PubMed Health⌕ Search

Biomedical subjects

J Agrell

Publications and source records attributed to J Agrell.

6 recordsLinked to original sources
PubMed2005

Within-plant variation in induced defence in developing leaves of cotton plants.

According to optimal defence theory (ODT) plants should invest in stronger defence in the most valuable parts, such as reproductive or young tissue. Cotton plants are known to express high resistance to herbivore feeding in the developing leaves at the top of the plant after herbivore-damage. Cotton plants also have developing leaves on side shoots from the nodes all along the plant. This allowed us to investigate within-plant distribution of defence between younger tissues at different locations on the plant. We found that all developing leaves showed increased resistance to feeding by larvae of the generalist moth Spodoptera littoralis after herbivore damage to leaves of the plant. An increase in the concentration of secondary compounds, terpenoid aldehydes, was found in developing leaves both at the top of the plant and on the side shoots. However, the resistance was stronger in the top leaves than in the side shoot leaves, showing that there is intra-plant variation in the induced response between different leaves of the same age. After the initial damage, larval feeding mainly occurred on the older, fully developed true leaves. Furthermore, the herbivore-induced resistance in the developing leaves reduced upward movement of feeding larvae on the plant and reduced the feeding on the upper parts of the plant over a period of at least 6 days. The plant thus benefits from defending all developing leaves by directing feeding to older, less valuable leaves and lower parts of the plant. The observed distribution of defence within cotton plants supports ODT.

Age Factors↗
PubMed2002

Metabolic rate and thermal conductance of lemmings from high-arctic Canada and Siberia.

The arctic climate places high demands on the energy metabolism of its inhabitants. We measured resting (RMR) and basal metabolic rates (BMR), body temperatures, and dry and wet thermal conductances in summer morphs of the lemmings Dicrostonyx groenlandicus and Lemmus trimucronatus in arctic Canada, and the BMR of D. torquatus, D. groenlandicus, L. sibiricus, L. bungei and L. trimucronatus in Siberia. In contrast to previous studies the data were collected on animals that had spent only a limited time in captivity. All parameters were analysed in relation to the variations in body mass (20-90 g). Body temperature and BMR were lower in D. groenlandicus than L. trimucronatus, which coincides with greater longevity in the former species. Wet and dry thermal conductances of both species were similar and comparable with those of other Myomorpha (mouse-type rodents), indicating no evidence for a previously claimed lower thermal conductance in lemmings. BMR in lemmings appeared to be higher than in other Arvicolidae (voles, lemmings and muskrats), which could relate to their typically high-latitude distribution. However, the more southerly living Lemmus species had higher BMR than the more northerly living Dicrostonyx species, which may be explained by the former having a relatively low-quality diet.

Animals↗
PubMed1995

Delayed density-dependence in a small-rodent population.

The role of delayed density-dependent processes in the dynamics of animal populations poses a problem for ecologists; although generally assumed important in populations that show cyclic or chaotic fluctuations, little experimental evidence for such processes exist. Through manipulation of vole densities within enclosed areas it was shown that reproduction, recruitment, and body growth rate in introduced populations were negatively affected by high previous density. In addition, female movement patterns shifted, and territoriality as well as home-range size was increased after high density. The observed changes in female spacing-behaviour suggested that negative effects of previous density were partly mediated by social interactions, and agreed with the finding that smaller (less competitive) females were the ones suffering most from increased competition. Contrary to expectations from recent work, predation could be excluded as the cause of delayed density-dependence in this study. Instead, chemical analyses of a dominating food plant suggested that herbivory at high vole-density had delayed negative effects on food quality.

Animals↗
PubMed1979

Evaluation of commercial enzyme reagent kits by use of a semiautomated chemistry analyzer.

The overall performances of several enzyme reagent kits for alkaline phosphatase, creatine kinase, lactic dehydrogenase, and aspartate aminotransferase were evaluated using an ABA-100 Bichromatic Analyzer. Interassay precision using this instrument with commercial reagents compared well with published data for similar analyses performed at university hospitals and referral laboratories. Significantly poorer precision with lower limits of linearity was observed when reagents recommended for use at 30 C were used at 37 C. Significant differences in measured levels of creatine kinase, lactic dehydrogenase, and aspartate aminotransferase due to different lots of expendable cuvettes were found for elevated levels of these enzymes. All kit reagents met manufacturers' claims for stability; however, different absolute levels of lactic dehydrogenase were observed with one kit reagent on successive days. Slight hemolysis affected creatine kinase levels measured with some reagent kits significantly more than others.

Alkaline Phosphatase↗