Hemin-decreased cadmium uptake in pak choi (Brassica chinensis L.) seedlings is heme oxygenase-1 dependent and relies on its by-products ferrous iron and carbon monoxide

Carbon monoxide is involved in melatonin-enhanced drought resistance in tomato seedlings by enhancing chlorophyll synthesis pathway

BACKGROUND

Drought is thought to be a major abiotic stress that dramatically limits tomato growth and production. As signal molecule, melatonin (MT) and carbon monoxide (CO) can enhance plant stress resistance. However, the effect and underlying mechanism of CO involving MT-mediated drought resistance in seedling growth remains unknown. In this study, tomato (Solanum lycopersicum L. 'Micro-Tom') seedlings were used to investigate the interaction and mechanism of MT and CO in response to drought stress.

RESULTS

The growth of tomato seedlings was inhibited significantly under drought stress. Exogenous MT or CO mitigated the drought-induced impairment in a dose-dependent manner, with the greatest efficiency provided by 100 and 500 µM, respectively. But application of hemoglobin (Hb, a CO scavenger) restrained the positive effects of MT on the growth of tomato seedlings under drought stress. MT and CO treatment promoted chlorophyll a (Chl a) and chlorophyll a (Chl b) accumulations. Under drought stress, the intermediate products of chlorophyll biosynthesis such as protoporphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-Proto IX), potochlorophyllide (Pchlide) and heme were increased by MT or CO, but uroporphyrinogen III (Uro III) content decreased in MT-treated or CO-treated tomato seedlings. Meanwhile, MT or CO up-regulated the expression of chlorophyll and heme synthetic-related genes SlUROD, SlPPOX, SlMGMT, SlFECH, SlPOR, SlChlS, and SlCAO. However, the effects of MT on chlorophyll biosynthesis were almost reversed by Hb.

CONCLUSION

The results suggested that MT and CO can alleviate drought stress and facilitate the synthesis of Chl and heme in tomato seedlings. CO played an essential role in MT-enhanced drought resistance via facilitating chlorophyll biosynthesis pathway.

Metabolic Adaptations in Rapeseed: Hemin-Induced Resilience to NaCl Stress by Enhancing Growth, Photosynthesis, and Cellular Defense Ability

This study aimed to investigate whether presoaking with hemin (5 μmol·L-1) could alleviate NaCl stress during rapeseed seedlings' growth and its role in the regulation of photosynthesis. In this experiment, 'HUAYOUZA 62 (HYZ 62)' and 'HUAYOUZA 158R (158R)' were used as materials for pot experiments to study the morphology, photosynthetic characteristics, antioxidant activity, and osmoregulatory factors of seedlings under different salt concentrations, as well as the regulatory effects of hemin-presoaked seeds. Our findings revealed that, compared the control, NaCl stress inhibited the growth of two rapeseed varieties, decreased the seedling emergence rate, and increased the content of malondialdehyde (MDA), the electrolyte leakage rate (EL) and antioxidant enzyme activity. Hemin soaking alleviated the adverse effects of salt stress and increased plant height, root elongation and dry matter accumulation. Compared with all NaCl treatments, hemin significantly enhanced photosynthetic indexes, including a percent increase of 12.99-24.36% and 5.39-16.52% in net photosynthetic rate (Pn), 17.86-48.08% and 8.6-23.44% in stomatal conductivity (Gs), and 15.42-37.94% and 11.09-19.08% in transpiration rate (Tr) for HYZ62 and 158R, respectively. Moreover, hemin soaking also increased antioxidant enzyme activities, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX), reducing the malondialdehyde, and thus resulting in the alleviation of oxidative damage caused by NaCl stress. Furthermore, hemin stimulated the formation of soluble protein, which effectively regulated the osmo-protective qualities. The current findings strongly elucidate that hemin soaking could effectively alleviate the negative impacts of NaCl stress by regulating the morphological, photosynthetic, and antioxidant traits. This study provides a new idea regarding the effect of Hemin on the salt tolerance of rapeseed, and provides a basis for the practical application of Hemin in saline-alkali soil to improve the salt tolerance of cultivated rapeseed.

Regulatory effects of Hemin on prevention and rescue of salt stress in rapeseed (Brassica napus L.) seedlings

BACKGROUND

Salt stress severely restricts rapeseed growth and productivity. Hemin can effectively alleviate salt stress in plants. However, the regulatory effect of Hemin on rapeseed in salt stress is unclear. Here, we analyzed the response and remediation mechanism of Hemin application to rapeseed before and after 0.6% (m salt: m soil) NaCl stress. Experiment using two Brassica napus (AACC, 2n = 38) rapeseed varieties Huayouza 158R (moderately salt-tolerant) and Huayouza 62 (strongly salt-tolerant). To explore the best optional ways to improve salt stress resistance in rapeseed.

RESULTS

Our findings revealed that exogenous application of Hemin enhanced morph-physiological traits of rapeseed and significantly attenuate the inhibition of NaCl stress. Compared to Hemin (SH) treatment, Hemin (HS) significantly improved seedlings root length, seedlings height, stem diameter and accumulated more dry matter biomass under NaCl stress. Moreover, Hemin (HS) significantly improved photosynthetic efficiency, activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and decreased electrolyte leakage (EL) and malondialdehyde (MDA) content, thus resulting in the alleviation of oxidative membrane damage. Hemin (HS) showed better performance than Hemin (SH) under NaCl stress.

CONCLUSION

Hemin could effectively mitigate the adverse impacts of salt stress by regulating the morph-physiological, photosynthetic and antioxidants traits of rapeseed. This study may provide a basis for Hemin to regulate cultivated rapeseed salt tolerance and explore a better way to alleviate salt stress.

In situ imaging of signaling molecule carbon monoxide in plants with a fluorescent probe

Carbon monoxide (CO) is a recently discovered gasotransmitter. In animals, it has been found that endogenously produced CO participates in the regulation of various metabolic processes. Recent research has indicated that CO, acting as a signaling molecule, plays a crucial regulatory role in plant development and their response to abiotic stress. In this work, we developed a fluorescent probe, named COP (carbonic oxide Probe), for the in situ imaging of CO in Arabidopsis thaliana plant tissues. The probe was designed by combining malononitrile-naphthalene as the fluorophore and a typical palladium-mediated reaction mechanism. When reacted with the released CO, COP showed an obvious fluorescence enhancement at 575 nm, which could be observed in naked-eye conditions. With a linear range of 0-10 μM, the limit of detection of COP was determined as 0.38 μM. The detection system based on COP indicated several advantages including relatively rapid response within 20 min, steadiness in a wide pH range of 5.0-10.0, high selectivity, and applicative anti-interference. Moreover, with a penetration depth of 30 μm, COP enabled 3D imaging of CO dynamics in plant samples, whether it was caused by agent release, heavy metal stress, or inner oxidation. This work provides a fluorescent probe for monitoring CO levels in plant samples, and it expands the application field of CO-detection technology, assisting researchers in understanding the dynamic changes in plant physiological processes, making it an important tool for studying plant physiology and biological processes.

Carbon monoxide/heme oxygenase system in plant: Roles in abiotic stress response and crosstalk with other signals molecules

Carbon monoxide (CO) has been recognized as a crucial gasotransmitter mainly produced by heme oxygenase (HO)-catalyzed heme degradation in plant. Recent studies have shown that CO plays an important role in regulating growth and development of plant, as well as and responding to a variety of abiotic stresses. Meanwhile, many studies have reported on CO working in combination with other signal molecules to mitigate abiotic stress. Here, we presented a comprehensive overview of recent developments in which CO reduces plant damage caused by abiotic stresses. The regulation of antioxidant system, photosynthetic system, ion balance and transport are the main mechanisms of CO-alleviated abiotic stress. We also proposed and discussed the relationship between CO and other signal molecules, including nitric oxide (NO), hydrogen sulfide (H2S), hydrogen gas (H2), abscisic acid (ABA), indole 3-acetic acid (IAA), gibberellin (GA), cytokine (CTK), salicylic acid (SA), jasmonic acid (JA), hydrogen peroxide (H2O2) and calcium ion (Ca2+). Furthermore, the important role of HO genes in alleviating abiotic stress was also discussed. We proposed promising and new research directions for the study of plant CO, which can provide further insights on the role of CO in plant growth and development under abiotic stress.

Enantioselective Response of Wheat Seedlings to Imazethapyr: From the Perspective of Fe and the Secondary Metabolite DIMBOA

The responses of trace elements and secondary metabolites to stress can reflect plant adaptation to the environment. If and how the imperative trace element Fe and the defensive secondary metabolite 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazine-3(4H)-one (DIMBOA) mediate the toxicity of chiral herbicides to nontarget plants remains inconclusive. We found that the herbicidal-active imazethapyr enantiomer [(R)-IM] stimulated heme oxygenase-1 activity, triggered the release of the catalytic product Fe²⁺, increased reactive oxygen species production, decreased the DIMBOA content, and increased the DIMBOA-Fe content. XAFS analyses and in vitro Fenton assays demonstrated that DIMBOA could relieve phytotoxicity by chelating excessive Fe³⁺ to restore Fe homeostasis. The free radical scavenging ability of the chelate of DIMBOA and Fe was also involved. This work refines the dual role of DIMBOA and Fe in mediating the enantioselective phytotoxicity of chiral herbicides, which provides a new direction for improving the herbicide resistance of crops.

Improving the anthocyanin accumulation of hypocotyls in radish sprouts by hemin-induced NO

BACKGROUND

The health benefits of anthocyanins impel researchers and food producers to explorer new methods to increase anthocyanin contents in plant foods. Our previous studies revealed a positive role of nitric oxide (NO) in anthocyanin accumulation in radish (Raphanus sativus L.) sprouts. The application of hemin, an inducer of heme oxygenase-1 (HO-1), can effectively elevate NO production in vivo. Hemin treatment also improves plant growth and stress tolerance. This study is aimed to assess the effects of hemin treatment on anthocyanin production in radish sprouts, and to investigate whether NO signalling is involved in this process.

RESULTS

The application of hemin significantly up regulated the expressions of many anthocyanins biosynthesis related structure and regulatory genes, leading to increased anthocyanins accumulation in radish hypocotyls. Hemin treatment also raised NO contents in radish sprouts, probably through enhancing nitrate reductase (NR) activity and Nitric Oxide-Associated 1 (NOA1) expression. Comparing the effects of Zinc Protoporphyrin (ZnPP, HO-1 activity inhibitor), Sodium Nitroprusside (SNP, NO donor) and carboxy-PTIO (cPTIO, NO-scavenger) on anthocyanin and NO production, a positive role of NO signalling has been revealed in hemin-derived anthocyanin accumulation. A positive feedback loop between HO-1 and NO may be involved in regulating this process.

CONCLUSIONS

Hemin induced anthocyanin accumulation in radish sprouts through HO-1 and NO signalling network.

Heme oxygenase-nitric oxide crosstalk-mediated iron homeostasis in plants under oxidative stress

Plant growth under abiotic stress conditions significantly enhances intracellular generation of reactive oxygen species (ROS). Oxidative status of plant cells is directly affected by the modulation of iron homeostasis. Among mammals and plants, heme oxygenase-1 (HO-1) is a well-known antioxidant enzyme. It catalyzes oxygenation of heme, thereby producing Fe²⁺, CO and biliverdin as byproducts. The antioxidant potential of HO-1 is primarily due to its catalytic reaction byproducts. Biliverdin and bilirubin possess conjugated π-electrons which escalate the ability of these biomolecules to scavenge free radicals. CO also enhances the ROS scavenging ability of plants cells by upregulating catalase and peroxidase activity. Enhanced expression of HO-1 in plants under oxidative stress accompanies sequestration of iron in specialized iron storage proteins localized in plastids and mitochondria, namely ferritin for Fe³⁺ storage and frataxin for storage of Fe-S clusters, respectively. Nitric oxide (NO) crosstalks with HO-1 at multiple levels, more so in plants under oxidative stress, in order to maintain intracellular iron status. Formation of dinitrosyl-iron complexes (DNICs) significantly prevents Fenton reaction during oxidative stress. DNICs also release NO upon dissociation in target cells over long distance in plants. They also function as antioxidants against superoxide anions and lipidic free radicals. A number of NO-modulated transcription factors also facilitate iron homeostasis in plant cells. Plants facing oxidative stress exhibit modulation of lateral root formation by HO-1 through NO and auxin-dependent pathways. The present review provides an in-depth analysis of the structure-function relationship of HO-1 in plants and mammals, correlating them with their adaptive mechanisms of survival under stress.

Mechanisms of calcium sulfate in alleviating cadmium toxicity and accumulation in pak choi seedlings

Gypsum (calcium sulfate dihydrate, CaSO₄ ·2H₂O) is commonly applied to improve soil quality and nutrient supply. Previous studies also suggested it is a cost-effective soil amendment in alleviating cadmium (Cd) toxicity and accumulation in plants. The aim of this study was to investigate how this is achieved. We used pak choi as our research material because it is a popular vegetable in Asia, and as a leafy vegetable, it accumulates higher Cd level than other types of vegetable. Under Cd stress, application of CaSO₄ promoted pak choi seedling growth, decreased the oxidative stress in roots, reduced Cd accumulation, and enhanced the photosynthesis in shoots. We revealed the inhibition of Cd²⁺ absorption by CaSO₄ is largely due to the competition between Ca²⁺ and Cd²⁺ for ion channels or transporter. Moreover, under Cd stress, CaSO₄ facilitated the sulphate assimilation, increased the biosynthesis of phytochelatins, and activated the expression of transporters for vacuolar sequestration. Together, CaSO₄ could benefit plant growth and enhance Cd tolerance by suppressing Cd root uptake and lowering the Cd content in cytoplasm.

BcNRAMP1 promotes the absorption of cadmium and manganese in Arabidopsis

Cadmium (Cd) is a toxic nonessential metal that poses a health risk for humans. Cd is easily accumulated in leaf vegetables than in other vegetables. Leafy vegetables are one of the major dietary Cd sources for the human body. In this study, pak choi was used as our experimental material as it is an important leafy vegetable, especially in Asia. A NRAMP transporter - BcNRAMP1 was identified in pak choi, which is involved in manganese (Mn) and Cd uptake in yeast and in planta. BcNRAMP1 is expressed in the whole plant body of pak choi, with a higher abundance in root tissues than in shoots. Mn deficiency and Cd exposure strongly induced BcNRAMP1 transcription levels. Through transient expression of BcNRAMP1-GFP fusion protein in tobacco leaf epidermal cells, BcNRAMP1 was revealed as a plasma membrane protein. Expressing BcNRAMP1 in yeast enhanced yeast cells to absorb Mn, Cd, and iron (Fe). Overexpression of BcNRAMP1 in Arabidopsis wild-type and nramp1 mutant increased and complemented Mn and Cd transportation and accumulation, respectively. Using noninvasive microelectrode ion flux measurements, a direct evidence that BcNRAMP1 acts on Cd influx in Arabidopsis root cells was provided. The results of this study reveal that BcNRAMP1 functions as a NRAMP protein in planta, absorbing nutrient metal Mn and the toxic metal Cd.

Involvement of several putative transporters of different families in β-cyclocitral-induced alleviation of cadmium toxicity in quinoa (Chenopodium quinoa) seedlings

Cadmium (Cd) has a serious negative impact on crop growth and human food security. This study investigated the alleviating effect of β-cyclocitral, a potential heavy metal barrier, on Cd stress in quinoa seedlings and the associated mechanisms. Our results showed that β-cyclocitral alleviated Cd stress-induced growth inhibition in quinoa seedlings and promoted quinoa seedling root development under Cd stress. Moreover, it maintained the antioxidant system of quinoa seedlings, including the enzymatic, i.e., superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and nonenzymatic, i.e., reduced glutathione (GSH) and ascorbic acid (ASA), antioxidants, which eliminate the damage from excessive reactive oxygen species (ROS). Our results showed that β-cyclocitral could reduce the amount of Cd absorbed by roots. Furthermore, we systematically identified five transporter families from the quinoa genome, and the RT-qPCR results showed that ZIP, Nramp and YSL gene families were downregulated by β-cyclocitral to reduce Cd uptake by roots. Thus, β-cyclocitral promoted the growth, photosynthetic capacity and antioxidant capacity of the aboveground parts of quinoa seedlings. Taken together, these results suggested that the β-cyclocitral-induced decrease in Cd uptake may be caused by the downregulation of several selected transporter genes.

Exogenous hemin improves Cd2+ tolerance and remediation potential in Vigna radiata by intensifying the HO-1 mediated antioxidant defence system

The present study evaluated the effects of exogenous hemin on cadmium toxicity in terms of metal accretion and stress resilience in Vigna radiata L. (Wilczek). One-week-old seedlings were treated with CdCl₂ (50 μM) alone and in combination with hemin (0.5 mM) in half-strength Hoagland medium for 96 h. The optimum concentrations of Cd and hemin were determined on the basis of haem oxygenase-1 activity. The results demonstrated that under Cd stress, plants accumulated a considerable amount of metal in their tissues, and the accumulation was higher in roots than in leaves, which significantly reduced the plant biomass and chlorophyll content by increasing the oxidative stress (MDA and H₂O₂ content). However, hemin supplementation under Cd,-stress improved plant growth by enhancing the harvestable biomass and photosynthetic pigments, increasing antioxidant activities (SOD, APX, POD, HO-1 and proline), lowering oxidative damage and increasing Cd tolerance in plants. Furthermore, the application of hemin enhances the removal efficiency of Cd in V. radiata by increasing the uptake of Cd via roots and its translocation from roots to foliar tissues. Thus, the study suggests that hemin has the potential to improve the stress tolerance and phytoremediation ability of heavy metal-tolerant plants so that they can be used instead of hyperaccumulators for remediation of Cd-contaminated environments.