PLANT ADAPTATION TO ANTHROPOGENIC FACTORS - 2017

1. GENERAL CHARACTERISTICS OF ADAPTIVE RESPONSES. BASIC CONCEPTS OF ADAPTATION DEVELOPMENT

An obligatory property of any Organism, including plants, is The ability to protect itself against adverse abiotic and biotic environmental factors. This function emerged simultaneously with the appearance of the first living creatures and evolved and improved throughout subsequent evolution. Resistance is manifested only when an organism possesses the reserve of adaptive "memory" required for a given situation, which enables it to realize its survival potential. Therefore, to analyze potential resistance mechanisms, one must distinguish between the levels of adaptive capabilities.

Adaptation is a set of morphological, physiological, and biochemical primary adaptive responses that ensure species-specific plant survival under vertical and biotic interactions, as well as under conditions unfavorable for a given species. Adaptation is possible only when an organism is capable of exhibiting resistance at any level (from cellular to population) and adjusting its vital activity to new conditions.

All adaptation processes are aimed at maintaining the Homeostasis necessary for the organism's vital activity. Living nature is characterized by adaptive capabilities that arose in the course of evolution. Lamarck understood evolution as the direct inheritance of acquired adaptive traits. Darwin considered natural Selection of living forms best adapted to the conditions of various communities and ecosystems as the driving force of evolution. Adaptivity and purposiveness as a constant driving force underlie non-Darwinian theories of evolution—orthogenesis and nomogenesis (Eimer, Berg). According to Darwin, "adaptation" was the term most frequently used by 19th-century biologists.

Today, adaptation remains at the center of major debates regarding The Nature of Gene and heredity, the limits of allowable alterations to Earth's natural resources, and the possibility of survival under conditions of escalating anthropogenic ecological stress.

The adaptation of any organism to specific living conditions in an individual is achieved through genetic adaptation, acclimatization, and rapid adaptation.

Genetic adaptation occurs over many generations. This process utilizes all possible adaptation strategies, including Mutations. That is, adaptive responses occur not only at the phenotypic level, but also at The Genome level.

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 whereby an organism adapts to changes in multiple environmental parameters under natural conditions.

Acclimation is ADAPTATION TO A single factor, for instance, under phytotron conditions where all other parameters remain constant.

Acclimatization and acclimation are generally accompanied by changes in Gene Expression, leading to the appearance in Cells of Proteins that are unusual under other conditions. However, information about these proteins already exists in the organism's genome rather than appearing de novo.

Finally, rapid adaptation is 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, Bioenergetics, pH, and ion concentrations in cellular compartments change.

The level of resistance, and consequently its adaptation 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 as Changes in the ionic and molecular COMPOSITION OF THE Cell sap 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, altering their functional activity. This type of adaptation causes a shift in the direction and intensity of many functional cell systems. This is The Essence of the primary PLANT RESPONSE TO stress. Resistance formed through such restructuring ultimately determines the physiological response at the whole-organism level.

Physiological adaptation is a consequence of biochemical adaptation and manifests, for example, in changes in the intensity of Photosynthesis, Respiration, growth, development, and ultimately productivity, which decreases under the action of stress factors. Prior to the appearance of a physiological response, changes occur at THE MOLECULAR LEVEL; The ratio of Catabolism to anabolic processes changes, as does the coupling of functional cell systems, particularly Organelles such as METABOLISM/14.html">Chloroplasts and Mitochondria.

Anatomical-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 under various ecological conditions.

Despite The Diversity of environmental conditions and the immense number of individual plant reaction variants, any adaptation can be described based on three fundamental concepts.

The first of these is the reflex theory, created in the penultimate century by Russian scientists. Its main elements include the perception of an external signal, Processing of the received information—that is, Translation into the "internal" language of cell (organ) biochemistry—and The formation of an adequate response that increases the likelihood of survival under altered conditions. The chain of events from the perception of an external signal, through its processing, to transmission to effector working organs that complete the response to environmental changes can be viewed as a system of elementary primary adaptive reactions.

The second is the concept of source-sink relations. In the absence of a Central Nervous system in plants, source-sink relations serve as the primary mechanism for the operational integration of producing and consuming structures under constantly changing environmental conditions. Primary adaptive plant responses are integrated into source-sink systems, which represent a fully self-sufficient system of interaction between spatially and functionally separated plant structures. It is within the framework of the source-sink system that a balanced exchange of resources occurs between the producing and consuming parts of plants. Source-sink systems are highly plastic and respond both to EXTERNAL FACTORS AND to changes in the functional activity of various plant parts. For example, a growing leaf consumes photoassimilates from the outside (acting as a sink), whereas a fully developed leaf exports photosynthetic products and acts as a source. One of the simplest source-sink systems is a seedling, where the aboveground part supplies photoassimilates to the ROOT, and the root supplies the aboveground part with mineral nutrients and Water. A. T. Mokronosov suggested calling such self-sufficient source-sink systems source-sink units. In mature, differentiated plants containing vegetative and generative shoots, root suckers, and other functionally distinct structures, quite A large number of source-sink units can coexist simultaneously.

The third is the concept of adaptive strategy types. This theoretical framework analyzes the Morphology/3.html">MAIN DIRECTIONS OF resource allocation in plants: where precisely, to which processes or structures, and to which source-sink units resources are "allocated" first. The three MAIN TYPES OF plant "strategic behavior" systems (according to Ramensky and Grime)—competitors ("lions"), stress-tolerators ("camels"), and ruderales ("jackals")—are quite clearly distinguished by their main flows of material-energy resources and, accordingly, external manifestations of adaptation. British researcher E. Pianka developed THE CONCEPT OF two polar types, K and r, which are distinguished by the proportion of life energy used for reproduction. In the first case (K), the plant's main life energy goes toward maintaining vegetative activity (growth and maintaining the adult organism), whereas In the second case (r), a large amount of energy is used for reproduction, for "producing" a large number of offspring scattered at random, allowing the species to survive through a powerful "seed bank."

Combining both concepts, plants can be divided into the following types:

K-strategists (competitors) - maintain vegetative growth (biomass accumulation) under moderate environmental stress and high plant cover productivity. The main adaptive process is the maintenance of vegetative growth;

S-strategists (stress-tolerators) - upon exposure to a stressor, halt current growth and slow the transition to flowering; consequently, resources are not allocated to seed formation, and the bulk of resources is expended on adaptation processes, which may not manifest in morphological changes (e.g., increased energy costs for respiration, maintaining membrane gradients under drought or soil salinity);

R-strategists (ruderales) - under stress conditions, cease visible growth, shorten or completely eliminate juvenile phases, which leads to accelerated flowering and seed formation. The main adaptive process is the allocation of all available resources to seeds.