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

High concentrations of sodium (Na + ), chloride (Cl - ), calcium (Ca 2+ ), and sulphate (SO 4 2- ) are frequently found in saline soils. Crop plants cannot successfully develop and produce because salt stress impairs the uptake of Ca 2+ , potassium (K + ), and water into plant cells. Different intracellular and extracellular ionic concentrations change with salinity, including those of Ca 2+ , 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. Ca 2+ 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 Ca 2+ concentration can rise to 10 times or more from its resting level of 50-100 nanomolar. Reactive oxygen species (ROS) are linked to the Ca 2+ alterations and are produced by stress. Depending on the type, frequency, and intensity of the stress, the cytosolic Ca 2+ signals oscillate, are transient, or persist for a longer period and exhibit specific "signatures". Both the influx and efflux of Ca 2+ affect the length and amplitude of the signal. According to several reports, under stress Ca 2+ alterations can occur not only in the cytoplasm of the cell but also in the cell walls, nucleus, and other cell organelles and the Ca 2+ 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 Ca 2+ , K + , and pH cause intracellular signaling and homeostasis. Similar mechanisms in the model plant Arabidopsis 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.