Sodium efflux in plant roots: What do we really know?

Britto, Dev T.; Kronzucker, Herbert J.

doi:10.1016/j.jplph.2015.08.002

Cited by 42 publications

(50 citation statements)

References 143 publications

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“…Movement out of vacuoles possibly through ion channels would be much slower than diffusion in water (Liu & Eisenberg, 2015). Movement of isotope by diffusion is supported by the results of Britto & Kronzucker (2015) and Flam-Shepherd et al (2018) who showed that efflux of 24 Na + from roots was unaffected by respiratory inhibitors. This rapid diffusion of tracer independent of the bulk Na + would also explain the rapid influxes measured with wheat in 25 mM NaCl (Davenport et al, 2005), where the 22 Na + influx rate dropped from 15 lmol g À1 (FW) h À1 over the first 30 s to 3.6 over the next 3 min to 0.8 over the next 4 h and was then steady (Table S2).…”

Section: Reviewmentioning

confidence: 86%

Osmotic adjustment and energy limitations to plant growth in saline soil

et al. 2019

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Summary Plant roots must exclude almost all of the Na+ and Cl– in saline soil while taking up water, otherwise these ions would build up to high concentrations in leaves. Plants evaporate c. 50 times more water than they retain, so 98% exclusion would result in shoot NaCl concentrations equal to that of the external medium. Taking up just 2% of the NaCl allows a plant to osmotically adjust the Na+ and Cl– in vacuoles, while organic solutes provide the balancing osmotic pressure in the cytoplasm. We quantify the costs of this exclusion by roots, the regulation of Na+ and Cl– transport through the plant, and the costs of osmotic adjustment with organic solutes in roots.

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Section: Reviewmentioning

confidence: 86%

Osmotic adjustment and energy limitations to plant growth in saline soil

et al. 2019

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“…In barley, radiotracer analysis revealed that Na + efflux mainly occurred in the root tip (three to four times that of proximal regions) of WT, while sos1 mutants showed reduced efflux in the root tip with no alteration in efflux at other regions, indicating SOS1-mediated efflux at the root tip and mainly apoplastic release in the bulk root (Hamam et al, 2016). While this concept of Na + extrusion mediated by SOS1 is widely accepted as a salt tolerance strategy, it was earlier viewed to be potentially deleterious for plants under salt stress, in the so-called “rapid transmembrane sodium cycling (RTSC)” (Malagoli et al, 2008; Britto and Kronzucker, 2015; Hamam et al, 2016). In this strategy, almost-uncontrollable Na + influx into plant roots is rapidly extruded back into the soil, a process believed to be mediated by SOS1 and deemed energetically costly for the plants.…”

Section: Resistance To Radial Transport and Xylem Loading Of Na+mentioning

confidence: 99%

“…This procedure is estimated to consume more ATP than is produced by respiratory processes in the root, thus creating energy deficits for other metabolic processes and consequently growth impairment (Malagoli et al, 2008; Pedersen and Palmgren, 2017). However, it has been recently suggested that a larger component of this flux would be apoplastic, and thus of minor energy cost for the root (Britto and Kronzucker, 2015; Hamam et al, 2016). However, this apoplastic fraction of the efflux has not been fully characterized.…”

Section: Resistance To Radial Transport and Xylem Loading Of Na+mentioning

confidence: 99%

The Role of Na+ and K+ Transporters in Salt Stress Adaptation in Glycophytes

et al. 2017

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Ionic stress is one of the most important components of salinity and is brought about by excess Na+ accumulation, especially in the aerial parts of plants. Since Na+ interferes with K+ homeostasis, and especially given its involvement in numerous metabolic processes, maintaining a balanced cytosolic Na+/K+ ratio has become a key salinity tolerance mechanism. Achieving this homeostatic balance requires the activity of Na+ and K+ transporters and/or channels. The mechanism of Na+ and K+ uptake and translocation in glycophytes and halophytes is essentially the same, but glycophytes are more susceptible to ionic stress than halophytes. The transport mechanisms involve Na+ and/or K+ transporters and channels as well as non-selective cation channels. Thus, the question arises of whether the difference in salt tolerance between glycophytes and halophytes could be the result of differences in the proteins or in the expression of genes coding the transporters. The aim of this review is to seek answers to this question by examining the role of major Na+ and K+ transporters and channels in Na+ and K+ uptake, translocation and intracellular homeostasis in glycophytes. It turns out that these transporters and channels are equally important for the adaptation of glycophytes as they are for halophytes, but differential gene expression, structural differences in the proteins (single nucleotide substitutions, impacting affinity) and post-translational modifications (phosphorylation) account for the differences in their activity and hence the differences in tolerance between the two groups. Furthermore, lack of the ability to maintain stable plasma membrane (PM) potentials following Na+-induced depolarization is also crucial for salt stress tolerance. This stable membrane potential is sustained by the activity of Na+/H+ antiporters such as SOS1 at the PM. Moreover, novel regulators of Na+ and K+ transport pathways including the Nax1 and Nax2 loci regulation of SOS1 expression and activity in the stele, and haem oxygenase involvement in stabilizing membrane potential by activating H+-ATPase activity, favorable for K+ uptake through HAK/AKT1, have been shown and are discussed.

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“…Some isotope flux calculations indicate that energy costs approach the ATP produced by respiration (e.g. Malagoli et al, 2008 for rice), although subsequent publications have questioned these results (Britto & Kronzucker, 2015;Flam-Shepherd et al, 2018;Munns et al 2020). These estimates are just for Na + in isolation and ignore the Cl À ion and feedback effects on other fluxes, such as loss of K + (Cuin et al, 2008) and NO 3 À (Teakle & Tyerman, 2010).…”

Section: Water and Ion Transportmentioning

confidence: 99%

Energy costs of salt tolerance in crop plants

et al. 2019

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Agricultureisexpandingintoregionsthatareaffectedbysalinity.Thisreviewconsiderstheenergetic costs of salinity tolerance in crop plants and provides a framework for a quantitative assessment of costs. Different sources of energy, and modifications of root system architecture that would maximize water vs ion uptake are addressed. Energy requirements for transport of salt (NaCl) to leaf vacuoles for osmotic adjustment could be small if there are no substantial leaks back across plasma membrane and tonoplast in root and leaf. The coupling ratio of the H +-ATPase also is a critical component. One proposed leak, that of Na + influx across the plasma membrane through certain aquaporin channels, might be coupled to water flow, thus conserving energy. For the tonoplast, control of two types of cation channels is required for energy efficiency. Transporters controlling the Na + and Cl À concentrations in mitochondria and chloroplasts are largely unknown and could be a major energy cost. The complexity of the system will require a sophisticated modelling approach to identify critical transporters, apoplastic barriers and root structures. This modelling approach will informexperimentationandallowaquantitativeassessmentoftheenergycostsofNaCltoleranceto guide breeding and engineering of molecular components.

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Sodium efflux in plant roots: What do we really know?

Cited by 42 publications

References 143 publications

Osmotic adjustment and energy limitations to plant growth in saline soil

Osmotic adjustment and energy limitations to plant growth in saline soil

The Role of Na+ and K+ Transporters in Salt Stress Adaptation in Glycophytes

Energy costs of salt tolerance in crop plants

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