Application of TiO2 nanoparticles enhances physiological and molecular defense mechanisms against Cd stress in fragrant rice

Nitric oxide confers cadmium tolerance in fragrant rice by modulating physio-biochemical processes, yield attributes, and grain quality traits

Physiological and molecular mechanism of defense in cotton against Verticillium dahliae

Cadmium (Cd) contamination in agricultural soils and its accumulation in plant organs have become a global issue due to its harmful effects on human health. The in-situ stabilizing technique, which involves using organic amendments, is commonly employed for removing Cd from agricultural soils. Thus, the current study investigated the effect of vermicompost (VC) on soil properties and plant physio-biochemical attributes, leaf ultrastructure analysis, antioxidant defense mechanisms, and grain yields of two different fragrant rice cultivars, Xiangyaxiangzhan (XGZ) and Meixiangzhan-2 (MXZ-2), under Cd-stress conditions. The results showed that Cd toxicity deteriorates soil quality, the plant’s photosynthetic apparatus, and the plant’s antioxidant defense mechanism. Moreover, under Cd stress, both cultivars produced significantly lower (p < 0.05) rice grain yields compared to non-Cd stress conditions. However, the VC application alleviated the Cd toxicity and improved soil qualitative traits, such as soil organic carbon, available nitrogen, total nitrogen, phosphorus, and potassium. Similarly, VC amendments improved leaf physiological activity, photosynthetic apparatus function, antioxidant enzyme activities and its related gene expression under Cd stress These enhancements led to increased grain yields of both fragrant under Cd toxicity. The addition of VC mitigated the adverse effects of Cd on the leaf chloroplast structure by reducing Cd uptake and accumulation in tissues. This helped prevent Cd-induced peroxidation damage to leaf membrane lipids by increasing the activities of antioxidant enzymes such as ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). On average across the growth stages, the Pos-Cd + VC3 treatment increased SOD, APX, CAT, and POD activities by122.2 and 112.5%, 118.6, and 120.6%, 44.6 and 40.6%, and 38.6 and 33.2% in MXZ-2 and XGZ, respectively, compared to the plants treated with Pos-Cd treated alone. Enhancements in leaf physiological activity and plant antioxidant enzyme activity strengthen the plant’s antioxidant defense mechanism against Cd toxicity. In addition, correlation analysis showed a strong relationship between the leaf net photosynthetic rate and soil chemical attributes, suggesting that improved soil fertility enhances leaf physiological activity and boosts rice grain yields. Of the treatments, Pos-Cd + VC3 proved to be the most effective treatment in terms of enhancing soil health and achieving high fragrant rice yields. Thus, the outcomes of this study show that the addition of VC in Cd-contaminated soils could be useful for sustainable rice production and safe utilization of Cd-polluted soil.

Increasing evidence shows that cadmium (Cd) toxicity causes severe perturbations on growth performance, physio-biochemical and molecular processes in crop plants. Molybdenum (Mo), an essential trace element, plays key roles in oxidative stress tolerance of higher plants. Hence, the present study has been conducted to investigate the possible role of Mo in alleviating Cd-induced inhibitions in two fragrant rice cultivars namely Guixiangzhan (GXZ) and Meixiangzhan-2 (MXZ-2). The results revealed that Mo application enhanced the plant dry biomass by 73.24% in GXZ and 58.09% in MXZ-2 under Cd stress conditions, suggesting that Mo supplementation alleviated Cd-induced toxicity effects in fragrant rice. The enhanced Cd-tolerance in fragrant rice plants prompted by Mo application could be ascribed to its ability to regulate Cd uptake and reduce Cd-induced oxidative stress as evident by lower hydrogen peroxide levels, electrolyte leakage and malondialdehyde contents in Cd-stressed plants. The ameliorative role of Mo against Cd-toxicity also reflected through its protection to the photosynthetic pigments, proline and soluble protein. Mo also induced antioxidant defense systems via maintaining higher contents of glutathione and ascorbate as well as enhancing the ROS-detoxifying enzymes such as catalase, peroxidase, superoxide dismutase and ascorbate peroxidase activities and up-regulating transcript abundance in both fragrant rice cultivars under Cd stress. Conclusively, Mo-mediated modulation of Cd toxicity in fragrant rice was through restricting Cd uptake, maintaining photosynthetic performance and alleviating oxidative damages via the strong anti-oxidative defense systems; however, GXZ cultivar is comparatively more Cd tolerant and Mo-efficient as evident from the less growth inhibition and biomass reduction as well as enhanced Mo-induced Cd stress tolerance and less oxidative damage than MXZ-2 fragrant rice cultivar.

Molecular priming as an approach to induce tolerance against abiotic and oxidative stresses in crop plants

Cadmium (Cd) stress causes serious disruptions in plant metabolism, physio-biochemical responses, crop yield, and grain quality characteristics. A pot experiment was conducted to investigate the role of molybdenum (Mo) in mitigating Cd-induced adversities on plant growth, yield attributes, and grain quality characteristics of a popular aromatic rice cultivar ‘Xiangyaxiangzhan’. The Mo was applied at 0.15 mg kg−1 soil in both control (no Cd) and Cd-contaminated (100 mg kg−1) soils. A treatment with Mo-free (−Mo) soil was also maintained for comparison. The results showed that Cd toxicity significantly (p < 0.05) reduced plant dry biomass, grain yield, photosynthetic efficiency, and pigment contents, and impaired chloroplast ultra-structural configuration and simultaneously destabilized the plant metabolism owing to higher accumulation of hydrogen peroxide, electrolyte leakage, and malondialdehyde contents. However, Mo supply improved grain yield and 2-acetyl-1-pyrroline content by 64.75% and 77.09%, respectively, under Cd stress, suggesting that Mo supply mitigated Cd-provoked negative effects on yield attributes and grain quality of aromatic rice. Moreover, Mo supply enhanced photosynthesis, proline, and soluble protein content, and also strengthened plant metabolism and antioxidant defense through maintaining higher activities and transcript abundance of ROS-detoxifying enzymes at the vegetative, reproductive, and maturity stages of aromatic rice plants under Cd toxicity. Collectively, our findings indicated that Mo supply strengthened plant metabolism at prominent growth stages through an improved enzymatic and non-enzymatic antioxidant defense system, thereby increasing grain yield and quality characteristics of aromatic rice under Cd toxicity.

Fragrant rice is highly valued for its unique aroma but is vulnerable to heavy metal stress, particularly cadmium (Cd). This study investigates the effects of cerium oxide nanoparticles (CeO2-NPs) on growth, photosynthetic properties, antioxidant enzyme activities, and aroma synthesis in fragrant rice seedlings under Cd stress. Heavy metal contamination in agriculture, particularly cadmium, is exacerbated by its high mobility. Nanotechnology, particularly the application of cerium oxide nanoparticles (CeO2-NPs), presents a significant yet underexplored potential for mitigating these detrimental effects. Our results demonstrate that CeO2-NPs significantly enhance the tolerance of fragrant rice seedlings to Cd stress. This is achieved primarily by reducing Cd uptake and suppressing the expression of genes responsible for Cd uptake and translocation. CeO2-NPs also improve the antioxidant capacity of the seedlings, alleviate the impairment of the photosynthetic system under Cd stress, and promote root and overall plant growth. Additionally, CeO2-NPs increase the aroma content of fragrant rice by enhancing the activity of aroma-related enzymes, increasing proline content, and subsequently elevating the levels of 2-acetyl-1-pyrroline (2-AP), a key aromatic compound. The study underscores the dual role of CeO2-NPs in mitigating Cd toxicity and enhancing aromatic quality in fragrant rice. These findings suggest that CeO2-NPs are a promising tool for protecting and improving the quality of fragrant rice in Cd-contaminated environments, offering a potential strategy for managing heavy metal stress in agriculture.

The present study evaluated the physiological and biochemical mechanisms through which exogenous salicylic acid (SA) mitigates cadmium (Cd) stress in maize. The different concentrations of Cd included 0, 5, 10 µM CdCl2.3H2O. Half of plants received salicylic acid as a soil drench. Results showed that Cd exposure reduced chlorophyll contents, chlorophyll fluorescence, photosynthetic rate and activity of catalase (CAT). However, Cd stress enhanced non-photochemical quenching (NPQ), the production of malondialdehyde (MDA) and activities of key antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (POD). The increased activities of antioxidant enzymes and concentration of MDA were reduced by exogenous application of SA as a soil drench. Our research proves that SA, as a novel endogenous plant hormone exerts beneficial physiological effects on plants as it has a dual role in scavenging active oxygen species (AOS) and modulating redox balance to enhance photosynthetic performance in cadmium-stressed maize plants. It was concluded that SA improved plant tolerance under Cd contamination and may have alleviated the inhibitory effect of Cd on photosynthesis by protecting maize plants against oxidative damage as indicated by the marked decline in net photosynthetic rates, quantum yield and chlorophyll content as well as alteration of antioxidants activity and accumulation of MDA. Collectively, results of the present study provide an insight into the alleviative role of SA in Cd-stressed maize and propose SA as a potential candidate in mitigating Cd toxicity.

Simple SummaryApart from their direct entomopathogenicity, many entomopathogenic fungi synthesize protein molecules that can trigger plant defense mechanisms against herbivore insect pests. This laboratory study determined the sub-lethal effects of a partially purified protein derived from Beauveria bassiana against whitefly Bemisia tabaci on tomato plants along with the subsequent gene expression analyses of key gens potentially linked to jasmonic acid (JA) and salicylic acid (SA) associated plant defense pathways. The exogenous foliar application of B. bassiana-derived protein significantly reduced the whitefly survival and fecundity parameters concomitantly with an up-regulation of all the plant defense associated genes, particularly of SA pathway genes. These findings demonstrate the putative role of this partially purified entomopathogenic fungal protein and suggest its further purification and characterization for using in future microbial pest control strategies against whiteflies and other sap-feeding insect pests.Plants rely on various physiological and molecular defense mechanisms against biotic stresses such as herbivore insects. Many entomopathogenic fungi synthesize protein molecules that can trigger these plant defenses. This laboratory study characterized the bioactivity of a partially purified protein derived from Beauveria bassiana (ARSEF 2860) against whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), which is an economically important pest of agricultural and horticultural crops worldwide. Different concentrations (i.e., 0.021, 0.042 and 0.063 μM) of fungal protein were bioassayed to determine their sub-lethal effect on the survival percentage and fecundity rate of B. tabaci on tomato (Lycopersicon esculentum) plants. In addition, the putative role of this partially purified B. bassiana protein in the defense mechanisms of plant was assessed through the expression analyses of important genes related to salicylic acid (SA)—and jasmonic acid (JA)—associated pathways using RT-qPCR. Results revealed a significant suppression of the survival percentage and fecundity rate of B. tabaci by the fungal protein. Lowest survival (41%) was recorded for the highest concentration of protein (0.063 μM), whereas mean survival for the other two protein concentrations (0.042 and 0.021 μM) were 62 and 71%, respectively. Likewise, the highest and lowest mean fecundity rates were observed for the control and the highest protein concentration (i.e., 3.3 and 1.8 eggs day−1 female−1, respectively). Furthermore, the exogenous application of B. bassiana-derived protein on tomato plants strongly up-regulated the SA-related genes (PAL, PR1, BGL2 and EDS1) and slightly up-regulated the JA-related genes (AOC, AOS, OPR3 and LOX) as compared to the control plants. These findings demonstrate the putative role of this partially purified B. bassiana protein fraction in inducing systemic resistance in the tomato plants against B. tabaci, suggesting its further purification and characterization to be used as novel biological pest control tool against B. tabaci and other sap-sucking insect pests.

Tea plant (Camellia sinensis (L) O. Kuntze) respond to herbivore attack through large changes in defense related metabolism and gene expression. Ectropis oblique (Prout) is one of the most devastating insects that feed on tea leaves and tender buds, which can cause severe production loss and deteriorate the quality of tea. To elucidate the biochemicals and molecular mechanism of defense against tea geometrid (TG), transcriptome and metabolome of TG interaction with susceptible (SG) and resistance (RG) tea genotypes were analyzed by using UPLC-Q-TOF-MS, GC-MS, and RNA-seq technologies. This revealed that jasmonic acid was highly induced in RG, following a plethora of secondary metabolites involved in defense against TG could be induced by jasmonic acid signaling pathway. However, the constitutively present of salicylic acid in SG might be a suppressor of jasmonate signaling and thus misdirect tea plants against TG. Furthermore, flavonoids and terpenoids biosynthesis pathways were highly activated in RG to constitute the chemical barrier on TG feeding behavior. In contrast, fructose and theanine, which can act as feeding stimulants were observed to highly accumulate in SG. Being present in the major hub, 39 transcription factors or protein kinases among putative candidates were identified as master regulators from protein-protein interaction network analysis. Together, the current study provides a comprehensive gene expression and metabolite profiles, which can shed new insights into the molecular mechanism of tea defense against TG. The candidate genes and specific metabolites identified in the present study can serve as a valuable resource for unraveling the possible defense mechanism of plants against various biotic stresses.

Cadmium (Cd) pollution in soil has become a major environmental issue worldwide. However, the underlying molecular mechanism of low grain-Cd accumulation (GCA) in maize is still largely unknown. Herein, we report the mechanistic basis for low GCA in maize by a multiomics approach. The low GCA genotype L63 showed normal vacuolar formation and a lower capacity of xylem loading of Cd than the high-accumulator L42 under Cd stress. Transcriptomic sequencing identified 84 low-GCA-associated genes which are mainly involved in the S-adenosylmethionine (SAM) cycle, metal transport, and vacuolar sequestration. A metabolome analysis revealed that L63 plants had a more active SAM cycle and a greater capacity for terpenoid synthesis and phenylalanine metabolism than L42. Combining the analysis of transcriptome and metabolome characterized several genes as key genes involved in the determination of Cd accumulation. Our study identifies a mechanistic basis for low Cd accumulation in maize grains and provides candidate genes for genetic improvement of crops.

The contamination of Chinese medicinal materials with cadmium (Cd) is a pressing global issue that poses significant risks to human health. The beneficial effects of selenium (Se) have been established in improving plant growth and reducing Cd accumulation in plant under Cd stress. This study employed soil cultivation experiments to investigate the remediation effects of exogenous Se (0, 0.5, 1, and 2 mg kg⁻1) under varying levels of Cd stress (0, 0.6 and 4 mg kg⁻1). The findings revealed that Cd stress markedly impaired seedling growth, biomass, and physiological characteristics in Artemisia argyi. Regardless of Cd levels, exogenous Se significantly enhanced seedling biomass, improved antioxidant enzyme activity, and increased the plant’s antioxidant capacity, thereby mitigating Cd stress. Additionally, exogenous Se promoted A. argyi plant growth, decreased malondialdehyde (MDA) content in the shoots, and under two Cd stress environments of 0.6 and 4 mg kg⁻1, the application of 1 mg kg⁻1 Se reduced the Cd content in the aboveground parts of seedlings by 31.99 and 82.21%, respectively. We conclude 1 mg kg⁻1 Se could represent a promising strategy to contribute to the development and sustainability of crop production on soils contaminated with Cd at a concentration of up to 0.6 and 4 mg kg⁻1. These results indicate that exogenous Se activates physiological and biochemical defense mechanisms in A. argyi seedlings against Cd stress, offering a foundation for cultivating high-yield, high-quality A. argyi in Cd-contaminated soils.

Different maize varieties respond differentially to cadmium (Cd) stress. However, the physiological mechanisms that determine the response are not well defined. Antioxidant systems and sucrose metabolism help plants to cope with abiotic stresses, including Cd stress. The relationship of these two systems in the response to Cd stress is unclear. Seed is sensitive to Cd stress during germination. In this study, we investigated changes in the antioxidant system, sucrose metabolism, and abscisic acid and gibberellin concentrations in two maize varieties with low (FY9) or high (SY33) sensitivities to Cd under exposure to CdCl2 (20 mg L−1) at different stages of germination (3, 6, and 9 days).The seed germination and seedling growth were inhibited under Cd stress. The superoxide, malondialdehyde, and proline concentrations, and the superoxide dismutase, peroxidase, catalase, and lipoxygenase activities increased compared with those of the control (CK; without Cd). The expression levels of three genes (ZmOPR2, ZmOPR5, and ZmPP2C6) responsive to oxidative stress increased differentially in the two varieties under Cd stress. The activity of the antioxidant system and the transcript levels of oxidative stress–responsive genes were higher in the Cd-tolerant variety, FY9, than in the sensitive variety, SY33. Sucrose metabolism was increased under Cd stress compared with that of the CK and was more active in the Cd-sensitive variety, SY33. These results suggest that the antioxidant system is the first response to Cd stress in maize, and that sucrose metabolism is cooperative and complementary under exposure to Cd.

GABA-mediated inhibition of cadmium uptake and accumulation in apples

Heavy metal (HM) exposure is a critical abiotic stress that adversely affects plant growth, development, and agricultural sustainability. While trace amounts of HMs are essential for cellular processes, excessive accumulation disrupts osmotic balance, induces oxidative stress, and leads to severe metabolic disorders. This leads to excessive production of reactive oxygen species (ROS) and methylglyoxal. These compounds cause lipid peroxidation, protein and enzyme damage, DNA disruption, and overall cellular dysfunction. To mitigate HM toxicity, plants employ a range of physiological, biochemical, and molecular defense mechanisms, including antioxidant enzyme systems, metal chelation, phytohormonal regulation, and genetic adaptations. Recent advancements in genetic engineering, nanotechnology, and OMICs approaches have further enhanced our understanding of plant responses to HM stress, paving the way for innovative remediation strategies. This review explores the multifaceted impact of HMs on plant physiology and highlights adaptive responses that contribute to HM tolerance and stress mitigation.