Lanthanum ions intervened in enzymatic production and elimination of reactive oxygen species in leaves of rice seedlings under cadmium stress

Application of Lanthanum at the Heading Stage Effectively Suppresses Cadmium Accumulation in Wheat Grains by Downregulating the Expression of TaZIP7 to Increase Cadmium Retention in Nodes

Reducing cadmium (Cd) accumulation in wheat is an effective way to decrease the potential threats of Cd to human health. The application of lanthanum (La) in agricultural fields is eliciting extensive attention due to its beneficial effects on improving yields and inhibiting Cd accumulation in edible parts of crops. However, the potential mechanism of La-restricted Cd accumulation in crop grains is not entirely understood. Here, we investigated the effects of La and Cd accumulation in wheat grains by implementing application at the shooting and heading stages. Some associated mechanisms were explored. Results showed that La application at the shooting and heading stages considerably promoted the thousand-grain weight. La application at the shooting and heading stages increased Cd accumulation in the first node beneath the panicle (N1) but reduced Cd levels in the other tissues. La application at the heading stage exerted greater effects on Cd storage in N1 while reducing Cd concentrations in the other tissues compared with La application at the shooting stage. La addition substantially decreased the translocation of Cd from the lower nodes to the upper internodes, but increased Cd translocation from the lower internodes to the upper nodes. The expression of TaZIP7 in N1 was downregulated by La treatment. These results suggest that the effective reduction in Cd in wheat grains by La application at the heading stage is probably a consequence of the successful promotion of Cd storage in nodes by downregulating the expression of TaZIP7 during the grain-filling stage, thereby hindering the redirection Cd from nodes to grains.

Lanthanum(III)-amino acid chelate mitigates copper(II) stress in rice (Oryza sativa)

Lanthanum (La(III)) is recognized for its ability to mitigate heavy metal stress in plants. However, the inorganic La(III) salts and lanthanum oxide nanoparticles (La2O3 NPs) extensively used in agriculture are prone to soil immobilization, thereby compromising their bioavailability and posing environmental risks. This study synthesized and characterized the lanthanum(III)-amino acid chelate (La(III)-AA) from soybean protein isolate (SPI) hydrolysates. Maximum chelating rate (94.95%) was achieved under the conditions of mole ratio 1:1.5, pH 8.0, 50 ℃ and 5 h. Glu, Asp and Pro represent the primary La(III)-binding ligands. UV-vis and FTIR demonstrated that amino nitrogen and carboxyl oxygen participate in metal-ligand recognition. Scanning and Transmission electron microscopy showed that La(III) chelates with amino acids in a core-shell structure of uniform size. Consequently, a proposed chemical structure for the La(III)-AA complex was presented. A concentration of 20 mg/L La(III)-AA outperforms inorganic La salts in growth promotion and Cu detoxification. La(III)-AA significantly reduces the content of Cu (II) in rice tissues and enhances seedling tolerance to Cu (II) stress. This study provides a novel La(III)-based candidate for crop protection and furthers our understanding of rare earth element-induced mitigation of heavy metal stress.

Toxic effects of heavy metals Pb and Cd on mulberry (Morus alba L.) seedling leaves: Photosynthetic function and reactive oxygen species (ROS) metabolism responses

To explore the mechanism of how lead (Pb) and cadmium (Cd) stress affects photosynthesis of mulberry (Morus alba L.), we looked at the effects of different concentrations of Pb and Cd stress (at 100 and 200 μmol L^-1), which are two heavy metal elements, on leaf chlorophyll (Chl), photosynthesis gas exchange, Chl fluorescence, and reactive oxygen species (ROS) metabolism in mulberry leaves. The results showed that higher concentrations of Pb and Cd reduced leaf Chl content, especially in Chl a where content was more sensitive than in Chl b. Under Pb and Cd stress, the photosynthetic carbon assimilation capacity of mulberry leaves was reduced, which was a consequence of combined limitations of stomatal and non-stomatal factors. The main non-stomatal factors were decreased photosystem II (PSII) and photosystem I (PSI) activity and carboxylation efficiency (CE). Damage to the donor side of the PSII reaction center was greater than the acceptor side. After being treated with 100 μmol L^-1 of Pb and Cd, mulberry leaves continued to be able to dissipate excess excitation energy by starting non-photochemical quenching (NPQ), but when Pb and Cd concentrations were increased to 200 μmol L^-1, the protection mechanism that depends on NPQ was impaired. Excessive excitation energy from chloroplasts promoted a great increase of ROS, such as superoxide anion (O₂^•-) and H₂O₂. Moreover, under high Pb and Cd stress, superoxide dismutase (SOD) and ascorbate peroxidase (APX) were also inhibited to some extent, and excessive ROS also resulted in a significantly higher degree of oxidative damage. Compared with Cd, the effect of Pb stress at the same concentration level displayed a significantly lower impact on Chl content, photosynthetic carbon assimilation, and stomatal conductance. Meanwhile, Pb stress mainly damaged activity of the oxygen-evolving complex (OEC) located on PSII donor side, but it reduced the electronic pressure on the PSII acceptor side and PSI. Furthermore, under Pb stress, the NPQ, SOD, and APX activity were all significantly higher than those under Cd stress. Thus under Pb stress, the degree of photoinhibition and oxidative damage of PSII and PSI in mulberry leaves were significantly lower than under Cd stress.

Ameliorative effects of Lanthanum(Ⅲ) on Copper(Ⅱ) stressed rice (Oryza sativa) and its molecular mechanism revealed by transcriptome profiling

Rare earth elements are known to alleviate heavy metal stress. However, the potential mechanisms of the alleviation remain unclear. This study compared the effects of La(NO3)3 and La(NO3)3-amino acid chelates (La (Ⅲ)-AA) on growth, oxidative stress, ultrastructure, bioaccumulation and gene expression in rice. Results demonstrated that 20 mg/L La (Ⅲ)-AA can effectively ameliorate CuSO4 (50 mg/L) stress in rice by reducing oxidative stress and increasing chlorophyll content, thus promoting growth. ICP and TEM revealed an antagonistic effect between La (Ⅲ) and Cu(Ⅱ). Exogenous La (Ⅲ)-AA decreased Cu(Ⅱ) content in rice leaves, stems and roots by 55.56%, 59.46% and 26.29%, and ameliorated Cu(Ⅱ) damage by maintaining the ultrastructure of mesophyll cells. RNA sequencing identified 7020 differentially expressed genes, and 8 were validated by qRT-PCR. Indole-3-acetic acid (IAA) concentration was detected by HPLC. Correlation analysis between OsGH3.4-IAA-Expansin revealed that IAA content is negatively correlated with OsGH3.4 (r = -0.82, P < 0.05), and positively correlated with Expansin (r = 0.78, P < 0.05). It's assumed that La (Ⅲ)-induced OsGH3.4 could inhibit IAA-dependent Expansin expression, thereby conferring resistance to Cu stress. This work provides novel insights into the molecular basis underlying La (Ⅲ)-induced Cu(Ⅱ) tolerance in rice.

Root iron plaque alleviates cadmium toxicity to rice (Oryza sativa) seedlings

Iron plaque (IP) on root surface can enhance the tolerance of plants to environmental stresses. However, it remains unclear the impact of Fe²⁺ on cadmium (Cd) toxicity to rice (Oryza sativa) seedlings. In this study, the effects of different Fe²⁺ and Cd²⁺ concentration combinations on rice growth were examined hydroponically. Results indicated that Fe²⁺ concentration up to 3.2 mM did not damage rice roots while induced IP formation obviously. Cd²⁺ of 10 μM repressed rice growth significantly, while the addition of 0.2 mM Fe²⁺ to 10 μM Cd²⁺ solution (Cd+Fe) did not damage rice roots, indicating that Fe²⁺ could ameliorate Cd toxicity to rice seedlings. Microstructure analysis showed Cd+Fe treatment induced the formation of IP with dense and intricate network structure, Cd adsorption on the root surface was reduced significantly. Cd concentration of rice roots and shoots and Cd translocation from roots to shoots with Fe+Cd treatment were reduced by 34.1%, 36.0% and 20.1%, respectively, in comparison to a single Cd treatment. Noteworthy, the removal of IP resulted in a larger loss of root biomass under Cd treatment. In addition, Cd+Fe treatment increased the activities of root superoxide dismutase and catalase by 105.5% and 177.4%, and decreased H₂O₂ and O₂·^- accumulation of rice roots by 56.9% and 35.9%, and recovered Cd-triggered electrolyte leakage obviously, when compared with a single Cd treatment. The results from this experiment indicated that the formed dense IP on rice roots decreased Cd absorption and reactive oxygen species accumulation, and Fe²⁺ supply alleviated Cd toxicity to rice seedlings.

Ammonia exposure alters the expression of immune-related and antioxidant enzymes-related genes and the gut microbial community of crucian carp (Carassius auratus)

Chronic exposure of ammonia in fish can affect the activities of antioxidant enzymes but few studies investigate the influence of ammonia exposure on the expression of immune-related and antioxidant enzymes-related genes. Also, there is no study demonstrates the effect of ammonia exposure on gut microbial community of fish. In this study, crucian carp (Carassius auratus) were exposed to the ammonia concentrations, 0 (control), 10 mg L^-1 (low) or 50 mg L^-1 (high) for consecutive 30 days at 25 ± 1 °C temperature, respectively, and after that, the fish from all exposure groups were maintained in control conditions for another 15 days. The results showed that low concentration ammonia increased the expression of immune-related genes and antioxidant enzymes-related genes, but high concentration ammonia inhibited the expression of immune-related genes and antioxidant enzymes-related genes. After a 15-day treatment without ammonia, the expression of antioxidant enzymes-related genes and immune-related genes showed no significant changes compared with control. The results of high-throughput sequencing showed that gut microbial communities were significantly differentiated following ammonia exposure. The abundance of Bacteroides and Cetobacterium (two kinds of potential probiotics) increased while fish exposed to 10 mg L^-1 ammonia. The Flavobacterium (a potential fish pathogen) showed increasing trends when the exposure dose reached 50 mg L^-1, while the Bacteroides and Cetobacterium showed almost no abundance. The results also revealed that ammonia exposure concentration or time can alter the intestinal microbial community. In conclusion, ammonia exposure could induce the immune response in crucian carp, and alter the gut microbial community. The results may help us understand the correlations of gut microbial community shift and ammonia exposure and extend our knowledge to comprehend the effects of environmental factors on intestinal microbial community.

Hydrogen Peroxide, Signaling in Disguise during Metal Phytotoxicity

Plants exposed to excess metals are challenged by an increased generation of reactive oxygen species (ROS) such as superoxide ([Formula: see text]), hydrogen peroxide (H2O2) and the hydroxyl radical ((•)OH). The mechanisms underlying this oxidative challenge are often dependent on metal-specific properties and might play a role in stress perception, signaling and acclimation. Although ROS were initially considered as toxic compounds causing damage to various cellular structures, their role as signaling molecules became a topic of intense research over the last decade. Hydrogen peroxide in particular is important in signaling because of its relatively low toxicity, long lifespan and its ability to cross cellular membranes. The delicate balance between its production and scavenging by a plethora of enzymatic and metabolic antioxidants is crucial in the onset of diverse signaling cascades that finally lead to plant acclimation to metal stress. In this review, our current knowledge on the dual role of ROS in metal-exposed plants is presented. Evidence for a relationship between H2O2 and plant metal tolerance is provided. Furthermore, emphasis is put on recent advances in understanding cellular damage and downstream signaling responses as a result of metal-induced H2O2 production. Finally, special attention is paid to the interaction between H2O2 and other signaling components such as transcription factors, mitogen-activated protein kinases, phytohormones and regulating systems (e.g. microRNAs). These responses potentially underlie metal-induced senescence in plants. Elucidating the signaling network activated during metal stress is a pivotal step to make progress in applied technologies like phytoremediation of polluted soils.

Lanthanum rather than cadmium induces oxidative stress and metabolite changes in Hypericum perforatum

Physiology, oxidative stress and production of metabolites in Hypericum perforatum exposed to moderate Cd and/or La concentration (10 μM) were studied. La evoked increase in reactive oxygen species, malondialdehyde and proline but suppressed growth, tissue water content, glutathione, ascorbic acid and affected mineral nutrient contents more than Cd while the impact of Cd+La was not synergistic. Similar trend was observed at the level of superoxide dismutase gene expression. Shoot Cd amount increased in Cd+La while only root La increased in the same treatment. Extensive quantification of secondary metabolites revealed that La affected phenolic acids more pronouncedly than Cd in shoots and roots. Flavonols were suppressed by La that could contribute to the appearance of oxidative damage. Procyanidins increased in response to La in the shoots but decreased in the roots. Metabolic responses in Cd+La treatment resembled those of La treatment (almost identically in the roots). Phenylalanine ammonia-lyase activity was mainly suppressed by La. The presence of La also depleted amount of hypericin and expression of its putative gene (hyp-1) showed similar trend but accumulation of hyperforin increased under Cd or La excess. Clear differences in the stem and root anatomy in response to Cd or La were also found. Overall, H. perforatum is La-sensitive species and rather Cd ameliorated negative impact of La.