Effects of exogenous spermidine on poplar resistance to leaf and root herbivory as affected by soil cadmium stress

Cadmium induced defense enhance the invasive potential of Wedelia trilobata under herbivore infestation

Cadmium (Cd) pollution is on the rise due to rapid urbanization, which emphasize the potential adverse effects on plant biodiversity and human health. Wedelia as a dominant invasive species, is tested for its tolerance to Cd-toxicity and herbivore infestation. We investigate defense mechanism system of invasive Wedelia trilobata and its native congener Wedelia chinensis against the Cd-pollution and Spodoptera litura infestation. We found that Cd-toxicity significantly increase hydrogen peroxide (H2O2), Malondialdehyde (MDA) and hydroxyl ions (O2•) in W. chinensis 20.61%, 4.78% and 15.68% in leave and 27.44%, 25.52% and 30.88% in root, respectively. The photosynthetic pigments (Chla, Chla and Caro) and chlorophyll florescence (Fo and Fv/Fm) declined by (60.23%, 58.48% and 51.96%), and (73.29% and 55.75%) respectively in W. chinensis and (44.76%, 44.24% and 44.30%), and (54.66% and 45.36%) in W. trilobata under Cd treatment and S. litura. Invasive W. trilobata had higher enzymatic antioxidant SOD 126.9/71.64%, POD 97.24/94.92%, CAT 53.99/25.62% and APX 82.79/50.19%, and nonenzymatic antioxidant ASA 10.47/16.87%, DHA 15.07/27.88%, GSH 15.91/10.03% and GSSG 13.56/17.93% activity in leaf/root, respectively. Overall, W. trilobata accumulate higher Cd content 55.41%, 50.61% and 13.95% in root, shoot and leaf tissues respectively, than its native congener W. chinensis. While, nutrient profile of W. chinensis reveals less uptake of Fe, Cu and Zn than W. trilobata. W. trilobata showed efficient alleviation of oxidative damage through upregulating the genes related to key defense such as SOD, POD, CAT, APX, GR, PROL, FLV, ABA and JAZ, and metal transporter in leaves, shoot and root tissues, respectively. Conclusively, W. trilobata efficiently employed Cd-triggered defense for successful invasion, even under S. litura infestation, in Cd-contaminated soil.

Advances in the Involvement of Metals and Metalloids in Plant Defense Response to External Stress

Plants, as sessile organisms, uptake nutrients from the soil. Throughout their whole life cycle, they confront various external biotic and abiotic threats, encompassing harmful element toxicity, pathogen infection, and herbivore attack, posing risks to plant growth and production. Plants have evolved multifaceted mechanisms to cope with exogenous stress. The element defense hypothesis (EDH) theory elucidates that plants employ elements within their tissues to withstand various natural enemies. Notably, essential and non-essential trace metals and metalloids have been identified as active participants in plant defense mechanisms, especially in nanoparticle form. In this review, we compiled and synthetized recent advancements and robust evidence regarding the involvement of trace metals and metalloids in plant element defense against external stresses that include biotic stressors (such as drought, salinity, and heavy metal toxicity) and abiotic environmental stressors (such as pathogen invasion and herbivore attack). We discuss the mechanisms underlying the metals and metalloids involved in plant defense enhancement from physiological, biochemical, and molecular perspectives. By consolidating this information, this review enhances our understanding of how metals and metalloids contribute to plant element defense. Drawing on the current advances in plant elemental defense, we propose an application prospect of metals and metalloids in agricultural products to solve current issues, including soil pollution and production, for the sustainable development of agriculture. Although the studies focused on plant elemental defense have advanced, the precise mechanism under the plant defense response still needs further investigation.

Polyamines and hormesis: Making sense of a dose response dichotomy

The diverse biological effects of polyamines (putrescine, spermidine and spermine) were reviewed in the context of hormesis in an integrative manner for the first time. The findings illustrate that each of these polyamines commonly induces hormetic dose responses in a wide range of biological models and types of cells for multiple endpoints in numerous plant species and animal models. Plant research emphasized preconditioning experimental studies in which the respective polyamines conferred some protection against the damaging effects of a broad range of environmental stressors such as drought, salinity, cold/heat, heavy metals and UV-damage in an hormetic manner. Polyamine-based animal hormesis studies emphasized biomedical endpoints such as longevity and neuroprotection. These findings have important biological and biomedical implications and should guide experimental designs of low dose investigations.

CaSPDS, a Spermidine Synthase Gene from Pepper (Capsicum annuum L.), Plays an Important Role in Response to Cold Stress

Spermidine synthase (SPDS) is a key enzyme in the polyamine anabolic pathway. SPDS genes help regulate plant response to environmental stresses, but their roles in pepper remain unclear. In this study, we identified and cloned a SPDS gene from pepper (Capsicum annuum L.), named CaSPDS (LOC107847831). Bioinformatics analysis indicated that CaSPDS contains two highly conserved domains: an SPDS tetramerisation domain and a spermine/SPDS domain. Quantitative reverse-transcription polymerase chain reaction results showed that CaSPDS was highly expressed in the stems, flowers, and mature fruits of pepper and was rapidly induced by cold stress. The function of CaSPDS in cold stress response was studied by silencing and overexpressing it in pepper and Arabidopsis, respectively. Cold injury was more serious and reactive oxygen species levels were greater in the CaSPDS-silenced seedlings than in the wild-type (WT) seedlings after cold treatment. Compared with the WT plants, the CaSPDS-overexpression Arabidopsis plants were more tolerant to cold stress and showed higher antioxidant enzyme activities, spermidine content, and cold-responsive gene (AtCOR15A, AtRD29A, AtCOR47, and AtKIN1) expression. These results indicate that CaSPDS plays important roles in cold stress response and is valuable in molecular breeding to enhance the cold tolerance of pepper.

UVB-Pretreatment-Enhanced Cadmium Absorption and Enrichment in Poplar Plants

The phenomenon of cross adaptation refers to the ability of plants to improve their resistance to other stress after experiencing one type of stress. However, there are limited reports on how ultraviolet radiation B (UVB) pretreatment affects the enrichment, transport, and tolerance of cadmium (Cd) in plants. Since an appropriate UVB pretreatment has been reported to change plant tolerance to stress, we hypothesized that this application could alter plant uptake and tolerance to heavy metals. In this study, a woody plant species, 84K poplar (Populus alba × Populus glandulosa), was pretreated with UVB and then subjected to Cd treatment. The RT-qPCR results indicated that the UVB-treated plants could affect the expression of Cd uptake, transport, and detoxification-related genes in plants, and that the UVB-Pretreatment induced the ability of Cd absorption in plants, which significantly enriched Cd accumulation in several plant organs, especially in the leaves and roots. The above results showed that the UVB-Pretreatment further increased the toxicity of Cd to plants in UVB-Cd group, which was shown as increased leaf malonaldehyde (MDA) and hydrogen peroxide (H₂O₂) content, as well as downregulated activities of antioxidant enzymes such as Superoxide Dismutase (SOD), Catalase (CAT), and Ascorbate peroxidase (APX). Therefore, poplar plants in the UVB-Cd group presented a decreased photosynthesis and leaf chlorosis. In summary, the UVB treatment improved the Cd accumulation ability of poplar plants, which could provide some guidance for the potential application of forest trees in the phytoremediation of heavy metals in the future.

A novel phytoremediation technology for polluted cadmium soil: Salix integra treated with spermidine and activated carbon

A variety of plants have been used as phytoremediation materials to remove Cd from polluted soil. However, the disadvantages of using plants for decontamination include low biomass, low uptake, and inefficiency. We conducted experiments to determine the effects of spermidine and activated carbon treatments of Salix integra on Cd removal. The results showed that exogenous spermidine and activated carbon increased plant growth and root development compared with the CK. The increased dry mass (39.65-92.95%) with the combined spermidine and activated carbon treatments was higher than that with either single treatment (14.79-62.80%). The root length, surface area, root volume, and root diameter with the combined spermidine and activated carbon treatments (53.51-189.35%, 113.08-207.62%, 111.71-499.27%, and 32.51-106.62%, respectively) were higher than those of the lone application treatments (19.35-132.23%, 52.33-111.57%, 35.08-297.07%, and 24.22-81.38%, respectively). In addition, spermidine and activated carbon application reduced the toxicity of Cd to S. integra by improving the antioxidant capacity, thereby increasing the accumulation of Cd. The application of spermidine and activated carbon also changed the distribution of Cd in each part of S. integra. There was increased accumulation of Cd in the shoots and better absorption by the S. integra shoots, thereby improving their Cd remediation efficiency. The combined 0.8 mM spermidine and 0.5 g kg^-1 activated carbon were most effective on removing Cd from the soil. The Cd removal efficiency was 78.11-120.86% higher than that of the CK. Our results may provide foundational information for understanding the mechanisms for the sustainable remediation of Cd-contaminated soil using a combination of spermidine and activated carbon.

Integrative chemical and omics analyses reveal copper biosorption and tolerance mechanisms of Bacillus cereus strain T6

A comprehensive understanding of the cellular response of microbes to metal stress is necessary for the rational development of microbe-based biosorbents for metal removal. The present study investigated the copper (Cu) sorption and resistance mechanism of Bacillus cereus strain T6, a newly isolated Cu-resistant bacterium, by integrative analyses of physiochemistry, genomics, transcriptomics, and metabolomics. The growth inhibition assay and biosorption determination showed that this bacterium exhibited high tolerance to Cu, with a minimum inhibitory concentration of 4.0 mM, and accumulated Cu by both extracellular adsorption and intracellular binding. SEM microscopic images and FTIR spectra showed significant cellular surface changes at the high Cu level but not at low, and the involvement of surface functional groups in the biosorption of Cu, respectively. Transcriptomic and untargeted metabolomic analyses detected 362 differentially expressed genes and 60 significantly altered metabolites, respectively. Integrative omics analyses revealed that Cu exposure dramatically induced a broad spectrum of genes involved in Cu transport and iron homeostasis, and suppressed the denitrification pathway, leading to significant accumulation of metabolites for metal transporter synthesis, membrane remolding, and antioxidant activities. The results presented here provide a new perspective on the intricate regulatory network of Cu homeostasis in bacteria.

Genome-wide analysis and expression profiling of Cation/H+ exchanger (CAX) family genes reveal likely functions in cadmium stress responses in poplar

Cadmium, a toxic heavy metal, seriously affects human health and ecological security. The cation/H⁺ exchanger (CAX) family is a unique metal transporter that plays a crucial role in Cd acquisition, transfer, and remission in plants. Although there are many studies related to the genome-wide analysis of Populus trichocarpa, little research has been done on the CAX family genes, especially concerning Cd stress. In this study, genome-wide analysis of the Populus CAX family identified seven stress-related CAX genes. The evolutionary tree indicated that the CaCA family genes were grouped into four clusters. Moreover, seven pairs of genes were derived by segmental duplication in poplars. Cis-acting element analysis identified numerous stress-related elements in the promoters of diverse PtrCAXs. Furthermore, some PtrCAXs were up-regulated by drought, beetle, and mechanical damage, indicating their possible function in regulating stress response. Under cadmium stress, all CAX genes in the roots were up-regulated. Our findings suggest that plants may regulate their response to Cd stress through the TF-CAXs module. Comprehensively investigating the CAX family provides a scientific basis for the phytoremediation of heavy metal pollution by Populus.