Plant Physiology - Musienko M.M. 2001

Adaptation and plant resistance mechanisms
Salt tolerance

Approximately 9-10^e ha of all land on the planet is characterized by an elevated salt content. Structure/149.html">The problem of Salt Tolerance is also extremely relevant to our country, as the majority of irrigated lands, especially in the south of Ukraine, suffer from salinization. According to B.P. Stroganov, METABOLISM/2.html">THE CONCEPT OF salt tolerance should be divided into chloride tolerance, sulfate tolerance, carbonate tolerance, and so on; in other words, universal salt tolerance does not exist.

Wild and cultivated plants respond differently to The impact of various salts. Some plants can thrive even when The amount of soluble salts exceeds 1%.

Plants adapted to such conditions are called halophytes. They can withstand salinity levels exceeding 300 mM. Their adaptation to life on saline soils is achieved through various mechanisms. Accordingly, halophytes are divided into several groups: euhalophytes or true halophytes (for example, glasswort — Salicornia herbacea), which are capable of accumulating large amounts of salts in their vacuoles within their Tissues, up to 10% relative to the total Water content of the plant. For this reason, they develop high osmotic pressure and significant suction force, which enables them to absorb water in highly saline soils.

The second group consists of crinohalophytes or salt-excreting halophytes (for example, tamarisk shrubs — Tamarix speciosa). They excrete absorbed salts through specialized salt glands, the number of which increases with rising soil salinity. Salt-excreting halophytes do not feature succulent Organization, but they are characterized by a high Transpiration rate.

The third group includes glycohalophytes — salt-excluding halophytes (for example, wormwood — Artemisia salina), whose Cells maintain high osmotic pressure at the expense of photoassimilates, as their Cell membranes have low permeability to salts.

Cultivated plants have low salt tolerance; among cereals, sorghum (Andropogon sorghum) exhibits the highest resistance, while cotton, sunflowers, and watermelons show increased tolerance.

Plant salt tolerance depends on their ability to maintain ionic Homeostasis in the Cytosol under conditions of salinity. This ability implies that the molecular mechanisms regulating cellular metabolism function normally even at high external salt concentrations.

Salt ions that enter The Cell via passive transport are actively removed from the cytosol through energy-dependent processes. The primary mechanism of Active Transport is the H⁺-pump, which generates an Electrochemical Potential gradient, providing the proton-motive force for The transport of Na⁺ and Cl^- ions. Under salinity conditions, other ion pumps likely function in the Plasmalemma of halophytes alongside the H⁺-ATPase. The ion content in the cytosol is determined by both The rate of active transport and the barrier Functions of the membranes.

Salt stress is invariably combined with osmotic stress, leading to a loss of cellular turgor. In response to salinization, most plants react as follows:

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Recently, cell cultures have been increasingly utilized to study the Toxic effects of salts and cellular resistance mechanisms (Sidorov, 1992). During cellular adaptation to salt stress, the expression of a 26 kDa polypeptide Gene has been detected. The synthesis of this polypeptide is observed in sensitive cells only at later stages of adaptation or in resistant cell lines. It was found to exist in two forms — water-soluble (osmotin 1) and detergent-soluble (osmotin 2) in an approximate ratio of 2:3. It is believed that cellular mechanisms of salt resistance are similar in both in vitro cells and whole plants; therefore, cellular-level Selection opens up realistic possibilities for obtaining salt-tolerant plant varieties.

Overall, the genetic nature of plant salt tolerance selected through cell culture requires detailed investigation in the future. Although callus or suspension cultures are used for in vitro selection in most cases, The Use of isolated protoplast cultures is also feasible. Research into the CELLULAR AND MOLECULAR-Genetic foundations of resistance to salinity and other stress factors is currently regarded as a biotechnological alternative to traditional breeding.