An Insight into Abiotic Stress and Influx Tolerance Mechanisms in Plants to Cope in Saline Environments

Abstract

Salinity is significant abiotic stress that affects the majority of agricultural, irrigated, and cultivated land. It is an issue of global importance, causing many socio-economic problems. Salt stress mainly occurs due to two factors: (1) soil type and (2) irrigation water. It is a major environmental constraint, limiting crop growth, plant productivity, and agricultural yield. Soil salinity is a major problem that considerably distorts ecological habitats in arid and semi-arid regions. Excess salts in the soil affect plant nutrient uptake and osmotic balance, leading to osmotic and ionic stress. Plant adaptation or tolerance to salinity stress involves complex physiological traits, metabolic pathways, the production of enzymes, compatible solutes, metabolites, and molecular or genetic networks. Different plant species have different salt overly sensitive pathways and high-affinity K⁺ channel transporters that maintain ion homeostasis. However, little progress has been made in developing salt-tolerant crop varieties using different breeding approaches. This review highlights the interlinking of plant morpho-physiological, molecular, biochemical, and genetic approaches to produce salt-tolerant plant species. Most of the research emphasizes the significance of plant growth-promoting rhizobacteria in protecting plants from biotic and abiotic stressors. Plant growth, survival, and yield can be stabilized by utilizing this knowledge using different breeding and agronomical techniques. This information marks existing research areas and future gaps that require more attention to reveal new salt tolerance determinants in plants-in the future, creating genetically modified plants could help increase crop growth and the toleration of saline environments.

Keywords: SOS pathway and HKT channels; glycophytes; halophytes; ionic homeostasis; osmolytes; sensing.

Figure 1

Schematic representation of effects and causes of abiotic stresses on different life forms, ecosystems, and crop yields.

Figure 2

Schematic representation of adaptive strategies for salt tolerance in plants, including tolerance and avoidance mechanisms; the differentiation of plants into glycophytes and halophytes based on their responses to salt stress.

Figure 3

Schematic representation of osmotic and ionic stresses in plants in relation to salt stress. Adaptive mechanisms of plants, including osmotic adjustment and morpho-physiological adaptations, to maintain ionic homeostasis in their cell solutions.

Figure 4

SOS signaling pathway functions in ion homeostasis and Na⁺ extrusion from cytosol; A rise in cytosolic calcium is induced by high extracellular salt concentrations. The calcium sensor SOS3 interacts with and activates the protein kinase SOS2 when it detects a signal. The ion transporter activities of transcription factors (TFs) are then regulated by activated SOS2 to regulate ion homeostasis or gene expression. The SOS1 Na⁺/H⁺ antiporter, the NHX vacuolar Na⁺/H⁺ exchangers, and the Na⁺/H⁺ transporter HKT1 are all SOS2 targets. Tonoplast ATPase and pyrophosphates, water channels, and the K⁺ transporter are among the other targets.

Figure 5

A generalized schematic representation of salt stress in plants leading to ionic and osmotic stress and the resulting tolerance mechanisms including the SOS signaling pathway, ionic homeostasis, osmotic adjustment, the production of metabolites and compatible solutes, rhizosphere microbial activities, and the production of phytohormones to alleviate various stresses, especially salt stress in plants.