Low unidirectional sodium influx into root cells restricts net sodium accumulation in Thellungiella halophila, a salt-tolerant relative of Arabidopsis thaliana

Abstract

Thellungiella halophila is a useful model species for research into plant salt tolerance. It is closely related to Arabidopsis thaliana, but shows considerably higher salt tolerance. Comparative analysis of ion homeostasis in the two species allows the identification of ion transport pathways that are critical for salt tolerance and provides the basis for future studies into their molecular features. Previous studies indicated that salt tolerance in T. halophila is accompanied by low accumulation of Na in the leaves. Kinetic analysis of net ion uptake over three days confirmed lower Na uptake and K loss in T. halophila compared with A. thaliana. Differential net Na uptake rates were still apparent after 6 weeks of salt treatment. To assess the contribution of unidirectional Na fluxes to net Na uptake, kinetic studies of (22)Na fluxes were carried out in both species. The results show that unidirectional root Na influx is significantly lower in salt-grown T. halophila plants than in A. thaliana exposed to the same level of salinity (100 mM). Quantitative comparison of unidirectional influx and net Na accumulation suggests that both species operate efficient Na efflux, which partly compensates for Na influx. Kinetic analysis of (22)Na efflux indicated higher root Na efflux in A. thaliana than in T. halophila. Thus A. thaliana appears to spend more energy on Na export while nevertheless accumulating more Na than T. halophila. It is proposed that limitation of Na influx is the main mechanism by which T. halophila secures low net Na accumulation in saline conditions. This strategy provides the basis for a positive balance between growth and net Na uptake rates, which is essential for survival in high salt.

Calcium regulates K⁺/Na⁺ homeostasis in rice (Oryza sativa L.) under saline conditions

“…Furthermore, rate of Na + cycling varied with plant species under saline conditions. For example, rate in Arabidopsis it was 77% (Wang et al 2006); salttolerance wheat showed higher ratio of efflux to influx (99%) compared with salt-sensitive wheat (93%) (Davenport et al 2005). In the present study, rice also showed high ratios of efflux to influx 94% and 98% under 25 and 125 mmol/L NaCl (Table 1).…”

Histone Deacetylase Complex1 Expression Level Titrates Plant Growth and Abscisic Acid Sensitivity in Arabidopsis

“…Addition of 80 mM NaCl is a physiologically relevant sublethal salt stress dose for moderately salt-tolerant plants such as Arabidopsis (Wang et al, 2006) and did not cause severe chlorosis or desiccation over the course of this experiment (see photos in Figure 11B). However, the treatment reduced shoot water content (from 92% 6 1% to Transcript levels of salt-responsive genes in the wild type (WT; black), hdc1-1 knockout (KO; white), and HDC1 overexpressing line (OX; gray).…”

Genome Structures and Halophyte-Specific Gene Expression of the Extremophile Thellungiella parvula in Comparison with Thellungiella salsuginea (Thellungiella halophila) and Arabidopsis

“…Suggested mechanisms for tolerance to stress and nutrient-limiting conditions include control over stomatal conductance (Inan et al, 2004), greater discriminatory power of K + -and Na + -transport systems (Volkov et al, 2004;Volkov and Amtmann, 2006), and nitrogen utilization efficiency (Kant et al, 2008). However, a genetic basis of the differences in tolerance could only be deduced by attempts at establishing Arabidopsis-like resources and databases (Inan et al, 2004;Taji et al, 2004Taji et al, , 2008Wang et al, 2004Wang et al, , 2006Gong et al, 2005;Wong et al, 2005;Zhang et al, 2008;Oh et al, 2009). Merging the forthcoming T. parvula genome sequence in a three-way comparison that includes Arabidopsis and T. salsuginea (pending; http://www.jgi.doe.gov/ sequencing/why/50029.html) will provide a powerful way to probe for the essence of halophytism, in particular if other crucifer species and ecotypes of wellstudied species are included (Weigel and Mott, 2009;Orsini et al, 2010).…”

“…A number of tools for comparative molecular characterizations have been developed for T. salsuginea, including tagged mutants, EST collections, and fulllength cDNA collections (Inan et al, 2004;Taji et al, 2004Taji et al, , 2008Wang et al, 2004Wang et al, , 2006Gong et al, 2005;Wong et al, 2005). To date, results of stress challenge studies have identified transcriptome responses that are broadly similar to those shown by Arabidopsis.…”