ECOLOGICAL BIOCHEMISTRY - Study Guide - V. M. Isaenko 2005

Chapter 8. RESISTANCE AND ADAPTATION OF PLANTS AND ANIMALS

8.1. General Concepts of Resistance, Adaptation, Organismal Stability, and Stress Responses

Technological accidents and disasters, land reclamation and other engineering works, careless attitudes toward environmental conservation measures, etc., have led to a significant deterioration of ecosystems. In this context, the Resistance and Adaptation of organisms are of paramount importance.

Organismal resistance is The ability to withstand (defend against) The impact of adverse factors without disrupting normal vital activity; it is a reliability factor of living systems. In this sense, resistance characterizes the functioning of organisms. The extraordinary diversity of life on Earth is a testament to this resistance, as unstable life forms cannot survive.

Resistance is primarily ensured by the complex network of metabolic reactions and energy transformations. Genetic and physiological mechanisms for maintaining resistance, perceiving environmental cues, and responding adequately are also crucial. While resistance characterizes the ability to withstand a specific factor, stability is a broader, more generalized property of living organisms that defines their development under specific ecological conditions. Furthermore, resistance is associated with countering negative impacts only for a limited time—precisely when protective capacities must be deployed for survival. Stability, however, ensures normal physiological function throughout the entire lifespan.

Adaptation is the ability of organisms to adjust to changing environmental conditions while simultaneously increasing their chances of survival and reproduction. In turn, adaptation is only possible if organisms possess underlying resistance.

Several types of adaptation are distinguished. Genetic adaptation occurs over multiple generations, manifests at the population (species) level, and is implemented through Mechanisms of Genetic Variability and heredity. Biochemical adaptation leads to adjustments in chemical composition, METABOLISM, and energy transformation in response to habitat conditions. Biochemical adaptation underpins physiological adaptation—a suite of organismal reactions that ensure functional adjustment. Anatomical and morphological adaptation is manifested in the Structural Features of both the Organism as a whole and individual Cells in particular.

Rapid cellular adaptation does not involve genetic-level changes; instead, it results in specific alterations in enzyme activity, ionic composition, and other cellular parameters.

Acclimatization, as The process of adjusting to multiple environmental factors under natural conditions, is also a form of adaptation.

Resistance and the immediate manifestation of protective properties are closely linked to THE CONCEPT OF stress—a set of nonspecific changes occurring in organisms under The Influence of various factors, involving the reorganization of defense mechanisms. These factors (stressors) are categorized into physical (low or high Temperature, humidity, light, electromagnetic, ionizing, and Other types of radiation), chemical (salts, acids, various xenobiotics), and biological factors (predators for animals, competition, pests, pathogens, etc.).

Primary nonspecific processes (stress responses) occurring at THE CELLULAR LEVEL include the Disintegration of polyribosomes; macromolecule biodegradation driven by enhanced hydrolytic and other processes; increased membrane permeability; promotion of free-radical processes; suppression (and in some cases enhancement) of biosynthetic processes; uncoupling of oxidation and phosphorylation in Cell/35.html">Mitochondria, leading to reduced ATP synthesis; and wasteful ATP consumption.

One of the most essential organismal responses to stress is the synthesis of stress Proteins. These are specific Polypeptides absent under normal conditions that are synthesized transiently (over the course of several hours) exclusively in response to stress. These proteins play a protective or adaptive role.

Stress resistance depends on the phase of ontogenesis, with young organisms being the most vulnerable. Several Phases of the organismal stress response are distinguished. If the stressor does not reach a certain threshold level, adaptation processes may occur, leading to resistance against that negative factor. Once a sub-threshold stressor ceases, the organism's Functions can fully recover. Supra-threshold stress levels, however, can cause fatal damage. Notably, the simultaneous action of multiple stressors can produce a synergistic effect, whereby one stressor amplifies the impact of another.

To prevent stress-induced damage, organisms rely on a stabilization system based on Homeostasis—a complex set of adaptive reactions aimed at eliminating (or maximally limiting) the impact of factors that disrupt the relative dynamic equilibrium of the internal environment.

Conversely, to mitigate damage that has already occurred, There is a repair system operating at various levels. For example, at THE MOLECULAR LEVEL, this involves enzymatic DNA Repair, while at the organismal level, it involves organ regeneration.

It has been established that organisms can synthesize specific stress proteins in response to various environmental shifts (temperature, humidity, oxygen levels, xenobiotics, etc.) that are not produced under normal conditions. Gene Expression under stress is a relatively rapid organismal response, with stress proteins synthesized within minutes of exposure to adverse conditions and continuing over several hours. These proteins are believed to play a key role in forming protective and adaptive functions.