Response to stress

Heavy equipment had passed over the site of failure initiation shortly before the rupture was discovered. It is probable that stresses associated with the heavy equipment initiated a fracture in the severely corroded pipe bottom. Once the fracture initiated, it propagated down the length of the line in response to stresses imposed by internal pressure. 

In addition to reproductive effects, fish exposed to endocrine disrupters may have a decreased response to stress or decreased growth and metabolism which can affect their ability to survive, or to defend themselves against predators. All of these factors can affect the ability of the species to survive and to reproduce itself in sufficient numbers to maintain the stocks on which our commercial and sport fisheries are based. Not all fish species will be equally susceptible to the effects of endocrine disrupters. Selective sensitivity to such effects, especially those affecting reproduction, may well lead to major changes in the flora and fauna of some of our major aquatic ecosystems as the balance between fish, mammals, invertebrates and plants, and between predators and prey, is destabilised... 

By calculating the energy to heat it is possible to determine the vibration levels to which the structure can be exposed and still exhibit critical damping. There is one area that must be evaluated. Plastics exhibit a spectrum of response to stress and there are certain straining rates that the material will react to almost elastically. If this characteristic response corresponds to a frequency to which the structure is exposed the damping effect is minimal and the structure may be destroyed. In order to avoid the possibility of this occurring, it is desirable to have a curve of energy absorption vs. frequency for the material that will be used. 

Pepin et al. (1992) generated transgenic mice in which antisense RNA complementary to GR cDNA led to reduced expression mostly in neuronal tissues. Consequently, this was found to result in an impaired behavior, a defective response to stress as well as in obesity. King et al. (1995) generated transgenic mice where reduced GR expression was limited to the thymus. This leads to an altered thymocyte development, changes in the T-cell repertoire, and a reduced risk to develop autoimmune diseases. 

Family of transcription factors that modulate the expression of genes which control immune, inflammatory, and acute-phase responses, as well as cell growth, responses to stress, apoptosis, and oncogenesis. All members of this family have a Rel-homology domain that contains sequences responsible for dimerization and DNA binding. In vertebrates, this family includes NF-kB1 (also known as p50), NF-kB2 (also known as p52), Rel (also known as cRel), Rel-A (also known as p65), and Rel-B. 

Physiologic stress evokes a molecular response essential to protecting the human body from cellular injury and death. Over the last two decades, molecular determinants of cellular responses to stress have become better understood, as well as their relationship to human health, development, aging, and disease. Molecular re-... 

River functioning (globally expressed as metabolism) does not often show unidirectional responses to stress, and therefore makes difficult the prediction of changes. Gross Primary Production (GPP) may be first enhanced because the decrease of water flow may result in shallower water depths and lead to more underwater light... 

In recent years the extended controversy concerning the appropriate terminology to use in studies of plant responses to stressful environments (e.g. Kramer, 1980 Levitt, 1980 Harper, 1982) has often detracted attention from the identification and understanding of underlying principles. Despite this it is useful at this stage to outline the main concepts involved and attempt to provide a generally acceptable common framework for further discussions. 

The techniques of molecular biology have particular potential for rapidly introducing small numbers of single genes. Unfortunately there is strong evidence that the complex compensation mechanisms that exist in plants, and the interactions between different whole-plant and biochemical responses to stress, will make the direct improvement of environmental stress tolerance in crop plants by genetic engineering rather more difficult... 

Whole-plant responses to stress in natural and agricultural systems... 

After describing some of the main implications of Plant Strategy Theory for the study of stress responses, brief accounts are provided of two additional dimensions of variation in plant response to stress these consist of stored growth and resistance to mechanical stress. 

The search for a predictive model of plant responses to stress... 

A quite different approach to the study of plant responses to stress has been explored by those ecologists who have followed the example of Harper (1977) in applying to plants techniques originally deployed in investigations of animal populations. Here the methodology has been demographic and the resulting data have allowed responses to stress to be analysed in terms of fluctuations in the rates of mortality and recruitment of either plant populations or plant parts (e.g. leaves, inflorescences). 

This clearly overstates the potential of demographic study to provide a mechanistic understanding of plant responses to environments and, if implemented, would lead to unnecessary delay in the development of generalising principles. The remainder of this chapter is founded on the assumption that the most direct route to a coherent predictive theory of plant responses to stress is likely to involve a synthesis of insights derived from plant population biology, ecophysiology, and many other fields of botanical endeavour. 

In addition to the mechanisms of stress response so far considered, there are several others which have attracted the attention of plant ecologists. These include innate or environmentally determined forms of dormancy in seeds, spores, and vegetative buds, many of which represent adaptive responses restricting plant growth and development to favourable seasons or sites. Dormancy has been the subject of numerous publications and will not be considered here. Instead, opportunity will be taken to refer to two forms of plant response to stress which until recently have received only scarce attention. The first is the phenomenon of stored growth whilst the second involves the response of the developing shoot to mechanical impedance. 

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