The Influence of Temperature on a K+-Channel and on a Carrier-Type Transporter in Nitella

Fisahn, J. and Hansen, U-P. 1986. The influence of temperatureon a K⁺ -channel and on a carrier type transporter in Nilella—J.exp. Bot. 37. 440–460. In Nitella, the effects of temperature on membrane potentialand on resistance consist of several components. The evaluationof their associated time-constants measured in linear(ized)temperature responses at a resting potential of–120 mVprovides an approach to their identification. For changes slowerthan c. 1 s, the temperature effect on membrane potential andresistance does not originate from temperature action on theinvolved transporter, but is mediated by signals from temperaturesensitive metabolic processes. In the case of potential, theseprocesses seem to be identical to those which also mediate thelight effect: pH-regulation, and two direct signals from photosynthesis,as indicated by the similarities of the related time-constants( respectively). The temperature effect on resistance displays only one time-constant of 40 sinmost experiments. The related process is unknown. The non-coincidenceof the time-constants of the effect on potential and on resistanceimplies the involvement of a carrier-type transporter (H+-pumpor cotransporter) in the effect on potential, and of a K+channelin the effect on resistance. The K+-channel is identified bythe reversal potential of the effect on membrane potential measuredin cells depolarized or hyperpolarized by an injected electricalcurrent Under these conditions the temperature effect on resistancedominates the effect on potential. Key words: H⁺-pump, K⁺-channel, kinetic analysis, Nitella, oscillation, pH-regulation, reversal, potential, temperature, time-constants     

Changes in the abundance and composition of cyclopoid copepods following fish manipulation in eutrophic Lake Væng, Denmark

1. The seasonal cycle of cyclopoid copepods during and following an approximately 50% reduction in planktivorous fish biomass was studied in shallow, eutrophic Lake Vaeng, Denmark, from 1986 to 1990. 2. The dominant cyclopoid copepods changed from Cyclops vicinus and Mesacyclops leuckarti during 1986–1989 to M. leuckarti and Megacyclops viridis in 1990. The abundance of cyclopoid copepods gradually increased from 1986 to 1988–89, decreased in autumn 1989 and markedly decreased in 1990. 3. The increase in the abundance of cyclopoid copepods from 1986 to 1988 is attributed mainly to the reduction in fish predation pressure, there being no concomitant increase in edible phytoplankton. The appearance of M. viridis in 1990, and the general decrease in cyclopoid copepod density in autumn 1989 and in 1990, are attributed to the appearance of submerged macrophytes. 4. Temperature, predation and availability of edible phytoplankton appear to determine whether C. vicinus or M. leuckarti dominates the cyclopoid copepod population of eutrophic Lake Væng.     

Seedling Growth and Storage Characteristics of Seeder and Resprouter Species of Mediterranean-type Ecosystems of S. W. Australia

Juvenile (2–4 years old) plants of a taxonomically diverserange of dicotyledonous species were examined following recruitmentfrom seed in recently burnt habitats in S.W. Australia. Obligateseeder species (those succumbing to fire) had on average, analmost threefold greater total plant d. wt and more than a fourfoldgreater shoot: root d. wt ratio than comparably-aged, cohabiting,resprouter species (those capable of surviving fire). Starchwas generally much more concentrated in root dry matter of resproutersthan seeders, and both categories exhibited greater starch storagecapacity in roots than shoots. Members of the Myrtaccae wereexceptional in not showing a greater root starch reserve inresprouter than in seeder species. and in carrying as high,or higher, starch levels in shoots as in roots. Anatomical investigationson roots provided instances of zero starch storage, storage,only in rays or in cortex, in rays and in xylem parenchyma,in rays and in cortex, or in all three locations. High starchratings of resprouter roots related mostly to higher starchgrain packing density at storage sites, but in certain instancesthese also reflected proportionally greater areas of tissuespecifically devoted to storage. Dry matter of shoots of bothseeders and resprouters generally contained higher levels ofN, P, K, Ca and Mg than that of roots, but there was no significantevidence of elements being more concentrated in resproutersthan in seeders. Fire response, seedlings, resprouter, obligate seeder, shoot: root ratio, starch storage, mineral nutrition     

The Effect of Fruiting upon Transpiration Rate and Stomatal Opening in Apple Leaves

The uptake of water by apple trees (Malus × domestica‘Golden Delicious’) was measured in a pot experiment and was found to be much greater in apple trees carrying many fruits than in comparable specimens without fruits. The main reason seemed to be differences in the transpiration rates of the leaves. This was corroborated by microscopic investigations which showed a higher degree of stomatal opening in the fruiting trees. In some cases minor reductions in water uptake per tree were caused by reducing the supplies of potassium and nitrogen.     

14C-studies on Apple Trees. IX. Seasonal Changes in the Formation of Fruit Constituents and their Subsequent Conversions

The formation and subsequent conversions of ¹⁴C-labelled compounds were followed in fruits of Malus domestica cvs. Golden Delicious and Cox's Orange Pippin after labelling proximate leaves with ¹⁴CO₂ at different times during the growing season. A few hours after labelling of the leaves, the larger share of fruit ¹⁴C was detected in sorbitol. This share descreased rapidly except in the late autumn. When labelling about 1 July (c. 1 month after bloom), 40–60% of the fruit ¹⁴C was permanently fixed in the methanol and water insoluble fraction. 25% or more was primarily found in organic acids, but this declined during the season to a few per cent. When labelling at the end of July, the dominating feature was the establishment of a peak of temporarily insoluble ¹⁴C, returning back to the soluble form through October and November. This was particularly pronounced in‘Cox's Organe Pippin'. Labelling with ¹⁴C at the end of August and at the end of September yielded increasing amounts of ¹⁴C in sugars. The labelling of fructose predominated, but as the autumn progressed the amount of label in sucrose increased. This was due to a conversion from ¹⁴C-compounds of older origin as well as to a larger share of the imported assimilates turning into sucrose at this time of the year. During prolonged storage of harvested fruits at 3°C, ¹⁴C in fructose increased at the expense of ¹⁴C in sucrose.     

Nest predation in Reed Buntings Emberiza schoeniclus: an experimental study

Predation is a major cause of nest failure in many bird species. High levels of nest loss may be a consequence of habitat fragmentation, leading to increased amounts of edge habitat. Yet the evidence for generally high nest predation rates along edges in fragmented landscapes is ambiguous. Using real nests of Reed Buntings Emberiza schoeniclus in which artificial Reed Bunting and real Japanese Quail Coturnix japonica eggs were placed, we experimentally tested for edge effects on nest predation in highly fragmented reed Phragmites sp. habitats in the Swiss lowlands. We also examined seasonal patterns of predation and the impacts of nest visits by observers. We found evidence for an edge effect at the water-sided reed edge, with nests located closer to the water being more likely to be predated than those further away. Predation probability increased from early to late season, suggesting that nest predation may be density dependent. Probability of nest predation was only weakly influenced by whether or not a nest was visited. Our results suggest that the intensive reed management currently applied in Swiss nature reserves may result in unnaturally high levels of nest losses in the Reed Bunting, because reed bands are not wide enough to allow nest placement at a safe distance from reed edges.     

RECENT BIOACOUSTIC PUBLICATIONS (2002 and earlier)

The vocal repertoire of the Asiatic Black Bear (Ursus thibetanus) has been poorly studied and until recently only two call types (chuffing and humming) have been described. Here I investigate the vocalizations of three wild orphaned cubs (two males and one female) reared by two observers in natural conditions in the Russian Far East. I grouped the calls into structural types, and then compared them with existing literature data on vocalizations of the same, as well as other species of the Ursidae family. In total, 1302 calls were classified visually from spectrograms into seven call types: whine, moan, yelp, grunt, snort, chuffing and humming. Classification results were verified with discriminant function analysis and randomization. I also fixed the presence of nonlinear phenomena (NLP) and articulation effects in calls. Whine was the most frequently recorded, as well as the most structurally variable call type due to a high rate of NLP. These results indicate that the vocal repertoire of the Asiatic Black Bear cubs is graded, but includes at least two discrete sound types. This work needs to be continued with further studies of vocalizations of cubs and adults of this species to verify the results of this preliminary study.     

Evaluating reproductive fitness and metabolic costs for insecticide resistance in Myzus persicae from Chile

The development of insecticide resistance in pest insects is an increasing problem for agriculture, forestry and public health. Aphids are ubiquitous herbivorous insects, with approximately 4700 known species, of which less than 5% exploit the agricultural environment successfully. Of these, the peach‐potato aphid Myzus persicae Sulzer is recognized as one of the most important pests worldwide because it has acquired resistance to many insecticides. Although resistance to insecticides provides important benefits for pests in agricultural fields that are treated with insecticides, it may be associated with fitness (or other) costs in environments that are insecticide free. In the present study, the fitness and energy costs that might be experienced by M. persicae in an insecticide‐free environment when carrying at least one insecticide resistance mutation (IRM), or by having an increased production of esterases, are evaluated. The study investigates whether genotypes that have an IRM also have enhanced esterase production, whether there is any metabolic cost associated with insecticide resistance, and whether there are any fitness costs associated with insecticide resistance and metabolic expenditure. The intrinsic rate of increase, standard metabolic rate (i.e. a measure of maintenance costs) and constitutive esterase activity are determined for 30 different multilocus genotypes carrying (or not carrying) at least one of the two most frequent insecticide resistance mutations (MACE and kdr/super‐kdr) that occur in Chile. The results show that genotypes carrying at least one IRM have higher levels of total esterase activity than genotypes without an IRM, that there is no evidence of an energy cost associated with total esterase activity or IRM, and no evidence for a reproductive fitness cost associated with total esterase activity, IRM or metabolic rate. The results agree with previous studies showing linkage disequilibrium between insecticide resistance mechanisms, although they contrast with those of studies that report fitness costs associated with insecticide resistance in Myzus persicae.