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Very Different Levels (very + different_level)
Selected AbstractsA CENTENNIAL CELEBRATION FOR QUANTITATIVE GENETICSEVOLUTION, Issue 5 2007Derek A. Roff Quantitative genetics is at or is fast approaching its centennial. In this perspective I consider five current issues pertinent to the application of quantitative genetics to evolutionary theory. First, I discuss the utility of a quantitative genetic perspective in describing genetic variation at two very different levels of resolution, (1) in natural, free-ranging populations and (2) to describe variation at the level of DNA transcription. Whereas quantitative genetics can serve as a very useful descriptor of genetic variation, its greater usefulness is in predicting evolutionary change, particularly when used in the first instance (wild populations). Second, I review the contributions of Quantitative trait loci (QLT) analysis in determining the number of loci and distribution of their genetic effects, the possible importance of identifying specific genes, and the ability of the multivariate breeder's equation to predict the results of bivariate selection experiments. QLT analyses appear to indicate that genetic effects are skewed, that at least 20 loci are generally involved, with an unknown number of alleles, and that a few loci have major effects. However, epistatic effects are common, which means that such loci might not have population-wide major effects: this question waits upon (QTL) analyses conducted on more than a few inbred lines. Third, I examine the importance of research into the action of specific genes on traits. Although great progress has been made in identifying specific genes contributing to trait variation, the high level of gene interactions underlying quantitative traits makes it unlikely that in the near future we will have mechanistic models for such traits, or that these would have greater predictive power than quantitative genetic models. In the fourth section I present evidence that the results of bivariate selection experiments when selection is antagonistic to the genetic covariance are frequently not well predicted by the multivariate breeder's equation. Bivariate experiments that combine both selection and functional analyses are urgently needed. Finally, I discuss the importance of gaining more insight, both theoretical and empirical, on the evolution of the G and P matrices. [source] Treatment with oxidizing agents damages the inner membrane of spores of Bacillus subtilis and sensitizes spores to subsequent stressJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2004D.E. Cortezzo Abstract Aims:, To determine if treatment of Bacillus subtilis spores with a variety of oxidizing agents causes damage to the spore's inner membrane. Methods and Results:, Spores of B. subtilis were killed 80,99% with wet heat or a variety of oxidizing agents, including betadine, chlorine dioxide, cumene hydroperoxide, hydrogen peroxide, OxoneTM, ozone, sodium hypochlorite and t-butylhydroperoxide, and the agents neutralized and/or removed. Survivors of spores pretreated with oxidizing agents exhibited increased sensitivity to killing by a normally minimal lethal heat treatment, while spores pretreated with wet heat did not. In addition, spores treated with wet heat or the oxidizing agents, except sodium hypochlorite, were more sensitive to high NaCl in plating media than were untreated spores. The core region of spores treated with at least two oxidizing agents was also penetrated much more readily by methylamine than was the core of untreated spores, and spores treated with oxidizing agents but not wet heat germinated faster with dodecylamine than did untreated spores. Spores of strains with very different levels of unsaturated fatty acids in their inner membrane exhibited essentially identical resistance to oxidizing agents. Conclusions:, Treatment of spores with oxidizing agents has been suggested to cause damage to the spore's inner membrane, a membrane whose integrity is essential for spore viability. The sensitization of spores to killing by heat and to high salt after pretreatment with oxidizing agents is consistent with and supports this suggestion. Presumably mild pretreatment with oxidizing agents causes some damage to the spore's inner membrane. While this damage may not be lethal under normal conditions, the damaged inner membrane may be less able to maintain its integrity, when dormant spores are exposed to high temperature or when germinated spores are faced with osmotic stress. Triggering of spore germination by dodecylamine likely involves action by this agent on the spore's inner membrane allowing release of the spore core's depot of dipicolinic acid. Presumably dodecylamine more readily alters the permeability of a damaged inner membrane and thus more readily triggers germination of spores pretreated with oxidizing agents. Damage to the inner spore membrane by oxidizing agents is also consistent with the more rapid penetration of methylamine into the core of treated spores, as the inner membrane is likely the crucial permeability barrier to methylamine entry into the spore core. As spores of strains with very different levels of unsaturated fatty acids in their inner membrane exhibited essentially identical resistance to oxidizing agents, it is not through oxidation of unsaturated fatty acids that oxidizing agents kill and/or damage spores. Perhaps these agents work by causing oxidative damage to key proteins in the spore's inner membrane. Significance and Impact of the Study:, The more rapid heat killing and germination with dodecylamine, the greater permeability of the spore core and the osmotic stress sensitivity in outgrowth of spores pretreated with oxidizing agents is consistent with such agents causing damage to the spore's inner membrane, even if this damage is not lethal under normal conditions. It may be possible to take advantage of this phenomenon to devise improved, less costly regimens for spore inactivation. [source] Magnitude of nighttime transpiration does not affect plant growth or nutrition in well-watered ArabidopsisPHYSIOLOGIA PLANTARUM, Issue 3 2009Mairgareth A. Christman Significant water loss occurs throughout the night via partially open stomata in many C3 and C4 plant species. Although apparently wasteful in terms of water use, nighttime transpiration (Enight) is hypothesized to benefit plants by enhancing nutrient supply. We tested the hypothesis that plants with greater Enight would have improved plant nutrient status and greater fitness, estimated as pre-bolting biomass, for Arabidopsis thaliana. Two very different levels of Enight were generated in plants by exposing them to high vs low nighttime leaf-to-air vapor pressure deficits (VPDleaf) in controlled environment chambers. An assessment of responses of nighttime leaf conductance (gnight) to VPDleaf indicated that Enight differed by at least 80% between the treatments. This large difference in Enight, imposed over the entire vegetative growth phase of Arabidopsis, had no effect on leaf nutrient content (N, Ca, K) or pre-bolting rosette biomass. The lack of response to differences in Enight held true for both a high and a low nitrogen (N) treatment, even though the low N treatment decreased leaf N and biomass by 40,60%. The N treatment had no effect on gnight. Thus, higher Enight did not provide a nutrient or growth benefit to Arabidopsis, even when the plants were N-limited. [source] Immunocytochemical mapping and quantification of expression of a putative type 1 serotonin receptor in the crayfish nervous systemTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 3 2005Nadja Spitzer Abstract Serotonin is an important neurotransmitter that is involved in modulation of sensory, motor, and higher functions in many species. In the crayfish, which has been developed as a model for nervous system function for over a century, serotonin modulates several identified circuits. Although the cellular and circuit effects of serotonin have been extensively studied, little is known about the receptors that mediate these signals. Physiological data indicate that identified crustacean cells and circuits are modulated via several different serotonin receptors. We describe the detailed immunocytochemical localization of the crustacean type 1 serotonin receptor, 5-HT1crust, throughout the crayfish nerve cord and on abdominal superficial flexor muscles. 5-HT1crust is widely distributed in somata, including those of several identified neurons, and neuropil, suggesting both synaptic and neurohormonal roles. Individual animals show very different levels of 5-HT1crust immunoreactivity (5-HT1crustir) ranging from preparations with hundreds of labeled cells per ganglion to some containing only a handful of 5-HT1crustir cells in the entire nerve cord. The interanimal variability in 5-HT1crustir is great, but individual nerve cords show a consistent level of labeling between ganglia. Quantitative RT-PCR shows that 5-HT1crust mRNA levels between animals are also variable but do not directly correlate with 5-HT1crustir levels. Although there is no correlation of 5-HT1crust expression with gender, social status, molting or feeding, dominant animals show significantly greater variability than subordinates. Functional analysis of 5-HT1crust in combination with this immunocytochemical map will aid further understanding of this receptor's role in the actions of serotonin on identified circuits and cells. J. Comp. Neurol. 484:261,282, 2005. © 2005 Wiley-Liss, Inc. [source] | ||||||||||