Plant Physiology - Musiyenko, M. M. 2001

Plant Adaptation and Resistance Mechanisms
Resistance and Adaptation

A sharp aggravation of the global ecological situation resulting from anthropogenic impact, global warming, and climate aridization makes Structure/149.html">The problem of adaptation and resilience one of the central issues in biology and modern plant physiology. This problem is particularly acute for Ukraine today, when the degradation of natural ecosystems—for example, in the steppe zone, the Chornobyl disaster zone, and As a result of mismanagement of land reclamation programs—leads to the complete degradation of natural ecosystems and changing environmental conditions. Significant progress in studying the mechanisms of adaptation and resilience of plant organisms has become possible due to the exploration of the Physiological aspects of this phenomenon, the expansion of methodological capabilities, and the integration of molecular genetic approaches into plant physiology. Although the resilience of living objects, including plants as an existing reality, is beyond doubt (after all, non-resilient forms of life do not exist), the term itself still lacks a clear definition in the literature.

Resilience is both an Organism's reaction to adverse factors and its ability to withstand stress loads, as well as the probability of the biological object's effective functioning, and a form or factor of the organism's reliability as a living system.

Breeders define plant resilience as The ability to maintain high productivity under unfavorable conditions; ecologists define it as the ability of a living system, through internal defense mechanisms, to resist external stress impacts, protect against them, and adapt to them without significant changes in Structural and functional parameters, or to quickly return to a stable, parastable state if this impact caused only a temporary deviation of the system from a given program. One way or another, resilience is associated with the idea of self-preservation, and each researcher infuses this concept with an element of individual approach. All these Definitions contain a grain of truth and subjectivity, given that resilience is an important property of the plant organism that conveys The phenomenon of life itself, and that Various Forms of resilience should be viewed within the Increasing complexity of evolutionary development. The ability of a plant organism to resist adverse influences reflects the measure of its reliability. What processes within the organism ensure its resilience?

On the one hand, this is undoubtedly METABOLISM as a totality of metabolic processes, the function of which is to provide the biosystem with energy and plastic substances. On the other hand, it is the perception, preservation, Processing, and utilization of information, that is, the genetic and physiological mechanisms regulating life activity. The Regulatory Systems of the organism primarily ensure the maintenance of a non-equilibrium stationary state, meaning an adequate supply of energy to the organism. The disruption of energy supply is the boundary of life, since a biological system, on the one hand, is open in nature, and on the other hand, is far from a state of equilibrium with the environment.

Maintaining a non-equilibrium stationary state is a necessary condition for life. High-quality functioning of the organism is possible within a relatively narrow range of fluctuations in external factors, under so-called adequate conditions. Viability under these conditions requires the engagement of additional regulatory mechanisms to ensure the stationary state of the internal environment, and subsequently the non-equilibrium stationary state as well. If this is impossible, the organism perishes. It is believed that the resilience of a system can be determined only in relation to one or more specific factors, but this does not yet mean that this system is stable.

Under THE CONCEPT OF stability, ecologists understand the sum of various forms of resilience over time. Stable systems cannot be non-resilient, but systems resilient to a particular factor are not necessarily stable. Stability is a generalized property of a living system that characterizes its normal development according to a genetic program under specific ecological conditions, whereas resilience is a specific property of a living system that characterizes its ability to withstand adverse impacts of a certain ecological factor (Holubets, 1992). They also differ in temporal and spatial parameters. Thus, stability is determined by the overall structural and functional Organization OF THE system throughout its entire existence, while resilience is associated with specific structural and functional indicators of the system, predominantly over a short period of time.

The term resilience should be used when it is necessary to determine how a particular factor currently affects an organism or living system, or how they preserve their properties or restore them after the NEGATIVE IMPACT OF an unfavorable factor.

Resilience manifests itself only when the organism is characterized by the reserve of adaptive memory required for a given situation, which enables it to realize its potential for survival. Therefore, to analyze the possible mechanisms of resilience, one must distinguish between the levels of adaptive capabilities.

Adaptation is possible only when the organism is able to demonstrate resilience at any level (from cellular to population) and adjust its life activity to new conditions.

A distinction is made between genetic adaptation, acclimation, acclimatization, and rapid adaptation.

Genetic adaptation occurs over many generations, utilizing all possible adaptation strategies, including Mutations. Other types of adaptation manifest only at the phenotypic level, meaning that the organism's adaptation occurs within the limits of information stored and implemented by the genotype.

Acclimatization is the process by which an organism adapts to changes in several environmental parameters under natural conditions.

Acclimation is the adaptation to one of them, for example, in phytotron conditions where all other factors are controlled.

Finally, rapid adaptation is an adaptation not associated with changes in Gene Expression or significant restructuring of cellular structures. Only the conformation of certain macromolecules, the level of enzyme activity, The Nature of their action change, along with shifts in Bioenergetics, pH, ion concentrations in cellular compartments, etc.

The level of resilience, and consequently its mechanism, is determined both by the intensity of the stress factor and The rate of its deviation from the norm, and by the degree of biochemical (molecular), physiological, and anatomical-morphological adaptation.

Biochemical or molecular adaptation manifests in Changes in the ionic and molecular COMPOSITION OF THE Cell solution and membrane structures, as well as in the strengthening of bonds between chemical components that determine the Structure of Cell membranes. The Structure of Nucleic Acids also changes, leading to an alteration in their functional activity. This type of adaptation causes a shift in the direction and intensity of action of many functional systems of The Cell. This is the primary PLANT RESPONSE TO stress. Resilience formed through such restructuring generally determines the physiological response at the level of the whole organism.

Physiological adaptation is a consequence of biochemical adaptation and manifests, for example, in changes in the intensity of Photosynthesis, Respiration, growth, and development, and ultimately productivity, which decreases under the action of stress factors. Prior to the appearance of the physiological response, changes occur at THE MOLECULAR LEVEL; The ratio of Catabolism to anabolism changes, as does the coupling of the cell's functional systems, particularly Organelles such as Chloroplasts and Mitochondria.

Anatomical and morphological adaptation manifests in Specific features of the anatomical and MORPHOLOGICAL STRUCTURE OF Cells, Tissues, individual Organs, and the organism as a whole, which evolved in response to various ecological conditions.

All these processes are aimed at maintaining the Homeostasis necessary for life activity (Musienko and Daskalyuk, 1991):

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An essential role in these processes is played by changes at the membrane level, particularly in Membrane Lipids, which create an appropriate microenvironment for enzyme activity. Modern theory of biochemical adaptation focuses primarily on enzyme systems that ensure the organism's life under unfavorable conditions (Hochachka and Somero, 1988).