Accumulation and distribution of metal(loid)s in the halophytic saltmarsh shrub, Austral seablite, Suaeda australis in New South Wales, Australia

Systematic analysis of bZIP gene family in Suaeda australis reveal their roles under salt stress

BACKGROUND

Suaeda australis is one of typical halophyte owing to high levels of salt tolerance. In addition, the bZIP gene family assumes pivotal functions in response to salt stress. However, there are little reports available regarding the bZIP gene family in S. australis.

RESULTS

In this study, we successfully screened 44 bZIP genes within S. australis genome. Subsequently, we conducted an extensive analysis, encompassing investigations into chromosome location, gene structure, phylogenetic relationship, promoter region, conserved motif, and gene expression profile. The 44 bZIP genes were categorized into 12 distinct groups, exhibiting an uneven distribution among the 9 chromosomes of S. australis chromosomes, but one member (Sau23745) was mapped on unanchored scaffolds. Examination of cis-regulatory elements revealed that bZIP promoters were closely related to anaerobic induction, transcription start, and light responsiveness. Comparative transcriptome analysis between ST1 and ST2 samples identified 2,434 DEGs, which were significantly enriched in some primary biological pathways related to salt response-regulating signaling based on GO and KEGG enrichment analysis. Expression patterns analyses clearly discovered the role of several differently expressed SabZIPs, including Sau08107, Sau08911, Sau11415, Sau16575, and Sau19276, which showed higher expression levels in higher salt concentration than low concentration and a response to salt stress. These expression patterns were corroborated through RT-qPCR analysis. The six differentially expressed SabZIP genes, all localized in the nucleus, exhibited positive regulation involved in the salt stress response. SabZIP14, SabZIP26, and SabZIP36 proteins could bind to the promoter region of downstream salt stress-related genes and activate their expressions.

CONCLUSIONS

Our findings offer valuable insights into the evolutionary trajectory of the bZIP gene family in S. australis and shed light on their roles in responding to salt stress. In addition to fundamental genomic information, these results would serve as a foundational framework for future investigations into the regulation of salt stress responses in S. australis.

Tolerance of the Australian halophyte, beaded samphire, Sarcocornia quinqueflora, to Pb and Zn under glasshouse conditions: Evaluating metal uptake and partitioning, photosynthetic performance, biomass, and growth

Saltmarsh sediments are susceptible to accumulation of excessive concentrations of anthropogenically elevated metals such as lead (Pb) and zinc (Zn). The resident salt tolerant plants of saltmarsh ecosystems form the basal underpinning of these ecosystems. As such, metal-associated adverse impacts on their physiology can have detrimental flow-on effects at individual, population, and community levels. The present study assessed the accumulation and partitioning of ecologically relevant concentrations of Pb, Zn, and their combination in a dominant Australian saltmarsh species, Sarcocornia quinqueflora. Plants were hydroponically maintained under glasshouse conditions for 16 weeks exposure to either Pb (20 µg l-1), Zn (100 µg l-1), or their mixture. We evaluated the chronic toxicological effects of single and mixed metal treatments with reference to metal uptake and partitioning, photosynthetic performance, photosynthetic pigment concentration, biomass and growth. Lead was more toxic than Zn, and Zn appeared to have an antagonistic effect on the toxicological effects of Pb in S.quinqueflora in terms of metal uptake, photosynthetic performance, photosynthetic pigment concentrations, and growth. Indeed, the tolerance index was 55 % in plants treated with Pb compared to 77 % in Zn treated plants and 73 % in Pb+Zn treated plants. Finally, Sarcocornia quinqueflora primarily accumulated both Pb and Zn in roots at concentrations exceeding unity whilst translocation of these metals to above ground tissues was restricted regardless of treatment. This suggests that S. quinqueflora may be suitable for phytostabilisation of Zn, and of Pb particularly in the presence of Zn.

Uptake and distribution of metal(loid)s in two rare species of saltmarsh, blackseed samphire, Tecticornia pergranulata, and narrow-leafed wilsonia, Wilsonia backhousei, in New South Wales, Australia

The uptake and distribution of copper, zinc, arsenic, and lead was examined in two rare Australian saltmarsh species, Tecticornia pergranulata and Wilsonia backhousei. The bioconcentration factors and translocation factors were generally much lower than one, except for the Zn translocation factors for T. pergranulata. When compared to other Australian saltmarsh taxa, these species generally accumulated the lowest levels observed among taxa, especially in terms of their BCFs. Essential metals tended to be regulated, while non-essential metals increased in concentration with dose during transport among compartments, a pattern not previously observed in Australian saltmarsh taxa. The uptake of metals into roots was mainly explained by total sediment metal loads as well as more acidic pH, increased soil organic matter, and decreased salinity. The low uptake and limited translocation observed in these rare taxa may offer a competitive advantage for their establishment and survival in the last urbanised populations, where legacy metal contamination acts as a selective pressure.

Offspring of metal contaminated saltmarsh (Juncus acutus) exhibit tolerance to the essential metal Zn but not the nonessential metal Pb

Halophytes residing in metal-contaminated saltmarsh habitats may employ strategies to enhance fitness of the next generation. We aimed to test the hypothesis that Juncus acutus individuals inhabiting metal-contaminated locations would experience elevated tolerance of offspring to metals compared to plants residing in locations with no metal contamination history. J. acutus seeds (F₁ generation) were collected from F₀ parent plants residing at eight locations of a contemporary sediment metal gradient (contaminated to uncontaminated) across the coast of NSW, Australia (Hunter river, Lake Macquarie and Georges River). Seeds were exposed in the laboratory to incremental Zn (0.0-1.6 mM) and Pb (0.0-0.50 mM) for nine (9) days, and % germination, germination rate, root elongation and vigour index were assessed for the determination of tolerance. Greater root accumulation (BCF = 1.01) of Zn and subsequent translocation to aerial parts (culm BCF = 0.58 and capsule BCF = 0.85) were exhibited in parents plants, whereas Pb was excluded from roots (BCF = 0.60) and very little translocation to aerial portions of the plant was observed (culm BCF = 0.02 and capsule BCF = 0.05). F₁ offspring exhibited tolerance to Zn with EC₅₀ (% germination) significantly correlated with their parents' culm (R² = 0.93, p = 0.00) and capsule (R² = 0.57; p = 0.03) Zn. No correlations were observed between offspring Pb tolerance and Pb in parents' plant tissues. Enhanced tolerance to the essential metal Zn may be because Zn is very mobile in the parent plant and seeds experience greater Zn load as a significant portion of sediment Zn reaches capsules (85%). Thus, Zn tolerance in J. acutus seeds is likely attributable to acclimation via maternal transfer of Zn; however, further manipulative experiments are required to disentangle potential acclimation, adaptation or epigenetic effects in explaining the tolerance observed.

Spatial distribution and sources of heavy metals in the sediment and soils of the Yancheng coastal ecosystem and associated ecological risks

Studies of heavy metal pollution are essential for the protection of coastal environments. In this study, positive matrix factorization (PMF) and a GeoDetector model were used to evaluate the sources of heavy metal contamination and associated ecological risks along the Yancheng Coastal Wetland. The distribution of heavy metals was shown to be greatly affected by clay content, except for Cr in shoal. Components from 6.5 to 9φ have the strongest ability to absorb heavy metals, where the effects of Cd and Zn sequestration in the wetlands were most apparent. The abilities of various wetland environments to sequester heavy metals were shown to be Spartina alterniflora wetland > woodland > Phragmites australis wetland > aquaculture pond > shoal > paddy > meadow > dry land. The sources of the heavy metals included parent soil material (59%), agriculture (15%), and industrial pollutants (26%). According to the single-factor pollution index, there was no evidence of pollution except Cr and Pb. In general, the heavy metal pollution was insignificant. The order of pollution loading index was shoal > paddy field > dry land > Spartina Alterniflora wetland > aquaculture ponds > woodland > meadow > Phragmites australis wetland. The ecological harm of heavy metal exposure was slight except for Cd and Hg, where vehicle emissions appeared to be the main cause of heavy metal pollution.

The potential of saltmarsh halophytes for phytoremediation of metals and persistent organic pollutants: An Australian perspective

Persistent organic and inorganic pollutants are among the most concerning pollutants in Australian estuaries due to their persistent, ubiquitous, and potentially toxic nature. Traditional methods of soil remediation often fall short of practical implementation due to high monetary investment, environmental disturbance, and potential for re-contamination. Phytoremediation is gaining traction as an alternative, or synergistic mechanism of contaminated soil remediation. Phytoremediation utilises plants and associated rhizospheric microorganisms to stabilise, degrade, transform, or remove xenobiotics from contaminated mediums. Due to their apparent cross-tolerance to salt, metals, and organic contaminants, halophytes have shown promise as phytoremediation species. This review examines the potential of 93 species of Australian saltmarsh halophytes for xenobiotic phytoremediation. Considerations for the practical application of phytoremediation in Australia are discussed, including mechanisms of enhancement, and methods of harvesting and disposal. Knowledge gaps for the implementation of phytoremediation in Australian saline environments are identified, and areas for future research are suggested.

The accumulation and distribution of arsenic species and selected metals in the saltmarsh halophyte, spiny rush (Juncus acutus)

This study examined the accumulation of As species, Se, Cu, Zn, Cd and Pb in the halophyte Juncus acutus, collected from three anthropogenically impacted estuaries in NSW, Australia. As concentration ranged from 4 to 22 μg/g at Georges River, 2-16 μg/g at Lake Macquarie and 6 μg/g at Hunter Estuary. Inorganic As was accumulated mainly in roots with low translocation to culm with a greater abundance of AsV. However, AsIII (TF = 0.32) showed greater mobility from the roots to shoots than AsV (TF = 0.04), indicating a higher quantity of AsIII specific transporter assemblages in the plasmalemma of the endodermis or cytoplasmic reduction of AsV to AsIII in culms. Metal(loid)s, including As (90%), were predominantly in root tissues and very limited translocation to culm, indicating the species is a useful phytostabiliser. As and all other metal(loid)s in roots were correlated with sediment loads (p < 0.05, R² = 0.10-0.52), indicating the species would be an accumulative bioindicator.