Cadmium hampers salt tolerance of Sesuvium portulacastrum

Competitive ion uptake and transcriptional regulation as a coordinated dual mechanism of NaCl-mediated cadmium detoxification in Suaeda salsa

Cadmium (Cd), a highly toxic heavy metal, severely inhibits plant growth. Salt alleviates Cd stress in halophytes, however, the molecular mechanisms governing salt-mediated regulation of Cd toxicity remain poorly understood. This study elucidates the protective mechanism of NaCl in Cd-stressed Suaeda salsa seedlings. Cd exposure suppressed seedling growth and induced membrane lipid peroxidation. Conversely, NaCl application not only maintained normal growth but also effectively ameliorated Cd-induced phytotoxicity, potentially through osmotic adjustment mechanisms. Notably, using ion flux analysis, we found that NaCl attenuated Cd2+ influx into root epidermal cells, thereby enhancing Cd resistance. Pharmacological inhibition studies confirmed that Na + competitively inhibits Cd2+ uptake through shared channels/transporters. Furthermore, RT-qPCR gene expression profiling revealed that NaCl coordinately activated both ionic compartmentalization and efflux systems through upregulating plasma membrane-localized SsSOS1 and tonoplast-associated SsNHX1 for Na + extrusion and vacuolar sequestration, enhancing Cd2+ compartmentalization via SsCAX and SsVHA-B mediated transport and maintaining cellular homeostasis through SsHKT1 and SsPIP-mediated regulation of water and K+ balance, or indirectly inhibit Cd2+ influx. It reveals that salt weakens Cd2+ influx and enhances Cd tolerance by activating a coordinated gene regulatory network in Suaeda salsa. This finding offers valuable insights into phytoremediation strategies for enhancing crop resilience in Cd-contaminated saline soils.

Cadmium contamination impairs alkaline tolerance in sugar beet by inhibiting carbon fixation and tryptophan metabolism

The contamination of cadmium (Cd) may overlap with alkali stress, exerting a synergistic effect on crop growth. This study examined the morphological and physiological responses of sugar beet seedlings irrigated with Cd solution (50 mM CdCl2) to alkali stress (400 mM NaHCO3). Under alkali stress, the presence of Cd exacerbated the reduction in plant growth, the maximum quantum yield of photosystem II (Fv/Fm), chlorophyll content, and osmoregulatory substances (proline, soluble sugars). Cd augmented the concentration of MDA, O2·-, and H2O2, while reducing the expression of BvPOX. Concurrently, glutathione content, ascorbate peroxidase (APX) activity, and the glutathione transferase gene (BvGST) expression were also inhibited by Cd. Cd constrained the ribulose-5P content under alkali stress and the expression of the glyceraldehyde-3-phosphate dehydrogenase gene (BvGAPDH), thereby inhibiting the Calvin cycle. Additionally, the expression of the alcohol dehydrogenase gene (BvADH) was reduced, leading to decreased sucrose and starch content. Cd also accelerated pectin metabolism. Furthermore, Cd inhibited the expression of key genes involved in melatonin synthesis (aromatic-L-amino-acid/L-tryptophan decarboxylase gene, BvDDC/BvTDC and acetylserotonin O-methyltransferase gene, BvASMT), resulting in restricted tryptophan metabolism. This study provides insights into the inhibition of carbon fixation and tryptophan metabolism induced by Cd, its effects on the growth of beets under alkaline stress conditions.

How does NaCl enhance Cd tolerance in Inula crithmoides L? Insights into Cd uptake, compartmentalization, and chelation

This study investigated the effect of NaCl on the uptake, translocation, compartmentalization, and chelation of cadmium (Cd) in the halophyte Inula crithmoides. Seedlings were subjected hydroponically for 21 days to 25 and 50 μM Cd applied alone or combined with 100 mM NaCl. Findings revealed that, Cd alone induced intense chlorosis and necrosis and altered plant development resulting in diminished biomass production. However, NaCl alleviated Cd-induced toxicity by increasing biomass accumulation, associated with restoration of photosynthesis activity. At the level of whole plant, NaCl reduced Cd concentration in different organs as well as its translocation toward the shoots. At the cellular level, Na Cl changed the cell-compartmentalization of Cd in the shoots and roots by inducing a preferential accumulation into the soluble fraction (vacuole). NaCl increased the chelation of Cd to chloride and nitrate. As compared to Cd alone, salt addition to Cd-treated plants enhanced significantly succinic acid concentration in the leaves suggesting a possible role of this acid in Cd-chelation. Globally, NaCl alleviated Cd-induced phytotoxicity in this halophyte by reducing Cd absorption, translocation and increased Cd fixation to organic acids as well as through the changes in Cd2+ cell compartmentalization. Obtained data suggested that this fast growing halophyte could be used to rehabilitate Cd polluted saline soils.

High NaCl tolerance potential of Bruguiera cylindrica (L.) Blume compromised by mild CuSO4 concentration as evidenced by unique physiochemical features

Differential response of Bruguiera cylindrica to individual (CuSO₄) and combined (CuSO₄ NaCl) effect was evaluated. The plantlets were treated with control, 0.15 mM CuSO₄, 400 mM NaCl and 0.15 mM CuSO₄ + 400 mM NaCl. Under combined stress, higher accumulation of Cu in the roots indicate that the roots are the primary site of Cu accumulation and thus the plant perform as an excluder and photosynthetic efficiency reduced drastically and significant enhancement in the superoxide and hydroxyl free radicals which increase membrane lipid peroxidation, leading to cellular damage and destruction. As evidenced from SEM-EDXMA, increase in Cu and Na⁺ levels in xylem and pith regions of leaf and stem and the presence of deeply stained structures, denoting the probable formation of complex containing the metal. Increased CaOx crystal forming cells (crystal idioblasts) reveals the regulation of bioaccumulated Cu and Na⁺ by complexing with CaOx. Thus the study suggested that, 400 mM NaCl and 0.15 mM CuSO₄ treatments does not have negative impact on plant growth, the NaCl tolerance potential compromised in the presence of mild CuSO₄ concentration during combined stress.

Detection of Cadmium Risk to the Photosynthetic Performance of Hybrid Pennisetum

Photosynthesis plays an essential role in plant growth and crop yield, and the mechanisms of the effects of cadmium (Cd) on photosynthetic performance require more attention. The acute toxicity of Cd in soil to the photosynthetic capacity of Hybrid Pennisetum was evaluated using gas exchange parameters, A/Ci curves, light response curves, and chlorophyll a fluorescence transients after exposure to elevated Cd concentrations (0, 10, 20, 50, 70, and 100 mg kg-1) for a 3-month period. The results indicated that leaf Cd concentration in Hybrid Pennisetum increased with the strength of soil Cd stress and ranged from 4.9 to 15.8 μg g-1 DW. The accumulation of leaf Cd severely restricted photosynthesis and its non-stomatal limitation in regulating the photosynthetic performance of Hybrid Pennisetum. The leaf chloroplasts at 10 and 20 mg kg-1 Cd concentrations showed no noticeable change, but the chlorophyll content significantly decreased by 9.0-20.4% at 50-100 mg kg-1 Cd concentrations. The Cd treatments also decreased plant ribulose-1,5-bisphosphate (RuBP) activity (Vcmax ) and regeneration capacity (Jmax ), triose phosphate utilization (TPU), light-saturated photosynthesis (Amax ), apparent quantum yield (AQY), light saturation point (LSP), and dark respiration (Rday ), but Cd treatment increased the light compensation point (LCP). The shape of chlorophyll a fluorescence transients in leaves was altered under different Cd treatments. The increased OJ phase and the decreased IP phase in fluorescence induction curves suggested that Cd toxicity inhibited both light use efficiency and photodamage avoidance ability. These results suggested that the decrease in photosynthesis through exposure to Cd may be a result of the decrease in leaf chlorophyll content, Rubisco activity, and RuBP regeneration, inhibition of triose phosphate utilization, reduction of the ability to use light and provide energy, and restrictions on electron transport in PSII.

Comparative physiological and proteomic analyses of the chloroplasts in halophyte Sesuvium portulacastrum under differential salt conditions

Sesuvium portulacastrum, an important mangrove-associated true halophyte belongs to the family Aizoaceae, has excellent salt tolerance. Chloroplasts are the most sensitive organelles involved in the response to salinity. However, the regulation mechanism of chloroplasts of S. portulacastrum under salinity stress has not been reported. In this study, morphological and physiological analyses of leaves and comparative proteomics of chloroplasts isolated from the leaves of S. portulacastrum under different NaCl treatments were performed. Our results showed that the thickness of the palisade tissue, the leaf area, the maximum photochemical efficiency of photosystem II, and the electron transport rate increased remarkably after the plants were subjected to differential saline environments, indicating that salinity can increase photosynthetic efficiency and improve the growth of S. portulacastrum. Subsequently, 55 differentially expressed protein species (DEPs) from the chloroplasts of S. portulacastrum under differential salt conditions were positively identified by mass spectrometry. These DEPs were involved in multiple metabolic pathways, such as photosynthesis, carbon metabolism, ATP synthesis and the cell structure. Among these DEPs, the abundance of most proteins was induced by salt stress. Based on a combination of the morphological and physiological data, as well as the chloroplast proteome results, we speculated that S. portulacastrum can maintain photosynthetic efficiency and growth by maintaining the stability of the photosystem II complex, promoting the photochemical reaction rate, enhancing carbon fixation, developing plastoglobules, and preserving the biomembrane system of chloroplasts under salt stress.

Salinity influences the interactive effects of cadmium and zinc on ethylene and polyamine synthesis in the halophyte plant species Kosteletzkya pentacarpos

Salt marshes are major sinks for heavy metals where plants are often exposed to polymetallic contamination and high salinity. Seedlings from the wetland halophyte plant species Kosteletzkya pentacarpos were exposed during three weeks to nutrient solution containing 10 μM CdCl₂, 100 μM ZnCl₂ or a combination of the two metals (Cd + Zn) in the presence or absence of 50 mM NaCl. Synthesis of the senescing hormone ethylene was quantified together with the concentration of protecting polyamines (spermidine and spermine) and their precursor putrescine and analyzed in relation to senescence markers (soluble protein, malondialdehyde, chlorophyll content and assessment of cell membrane stability). Salinity reduced the deleterious impact of heavy metals on plant growth and decreased accumulation of the pollutants in the plants. Heavy metals increased ethylene synthesis but NaCl decreased it in plants exposed to Cd or to the combined treatment (Cd + Zn) but not in plants exposed to Zn alone. Putrescine increased while spermine and spermidine decreased in Cd-treated plants. Zinc had only a marginal impact on polyamine concentration. The highest putrescine and spermine concentrations were observed in plants exposed to the combined treatment. The inhibitor of ethylene synthesis (AVG; aminovynilglycine) partially restored plant growth, reduced putrescine content and increased spermidine and spermine concentration, leading to an attenuation of senescence, mainly in Cd-treated plants. Combined treatment induced a specific physiological status in K. pentacarpos which could not be fully explained by an additive effect of Cd and Zn. Results are discussed in relation to specificities of heavy metals impacts on plant response.

NaCl impact on Kosteletzkya pentacarpos seedlings simultaneously exposed to cadmium and zinc toxicities

Data regarding NaCl impact on halophyte plant species exposed to a polymetallic contamination remain scarce. Seedlings of the salt marsh species Kosteletzkya pentacarpos were simultaneously exposed to cadmium (10 μM) and zinc (100 μM) in the absence or presence of 50 mM NaCl. Heavy metal exposure reduced plant growth and increased Cd and Zn concentrations in all organs. Cd and Zn accumulation reduced net photosynthesis in relation to stomatal closure, decreased in chlorophyll concentration and alteration in chlorophyll fluorescence-related parameters. Salinity reduced Cd and Zn bioaccumulation and translocation, with a higher impact on Cd than Zn. It mitigated the deleterious impact of heavy metals on photosynthetic parameters. NaCl reduced the heavy metal-induced oxidative stress assessed by malondialdehyde, carbonyl, and H₂O₂ concentration. Subcellular distribution revealed that Cd mainly accumulated in the cell walls, but NaCl increased it in the cytosol fraction in the leaf and in the metal-rich granule fraction in the roots. It had no impact on Zn subcellular distribution. The additional NaCl contributed to a higher sequestration of Cd on phytochelatins and stimulated glutathione synthesis. The positive impact of NaCl on K. pentacarpos response to polymetallic pollution made this species a promising candidate for revegetation of heavy metal-contaminated salt areas.