Translocation Of Mn Research Articles

Overexpression of a Miscanthus sacchariflorus yellow stripe-like transporter MsYSL1 enhances resistance of Arabidopsis to cadmium by mediating metal ion reallocation

The yellow stripe-like (YSL) family of transporters mediates the uptake, translocation, and distribution of various mineral elements in vivo by transferring metal ions chelated with phytosiderophore or nicotianamine (NA). However, little is known about the roles of the YSL genes against cadmium in planta. In this study, we first cloned and characterized a vital member of the YSL gene family, MsYSL1, from the bioenergy plant Miscanthus sacchariflorus. MsYSL1 localized in the plasma membrane and was widely expressed throughout the whole seedling with the highest expression level in the stem. In addition, its expression in the root was stimulated by excess manganese (Mn), cadmium (Cd), and lead, and a shortage of iron (Fe), zinc (Zn), and copper. Functional complementation in yeast indicated that MsYSL1 showed transport activity for Fe(II)–NA and Zn–NA, but not for Cd–NA. Although they exhibited no significant differences versus the wild type under normal cultivation conditions, MsYSL1-overexpressing Arabidopsis lines displayed a higher resistance to Cd accompanied by longer root lengths, lower Cd, Zn, and Mn levels in roots, and higher Cd, Fe, and Mn translocation ratios under Cd stress. Moreover, genes related to NA synthesis, metal translocation, long-distance transport, and Cd exclusion were highly induced in transgenic lines under Cd stress. Thus, MsYSL1 may be an essential transporter for diverse metal–NAs to participate in the Cd detoxification by mediating the reallocation of other metal ions.

Male Populus cathayana than female shows higher photosynthesis and less cellular injury through ABA-induced manganese transporting inhibition under high manganese condition

High Mn poisoned male and female Populus cathayana. The toxicity could be alleviated by exogenous ABA application. Intriguingly, ABA granted higher resistance to males than to females under high Mn stress because ABA could induce more blocking of Mn translocation to leaf in males than in females. Abscisic acid (ABA) is involved in plants’ adaptive responses to various environmental stresses. However, little is known about the sex-related detoxification of ABA in plants under excess manganese (Mn) conditions. To reveal potentially different ABA detoxification mechanisms between Populus cathayana males and females against excess Mn exposure, photosynthesis performance, Mn2+ concentrations and morphologic changes were investigated. High Mn stress led to a more severe chloroplast destruction and, thus, greater reduction in the photosynthesis of P. cathayana females when compared to males. Under high Mn conditions, Mn reallocated mainly to leaves in females, while in males, it was distributed equally to roots and leaves. With the application of ABA, photosynthesis was restored more in males and more integrated grana in males than in females. It should be noted that Mn concentrations in males were lower in leaves and higher in roots and stems than those in females when treated with the combination of Mn and ABA. Conclusively, due to the reduction of root–shoot Mn transportation induced by ABA in P. cathayana males, males experienced less physiological injuries than do females, which suggest that males possess greater ABA-inducible resistance to Mn stress than do females.

Effects of changes in leaf properties mediated by methyl jasmonate (MeJA) on foliar absorption of Zn, Mn and Fe.

Foliar fertilization to overcome nutritional deficiencies is becoming increasingly widespread. However, the processes of foliar nutrient absorption and translocation are poorly understood. The present study aimed to investigate how cuticular leaf properties affect the absorption of foliar-applied nutrients in leaf tissues. Given that methyl jasmonate (MeJA) can cause alterations in leaf properties, we applied 1 mm MeJA to sunflower (Helianthus annuus), tomato (Solanum lycopersicum) and soybean (Glycine max) to assess changes in leaf properties. Using traditionally analytical approaches and synchrotron-based X-ray fluorescence microscopy, the effects of these changes on the absorption and translocation of foliar-applied Zn, Mn and Fe were examined. The changes in leaf properties caused by the application of MeJA increased foliar absorption of Zn, Mn and Fe up to 3- to 5-fold in sunflower but decreased it by 0·5- to 0·9-fold in tomato, with no effect in soybean. These changes in the foliar absorption of nutrients could not be explained by changes in overall trichome density, which increased in both sunflower (86%) and tomato (76%) (with no change in soybean). Similarly, the changes could be not attributed to changes in stomatal density or cuticle composition, given that these properties remained constant. Rather, the changes in the foliar absorption of Zn, Mn and Fe were related to the thickness of the cuticle and epidermal cell wall. Finally, the subsequent translocation of the absorbed nutrients within the leaf tissues was limited (<1·3mm) irrespective of treatment. The present study highlights the potential importance of the combined thickness of the cuticle and epidermal cell wall in the absorption of foliar-applied nutrients. This information will assist in increasing the efficacy of foliar fertilization.

Phytoremediation of metals using vetiver (Chrysopogon zizanioides (L.) Roberty) grown under different levels of red mud in sludge amended soil

Globally, 120milliontonnes of red mud is generated whose disposal and storage occupy large areas of potentially important arable lands. Red mud dumps are physically, nutritionally and biologically poor in nature. Vetiver (Chrysopogon zizanioides (L.) Roberty), a medicinally important perennial plant, known to control soil erosion, tolerates a wide range of pH and elevated levels of toxic metals. This information prompted to make use of red mud with sewage sludge, a nutrient rich bio-waste for growing vetiver. An experimental study was conducted using red mud at four rates (0, 5, 10 and 15% w/w) in soil amended with sewage sludge (soil: sludge: 2:1 w/w) to evaluate the effects on physico-chemical properties, plant growth performance, biomass and metal contents in vetiver under control (without sewage sludge and red mud) and different soil treatments. Application of red mud with sludge enhanced the levels of organic matter and nutrient status of the soil which offered suitable substrata to support plant growth. Heavy metal contents (Fe, Mn, Mg, Zn, Cu, Ni, Pb, Cd and Cr) increased with increase in red mud levels, however, their phytoavailable contents decreased. Addition of red mud resulted in significant improvement in root-shoot lengths, number of tillers culm−1, root-shoot ratio and biomass compared to the control. However, maximum improvement occurred in root (125.27%), shoot (79.91%) and total plant biomass (88.07%) under 10% red mud treatment compared to control. Vetiver is found to be a potential metal tolerant plant as tolerance index was >100%. Based on translocation and bioconcentration factors, the plant was found efficient in translocation of Mn and Cu from roots to shoot, whereas it acted as a potential phytostabilizer for Fe, Zn, Mg, Cd, Pb, Ni and Cr. The study suggests utilization of 10% red mud in sludge amended soil to sustain maximum plant growth coupled with enhanced phytoremediation potential of vetiver.

Bradyrhizobia and arbuscular mycorrhizal fungi modulate manganese, iron, phosphorus, and polyphenols in soybean (Glycine max (L.) Merr.) under excess zinc

The effect of Bradyrhizobia (R) and Arbuscular mycorrhiza (AM) on manganese, iron, phosphorus, and polyphenols was investigated in soybean cultivated in Zn treated soils. In a completely randomized 3×4 factorial, the experimental treatments – Zn addition (0, 200, and 400mg Zn kg−1 of soil), and Inoculation (uninoculated control, R, AM, and R+AM dual inoculation) were set up in the greenhouse. Zinc treatment increased Zn in roots and shoots, Fe in roots, frequency of root mycorrhization, P in root, and Mn translocation; but decreased Fe translocation, Mn in root, and total polyphenols. Symbionts effected micronutrient balancing in the plants. Mycorrhizal inoculants increased Zn in shoots, and modulated Mn and Fe in shoots and roots; within the whole-plant crosstalk in Zn, Mn, and Fe status. In dual inoculation, synergy for much enhanced Mn translocation was indicated in 400mg Zn kg−1 treatment. Modulations of Zn-Mn-Fe nutrition in dual inoculation was supported with a reduction in cumulative number of fallen leaves, and increases in leaf greenness, shoot P, and root polyphenols, to give higher shoot biomass. Our results suggest the possibility of optimizing the crop production and bio-inoculation outcomes by targeting Mn and Fe status (in roots, shoots, translocation, and ratios with Zn) during cultivation under excess Zn.

Isolation and characterization of a novel cadmium-regulated Yellow Stripe-Like transporter (SnYSL3) in Solanum nigrum.

SnYSL3 encodes a plasma-localized transporter delivering various metal-nicotianamine complexes. The expression of SnYSL3 is up-regulated by excess Cd, suggesting an important role for SnYSL3 in response to Cd stress. The Yellow Stripe-Like (YSL) transporters have been proposed to participate in metal uptake and long-range transport in model plants. In this study, we isolated and characterized a novel member of the YSL gene family, SnYSL3, from the cadmium hyperaccumulator Solanum nigrum. SnYSL3 was constitutively expressed and encodes a plasma membrane-localized protein. In situ RNA hybridization localized the SnYSL3 transcripts predominantly in vascular tissues and epidermal cells of the roots and stems, while in leaves, the mRNA levels were high in the vasculature. The SnYSL3 expression level was up-regulated by excess Cd, excess Fe and Cu deficiency. Heterologous expression of SnYSL3 in yeast revealed that SnYSL3 transports nicotianamine complexes containing Fe(II), Cu, Zn and Cd. SnYSL3 overexpression in Arabidopsis thaliana decreased Fe and Mn concentrations in the roots and increased the root-to-shoot translocation ratios of Fe and Mn. Under Cd exposure, the transgenic plants showed increased translocation ratios of Fe and Cd, but no difference was observed in Mn translocation from roots to shoots between the transgenic and wild-type lines. Although the accurate function of SnYSL3 remains to be confirmed, these results suggest that SnYSL3 is a transporter delivering a broad range of metal-nicotianamine complexes and is potentially important for the response to heavy metal stress, especially due to Cd and Fe.

Influence of 2,4-D and MCPA herbicides on uptake and translocation of heavy metals in wheat (Triticum aestivum L.)

The aim of the study was to estimate the influence of the 2,4-dichlorophenoxy acetic acid and 2-methyl-4-chlorophenoxyacetic acid on the uptake and translocation of Cd, Co, Ni, Cu, Zn, Pb and Mn by wheat (Triticum aestivum L.). Two farmland soils typical for the central Polish rural environment were used. Studies involved soil analyses, contents of bioavailable, exchangeable and total forms for all investigated metals. Atomic absorption spectrometry was used to determine the concentration of the elements. The best correlation between the herbicide rate and the metal concentration was visibly for the underground part of plants. Analysis of variance proved that herbicide treatment of wheat frequently influences the metal transfer from soil and their concentration in roots and shoots. In particular, higher herbicide rates prompted the significant increase of all metals concentration in roots. Additionally, transfer coefficients depended on the type of soil and the herbicide rate applied. Uptake of metals may be also influenced by the formation of sparingly water-soluble metal-herbicide complexes. Its intensity would then depend on the solubility of particular chemical entity with the low solvable Pb, Cu and Cd complexes being the least mobile.

The expression of heterologous Fe (III) phytosiderophore transporter HvYS1 in rice increases Fe uptake, translocation and seed loading and excludes heavy metals by selective Fe transport.

SummaryMany metal transporters in plants are promiscuous, accommodating multiple divalent cations including some which are toxic to humans. Previous attempts to increase the iron (Fe) and zinc (Zn) content of rice endosperm by overexpressing different metal transporters have therefore led unintentionally to the accumulation of copper (Cu), manganese (Mn) and cadmium (Cd). Unlike other metal transporters, barley Yellow Stripe 1 (HvYS1) is specific for Fe. We investigated the mechanistic basis of this preference by constitutively expressing HvYS1 in rice under the control of the maize ubiquitin1 promoter and comparing the mobilization and loading of different metals. Plants expressing HvYS1 showed modest increases in Fe uptake, root‐to‐shoot translocation, seed accumulation and endosperm loading, but without any change in the uptake and root‐to‐shoot translocation of Zn, Mn or Cu, confirming the selective transport of Fe. The concentrations of Zn and Mn in the endosperm did not differ significantly between the wild‐type and HvYS1 lines, but the transgenic endosperm contained significantly lower concentrations of Cu. Furthermore, the transgenic lines showed a significantly reduced Cd uptake, root‐to‐shoot translocation and accumulation in the seeds. The underlying mechanism of metal uptake and translocation reflects the down‐regulation of promiscuous endogenous metal transporters revealing an internal feedback mechanism that limits seed loading with Fe. This promotes the preferential mobilization and loading of Fe, therefore displacing Cu and Cd in the seed.

Sulfur Mediated Alleviation of Mn Toxicity in Polish Wheat Relates to Regulating Mn Allocation and Improving Antioxidant System.

Sulfur (S) is an essential macronutrient that has been proved to play an important role in regulating plant responses to various biotic and abiotic stresses. The present study was designed to investigate the effect of S status on polish wheat plant response to Mn toxicity. Results showed that Mn stress inhibited plant growth, disturbed photosynthesis and induced oxidative stress. In response to Mn stress, polish wheat plant activated several detoxification mechanisms to counteract Mn toxicity, including enhanced antioxidant defense system, increased Mn distribution in the cell wall and up-regulated genes involved in S assimilation. Moderate S application was found to alleviate Mn toxicity mainly by sequestering excess Mn into vacuoles, inhibiting Mn translocation from roots to shoots, stimulating activities of antioxidant enzymes and enhancing GSH production via up-regulating genes involved in S metabolism. However, application of high level S to Mn-stressed plants did not significantly alleviated Mn toxicity likely due to osmotic stress. In conclusion, moderate S application is beneficial to polish wheat plant against Mn toxicity, S exerts its effects via stimulating the antioxidant defense system and regulating the translocation and subcellular distribution of Mn, in which processes GSH plays an indispensable role.

Manganese accumulation and solid-phase speciation in a 3.5 m thick mud sequence from the estuary of an acidic and Mn-rich creek, northern Baltic Sea

In sediments, manganese (Mn) is typically enriched in the form of authigenic Mn hydroxides at the water-sediment interface where intensive redox cycling of Mn occurs. Here we show, based on existing hydrochemical and geochemical (sediment core) data and new detailed chemical and mineralogical characterization of a 3.5m long sediment core from a Boreal estuary, that the behavior of Mn can be profoundly different and more complex in estuarine settings receiving an abundance of terrestrial Mn. The most notable feature in the 3.5m long sediment core is two depth intervals (60–155cm and 181–230cm) where there are strong fine-scale variations in Mn concentrations with peaks episodically reaching up to 10–25gkg−1 and 6.7–12gkg−1, respectively. X-ray absorption spectroscopy and sequential chemical extraction show that Mn occurs mainly as authigenic rhodochrosite at these two depth intervals and is mainly surface-sorbed in other sections with relatively low and stable Mn concentrations. The data suggests that the strong fine-scale variations in Mn concentrations are a reflection of the extent of formation and settling of Mn hydroxides, the precursors of the authigenic rhodochrosite (and also of the surface-sorbed Mn), rather than Mn input to the estuary or redox-related Mn translocation within the sediment. There was agreement between the results of linear combination fitting of extended X-ray absorption fine structure data and a 7-step sequential chemical extraction (SCE) in terms of quantification of surface-sorbed Mn species, whereas the SCE experiment failed to fractionate a majority of rhodochrosite into SCE step-2 (1M NH4-acetate at pH6), which is frequently employed to dissolve carbonate. We ascribe this discrepancy to only partial dissolution of rhodochrosite in the weakly acidic (pH=6) NH4-acetate leach.

Silicon decreases both uptake and root-to-shoot translocation of manganese in rice.

Silicon (Si) is known to alleviate manganese (Mn) toxicity in a number of plant species; however, the mechanisms responsible for this effect are poorly understood. Here, we investigated the interaction between Si and Mn in rice (Oryza sativa) by using a mutant defective in Si uptake. Silicon alleviated Mn toxicity in the wild-type (WT) rice, but not in the mutant exposed to high Mn. The Mn concentration in the shoots was decreased, but that in the roots was increased by Si in the WT. In contrast, the Mn concentration in the roots and shoots was unaffected by Si in the mutant. Furthermore, Si supply resulted in an increased Mn in the root cell sap, decreased Mn in the xylem sap in the WT, but these effects of Si were not observed in the mutant. A short-term labelling experiment with (54)Mn showed that the uptake of Mn was similar between plants with and without Si and between WT and the mutant. However, Si decreased root-to-shoot translocation of Mn in the WT, but not in the mutant. The expression of a Mn transporter gene for uptake, OsNramp5, was unaffected by a short exposure (<1 d) to Si, but down-regulated by relatively long-term exposure to Si in WT. In contrast, the expression of OsNramp5 was unaffected by Si in the mutant. These results indicated that Si-decreased Mn accumulation results from both Si-decreased root-to-shoot translocation of Mn, probably by the formation of Mn-Si complex in root cells, and uptake by down-regulating Mn transporter gene.

Response of two rice cultivars differing in their sensitivity towards arsenic, differs in their expression of glutaredoxin and glutathione S transferase genes and antioxidant usage

Embodied study investigates the role of GRX and associated antioxidant enzymes in the detoxification mechanism between arsenic (As) sensitive (Usar-3) and tolerant cultivar (Pant Dhan 11) of Oryza sativa against As(III) and As(V), under GSH enriched, and GSH deprived conditions. The overall growth and physiological parameters in sensitive cultivar were lower than the tolerant cultivar, against various treatments of As(III) and As(V). The As accumulation in sensitive cv. against both As(III) and As(V) was lower than the corresponding treatments in tolerant cv. However, the As translocation against As(V) was lower (35% and 64%, resp.) than that of As(III), in both the cultivars. In sensitive cv. translocation of Zn and Cu was influenced by both As(V) and As(III) whereas, in tolerant cv. the translocation of Cu, Mn and Zn was influenced only by As(III). Translocation of Fe was negatively influenced by translocation of As in sensitive cv. and positively in tolerant cv. Strong correlation between H2O2, SOD, GRX, GR, GST and GSH/GSSG in sensitive cv. and between DHAR, APX, MDHAR and AsA in tolerant cv. demonstrates the underlying preference of GSH as electron donor for detoxification of H2O2 in sensitive cv. and AsA in tolerant cv. Higher expression of the four GRX and two GST genes in the sensitive cv. than tolerant cv, suggests that under As stress, GRX are synthesized more in the sensitive cv. than tolerant cv. Also, the expression of four GRX genes were higher against As(V) than As(III). The higher As accumulation in the tolerant cv. is due to lower GST expression, is attributed to the absence of thiolation and sequestration of As in roots, the translocation of As to shoots is higher.

Can earthworms alleviate nutrient disorders of plants subjected to calcium carbonate excess?

Earthworms are recognized to affect soil nutrient cycling with important consequences for plant growth. Nutrient bioavailability is often limited in calcareous soils. Exactly how earthworms can impact availability of nutrients in higher plants grown on calcareous soils still remains an open question. The objectives of this study were to investigate in pot experiments complex nutrient dynamics of interactions between non-calcareous soil and earthworms with special emphasis on the availability of iron (Fe), zinc (Zn), manganese (Mn) and nitrogen (N) to plants (Cucumis sativus L. and Zea mays L.) subjected to calcium carbonate (CaCO3) excess. A combination approach was performed including analysis of nutrient mobility in casts/soil, micronutrient movement via xylem of plants and plant elemental analysis. Addition of CaCO3 (5% DW) significantly lowered the concentrations of Zn and Mn in xylem sap and/or shoot (by 1.8–5.7 times) of both cucumber and maize in comparison with plants that had not received CaCO3. Bioavailability of Fe, however, was not affected by CaCO3 treatment. Beneficial effects of earthworms— endogeic Aporrectodea caliginosa (Savigny) and anecic Lumbricus terrrestris L., for plant nutrient acquisition include an increased mobility of all micronutrients (by 1.3–4.0 times) and N (by 1.5–27 times) in casts or soil either with or without CaCO3 treatment. However, these earthworm species were generally not of major importance in improving Zn and Mn translocation from roots to shoot in cucumber and maize, which was strongly impaired in CaCO3 applied soil. The results clearly demonstrated that earthworm capabilities to alleviate plant Zn and Mn deficiencies induced by CaCO3 applications are limited.

A Newly Identified Passive Hyperaccumulator Eucalyptus grandis × E. urophylla under Manganese Stress.

Manganese (Mn) is an essential micronutrient needed for plant growth and development, but can be toxic to plants in excess amounts. However, some plant species have detoxification mechanisms that allow them to accumulate Mn to levels that are normally toxic, a phenomenon known as hyperaccumulation. These species are excellent candidates for developing a cost-effective remediation strategy for Mn-polluted soils. In this study, we identified a new passive Mn-hyperaccumulator Eucalyptus grandis × E. urophylla during a field survey in southern China in July 2010. This hybrid can accumulate as much as 13,549 mg/kg DW Mn in its leaves. Our results from Scanning Electron Microscope (SEM) X-ray microanalysis indicate that Mn is distributed in the entire leaf and stem cross-section, especially in photosynthetic palisade, spongy mesophyll tissue, and stem xylem vessels. Results from size-exclusion chromatography coupled with ICP-MS (Inductively coupled plasma mass spectrometry) lead us to speculate that Mn associates with relatively high molecular weight proteins and low molecular weight organic acids, including tartaric acid, to avoid Mn toxicity. Our results provide experimental evidence that both proteins and organic acids play important roles in Mn detoxification in Eucalyptus grandis × E. urophylla. The key characteristics of Eucalyptus grandis × E. urophylla are an increased Mn translocation facilitated by transpiration through the xylem to the leaves and further distribution throughout the leaf tissues. Moreover, the Mn-speciation profile obtained for the first time in different cellular organelles of Eucalyptus grandis × E. urophylla suggested that different organelles have differential accumulating abilities and unique mechanisms for Mn-detoxification.

Translocation of Cd and Mn from Bark to Leaves in Willows on Contaminated Sediments: Delayed Budburst Is Related to High Mn Concentrations

Changes in the hydrology of sediments in tidal marshes or landfills may affect the uptake of metals in the vegetation. Leaf and stem samples of Salix cinerea (grey sallow) were collected during four consecutive growing seasons at six contaminated plots on a polluted dredged sediment landfill and one plot on an uncontaminated reference site. The first three contaminated plots were already emerged in the first half of the first growing season, while the other three were submerged in the first year, but became increasingly dry over the study period. Foliar and stem cutting concentrations for Cd, Zn and Mn increased on the latter three plots over the four years. Willow bark contained high concentrations of Cd, Zn and Mn. In two consecutive greenhouse experiments with willow cuttings from different origins (uncontaminated and contaminated sites) and grown under different soil conditions (uncontaminated and contaminated), we observed an important translocation of Mn from bark to shoots. In a third experiment with willow cuttings collected on soils with a range of heavy metal concentrations and, thus, with a broad range of Cd (4–67 mg/kg dry matter), Zn (247–660 mg/kg dry matter) and Mn (38–524 mg/kg dry matter) concentrations in the bark, high Mn concentrations in the bark were found to affect the budburst of willow cuttings, while no association of delayed budburst with Cd and Zn concentrations in the bark was found. We conclude that wood and, especially, bark are not a sink for metals in living willows. The high Mn concentrations in the bark directly or indirectly caused delayed or restricted budburst of the willow cuttings.

Accumulation of Metals and Boron in Phragmites australis Planted in Constructed Wetlands Polishing Real Electroplating Wastewater

The concentration of metals (Al, Cu, Fe, Mn, Ni, Zn) and B were determined in the above- and belowground biomass of Phragmites australis collected from the microcosm constructed wetland system used for the polishing of real electroplating wastewater. Translocation factor and bioconcentration factor were determined. Pearson correlation test was used to determine correlation between metal concentration in substrate and above- and belowground parts of Phragmites australis. The obtained results suggested that Phragmites australis did not play a major role as an accumulator of metals. It was observed also that the substrate could have exerted an effect on the translocation of Ni, Cu, Zn and Mn. The analysed concentrations of metals and B in biomass were in the range or even below the concentrations reported in the literature with the exception of Ni. The aboveground biomass was found suitable as a composting input in terms of metals concentrations.

Effect of exogenous salicylic acid on manganese toxicity, mineral nutrients translocation and antioxidative system in polish wheat (Triticum polonicum L.)

The present study investigated the morphological and physiological effect of salicylic acid (SA) on manganese toxicity in dwarf polish wheat (Triticum polonicum L.) seedlings grown hydroponically. Our findings showed that Mn stress could decrease plant growth, cause serious chlorosis and injury the photosynthetic apparatus. An increase of Mn accumulation and the inhibition of the K and Ca absorption and the Mg, Fe and Zn translocation were observed under Mn stress. Also, there was a considerable increase in H2O2 and TBARS (thiobarbituric acid-reactive substances) content in both the roots and leaves under Mn condition. The combination of SA and Mn treatment decreased the transport of Mn, Fe and Zn from roots to shoots and increased the Ca absorption and Mg translocation. In antioxidant system, such as CAT, APX, GR, DHAR, GSH and AsA, the combined treatment significantly increased the antioxidant content and antioxidative enzyme activities compared to the Mn stress alone. The level of ROS and lipid peroxidation significantly decreased under the combination of SA and Mn. These results suggested that SA-induced Mn tolerances in polish wheat are mainly by inhibiting Mn translocation, enhancing enzymatic activities and nonenzymatic antioxidants contents, and regulating nutrient absorption and distribution in plants.

A possible mechanism of mineral responses to elevated atmospheric CO2 in rice grains

Increasing attentions have been paid to mineral concentration decrease in milled rice grains caused by CO2 enrichment, but the mechanisms still remain unclear. Therefore, mineral (Ca, Mg, Fe, Zn and Mn) translocation in plant-soil system with a FACE (Free-air CO2 enrichment) experiment were investigated in Eastern China after 4-yr operation. Results mainly showed that: (1) elevated CO2 significantly increased the biomass of stem and panicle by 21.9 and 24.0%, respectively, but did not affect the leaf biomass. (2) Elevated CO2 significantly increased the contents of Ca, Mg, Fe, Zn, and Mn in panicle by 61.2, 28.9, 87.0, 36.7, and 66.0%, respectively, and in stem by 13.2, 21.3, 47.2, 91.8, and 25.2%, respectively, but did not affect them in leaf. (3) Elevated CO2 had positive effects on the weight ratio of mineral/biomass in stem and panicle. Our results suggest that elevated CO2 can favor the translocation of Ca, Mg, Fe, Zn, and Mn from soil to stem and panicle. The CO2-led mineral decline in milled rice grains may mainly attribute to the CO2-led unbalanced stimulations on the translocations of minerals and carbohydrates from vegetative parts (e.g., leaf, stem, branch and husk) to the grains.

H2O2 pretreated rice seedlings specifically reduces arsenate not arsenite: difference in nutrient uptake and antioxidant defense response in a contrasting pair of rice cultivars.

The study investigated the reduction in metalloid uptake at equimolar concentrations (~53.3μM) of As(III) and As(V) in contrasting pair of rice seedlings by pretreating with H2O2 (1.0μM) and SA (1.0mM). Results obtained from the contrasting pair (arsenic tolerant vs. sensitive) of rice seedlings (cv. Pant Dhan 11 and MTU 7029, respectively) shows that pretreatment of H2O2 and H2O2 + SA reduces As(V) uptake significantly in both the cultivars, while no reduction in the As(III) uptake. The higher growth inhibition, higher H2O2 and TBARS content in sensitive cultivar against As(III) and As(V) treatments along with higher As accumulation (~1.2mgg(-1) dw) than incv. P11, unravels the fundamental difference in the response between the sensitive and tolerant cultivar. In the H2O2 pretreated plants, the translocation of As increased in tolerant cultivar against AsIII, whereas, it decreased in sensitive cultivar both against AsIII and AsV. In both the cultivars translocation of Mn increased in the H2O2 pretreated plants against As(III), whereas, the translocation of Cu increased against As(V). In tolerant cultivar the translocation of Fe increased against As(V) with H2O2 pretreatment whereas, it decreased in the sensitive cultivar. In both the cultivars, Zn translocation increased against As(III) and decreased against As(V). The higher level of H2O2 and SOD (EC 1.15.1.1) activity in sensitive cultivar whereas, higher, APX (EC 1.11.1.11), GR (EC 1.6.4.2) and GST (EC 1.6.4.2) activity in tolerant cultivar, also demonstrated the differential anti-oxidative defence responses between the contrasting rice cultivars.

OsNRAMP5 contributes to manganese translocation and distribution in rice shoots.

Manganese (Mn) is an essential micronutrient for plants playing an important role in many physiological functions. OsNRAMP5 is a major transporter responsible for Mn and cadmium uptake in rice, but whether it is involved in the root-to-shoot translocation and distribution of these metals is unknown. In this work, OsNRAMP5 was found to be highly expressed in hulls. It was also expressed in leaves but the expression level decreased with leaf age. High-magnification observations revealed that OsNRAMP5 was enriched in the vascular bundles of roots and shoots especially in the parenchyma cells surrounding the xylem. The osnramp5 mutant accumulated significantly less Mn in shoots than the wild-type plants even at high levels of Mn supply. Furthermore, a high supply of Mn could compensate for the loss in the root uptake ability in the mutant, but not in the root-to-shoot translocation of Mn, suggesting that the absence of OsNRAMP5 reduces the transport of Mn from roots to shoots. The results suggest that OsNRAMP5 plays an important role in the translocation and distribution of Mn in rice plants in addition to its role in Mn uptake.