells. In these cells as in murine Cloudman S91 cells, melanogenic responsiveness to melanocyte-stimulating hormone (MSH) varies with cell density in culture. Our objective in this study was to learn more about the intracellular systems involved in the control of melanogenesis, particularly the role played by calcium. The melanogenic response to αMSH was compared to the response to drugs affecting intracellular free calcium and calmodulin over a range of cell densities in B16F1 cells. αMSH-stimulated melanin production was extremely density-dependent but αMSH-stimulated cyclic AMP production was independent of cell density. The melanogenic response to agents that increased intracellular calcium (A23187) or inhibited intracellular calmodulin varied with cell density. A drug (TMB8) that lowered intracellular free calcium, however, increased melanogenesis independently of cell density. At high cell density it was found that an elevation in calcium decreased melanogenesis, whereas agents that reduced calcium or inhibited calmodulin activity increased melanogenesis. At low cell density, however, the inhibitory response to A23187 was lost and in some experiments even stimulated melanogenesis. These data suggest that the calcium/calmodulin signalling system has an inhibitory influence on melanogenesis, and its expression, which depends upon cell density, may also modulate the response to stimulatory agents such as αMSH.     

Leaf expansion of four sunflower (Helianthus annuus L) cultivars in relation to water deficits. I. Patterns during plant development

Abstract. The influence of a slow stress and recovery cycle on the pattern of leaf expansion in four diverse sunflower cultivars ( Helianthus annuus L. cvs. Hysun 31, Havasupai, Hopi and Seneca) was studied in a glasshouse. Stress had no significant effect on the time of flower bud emergence and anthesis, or on final leaf number, but delayed the appearance of leaves at high insertions in all cultivars except Hysun 31.
Leaf expansion was markedly reduced as the predawn leaf water potential decreased from −0.35 to −0.60 MPa, and the predawn turgor pressure decreased from 0.3 to 0.2 MPa, and expansion ceased at a predawn leaf water potential of about −1.0 MPa, i.e. when the predawn turgor pressure reached zero.
The leaves most reduced in final size when water was withheld were those at the insertions which grew the most rapidly in unstressed plants. The maximum reduction in final leaf size of 25–35% was similar in all cultivars and was due to retardation of the rate of leaf expansion: the duration of leaf expansion was actually increased by stress. However, leaves that were initiated during stress, but emerged after rewatering, had final leaf areas at least equal to those in the unstressed plants: in the cultivar Seneca, the final size of leaves of high insertion was significantly greater in stressed than unstressed plants, whereas in the three other cultivars the final leaf sizes were similar in both treatments. All four cultivars examined adjusted osmotically to the same degree, but leaf water potentials in one, Seneca, increased more rapidly after rewatering than in the other three, and this may have contributed to the greater relative leaf size in the leaves of high insertion in this cultivar.