Ion Changes and Signaling under Salt Stress in Wheat and Other Important Crops

High concentrations of sodium (Na⁺), chloride (Cl⁻), calcium (Ca²⁺), and sulphate (SO₄²⁻) are frequently found in saline soils. Crop plants cannot successfully develop and produce because salt stress impairs the uptake of Ca²⁺, potassium (K⁺), and water into plant cells. Different intracellular and extracellular ionic concentrations change with salinity, including those of Ca²⁺, K⁺, and protons. These cations serve as stress signaling molecules in addition to being essential for ionic homeostasis and nutrition. Maintaining an appropriate K⁺:Na⁺ ratio is one crucial plant mechanism for salt tolerance, which is a complicated trait. Another important mechanism is the ability for fast extrusion of Na⁺ from the cytosol. Ca²⁺ is established as a ubiquitous secondary messenger, which transmits various stress signals into metabolic alterations that cause adaptive responses. When plants are under stress, the cytosolic-free Ca²⁺ concentration can rise to 10 times or more from its resting level of 50–100 nanomolar. Reactive oxygen species (ROS) are linked to the Ca²⁺ alterations and are produced by stress. Depending on the type, frequency, and intensity of the stress, the cytosolic Ca²⁺ signals oscillate, are transient, or persist for a longer period and exhibit specific “signatures”. Both the influx and efflux of Ca²⁺ affect the length and amplitude of the signal. According to several reports, under stress Ca²⁺ alterations can occur not only in the cytoplasm of the cell but also in the cell walls, nucleus, and other cell organelles and the Ca²⁺ waves propagate through the whole plant. Here, we will focus on how wheat and other important crops absorb Na⁺, K⁺, and Cl⁻ when plants are under salt stress, as well as how Ca²⁺, K⁺, and pH cause intracellular signaling and homeostasis. Similar mechanisms in the model plant <i>Arabidopsis</i> will also be considered. Knowledge of these processes is important for understanding how plants react to salinity stress and for the development of tolerant crops.