Characteristics of Na⁺and K⁺absorption inSuaeda salsa(L.) Pall.

Abstract

Suaeda salsa can grow well in saline soils with high sodium (Na)-low potassium (K) concentrations. While high Na accumulation in plant tissues plays an important role in osmoregulation and maintenance of water absorption for normal growth of Suaeda salsa, characteristics of Na and K absorption in S. salsa grown in such saline soils have not been elucidated. We thus examined Na and K absorption characteristics of S. salsa grown in nutrient solutions of graded sodium chloride (NaCl) with 1 mmol L À1 K or of graded potassium chloride (KCl) with 1 mmol L À1 Na. The K accumulation capacity in S. salsa plant tissues was greater than the Na accumulation capacity. Although Na showed no competitive effects on K absorption, K application suppressed Na absorption drastically. Selectivity for K over Na in the absorption system became higher than that for Na over K concomitantly with increased Na or K concentration in the medium, indicating that Suaeda salsa is able to absorb K effectively with absorption of a large amount of Na. Sodium absorption was significantly decreased by tetraethylammonium (typical K channel inhibitor). Calcium (Ca) application increased not Na absorption but K absorption, resulting in enhancement of selectivity for K over Na. We speculate Na absorption pathways in S. salsa are partly mediated by AKT1 (Arabidopsis K transporter 1) type K channel and LCT (a low-affinity cation transporter) and NSCCs (non-selective cation channels) are not the major Na absorption pathway. These results may provide an explanation for the fact that S. salsa can grow well under saline soils with high Na-low K concentrations.

Germination, growth and physiological responses of Senegalia senegal (L.) Britton, Vachellia seyal (Delile) P. Hurter and Prosopis juliflora (Swartz) DC to salinity stress in greenhouse conditions

“…Previous studies have shown that salinity increases Na + and Cl and decreased K + and K + /Na + in plant leaves (Saghir et al, 2002;Hosseini and Thengane, 2007;Taffouo et al, 2010;Silini et al, 2016) found. This implies a competition between Na + and K + absorption in plants, resulting in a Na + /K + antagonism (Mori et al, 2011). The reduction in K + uptake caused by Na + is likely to be the result of the competitive intracellular influx of both ions (Tripathi and Müller, 2015).…”

The inward-rectifying K+ channel SsAKT1 is a candidate involved in K+ uptake in the halophyte Suaeda salsa under saline condition

“…Besides, due to the physicochemical similarities between Na + and K + , Na + competes for K + absorption sites in root cells, causing reduction of K + absorption under high Na + concentrations, and resulting in drastic reduction of plant growth and even death (Maathuis and Amtmann 1999;Schachtman and Liu 1999;Schachtman 2000). However, the growth of Suaeda species, such as S. salsa, S. glauca, S. fruticosa, S. maritima, is enhanced by external Na + treatments (25-400 mM) rather than suppressed, while K + concentrations in these plants also increased or remained relatively stable (Khan et al 2000;Mori et al 2010Mori et al , 2011Song et al 2009;Wang et al 2007;Yang et al 2008;Yeo 1981;Yeo and Flowers 1980). Some studies showed that the transcription level of genes related to K + uptake like AtAKT1 and OsAKT1 were down-regulated by salt stress accompanied with a decrease of K + absorption (Fuchs et al 2005;Kaddour et al 2009).…”

“…S. salsa grows optimally in the presence of about 200 mM NaCl (Song and Wang 2014) and accumulates Na + to the concentration of about 400 mM based on the tissue water content in its leaves without injury, indicating that S. salsa is a typical salt-accumulating halophyte (Wang et al 2004(Wang et al , 2007Zhang et al 2013). Although Na + has been shown to suppress K + influx (at both highand low-affinity ranges, particularly in the low-affinity range at millimolar concentrations) in many plant species (Kronzucker et al 2013), the selectivity for K + over Na + in S. salsa increased dramatically with an increase of NaCl concentration in medium, indicating that S. salsa was able to absorb K + effectively while taking in a large amount of Na + (Mori et al 2011): under various NaCl treatments, K + absorption rate and the concentration of K + in whole plants of S. salsa was maintained at a relatively constant level (Mori et al 2011). Thus, absorbing K + effectively and maintaining the stability of K + concentration in the plant might be key requirements for growth of S. salsa in highly saline soils.…”

Common reed absorbs K+ more selectively than rice against high Na+/K+ ratio in nutrient solution

“…Subsequently, we calculated the selective accumulation (SA K ) and selective transport (ST K ) of K based on the data presented in Fig. 1, according to Mori et al (2011) and Moinuddin et al (2014), to examine whether common reed has a greater ability than that of rice for selective K + uptake under excess Na + concentrations. Common reed had remarkably higher SA K than rice, both in the whole plant and in the roots ( Fig.…”