• Energy Research

AbstractPlant salinity tolerance is a physiologically complex trait, with numerous mechanisms contributing to it. In this work, we show that the ability of leaf mesophyll to retain K+ represents an important and essentially overlooked component of a salinity tolerance mechanism. The strong positive correlation between mesophyll K+ retention ability under saline conditions (quantified by the magnitude of NaCl‐induced K+ efflux from mesophyll) and the overall salinity tolerance (relative fresh weight and/or survival or damage under salinity stress) was found while screening 46 barley (Hordeum vulgare L.) genotypes contrasting in their salinity tolerance. Genotypes with intrinsically higher leaf K+ content under control conditions were found to possess better K+ retention ability under salinity and, hence, overall higher tolerance. Contrary to previous reports for barley roots, K+ retention in mesophyll was not associated with an increased H+‐pumping in tolerant varieties but instead correlated negatively with this trait. These findings are explained by the fact that increased H+ extrusion may be needed to charge balance the activity and provide the driving force for the high affinity HAK/KUP K+ transporters required to restore cytosolic K+ homeostasis in salt‐sensitive genotypes.

Salinity is an issue impairing crop production across the globe. Under salinity stress, besides the osmotic stress and Na+ toxicity, ROS (reactive oxygen species) overaccumulation is a secondary stress which further impairs plant performance. Chloroplasts, mitochondria, the apoplast, and peroxisomes are the main ROS generation sites in salt-stressed plants. In this review, we summarize ROS generation, enzymatic and non-enzymatic antioxidant systems in salt-stressed plants, and the potential for plant biotechnology to maintain ROS homeostasis. Overall, this review summarizes the current understanding of ROS homeostasis of salt-stressed plants and highlights potential applications of plant nanobiotechnology to enhance plant tolerance to stresses.

Plants under salt stress require additional energy supply to fuel salt tolerance mechanisms and growth. Bandehagh and Taylor (2020) establish that plants must strike a balance between energy supply and demand to maintain growth and development during salt stress. This review (1) summaries how salt stress affects different physiological and biochemical process altering the abundance of different metabolites that are feeding into regular and alternative respiratory pathways and shunts; (monomeric complex I, dimeric complex III and I + III2 supercomplex) found to be higher in halophyte mitochondria in comparison with glycophyte, implying efficient electron transfer from complex I to complex III in halophyte mitochondria. Further, the stability of ATP synthase (complex V) also found to be higher in halophyte suggesting halophyte mitochondria better equipped to supply additional ATP required to support salt stress response.Synthesis of organic compatible solutes is an important component for plant salt stress tolerance. In this regard, proline plays an important role in protecting plants from under salinity conditions and showed that salt tolerance is associated with changes in lipid metabolic processes. They also discovered the important role of phosphatidylserine (PS) in mediating enzyme activity, and exogenous application of PS alleviated the effects of NaCl tissue toxicity. The results showed that the superior K + retention ability in both mature and elongation zone of rice root is the key trait conferring its differential salinity stress tolerance. They suggested that besides the superior ability to activate root H + -ATPase pump operation, this key trait is also related to the reduced sensitivity of K + efflux channels to reactive oxygen species and the lower upregulation in OsGORK and higher upregulation of OsAKT1.A key trait long recognized to improve salinity tolerance in many plants is the maintenance of a low Na + /K + ratio. Transient expression experiment showed that JcHDZ07 is a nuclear-localized protein.In improving Na + exclusion ability to maintain root ion homeostasis to ensure a relatively 9 low shoot Na + concentration under saline conditions; 2) maintaining a high shoot sugar content under saline conditions which is enabled by protecting photosystems structures, enhancing photosynthetic performance and sucrose synthetase activity, and inhibiting sucrose degradation. Further, authors suggested that targeting the key genes related to the regulatory mechanisms could provide opportunities to breed more salt tolerant sweet sorghum.Overall, we hope this special issue of benefit to plant breeders and land managers by delivering novel information and insights on the salinity stress response, signalling and adaptive mechanisms operating in plants.