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排序方式: 共有160条查询结果,搜索用时 15 毫秒
1.
T. Fatima Mitterboeck Sarah J. Adamowicz 《Proceedings. Biological sciences / The Royal Society》2013,280(1767)
The loss of flight ability has occurred thousands of times independently during insect evolution. Flight loss may be linked to higher molecular evolutionary rates because of reductions in effective population sizes (Ne) and relaxed selective constraints. Reduced dispersal ability increases population subdivision, may decrease geographical range size and increases (sub)population extinction risk, thus leading to an expected reduction in Ne. Additionally, flight loss in birds has been linked to higher molecular rates of energy-related genes, probably owing to relaxed selective constraints on energy metabolism. We tested for an association between insect flight loss and molecular rates through comparative analysis in 49 phylogenetically independent transitions spanning multiple taxa, including moths, flies, beetles, mayflies, stick insects, stoneflies, scorpionflies and caddisflies, using available nuclear and mitochondrial protein-coding DNA sequences. We estimated the rate of molecular evolution of flightless (FL) and related flight-capable lineages by ratios of non-synonymous-to-synonymous substitutions (dN/dS) and overall substitution rates (OSRs). Across multiple instances of flight loss, we show a significant pattern of higher dN/dS ratios and OSRs in FL lineages in mitochondrial but not nuclear genes. These patterns may be explained by relaxed selective constraints in FL ectotherms relating to energy metabolism, possibly in combination with reduced Ne. 相似文献
2.
Paola G. Andreis Piera Rebuffat Anna S. Belloni Giuliano Neri Letizia Cavallini Giuseppe Gottardo Giuseppina Mazzocchi Alberta Coi Ludwik K. Malendowicz Dr. Gastone G. Nussdorfer 《Cell and tissue research》1989,258(1):43-51
Summary The morphology and function of isolated inner (zona fasciculata/reticularis) adrenocortical cells of rats pretreated with ACTH for 3, 6, 9 or 12 days were investigated. ACTH treatment induced a notable time-dependent enhancement in the steroidogenic capacity (corticosterone production) and growth of inner cells. The volumes of cells, mitochondrial compartment, membrane space [the cellular space occupied by smooth endoplasmic reticulum (SER) membranes] and lipid-droplet compartment, as well as the surface area of mitochondrial cristae and SER tubules, were increased in relation to the duration of ACTH pretreatment, and showed a highly significant positive linear correlation with both basal and stimulated corticosterone production. The acute exposure of isolated cells to ACTH provoked a striking lipid-droplet depletion, the extent of which was linearly and positively correlated with stimulated corticosterone secretion. The hypertrophy of the mitochondrial compartment and SER are interpreted as the morphological counterpart of the enhanced steroidogenic capacity of inner adrenocortical cells, inasmuch as the enzymes of steroid synthesis are located in these two organelles, and it is well known that chronic ACTH exposure stimulates the de novo synthesis of many of them in vivo. The rise in the number of lipid droplets, in which cholesterol is stored, is interpreted as being due to the fact that, under chronic ACTH treatment, the processes leading to cholesterol accumulation in adrenocortical cells (exogenous uptake and endogenous synthesis) exceed those of its utilization in basal steroid secretion. Cholesterol accumulated in lipid droplets as a reserve material may be rapidly utilized after acute ACTH exposure to meet the needs of the enhanced steroidogenic capacity of adrenocortical cells. 相似文献
3.
Ludwik K. Malendowicz 《Cell and tissue research》1974,151(4):525-536
Summary Adrenal glands of adult female rats are heavier than the glands of corresponding male rats. Postpubertal orchiectomy increases the adrenal weight, an effect restored by testosterone replacement. Under the same conditions ovariectomy of 8 weeks duration does not change the adrenal weight while estradiol replacement enhances the relative adrenal weight.Karyometric studies have shown that nuclei in the female zona fasciculata cells are larger (app. 18%) than those of the male. Similar but only slight differences (2%) were observed in the zona reticularis. Orchiectomy results in enlargement of cell nuclei within all zones of the adrenal cortex; testosterone replacement has the opposite effect. Ovariectomy of 8 weeks duration slightly enhances the volume of nuclei of the zona glomerulosa cells, has no effect on the nuclei of the zona fasciculata and reduces the volume of nuclei in the zona reticularis. Estradiol replacement reduces the volume of nuclei of the zona glomerulosa cells but increases nuclear volume in the zona fasciculata and in the zona reticularis.Thus testosterone has an inhibitory effect on the adrenal cortex of the rat while the physiologic effect of estradiol on the morphology of this gland, particularly on the zona fasciculata cells is rather dubious.The author wishes to thank Mrs. B. Westerska and Miss K. Siejak for excellent technical assistance.This research was supported in part by a grant from the Zoological Committee, 2nd Department, Polish Academy of Sciences.This paper is dedicated to the memory of late Kazimierz Mietkiewski, M.D., Ph.D. whose encouragements and suggestions were most stimulating for my work. 相似文献
4.
5.
Cardenas-Navarro R; Adamowicz S; Gojon A; Robin P 《Journal of experimental botany》1999,50(334):625-635
The effects of light and NO3- nutrition on
15NO3- influx in roots were
investigated in young, 19-d-old, induced tomato plants grown at a constant
air and solution temperature of 20C. Nitrate
influx was measured by 15N accumulation for 5 min,
on plants exposed to a wide range of exogenous concentrations, from 10 x
10-3 to 30 mol m-3. Influx
kinetics, fitted to the data following a non-linear procedure, showed
multiphasic patterns. The best fits were obtained when three pure and
non-additive Michaelis-Menten kinetics were applied, with phase transitions
at approximately 0.8 and 4 mol m-3. In plants grown
at 3.0 mol m-3 NO3-, the
asymptotic maximum influx rate (Imax) of each phase
declined during the night until 24 h darkness. At the end of the day
period, about a 2-fold enhancement of Imax was
observed when plants were pretreated for 3 d with 0.2 instead of 3.0 mol
m-3 NO3-. The influx rates
measured at any given NO3- concentration and the
Imax for any phase showed a negative non-linear
correlation with plant nitrate concentration. Furthermore, the results
suggest the existence of a set point, approximately 66 mol
m-3 plant nitrate, for which influx is null at any
given solution nitrate concentration. A model using modified
Michaelis-Menten kinetics is proposed to predict the influx rate as a
function of both solution and plant NO3-
concentrations. 相似文献
6.
7.
This study provides C-value (haploid nuclear DNA content) estimates for 31 species of ladybird beetles (representing 6 subfamilies and 8 tribes), the first such data for the family Coccinellidae. Despite their unparalleled diversity, the Coleoptera have been very poorly studied in terms of genome size variation, such that even this relatively modest sample of species makes the Coccinellidae the third best studied family of beetles, behind the Tenebrionidae and Chrysomelidae. The present study provides a comparison of patterns of genome size variation with these two relatively well-studied families. No correlation was found between genome size and body size in the ladybirds, in contrast to some other invertebrate groups but in keeping with findings for other beetle families. However, there is some indication that developmental time and/or feeding ecology is related to genome size in this group. Some phylogenetic patterns and possible associations with subgenomic features are also discussed. 相似文献
8.
It has long been known that polyploid organisms are more prevalent in arctic than in temperate environments. Past explanations for this geographical trend have focused on the role of glacial cycles in generating polyploids and the influence of abiotic factors in favouring polyploidy in the north. In combination, these mechanisms probably suffice to explain the observed geographical cline in ploidy levels in members of the Daphnia pulex complex in the Holarctic. While only diploid members of the D. pulex complex are found in the temperate regions of North America and Europe, allozyme and DNA quantification analyses indicate that the southern Argentine pulex-complex fauna is dominated by polyploids. Indeed, the present study is the first to document the presence of polyploid members of the D. pulex complex in any temperate climate. The results of phylogeographic analyses suggest that this difference in polyploid distribution between the northern and southern hemispheres is based more on ecological and historical contingencies than direct selection for polyploidy. Specifically, competition with diploid relatives probably limits the lower latitudinal range of polyploids in the north, but appears not to have occurred in Argentina. Because of these differences, the present study provides important insights into the diverse factors that determine the distributions and evolutionary fates of polyploid organisms. 相似文献
9.
Diurnal nitrate uptake in young tomato (Lycopersicon esculentum Mill.) plants: test of a feedback-based model 总被引:3,自引:0,他引:3
A simple model is proposed to describe diurnal net nitrate uptake rate
patterns observed experimentally on young plants grown under constant
non-limiting nutrition. It rests on two hypotheses: net uptake rate is
under negative feedback control by internal plant nitrate content, and
nitrogen metabolism occurs only during the light period. The model
parameters were determined from the results of three independent
experiments performed under non-disturbing conditions in a growth room at
constant air and solution temperatures. Net hourly nitrate uptake rate was
measured through a diurnal cycle and after an extended 28 h period of
darkness. It increased continuously during the light period and decreased
during the dark period. Under prolonged darkness, net uptake declined to an
asymptotic positive uptake rate of about 10-5 mol
h-1 g-1 total plant dry
weight. The measured hourly nitrate uptake rate values were consistent with
independent determinations of long-term nitrate and total N accumulations
in the plant. Realistic simulations of experimental data are achieved with
the proposed model. Furthermore, the maintenance of a positive net uptake
rate, measured in non-growing plants subjected to prolonged darkness, is
explained in the model by the continuous increase of plant water content.
The importance of the diurnal variations of plant water content for nitrate
uptake rate is emphasized and gives consistency to the homeostasis
hypothesis of the model. The diurnal changes in nitrate uptake predicted by
the model are strongly dependent on the assumption made for diurnal changes
in nitrate assimilation. While the purely photosynthetic assumption is
convenient, a more realistic metabolism sub-model is
needed. 相似文献
10.