Plant Salinity Tolerance

Abstract

Soil salinity is one of the major abiotic stresses limiting plant growth and resulting in crop yield reductions. The adverse effects of salinity stress on plant growth happens in two phases: the osmotic phase, which occurs immediately after salt stress and results in a rapid inhibition in plant growth; and the ionic phase, which occurs after several days or weeks of salt stress, when ions accumulate to high toxic concentrations in the shoot and affects shoot function. Plants have evolved several mechanisms to deal with salt stress, which can be divided into three mechanisms: osmotic tolerance, ion exclusion and tissue tolerance. Key Concepts Osmotic stress causes a rapid and immediate inhibition of plant growth as a result of high salt concentration around the roots. Ionic stress occurs after several days or weeks of salt exposure, when Na + accumulates in the shoot to toxic concentrations. Osmotic tolerance is the ability of plants to maintain growth immediately after salt stress; it appears as an ability to better maintain growth and stomatal opening. Ion exclusion is the ability to exclude Na + from the shoots by the roots, to prevent accumulation of Na + in the shoot; it depends on the up‐ and downregulation of specific ion transporters to control the amount of Na + being transported to the shoot. Tissue tolerance is the ability of plants to tolerate elevated levels of Na + in the shoot; it requires Na + compartmentalisation into the vacuole and accumulation of compatible solutes in the cytoplasm. Halophytes are plants native to saline environments and that have high salinity tolerance. Glycophytes are salt‐sensitive plants, being a large majority of plants. Stomatal closure is closing of the stomatal pores to prevent water loss during salt and drought stress; it is stimulated by ABA, among other triggers Vacuolar Na + sequestration is an important tissue tolerance mechanism; It involves Na + transport from cytosol into vacuole to help maintain low cytosolic Na + . Salt bladders arise from epidermal cells; they are modified trichomes and provide an important mechanism of salt exclusion from the main part of leaves in halophytes.

Field Crop Responses and Management Strategies to Mitigate Soil Salinity in Modern Agriculture: A Review

“…Salinity stress significantly negatively impacts plant growth and development (Table 1); however, plants' responses can differ according to the extent of the plant's stress and the plant's growth stage. Overall, salinity affects plant growth in two phases [41]. The first phase of a decrease in plant growth occurs within minutes, where a high concentration of salts reduces the water uptake and growth rate due to the osmotic effects.…”

“…Because stomatal guard cells possess a range of mechano-sensitive ion channels, they could potentially transduce a change in the xylem pressure caused by salinity into altered stomatal apertures [48,49]. Furthermore, plants grown under salt stress suffer physiological and metabolic changes such as reduced enzyme activity, CO 2 assimilation, protein biosynthesis, leaves water relations, and photosystem II (PS II) [41,50].…”

“…In the second phase of growth reduction, salts accumulate in plant leaves, reaching threshold levels and causing toxicity. This phase is longer and can take a few days up to weeks or even months to complete [41]. During the second phase of growth reduction, higher Na + accumulation in the intracellular spaces can inhibit the enzymatic activities.…”

“…Studies showed that the functions of the bio-macromolecules are significantly influenced by the ionic strength and the electrostatic interactions of the cytoplasmic solution [54]. As a result, plants under the second phase of growth reduction show chlorosis, necrosis, premature leaf senescence and reduced leaf area due to the reduction in the photosynthetic activity and the overall cell metabolism [41]. The threshold level of ion toxicity varies for plant species and even among cultivars and hybrids.…”

The Drought-Mediated Soybean GmNAC085 Functions as a Positive Regulator of Plant Response to Salinity

“…Unfortunately, it is predicted that salinity will continue to spread to other parts of the world in the near future as a consequence of climate change and inappropriate farming practices [3]. It is known that under stress conditions, various biological processes in plants are negatively affected, including reduction in shoot growth, photosynthesis and biomass accumulation; promotion of senescence; and decrease in seed quantity and quality [4][5][6]. From an agricultural perspective, yield loss not only threatens global food security but also reduces the income of farmers.…”