Tolerance To Cd Stress Research Articles

Epigenetics for crop adaptation to climate change

Epigenetics for crop adaptation to climate change

Overexpression of acdS in Petunia hybrida Improved Flower Longevity and Cadmium-Stress Tolerance by Reducing Ethylene Production in Floral and Vegetative Tissues.

The role of acdS, which encodes the 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase enzyme, in extending flower longevity and improving tolerance to cadmium (Cd) stress was assessed using transgenic Petunia hybrida cv. ‘Mirage Rose’ overexpressing acdS and wild-type (WT) plants. The overexpression of acdS reduced ethylene production in floral tissue via suppression of ethylene-related genes and improved flower longevity, approximately 2 to 4 days longer than WT flowers. Under Cd stress, acdS significantly reduced Cd-induced ethylene production in vegetable tissues of transgenic plants through suppression of ethylene-related genes. This resulted in a lower accumulation of ethylene-induced reactive oxygen species (ROS) in the transgenic plants than in WT plants. In addition, expression of the genes involved in the activities of antioxidant and proline synthesis as well as the metal chelation process was also higher in the former than in the latter. Moreover, Cd accumulation was significantly higher in WT plants than in the transgenic plants. These results are linked to the greater tolerance of transgenic plants to Cd stress than the WT plants, which was determined based on plant growth and physiological performance. These results highlight the potential applicability of using acdS to extend flower longevity of ornamental bedding plants and also reveal the mechanism by which acdS improves Cd-stress tolerance. We suggest that acdS overexpression in plants can extend flower longevity and also help reduce the negative impact of Cd-induced ethylene on plant growth when the plants are unavoidably cultivated in Cd-contaminated soil.

OsNAC15 Regulates Tolerance to Zinc Deficiency and Cadmium by Binding to OsZIP7 and OsZIP10 in Rice.

Zinc (Zn) deficiency and cadmium (Cd) stress are severe threats to the growth and development of plants. Increasing Zn content and/or decreasing Cd content in grain are also important objectives of rice breeding. However, the molecular mechanisms of Zn deficiency tolerance (ZDT) and Cd stress tolerance (CDT) are largely unknown in rice. Here, we report that a NAM/CUC2-like transcription factor, OsNAC15, contributes to ZDT and CDT in rice. Knockout of OsNAC15 reduced ZDT and CDT at the vegetative stage. OsNAC15 expresses in all tissues of different developmental stages, and is repressed by Zn deficiency and induced by Cd stress. OsNAC15 is a functional transcription factor with transactivation and DNA binding activities. Expression analysis of rice ZIP family genes suggested that the knockout of OsNAC15 activates or inhibits their transcriptions under Zn deficiency or Cd stress conditions. The yeast one-hybrid assay, transient transcriptional activity assay using the dual-luciferase reporter system and electrophoretic mobility shift assay demonstrated that OsNAC15 directly binds to the zinc deficiency-responsive element motifs in the promoters of OsZIP7 and OsZIP10 to repress their transcriptions. The OsNAC15–OsZIP7/10 module is an essential foundation for further study on the regulatory mechanisms of ZDT and CDT in rice.

Melatonin and nitric oxide: Dual players inhibiting hazardous metal toxicity in soybean plants via molecular and antioxidant signaling cascades

Melatonin (MT), a ubiquitous signaling molecule, is known to improve plant growth. Its regulatory function alongside nitric oxide (NO) is known to induce heavy metal (Cd and Pb) stress tolerance, although the underlying mechanisms remain unknown. Here, we observed that the combined application of MT and NO remarkably enhanced plant biomass by reducing oxidative stress. Both MT and NO minimized metal toxicity by significantly lowering the levels of endogenous abscisic acid and jasmonic acid via downregulating NCED3 and upregulating catabolic genes (CYP707A1 and CYP707A2). MT/NO-induced mitigation of Cd and Pb stress was associated with increased endo-melatonin and variable endo-S-nitrosothiol levels caused by enhanced expression of gmNR and gmGSNOR mRNAs. Remarkably, the combined application of MT/NO reduced soil Cd and Pb mobilization by increasing the uptake of Ca2+ and K+ and increasing the exudation of organic acids into the rhizosphere. These results correlated with the upregulation of MTF-1 and WARKY27 during metal translocation. MT/NO regulates the MAPK and CDPK cascades to promote plant cell survival and Ca2+ signaling, thereby imparting resistance to heavy metal toxicity. In conclusion, MT/NO modulates the stress-resistance machinery to mitigate Cd and Pb toxicity by regulating the activation of antioxidant and molecular transcription factors.

Physiological and metabolic dynamism in mycorrhizal and non-mycorrhizal Oryza sativa (var. Varsha) subjected to Zn and Cd toxicity: a comparative study.

Arable lands getting contaminated with heavy metals have a very high negative impact on crop plants. The establishment of the mycorrhizal association with crop plants is a sustainable strategy to overcome metal toxicity. The major aim of this study was to analyze mycorrhizae-mediated alterations on the physiology and metabolism of Oryza sativa, as well as the impact of these alterations in the metal tolerance potential of the host on exposure to cadmium (Cd) and zinc (Zn) stresses. For this, 45 d old O. sativa (var. Varsha) plants inoculated with Claroideoglomus claroideum were exposed to 1.95 g Zn kg-1 soil and 0.45 g Cd kg-1 soil. Mycorrhization significantly increased shoot weight, root weight, moisture content, and chlorophyll biosynthesis under Cd and Zn stresses. Mycorrhization mitigated the oxidative stress elicited in O. sativa by the elevated Cd and Zn content, and it aided in maintaining the metabolite's level and rate of photosynthesis as compared to non-mycorrhizal plants. The circular-shaped unique structures seen as opening on the leaf surface of non-mycorrhizal plants under Zn stress, possibly for the emission of volatile compounds synthesized as a result of Zn stress, have a great chance of leaf tissue destruction. This structural modification was characterized in the case of Zn stress and not in Cd stress and can lead to the reduction of photosynthesis in O. sativa exposed to Zn stress. The reduction in oxidative stress could be correlated to the reduced uptake and transport of Cd and Zn ions in mycorrhizal plants. The exudation of tributyl acetyl citrate, 3-beta-acetoxystigmasta-4,6,22-triene, and linoleic acid from the mycorrhizal roots of rice plants has a crucial role in the stabilization of metal ions. This study proposes mycorrhization as a strategy to strengthen the Cd and Zn stress tolerance level of rice plants by regulating the physiology and metabolomics of the host plant.

Transcriptome Analysis Reveals the Stress Tolerance to and Accumulation Mechanisms of Cadmium in Paspalum vaginatum Swartz.

Cadmium (Cd) is a non-essential heavy metal and high concentrations in plants causes toxicity of their edible parts and acts as a carcinogen to humans and animals. Paspalum vaginatum is widely cultivating as turfgrass due to its higher abiotic stress tolerance ability. However, there is no clear evidence to elucidate the mechanism for heavy metal tolerance, including Cd. In this study, an RNA sequencing technique was employed to investigate the key genes associated with Cd stress tolerance and accumulation in P. vaginatum. The results revealed that antioxidant enzyme activities catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and glutathione S-transferase GST) were significantly higher at 24 h than in other treatments. A total of 6820 (4457/2363, up-/down-regulated), 14,038 (9894/4144, up-/down-regulated) and 17,327 (7956/9371, up-/down-regulated) differentially expressed genes (DEGs) between the Cd1 vs. Cd0, Cd4 vs. Cd0, and Cd24 vs. Cd0, respectively, were identified. The GO analysis and the KEGG pathway enrichment analysis showed that DEGs participated in many significant pathways in response to Cd stress. The response to abiotic stimulus, the metal transport mechanism, glutathione metabolism, and the consistency of transcription factor activity were among the most enriched pathways. The validation of gene expression by qRT-PCR results showed that heavy metal transporters and signaling response genes were significantly enriched with increasing sampling intervals, presenting consistency to the transcriptome data. Furthermore, over-expression of PvSnRK2.7 can positively regulate Cd-tolerance in Arabidopsis. In conclusion, our results provided a novel molecular mechanism of the Cd stress tolerance of P. vaginatum and will lay the foundation for target breeding of Cd tolerance in turfgrass.

Modulation of osmoprotection and antioxidant defense by exogenously applied acetate enhances cadmium stress tolerance in lentil seedlings

To examine the potential role of acetate in conferring cadmium (Cd) stress tolerance in lentil (Lens culinaris), several phenotypical and physio-biochemical properties have been examined in Cd-stressed lentil seedlings following acetate applications. Acetate treatment inhibited the translocation of Cd from roots to shoots, which resulted in a minimal reduction in photosynthetic pigment contents. Additionally, acetate-treated lentil showed higher shoot (1.1 and 11.72%) and root (4.98 and 30.64%) dry weights compared with acetate-non-treated plants under low-Cd and high-Cd concentrations, respectively. Concurrently, acetate treatments increase osmoprotection under low-Cd stress through proline accumulation (24.69%), as well as enhancement of antioxidant defense by increasing ascorbic acid content (239.13%) and catalase activity (148.51%) under high-Cd stress. Acetate-induced antioxidant defense resulted in a significant diminution in hydrogen peroxide, malondialdehyde and electrolyte leakage in Cd-stressed lentil seedlings. Our results indicated that acetate application mitigated oxidative stress-induced damage by modulating antioxidant defense and osmoprotection, and reducing root-to-shoot Cd transport. These findings indicate an important contribution of acetate in mitigating the Cd toxicity during growth and development of lentil seedlings, and suggest that the exogenous applications of acetate could be an economical and new avenue for controlling heavy metal-caused damage in lentil, and potentially in many other crops.

Enhanced Cd efflux capacity and physiological stress resistance: The beneficial modulations of Metarhizium robertsii on plants under cadmium stress

Due to the high migration capacity in agricultural soil-crop systems, cadmium (Cd) is accumulated in various crops and severely inhibits plant growth. In this study, we showed that, under Cd stress, the plant-symbiotic fungus Metarhizium robertsii reduced Cd accumulation in Arabidopsis thaliana shoots and roots by 21.8 % and 23.8 %, respectively. This is achieved by M. robertsii colonization-induced elevation of Cd efflux capacity via upregulation of three PCR genes, which is confirmed by the fact that the extent to which M. robertsii reduced Cd accumulation in the WT plants was greater than the inactivating mutants of the PCR genes. M. robertsii also alleviated Cd-induced leaf etiolation in A. thaliana by increasing the chlorophyll amount and modified plant physiological status to increase Cd stress tolerance via increasing production of catalase, peroxidase and glutathione and upregulating multiple HIPP proteins involved in sequestration of Cd. Notably, consistent with that in A. thaliana, the colonization of M. robertsii also reduced the Cd accumulation in Oryza sativa seedlings by upregulating the PCR gene OsPCR1, and increased chlorophyll amount and alleviated oxidative stress. Therefore, M. robertsii colonization reduced Cd accumulation in plants, and promoted plant growth and health by elevating Cd efflux capacity and modifying physiological status.

Shade and Cd Conditions Strongly Impact the Physiological Responses of Purple Perilla

Plant metabolic regulation is an important strategy for dealing with abiotic stress, which can initiate dramatic changes in metabolite profiles. Metabolomic studies have been extensively used to reveal the responses of plants to abiotic stress, but research concerning how shade growth conditions impact the physiological responses of purple Perilla under Cd stress is still rare. Therefore, the research was designed to observe the important metabolites of purple Perilla under shaded conditions and Cd stress. In this study, we compared the metabolite profiles of purple Perilla exposed to shade and Cd stresses. The results showed that the metabolite profiles of purple Perilla under these stresses could be classified separately. Compared with the normal sunlight treatment, important energy metabolic pathways, including the citrate cycle, and glyoxylate and dicarboxylate metabolism, were inhibited under shade stress. Metabolite analysis revealed that pyruvate was involved in numerous metabolic pathways under Cd stress, and decreased pyruvate was regarded as a metabolite marker for physiological changes. The results show that increased thiamine is an important intermediate that is beneficial for enhancement of Cd stress tolerance.

Exogenously Applied Trehalose Augments Cadmium Stress Tolerance and Yield of Mung Bean (Vigna radiata L.) Grown in Soil and Hydroponic Systems through Reducing Cd Uptake and Enhancing Photosynthetic Efficiency and Antioxidant Defense Systems.

Cadmium (Cd) toxicity is a serious environmental issue causing a significant reduction in crop growth and productivity globally. Trehalose (Tre) has emerged as an important reducing sugar that can reduce the adverse impacts of different abiotic stresses. Therefore, the present investigation was performed to determine the key role of Tre in alleviating Cd stress in the mung bean (Vigna radiata L.) crop. The study was comprised of different treatments of cadmium (0, 10, 20 mg kg−1 soil) and Tre (0, 15 and 30 mM). Cd stress significantly restricted the growth and yield of mung bean. However, Tre supplementation markedly improved growth and yield due to pronounced reductions in Cd uptake and Cd-induced oxidative stress as shown by the lower production of hydrogen peroxide (H2O2), electrolyte leakage (EL) and malondialdehyde (MDA) in Cd-stressed plants as well as by the enhanced activities of antioxidant enzymes (CAT, POD, APX and AsA). Moreover, the ameliorative role of Tre to Cd toxicity was also demonstrated by its ability to enhance chlorophyll contents, total soluble protein (TSP) and free amino acids (FAA). Taken together, Tre supplementation played a key beneficial role in improving Cd stress tolerance and yield traits of mung bean through restricting Cd uptake and enhancing photosynthetic capacity, osmolytes biosynthesis and antioxidant activities.

Microbiota and Cultivars Background Can Elevate Heat and Cd Stress Tolerance in Rice

Microbiota and Cultivars Background Can Elevate Heat and Cd Stress Tolerance in Rice

Potassium and melatonin-mediated regulation of fructose-1,6-bisphosphatase (FBPase) and sedoheptulose-1,7- bisphosphatase (SBPase) activity improve photosynthetic efficiency, carbon assimilation and modulate glyoxalase system accompanying tolerance to cadmium stress in tomato seedlings

The mechanism of the combined action of potassium (K) and melatonin (Mel) in modulating tolerance to cadmium (Cd) stress in plants is not well understood. The present study reveals the synergistic role of K and Mel in enhancing physiological and biochemical mechanisms of Cd stress tolerance in tomato seedlings. The present findings reveal that seedlings subjected to Cd toxicity exhibited disturbed nutrients balance [nitrogen (N) and potassium (K)], chlorophyll (Chl) biosynthesis [reduced δ-aminolevulinic acid (δ-ALA) content and δ-aminolevulinic acid dehydratase (δ-ALAD) activity], pathway of carbon fixation [reduced fructose-1,6-bisphosphatase (FBPase) and sedoheptulose-1,7- bisphosphatase (SBPase) activity] and photosynthesis process in tomato seedlings. However, exogenous application of K and Mel alone as well as together improved physiological and biochemical mechanisms in tomato seedlings, but their combined application proved best by efficiently improving nutrient uptake, photosynthetic pigments biosynthesis (increased Chl a and b, and Total Chl), carbon flow in Calvin cycle, activity of Rubisco, carbonic anhydrase activity, and accumulation of total soluble carbohydrates content in seedlings under Cd toxicity. Furthermore, the combined treatment of K and Mel suppressed overproduction of reactive oxygen species (hydrogen peroxide and superoxide), Chl degradation [reduced chlorophyllase (Chlase) activity] and methylglyoxal content in Cd-stressed tomato seedlings by upregulating glyoxalase (increased glyoxalase I and glyoxalase II activity) and antioxidant systems (increased ascorbate-glutathione metabolism). Thus, the present study provides stronger evidence that the co-application of K and Mel exhibited synergistic roles in mitigating the toxic effect of Cd stress by increasing glyoxalase and antioxidant systems and also by improving photosynthetic efficiency in tomato seedlings.

Differences in Cadmium Accumulation, Detoxification and Antioxidant Defenses between Contrasting Maize Cultivars Implicate a Role of Superoxide Dismutase in Cd Tolerance.

Cadmium (Cd), a readily absorbed and translocated toxic heavy metal, inhibits plant growth, interrupts metabolic homeostasis and induces oxidative damage. Responses towards Cd-stress differ among plant cultivars, and the complex integrated relationships between Cd accumulation, detoxification mechanisms and antioxidant defenses still need to be unraveled. To this end, 12 Egyptian maize cultivars were grown under Cd-stress to test their Cd-stress tolerance. Out of these cultivars, tolerant (TWC360 and TWC321), moderately sensitive (TWC324) and sensitive (SC128) cultivars were selected, and we determined their response to Cd in terms of biomass, Cd accumulation and antioxidant defense system. The reduction in biomass was highly obvious in sensitive cultivars, while TWC360 and TWC321 showed high Cd-tolerance. The cultivar TWC321 showed lower Cd uptake concurrently with an enhanced antioxidant defense system. Interestingly, TWC360 accumulated more Cd in the shoot, accompanied with increased Cd detoxification and sequestration. A principal component analysis revealed a clear separation between the sensitive and tolerant cultivars with significance of the antioxidant defenses, including superoxide dismutase (SOD). To confirm the involvement of SOD in Cd-tolerance, we studied the effect of Cd-stress on a transgenic maize line (TG) constitutively overexpressing AtFeSOD gene in comparison to its wild type (WT). Compared to their WT, the TG plants showed less Cd accumulation and improved growth, physiology, antioxidant and detoxification systems. These results demonstrate the role of SOD in determining Cd-tolerance.

Melatonin Confers Plant Cadmium Tolerance: An Update.

Cadmium (Cd) is one of the most injurious heavy metals, affecting plant growth and development. Melatonin (N-acetyl-5-methoxytryptamine) was discovered in plants in 1995, and it is since known to act as a multifunctional molecule to alleviate abiotic and biotic stresses, especially Cd stress. Endogenously triggered or exogenously applied melatonin re-establishes the redox homeostasis by the improvement of the antioxidant defense system. It can also affect the Cd transportation and sequestration by regulating the transcripts of genes related to the major metal transport system, as well as the increase in glutathione (GSH) and phytochelatins (PCs). Melatonin activates several downstream signals, such as nitric oxide (NO), hydrogen peroxide (H2O2), and salicylic acid (SA), which are required for plant Cd tolerance. Similar to the physiological functions of NO, hydrogen sulfide (H2S) is also involved in the abiotic stress-related processes in plants. Moreover, exogenous melatonin induces H2S generation in plants under salinity or heat stress. However, the involvement of H2S action in melatonin-induced Cd tolerance is still largely unknown. In this review, we summarize the progresses in various physiological and molecular mechanisms regulated by melatonin in plants under Cd stress. The complex interactions between melatonin and H2S in acquisition of Cd stress tolerance are also discussed.

Interplay of hydrogen peroxide and nitric oxide: systemic regulation of photosynthetic performance and nitrogen metabolism in cadmium challenged cyanobacteria.

In the present study, thepotential role of hydrogen peroxide (H2O2) and nitric oxide (NO) has been well recorded in the induction of cadmium (Cd) stress tolerance in cyanobacteria. In this regard, H2O2 and SNP (sodium nitroprusside, NO donor), were applied to Nostoc muscorum and Anabaena sp. exposed to Cd (6µM) stress, to analyze different physiological and biochemical parameters. Results revealed that treatment of Cd reduced the growth, pigment contents, photosynthetic oxygen yield and performance of PS II photochemistry (decreased chlorophyll a fluorescence parameters, i.e., ФPo, Ψo, ФEo, PIABS along with Fv/Fo and increased the energy fluxparameters, i.e., ABS/RC, TRo/RC, ETo/RC, DIo/RC along with Fo/Fv. Similarly, uptake of nitrate (NO3 -) and nitrite (NO2 -), as well as the activities of nitrate and ammonia assimilating enzymes along with carbohydrate content, were severely affected by Cd toxicity and notwithstanding this, glutamate dehydrogenase (GDH) activity exhibited reverse trend. Exogenous application of a very low dose (1µM) of H2O2 (only for 3h) and NO (SNP; 10µM) notably counteracted Cd-induced toxicity. Nevertheless, the positive impact of H2O2 got reversed under the treatment of PTIO (NO scavenger) and LNAME (inhibitor of nitric oxide synthase; NOS) while NO could work efficiently even in the presence of NAC (H2O2 scavenger) and DPI (inhibitor of NADPH oxidase); hence indicated towards the H2O2 mediated NO signaling in averting Cd induced toxicity in test cyanobacteria. In conclusion, current finding demonstrated a positive cross-talk between H2O2 and NO for providing tolerance to cyanobacteria against Cd stress.

Genetic engineering of glycinebetaine synthesis enhances cadmium tolerance in BADH-transgenic tobacco plants via reducing cadmium uptake and alleviating cadmium stress damage

Cadmium (Cd) is a toxic non-essential elements to plants, and its accumulation in plants can affect human health through the food chain. Glycinebetaine (GB) is an effective osmotic adjustment substance for plants to resist abiotic stress, and it plays important roles in various stresses. To investigate whether endogenous GB accumulation in vivo can enhance Cd tolerance, we used betaine aldehyde dehydrogenase (BADH) transgenic tobacco plants to explore the important role of GB under Cd stress conditions. The results showed that the tobacco exposed to cadmium stress, lead to growth inhibition and biomass reduction, decreased photosynthesis, decreased the absorption of essential minerals and increased oxidative stress. However, GB accumulation in transgenic tobacco plants significantly increased Cd tolerance, as evidenced by the decreased growth inhibition, enhanced photosynthetic rate and reduced reactive oxygen species accumulation. GB can regulate Cd uptake and transport, which results in reduced Cd accumulation. Moreover, GB also reduced K+ efflux under Cd stress and regulated ion transporter genes to maintain element balance. Our findings provide a novel role of GB in enhancing Cd stress tolerance in transgenic plants and thus propose GB as a potential candidate for relieving Cd toxicity in other crops.

Growth and Antioxidant Responses in Iron-Biofortified Lentil under Cadmium Stress.

Cadmium (Cd) is a hazardous heavy metal, toxic to our ecosystem even at low concentrations. Cd stress negatively affects plant growth and development by triggering oxidative stress. Limited information is available on the role of iron (Fe) in ameliorating Cd stress tolerance in legumes. This study assessed the effect of Cd stress in two lentil (Lens culinaris Medik.) varieties differing in seed Fe concentration (L4717 (Fe-biofortified) and JL3) under controlled conditions. Six biochemical traits, five growth parameters, and Cd uptake were recorded at the seedling stage (21 days after sowing) in the studied genotypes grown under controlled conditions at two levels (100 μM and 200 μM) of cadmium chloride (CdCl2). The studied traits revealed significant genotype, treatment, and genotype × treatment interactions. Cd-induced oxidative damage led to the accumulation of hydrogen peroxide (H2O2) and malondialdehyde in both genotypes. JL3 accumulated 77.1% more H2O2 and 75% more lipid peroxidation products than L4717 at the high Cd level. Antioxidant enzyme activities increased in response to Cd stress, with significant genotype, treatment, and genotype × treatment interactions (p < 0.01). L4717 had remarkably higher catalase (40.5%), peroxidase (43.9%), superoxide dismutase (31.7%), and glutathione reductase (47.3%) activities than JL3 under high Cd conditions. In addition, L4717 sustained better growth in terms of fresh weight and dry weight than JL3 under stress. JL3 exhibited high Cd uptake (14.87 mg g−1 fresh weight) compared to L4717 (7.32 mg g−1 fresh weight). The study concluded that the Fe-biofortified lentil genotype L4717 exhibited Cd tolerance by inciting an efficient antioxidative response to Cd toxicity. Further studies are required to elucidate the possibility of seed Fe content as a surrogacy trait for Cd tolerance.

Efficacy of Indole Acetic Acid and Exopolysaccharides-Producing Bacillus safensis Strain FN13 for Inducing Cd-Stress Tolerance and Plant Growth Promotion in Brassica juncea (L.)

Untreated wastewater used for irrigating crops is the major source of toxic heavy metals and other pollutants in soils. These heavy metals affect plant growth and deteriorate the quality of edible parts of growing plants. Phytohormone (IAA) and exopolysaccharides (EPS) producing plant growth-promoting rhizobacteria can reduce the toxicity of metals by stabilizing them in soil. The present experiment was conducted to evaluate the IAA and EPS-producing rhizobacterial strains for improving growth, physiology, and antioxidant activity of Brassica juncea (L.) under Cd-stress. Results showed that Cd-stress significantly decreased the growth and physiological parameters of mustard plants. Inoculation with Cd-tolerant, IAA and EPS-producing rhizobacterial strains, however, significantly retrieved the inhibitory effects of Cd-stress on mustard growth, and physiology by up regulating antioxidant enzyme activities. Higher Cd accumulation and proline content was observed in the roots and shoot tissues upon Cd-stress in mustard plants while reduced proline and Cd accumulation was recorded upon rhizobacterial strains inoculation. Maximum decrease in proline contents (12.4%) and Cd concentration in root (26.9%) and shoot (29%) in comparison to control plants was observed due to inoculation with Bacillus safensis strain FN13. The activity of antioxidant enzymes was increased due to Cd-stress; however, the inoculation with Cd-tolerant, IAA-producing rhizobacterial strains showed a non-significant impact in the case of the activity of superoxide dismutase (SOD), peroxidase (POX) and catalase (CAT) in Brassica juncea (L.) plants under Cd-stress. Overall, Bacillus safensis strain FN13 was the most effective strain in improving the Brassica juncea (L.) growth and physiology under Cd-stress. It can be concluded, as the strain FN13 is a potential phytostabilizing biofertilizer for heavy metal contaminated soils, that it can be recommended to induce Cd-stress tolerance in crop plants.

Excretion from long glandular trichomes contributes to alleviation of cadmium toxicity in Nicotiana tabacum

The B-type cyclin gene, CycB2, serves as a negative regulator of glandular trichome initiation. Through targeted knockout of NtCycB2 in Nicotiana tabacum cv. K326 using the CRISPR/Cas9 system, we created a variety, HK326, which exhibits significantly increased density and larger glandular heads of long glandular trichomes. Under Cd-stress, HK326 exhibited enhanced Cd tolerance, as demonstrated by a robust root system, strengthened cell membrane stability, and higher photosynthetic parameters. HK326 exhibited enhanced Cd-stress tolerance due to a strong excretion capacity of long glandular trichomes by forming calcium oxalate crystals. Cd mainly accumulated in tobacco shoots rather than remained in roots. Specifically, Cd levels of the HK326 shoot surface were nearly two-fold of those of K326, resulting in less Cd internally in the roots and shoots. Gene expression patterns revealed 11 Cd transporter genes that were upregulated after Cd-stress in shoots, roots, and trichomes. Among them, the NtHMA2 gene encoding heavy metal ATPases and involved in the transport of divalent heavy metal cations was expressed consistently and significantly higher in HK326 than K326, both before and after Cd-stress. NtHMA2 expression was strong in trichomes, moderate in shoots, while weak in roots. The results indicate that NtHMA2 may be involved in Cd excretion from glandular trichomes. Our findings suggest HK326 may be an appropriate candidate plant for Cd-stress tolerance.

OsNAC300 Positively Regulates Cadmium Stress Responses and Tolerance in Rice Roots

Transcriptional regulation is involved in responding to cadmium (Cd) stress in plants. However, the molecular mechanisms of Cd stress responses regulated by transcription factors remain largely unknown in plants. In this study, a rice (Oryza sativa) NAC (no apical meristem [NAM]; Arabidopsis transcription activation factor [ATAF]; cup-shaped cotyledon [CUC]-related) family transcription factor, OsNAC300, was isolated and functionally characterized for its involvement in Cd stress responses and tolerance. OsNAC300 was localized to the nucleus. OsNAC300 was mainly expressed in roots and significantly induced by Cd treatment. Knockout of OsNAC300 resulted in increased sensitivity to Cd stress, while its overexpression lines enhanced tolerance to Cd stress. RNA-Seq analysis revealed that the mutant is impaired in regulating some important genes that were responsive to Cd stress in wild-type rice, such as the pathogenesis-related genes 10a (OsPR10a), OsPR10b, chalcone synthase 1 (OsCHS1), and several others, which was validated by reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis. Moreover, chromatin immunoprecipitation-qPCR assays and luciferase reporter assays demonstrated that OsNAC300 directly binds to the promoters of OsPR10a, OsPR10b, and OsCHS1 and activates their transcription. Overall, OsNAC300 is an important regulatory factor in Cd stress responses and tolerance in rice.