Environmental extremes

The sensitivity of cellular constituents to environmental extremes places another constraint on the reactions of metabolism. The rate at which cellular reactions proceed is a very important factor in maintenance of the living state. However, the common ways chemists accelerate reactions are not available to cells the temperature cannot be raised, acid or base cannot be added, the pressure cannot be elevated, and concentrations cannot be dramatically increased. Instead, biomolecular catalysts mediate cellular reactions. These catalysts, called enzymes, accelerate the reaction rates many orders of magnitude and, by selecting the substances undergoing reaction, determine the specific reaction taking place. Virtually every metabolic reaction is served by an enzyme whose sole biological purpose is to catalyze its specific reaction (Figure 1.19). 

The effects of environmental extremes on ecosystems The considerations of the effects of wind on structural damage in ecosystems conforms with the strict mechanical ideas about stress and strain. Such an approach can be expanded to consider the effects of extreme environmental conditions on ecosystem responses. An emphasis on the term extremes encourages the use of exact quantities and circumvents the use of the term stress. 

Ek osystem recovery from environmental extremes The examples which illustrated the responses of agricultural ecosystems to extreme events have been limited to short-term effects on productivity. For natural ecosystems which can not be replanted the recovery response to an environmental extreme is crucial, not only in the time taken for recovery but also in terms of the manner in which the ecosystem may change during and after the period of recovery. In this context, change is particularly concerned with the species which constitute an ecosystem, a consideration which is central to the aims of conservation. 

Thymus caespitosus Brot. occurs on the northwestern Iberian Peninsula and on the Madeiran and Azorean archipelagos. One of the Azores group is Sao Jorge, a small island, located at ca. 38°40 N, 28°03 W, with an area of about 246km and a width that does not exceed 10km at any point (see Fig. 2.27 for location of Azores). The island possesses a uniform climate and offers little in the way of environmental extremes. It is thus of some interest that significant quantitative chemical variation... 

Non-oxide ceramics such as silicon carbide (SiC), silicon nitride (SijN ), and boron nitride (BN) offer a wide variety of unique physical properties such as high hardness and high structural stability under environmental extremes, as well as varied electronic and optical properties. These advantageous properties provide the driving force for intense research efforts directed toward developing new practical applications for these materials. These efforts occur despite the considerable expense often associated with their initial preparation and subsequent transformation into finished products. 

Some critics of current commercial production methods suggest that antibiotics are necessary only because of the stressful rearing conditions and that the return to more extensive rearing systems would obviate the need for antibiotics. Returning to the extensive animal rearing systems would result in exposure to greater environmental extremes and increase the exposure to internal parasites and the associated susceptibility to diseases hence would increase rather than decrease the response to antibacterial agents. 

It is well documented that cysts (in general) can be highly resistant to environmental extremes (1, 12, 23). In the context of this discussion, however, the relevant extremes are those to which motile cells would have been exposed had they not encysted. 

Here again we find ourselves tempted to accept the easy answer that encystment is a necessary mechanism developed by a species to ensure survival through environmental extremes. If it is true that the species would have been capable of survival in many areas without resorting to dormancy, the ecological justification for encystment may then lie in more subtle factors, possibly those associated with genetic recombination during sexuality. 

When transferring fuel and fuel additives from storage to the pump and to its final point of use, different types of lines and hoses are utilized. Mild steel, stainless steel, and cross-linked polyethylene hose are the typical materials of construction used. These materials withstand the temperature and environmental extremes of outdoor installation and are compatible with fuels and most additives. 

Political influence on agency actions are part andparcel of policies in all developed nations, but the effect of environmental extremism on policy is more pronounced in Sweden than in most other countries. Why so ... 

Genetic resource Genetic material serving as a resource for human use. For plants, this includes modern cultivars (varieties), landraces, and wild and weedy relatives of crop species and the genes that these plants contain. Plant breeders and genetic engineers rely on a broad, diverse genetic base to enhance crop yields, quality, or adaptation to environmental extremes. 

Tolerance of a green alga, Scenedesmus komarekii, to environmental extremes... 

SRB are essentially ubiquitous in aqueous environments that contain organic carbon and sulfate (e.g., subsurface aquifers and lake sediments). Moreover, analysis of a key gene associated with sulfate reduction (dissimilatory sulfite reductase) indicates that microbial sulfate reduction is an ancient trait, suggesting that organisms may have contributed to sulfide mineral formation throughout much of Earth history (Wagner et al. 1998). SRB are tolerant to environmental extremes of heat (some are hyperthermophiles) and salinity (some are halophiles). 

The present chapter focuses on the effects of environmental stress on enzyme structure and function and the various mechanisms that respond to these stresses to alter enzyme function (and metabolic pathways). Many examples will be drawn from animals that live at environmental extremes, for it is here that we find the principles of enzyme structure and function most clearly illustrated. Because this subject is complex and covers a wide variety of different fields, the present chapter will highlight key principles using selected enzymes as examples. The reader is referred to other sources for more exhaustive treatments of individual topics in comparative biochemistry and enzyme adaptation (Crowe and Clegg, 1978 Ho-chachka and Somero, 1984 Gilles, 1985 Bowler and Fuller, 1987 Storey, 1988 Storey and Storey, 1988). 

Active wood-destroying sphaeromatids are found in warm temperate-tropical waters. They exhibit tolerance to a range of environmental extremes, including short periods of desiccation in hot conditions when wood is exposed, plus the ability to withstand very low salinity conditions for days at a time. 

Chelurids are widely distributed, and Chelura terebrans is found in wood in temperate and subtropical waters. Wood infested by both limnoriids and chelurids normally has the chelurid population closer to the surface while the limnoriids inhabit the deeper region. Chelurids are also less tolerant of environmental extremes and do not survive long in conditions of low salinity or low oxygen. 

---