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Biophysical and biochemical constraints imposed by salt stress: learning from halophytes.

Duarte B, Sleimi N, Caçador I - Front Plant Sci (2014)

Bottom Line: Otherwise, the lack of adaptation to a salt environment would negatively affect their electron transduction pathways and the entire energetic metabolism, the foundation of every plant photosynthesis and biomass production.The maintenance of ionic homeostasis is in the basis of all cellular counteractive measures, in particular in terms of redox potential and energy transduction.In the present work the biophysical mechanisms underlying energy capture and transduction in halophytes are discussed alongside with their relation with biochemical counteractive mechanisms, integrating data from photosynthetic light harvesting complexes, electron transport chains to the quinone pools, carbon fixation, and energy dissipation metabolism.

View Article: PubMed Central - PubMed

Affiliation: Centre of Oceanography, Faculty of Sciences, University of Lisbon Lisbon, Portugal ; Marine and Environmental Sciences Centre, Faculty of Sciences, University of Lisbon Lisbon, Portugal.

ABSTRACT
Soil salinization is one of the most important factors impacting plant productivity. About 3.6 billion of the world's 5.2 billion ha of agricultural dry land, have already suffered erosion, degradation, and salinization. Halophytes are typically considered as plants able to complete their life cycle in environments where the salt concentration is above 200 mM NaCl. Salinity adjustment is a complex phenomenon but essential mechanism to overcome salt stress, with both biophysical and biochemical implications. At this level, halophytes evolved in several directions, adopting different strategies. Otherwise, the lack of adaptation to a salt environment would negatively affect their electron transduction pathways and the entire energetic metabolism, the foundation of every plant photosynthesis and biomass production. The maintenance of ionic homeostasis is in the basis of all cellular counteractive measures, in particular in terms of redox potential and energy transduction. In the present work the biophysical mechanisms underlying energy capture and transduction in halophytes are discussed alongside with their relation with biochemical counteractive mechanisms, integrating data from photosynthetic light harvesting complexes, electron transport chains to the quinone pools, carbon fixation, and energy dissipation metabolism.

No MeSH data available.


Related in: MedlinePlus

Tamarix gallica leaves of individuals subjected to 200 and 0 mM NaCl Photo by B. Duarte (2012). Plants were originally collected in Tunisia and transplanted to the Centre of Oceanography greenhouse, where they were subjected to different salinity levels.
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Figure 1: Tamarix gallica leaves of individuals subjected to 200 and 0 mM NaCl Photo by B. Duarte (2012). Plants were originally collected in Tunisia and transplanted to the Centre of Oceanography greenhouse, where they were subjected to different salinity levels.

Mentions: Some of the evident adaptations to salt environments can be immediately detected just observing halophyte morphology. Typically, there are two mechanisms that halophytes use in order to overcome high salinity: secretion and exclusion. The secretion-based strategy implies the existence of specialized salt glands (Figure 1), located at the leaf surface. The main function of salt glands is the excretion of excessive Na+ (Shabala et al., 2014) as a way to reduce its negative effects on cell metabolism. This is probably the most studied tolerance adaptation mechanism in halophytes (Rozema et al., 1981; Waisel et al., 1986; Shabala et al., 2014). The excreted salt crystals on the leaf surface are then washed out by rain or tidal waters, preventing its reabsorption to the leaf cells (Balsamo et al., 1995). On the contrary a typical halophyte excluder retains high amounts of K+ and Ca2+ inside its cells to avoid Na+ uptake, enabling survival in soils with very high salt concentrations (Figure 2). The increased Ca2+ concentrations allow the cell membrane to maintain the K+/Na+ selectivity and thus maintain the ionic balance of the cell (Cramer et al., 1987). Alongside with this shoot-exclusion, there is often an observable increase in root Ca2+ concentration accompanied by a decrease of the Na+ root concentration. This exclusion strategy is well studied in Sarcocornia fruticosa, frequently followed by a dilution strategy, implying an increased cellular water uptake and thus decreasing the ionic concentration inside the cell (Figure 3). T. halophila also evidences a very similar strategy, retaining higher K+ and lower Na+ concentrations, while increasing its water uptake (Volkov and Amtmann, 2006). This differential ionic absorption is mediated by specific protein ionic channels, with a total of 32 salt induced differentially expressed proteins already identified in T. halophila (Pang et al., 2010). Under stress, K+ transporter proteins are preferentially expressed alongside with changes in membrane potential and ion selectivity, counteracting the elevated extracellular Na+ concentrations. Nevertheless, all these morphological adaptations have implications at both biophysical and biochemical levels.


Biophysical and biochemical constraints imposed by salt stress: learning from halophytes.

Duarte B, Sleimi N, Caçador I - Front Plant Sci (2014)

Tamarix gallica leaves of individuals subjected to 200 and 0 mM NaCl Photo by B. Duarte (2012). Plants were originally collected in Tunisia and transplanted to the Centre of Oceanography greenhouse, where they were subjected to different salinity levels.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4273624&req=5

Figure 1: Tamarix gallica leaves of individuals subjected to 200 and 0 mM NaCl Photo by B. Duarte (2012). Plants were originally collected in Tunisia and transplanted to the Centre of Oceanography greenhouse, where they were subjected to different salinity levels.
Mentions: Some of the evident adaptations to salt environments can be immediately detected just observing halophyte morphology. Typically, there are two mechanisms that halophytes use in order to overcome high salinity: secretion and exclusion. The secretion-based strategy implies the existence of specialized salt glands (Figure 1), located at the leaf surface. The main function of salt glands is the excretion of excessive Na+ (Shabala et al., 2014) as a way to reduce its negative effects on cell metabolism. This is probably the most studied tolerance adaptation mechanism in halophytes (Rozema et al., 1981; Waisel et al., 1986; Shabala et al., 2014). The excreted salt crystals on the leaf surface are then washed out by rain or tidal waters, preventing its reabsorption to the leaf cells (Balsamo et al., 1995). On the contrary a typical halophyte excluder retains high amounts of K+ and Ca2+ inside its cells to avoid Na+ uptake, enabling survival in soils with very high salt concentrations (Figure 2). The increased Ca2+ concentrations allow the cell membrane to maintain the K+/Na+ selectivity and thus maintain the ionic balance of the cell (Cramer et al., 1987). Alongside with this shoot-exclusion, there is often an observable increase in root Ca2+ concentration accompanied by a decrease of the Na+ root concentration. This exclusion strategy is well studied in Sarcocornia fruticosa, frequently followed by a dilution strategy, implying an increased cellular water uptake and thus decreasing the ionic concentration inside the cell (Figure 3). T. halophila also evidences a very similar strategy, retaining higher K+ and lower Na+ concentrations, while increasing its water uptake (Volkov and Amtmann, 2006). This differential ionic absorption is mediated by specific protein ionic channels, with a total of 32 salt induced differentially expressed proteins already identified in T. halophila (Pang et al., 2010). Under stress, K+ transporter proteins are preferentially expressed alongside with changes in membrane potential and ion selectivity, counteracting the elevated extracellular Na+ concentrations. Nevertheless, all these morphological adaptations have implications at both biophysical and biochemical levels.

Bottom Line: Otherwise, the lack of adaptation to a salt environment would negatively affect their electron transduction pathways and the entire energetic metabolism, the foundation of every plant photosynthesis and biomass production.The maintenance of ionic homeostasis is in the basis of all cellular counteractive measures, in particular in terms of redox potential and energy transduction.In the present work the biophysical mechanisms underlying energy capture and transduction in halophytes are discussed alongside with their relation with biochemical counteractive mechanisms, integrating data from photosynthetic light harvesting complexes, electron transport chains to the quinone pools, carbon fixation, and energy dissipation metabolism.

View Article: PubMed Central - PubMed

Affiliation: Centre of Oceanography, Faculty of Sciences, University of Lisbon Lisbon, Portugal ; Marine and Environmental Sciences Centre, Faculty of Sciences, University of Lisbon Lisbon, Portugal.

ABSTRACT
Soil salinization is one of the most important factors impacting plant productivity. About 3.6 billion of the world's 5.2 billion ha of agricultural dry land, have already suffered erosion, degradation, and salinization. Halophytes are typically considered as plants able to complete their life cycle in environments where the salt concentration is above 200 mM NaCl. Salinity adjustment is a complex phenomenon but essential mechanism to overcome salt stress, with both biophysical and biochemical implications. At this level, halophytes evolved in several directions, adopting different strategies. Otherwise, the lack of adaptation to a salt environment would negatively affect their electron transduction pathways and the entire energetic metabolism, the foundation of every plant photosynthesis and biomass production. The maintenance of ionic homeostasis is in the basis of all cellular counteractive measures, in particular in terms of redox potential and energy transduction. In the present work the biophysical mechanisms underlying energy capture and transduction in halophytes are discussed alongside with their relation with biochemical counteractive mechanisms, integrating data from photosynthetic light harvesting complexes, electron transport chains to the quinone pools, carbon fixation, and energy dissipation metabolism.

No MeSH data available.


Related in: MedlinePlus