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Plant responses to heterogeneous salinity: growth of the halophyte Atriplex nummularia is determined by the root-weighted mean salinity of the root zone.

ABSTRACT: Soil salinity is generally spatially heterogeneous, but our understanding of halophyte physiology under such conditions is limited. The growth and physiology of the dicotyledonous halophyte Atriplex nummularia was evaluated in split-root experiments to test whether growth is determined by: (i) the lowest; (ii) the highest; or (iii) the mean salinity of the root zone. In two experiments, plants were grown with uniform salinities or horizontally heterogeneous salinities (10-450 mM NaCl in the low-salt side and 670 mM in the high-salt side, or 10 mM NaCl in the low-salt side and 500-1500 mM in the high-salt side). The combined data showed that growth and gas exchange parameters responded most closely to the root-weighted mean salinity rather than to the lowest, mean, or highest salinity in the root zone. In contrast, midday shoot water potentials were determined by the lowest salinity in the root zone, consistent with most water being taken from the least negative water potential source. With uniform salinity, maximum shoot growth was at 120-230 mM NaCl; ~90% of maximum growth occurred at 10 mM and 450 mM NaCl. Exposure of part of the roots to 1500 mM NaCl resulted in an enhanced (+40%) root growth on the low-salt side, which lowered root-weighted mean salinity and enabled the maintenance of shoot growth. Atriplex nummularia grew even with extreme salinity in part of the roots, as long as the root-weighted mean salinity of the root zone was within the 10-450 mM range.

SUBMITTER: Bazihizina N

PROVIDER: S-EPMC3504498 | biostudies-literature | 2012 Nov

REPOSITORIES: biostudies-literature

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Plant responses to heterogeneous salinity: growth of the halophyte Atriplex nummularia is determined by the root-weighted mean salinity of the root zone.

Bazihizina Nadia N Barrett-Lennard Edward G EG Colmer Timothy D TD

Journal of experimental botany 20121103 18

Soil salinity is generally spatially heterogeneous, but our understanding of halophyte physiology under such conditions is limited. The growth and physiology of the dicotyledonous halophyte Atriplex nummularia was evaluated in split-root experiments to test whether growth is determined by: (i) the lowest; (ii) the highest; or (iii) the mean salinity of the root zone. In two experiments, plants were grown with uniform salinities or horizontally heterogeneous salinities (10-450 mM NaCl in the low- ...[more]

PMID: 23125356

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Project description:Background and aimsThe activity of H(+)-ATPase is essential for energizing the plasma membrane. It provides the driving force for potassium retention and uptake through voltage-gated channels and for Na(+) exclusion via Na(+)/H(+) exchangers. Both of these traits are central to plant salinity tolerance; however, whether the increased activity of H(+)-ATPase is a constitutive trait in halophyte species and whether this activity is upregulated at either the transcriptional or post-translation level remain disputed.MethodsThe kinetics of salt-induced net H(+), Na(+) and K(+) fluxes, membrane potential and AHA1/2/3 expression changes in the roots of two halophyte species, Atriplex lentiformis (saltbush) and Chenopodium quinoa (quinoa), were compared with data obtained from Arabidopsis thaliana roots.Key resultsIntrinsic (steady-state) membrane potential values were more negative in A. lentiformis and C. quinoa compared with arabidopsis (-144?±?3·3, -138?±?5·4 and -128?±?3·3?mV, respectively). Treatment with 100?mm NaCl depolarized the root plasma membrane, an effect that was much stronger in arabidopsis. The extent of plasma membrane depolarization positively correlated with NaCl-induced stimulation of vanadate-sensitive H(+) efflux, Na(+) efflux and K(+) retention in roots (quinoa?>?saltbush?>?arabidopsis). NaCl-induced stimulation of H(+) efflux was most pronounced in the root elongation zone. In contrast, H(+)-ATPase AHA transcript levels were much higher in arabidopsis compared with quinoa plants, and 100?mm NaCl treatment led to a further 3-fold increase in AHA1 and AHA2 transcripts in arabidopsis but not in quinoa.ConclusionsEnhanced salinity tolerance in the halophyte species studied here is not related to the constitutively higher AHA transcript levels in the root epidermis, but to the plant's ability to rapidly upregulate plasma membrane H(+)-ATPase upon salinity treatment. This is necessary for assisting plants to maintain highly negative membrane potential values and to exclude Na(+), or enable better K(+) retention in the cytosol under saline conditions.

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Project description:The study of salt tolerance mechanisms in halophyte plants can provide valuable information for crop breeding and plant engineering programs. The aim of the present study was to investigate whole transcriptome analysis of Aeluropus littoralis in response to salinity stress (200 and 400 mM NaCl) by de novo RNA-sequencing. To assemble the transcriptome, Trinity v2.4.0 and Bridger tools, were comparatively used with two k-mer sizes (25 and 32 bp). The de novo assembled transcriptome by Bridger (k-mer 32) was chosen as final assembly for subsequent analysis. In general, 103290 transcripts were obtained. The differential expression analysis (log2FC > 1 and FDR < 0.01) showed that 1861 transcripts expressed differentially, including169 up and 316 down-regulated transcripts in 200 mM NaCl treatment and 1035 up and 430 down-regulated transcripts in 400 mM NaCl treatment compared to control. In addition, 89 transcripts were common in both treatments. The most important over-represented terms in the GO analysis of differentially expressed genes (FDR < 0.05) were chitin response, response to abscisic acid, and regulation of jasmonic acid mediated signaling pathway under 400 mM NaCl treatment and cell cycle, cell division, and mitotic cell cycle process under 200 mM treatment. In addition, the phosphatidylcholine biosynthetic process term was common in both salt treatments. Interestingly, under 400 mM salt treatment, the PRC1 complex that contributes to chromatin remodeling was also enriched along with vacuole as a general salinity stress responsive cell component. Among enriched pathways, the MAPK signaling pathway (ko04016) and phytohormone signal transduction (ko04075) were significantly enriched in 400 mM NaCl treatment, whereas DNA replication (ko03032) was the only pathway that significantly enriched in 200 mM NaCl treatment. Finally, our findings indicate the salt-concentration depended responses of A. littoralis, which well-known salinity stress-related pathways are induced in 400 mM NaCl, while less considered pathways, e.g. cell cycle and DNA replication, are highlighted under 200 mM NaCl treatment.

Dataset Information

Plant responses to heterogeneous salinity: growth of the halophyte Atriplex nummularia is determined by the root-weighted mean salinity of the root zone.

Publications

Plant responses to heterogeneous salinity: growth of the halophyte Atriplex nummularia is determined by the root-weighted mean salinity of the root zone.

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