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Cadmium pollution in Moso bamboo forests poses a potential threat to the sustainable development of the bamboo industry. However, the effects of cadmium toxicity on Moso growth and its mechanisms of adaptation to cadmium stress are poorly understood. In this study, the physiological and transcriptional response of Moso to cadmium stress was investigated in detail using Moso seedlings in a hydroponic system. Cadmium toxicity severely inhibited the growth of roots but had little effect on biomass accumulation in the aerial parts. Cadmium accumulation in roots and aerial parts increased as external cadmium increased, with cadmium mainly localized in the epidermis and pericycle cells in the roots. The uptake and root-to-shoot translocation of cadmium was stimulated, but the photosynthetic process was suppressed under cadmium stress. A total of 3469 differentially expressed genes were identified from the transcriptome profile and those involved in cadmium uptake, transportation and detoxification were analyzed as candidates for having roles in adaptation to cadmium stress. The results suggested that Moso is highly efficient in cadmium uptake, xylem loading and translocation, as well as having a high capacity for cadmium accumulation. This work also provided basic information on physiological and transcriptional responses of Moso to cadmium toxicity.

Moso bamboo has been shown to accumulate high concentrations of iron and zinc in the seeds. However, the bioavailablity of iron and zinc in bamboo seeds is poorly understood. Here, we evaluated the bioaccessibility and bioavailability of iron and zinc in bamboo seeds using an in vitro digestion protocol. The bioaccessibility and bioavailability of iron in bamboo seeds were 1.6- and 1.7-fold higher than in rice, respectively, and the bioaccessibility and bioavailability of zinc in bamboo seeds were 1.9- and 2.6-fold higher than in rice, respectively. Boiling process reduced both the bioaccessibility and bioavailability of iron and zinc. In addition, bamboo seeds contained lower levels of phytic acid but higher levels of tannins. Iron and zinc were mainly concentrated in the embryo and the aleurone layer. These results suggested that Moso bamboo seeds are rich in iron and zinc and have potential as a food for iron and zinc biofortification.

Boron (B) is essential for growth and development, with the B requirement differing depending on the particular organs and tissues, but the molecular mechanisms underlying the preferential distribution of B to different tissues are poorly understood. We investigated the role of a rice gene (OsBOR1) encoding a B efflux transporter in the distribution of B to different tissues under different B supplies. OsBOR1 was highly expressed in the nodes at all growth stages. The OsBOR1 protein shows polar localization at the distal side of bundle sheath cells in nodes and xylem parenchyma cells of elongating leaf sheath, but in the mature leaf sheath and blade at the proximal side of bundle sheath cells. Furthermore, the expression of OsBOR1 was not affected by external B fluctuations, but the OsBOR1 protein was gradually degraded in response to high B. Knockout of this gene altered B distribution, decreasing the distribution of B to new leaves and panicles but increasing B distribution to old leaves. These results indicate that OsBOR1 expressed in nodes and leaf sheath is involved in the preferential distribution of B to different tissues in rice. Furthermore, the OsBOR1 undergoes degradation in response to high B for fine regulation of B distribution to different tissues.

Due to rapid urbanization and industrialization, many soils for crop production are contaminated by cadmium (Cd), a heavy metal highly toxic to many organisms. Cereal crops such as rice, wheat, maize, and barley are the primary dietary source of Cd for humans, and reducing Cd transfer from soil to their grains is therefore an important issue for food safety. During the last decade, great progress has been made in elucidating the molecular mechanisms of Cd transport, particularly in rice. Inter- and intraspecific variations in Cd accumulation have been observed in cereal crops. Transporters for Cd have been identified in rice and other cereal crops using genotypic differences in Cd accumulation and mutant approaches. These transporters belong to different transporter families and are involved in the uptake, vacuolar sequestration, root-to-shoot translocation, and distribution of Cd. Attempts have been made to reduce Cd accumulation in grains by manipulating these transporters through overexpression or knockout of the transporter genes, as well as through marker-assisted selection breeding based on genotypic differences in Cd accumulation in the grains. In this review, we describe recent progress on molecular mechanisms of Cd accumulation in cereal crops and compare different molecular strategies for minimizing Cd accumulation in grains.

Selenium is an essential micronutrient for human beings, but millions of people around the world suffer from Se deficiency. Soil fertilization and foliar fertilization are two major agronomic pract...

Uptake of boron (B) in rice (Oryza sativa) is mediated by the Low silicon rice 1 (OsLsi1) channel, belonging to the NOD26-like intrinsic protein III subgroup, and the efflux transporter B transporter 1 (OsBOR1). However, it is unknown how these transporters cooperate for B uptake and how they are regulated in response to B fluctuations. Here, we examined the response of these two transporters to environmental B changes at the transcriptional and posttranslational level. OsBOR1 showed polar localization at the proximal side of both the exodermis and endodermis of mature root region, forming an efficient uptake system with OsLsi1 polarly localized at the distal side of the same cell layers. Expression of OsBOR1 and OsLsi1 was unaffected by B deficiency and excess. However, although OsLsi1 protein did not respond to high B at the protein level, OsBOR1 was degraded in response to high B within hours, which was accompanied with a significant decrease of total B uptake. The high B-induced degradation of OsBOR1 was inhibited in the presence of MG-132, a proteasome inhibitor, without disturbance of the polar localization. In contrast, neither the high B-induced degradation of OsBOR1 nor its polarity was affected by induced expression of dominant-negative mutated dynamin-related protein 1A (OsDRP1AK47A) or knockout of the mu subunit (AP2M) of adaptor protein-2 complex, suggesting that clathrin-mediated endocytosis is not involved in OsBOR1 degradation and polar localization. These results indicate that, in contrast to Arabidopsis thaliana, rice has a distinct regulatory mechanism for B uptake through clathrin-independent degradation of OsBOR1 in response to high B.

Plants have evolved two strategies to acquire ferrous (Strategy I) or ferric (Strategy II) iron from soil. The iron-related bHLH transcription factor 2 (IRO2) has been identified as a key regulator of iron acquisition (Strategy II) in rice. However, its mode of action, subcellular localisation and binding partners are not clearly defined. Using RNA-seq analyses, we identified a novel bHLH-type transcription factor, OsbHLH156. The function of OsbHLH156 in Fe homeostasis was analysed by characterisation of the phenotypes, elemental content, transcriptome, interaction and subcellular localisation of OsbHLH156 and IRO2. OsbHLH156 is primarily expressed in the roots and transcript abundance is greatly increased by Fe deficiency. Loss of function of OsbHLH156 resulted in Fe-deficiency-induced chlorosis and reduced Fe concentration in the shoots under upland or Fe(III) supplied conditions. Transcriptome analyses revealed that the expression of most Fe-deficiency-responsive genes involved in Strategy II were not induced in the osbhlh156-1 mutant. Furthermore, OsbHLH156 was required for nuclear localisation of IRO2. We conclude that OsbHLH156 is required for a Strategy II uptake mechanism in rice, partnering with a previously identified 'master' regulator IRO2. Mechanistically it is required for the nuclear localisation of IRO2.

International audience; Background and aim Silicon is known to be able to substitute carbon in plant biomass, especially in cellulose, lignin and phenols. However, a more comprehensive picture regarding the effect of silicon accumulation on plant carbon quality (cellu-lose, lignin, phenol, wax, lipids, and free organic acids content) with regard to potential decompos-ability is still missing. Methods Two different rice varieties (French brown and red rice cultivars) were cultivated under five different soil silicon availabilities. After maturity we harvested the plants and analyzed them regarding carbon quality by FTIR spectroscopy and regarding plant silicon concentrations. Results Silicon accumulation was found to be dependent on silicon availability and on the specific rice cultivar. The lowering of carbon compounds content by silicon was found not to be restricted to cellulose, lignin and phenol. Silicon accumulation was able to decrease other carbon compounds such as fat, wax, lipids, and free organic acids, too. Conclusions Consequently, silicon is important for the carbon quality of silicon accumulating plants. Furthermore , silicon accumulation in plants is interfering with a large range of different carbon compounds potentially altering the leaf economic spectra, decomposability, and thus potentially interfering with the whole performance of ecosystems dominated by silicon accumulating plant species.

Cd accumulation in rice grain was effectively reduced by expressing OsHMA3, which encodes a transporter responsible for vacuolar Cd sequestration, under the control of the OsHMA2 promoter., Reducing cadmium (Cd) accumulation in rice grain is an important issue for human health. The aim of this study was to manipulate both expression and tissue localization of OsHMA3, a tonoplast-localized Cd transporter, in the roots by expressing it under the control of the OsHMA2 promoter, which shows high expression in different organs including roots, nodes, and shoots. In two independent transgenic lines, the expression of OsHMA3 was significantly enhanced in all organs compared with non-transgenic rice. Furthermore, OsHMA3 protein was detected in the root pericycle cells and phloem region of both the diffuse vascular bundle and the enlarged vascular bundle of the nodes. At the vegetative stage, the Cd concentration in the shoots and xylem sap of the transgenic rice was significantly decreased, but that of the whole roots and root cell sap was increased. At the reproductive stage, the concentration of Cd, but not other essential metals, in the brown rice of transgenic lines was decreased to less than one-tenth that of the non-transgenic rice. These results indicate that expression of OsHMA3 under the control of the OsHMA2 promoter can effectively reduce Cd accumulation in rice grain through sequestering more Cd into the vacuoles of various tissues.

Bamboo seed is traditionally regarded as a gift from nature, which is consumed as “bamboo rice” and used in traditional medicine in some regions of the world. However, the basic nutritional profile of bamboo seed is poorly understood. Here, we collected seeds of five species of bamboo and compared them with rice and wheat in terms of morphology, nutritional quality, and concentration and distribution of mineral elements. In general, bamboo seeds had a longer length and shorter width than rice and wheat, but showed a similar 1000-grain weight to wheat. The contents of soluble protein and soluble sugar in bamboo seeds were lower than in rice and wheat, but the starch content was similar. The concentration of some mineral elements in bamboo seeds showed multiple differences when compared with rice and wheat. In particular, the concentrations of the toxic heavy metals Cd and Pb were significantly higher in bamboo seeds than in rice and wheat. The distribution of different elements in seeds of bamboo, rice, and wheat was successfully visualized and clearly showed that mineral elements tended to be enriched in the embryo and pericarp, although some differences were detected in the cellular localization of elements in different species. Furthermore, a physiological experiment showed bamboo had higher root-to-shoot translocation of Cd and Pb than rice. These results present for the first time the nutrient profile of bamboo seeds; the high accumulation of essential minerals in bamboo seeds suggests that the seeds might be a good natural food for addressing mineral malnutrition.

Boron is especially required for the growth of meristem and reproductive organs, but the molecular mechanisms underlying the preferential distribution of B to these developing tissues are poorly understood. Here, we show evidence that a member of nodulin 26-like intrinsic protein (NIP), OsNIP3;1, is involved in this preferential distribution in rice (Oryza sativa). OsNIP3;1 was highly expressed in the nodes and its expression was up-regulated by B deficiency, but down-regulated by high B. OsNIP3;1 was polarly localized at the xylem parenchyma cells of enlarged vascular bundles of nodes facing toward the xylem vessels. Furthermore, this protein was rapidly degraded within a few hours in response to high B. Knockout of this gene hardly affected the uptake and root-to-shoot translocation of B, but altered B distribution in different organs in the above-ground parts, decreased distribution of B to the new leaves, and increased distribution to the old leaves. These results indicate that OsNIP3;1 located in the nodes is involved in the preferential distribution of B to the developing tissues by unloading B from the xylem in rice and that it is regulated at both transcriptional and protein level in response to external B level.

To reduce cadmium (Cd) intake, remediation of Cd-contaminated soil and breeding crops with low Cd accumulation are important. This study aims to isolate rice mutants with altered accumulation of Cd. We used rice seeds mutated by N-methyl-N-nitrosourea for screening. The mutant was physiologically, genetically, and molecularly characterized. Cd accumulation was compared among five rice varieties cultivated in a Cd-contaminated soil. From 1000 lines screened, we isolated a line (TCM213) with high Cd accumulation. There was no difference in the root Cd uptake, but a higher root-to-shoot translocation of Cd was found in TCM213 compared with a common rice cultivar, T-65. The expression and sequence of OsNramp5 and OsHMA2 did not differ between TCM213 and T-65. However, several SNPs and deletion were found in the sequence of OsHMA3, although its expression and tissue localization were similar to those of T-65. Genetic analysis of an F2 population derived from T-65 and TCM213 showed that the variation of OsHMA3 explained 72 % of variation in total Cd accumulation. TCM213 accumulated the largest Cd amount in the shoots among five Cd-accumulating varieties. High Cd accumulation in TCM213 results from loss of function of OsHMA3, and its high Cd accumulation has potential for efficient phytoremediation of Cd-contaminated soil.

Highlight Silicon alleviated manganese toxicity in rice by down-regulating both manganese transporter expression for uptake and manganese root-to-shoot translocation., 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 54Mn 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 (

Aims Both aluminum (Al) toxicity and phosphorus (P) deficiency are limiting factors of crop production on acid soils. Although Al-P interaction has been extensively studied, the results are controversial. The aim of thisstudyistoinvestigatetheeffectofinplantaPonAlinduced inhibition of root elongation in wheat (Triticum aestivum L.). Methods Roots of wheat (cv. Atlas 66) with different internal P concentrations were prepared by two methods; split-root and re-rooting in a hydroponic solution using three different P levels (0, 25 and 250 μM) to avoid direct precipitation of Al-P in the solution. Al toxicity was evaluated by root elongation inhibition and callose induction. The Al and P concentrations in the root tips were also compared among different treatments. Results Both split-root and re-rooting methods generated roots with different P concentrations in the tips when exposed to different P levels. Lower P in the root tips resulted in less Al-induced inhibition of the root elongation, less callose content and less Al accumulation, while higher root P caused a higher Al-induced inhibitionofthe root elongation, increased callose content and Al accumulation in the root tips. Furthermore, Al in the root cell sap was not altered by different P concentrations, but Al in the root cell wall was increased with increasing in planta P concentrations. Conclusions Al toxicity in wheat is associated with P in the root cell wall; lower root P enhanced Al tolerance, while higher root P aggravated Al toxicity in wheat.

Background and aims Manganese (Mn) and aluminium (Al) phytotoxicities occur mainly in acid soils. In some plant species, Al alleviates Mn toxicity, but the mechanisms underlying this effect are obscure. Methods Rice (Oryza sativa) seedlings (11 d old) were grown in nutrient solution containing different concentrations of Mn(2+) and Al(3+) in short-term (24 h) and long-term (3 weeks) treatments. Measurements were taken of root symplastic sap, root Mn plaques, cell membrane electrical surface potential and Mn activity, root morphology and plant growth. Key results In the 3-week treatment, addition of Al resulted in increased root and shoot dry weight for plants under toxic levels of Mn. This was associated with decreased Mn concentration in the shoots and increased Mn concentration in the roots. In the 24-h treatment, addition of Al resulted in decreased Mn accumulation in the root symplasts and in the shoots. This was attributed to higher cell membrane surface electrical potential and lower Mn(2+) activity at the cell membrane surface. The increased Mn accumulation in roots from the 3-week treatment was attributed to the formation of Mn plaques, which were probably related to the Al-induced increase in root aerenchyma. Conclusions The results show that Al alleviated Mn toxicity in rice, and this could be attributed to decreased shoot Mn accumulation resulting from an Al-induced decrease in root symplastic Mn uptake. The decrease in root symplastic Mn uptake resulted from an Al-induced change in cell membrane potential. In addition, Al increased Mn plaques in the roots and changed the binding properties of the cell wall, resulting in accumulation of non-available Mn in roots.

In rice Si decreases Cd accumulation in both the roots and shoots by suppressing the expression of transporter genes for Cd uptake and translocation., Silicon (Si) alleviates cadmium (Cd) toxicity and accumulation in a number of plant species, but the exact molecular mechanisms responsible for this effect are still poorly understood. Here, we investigated the effect of Si on Cd toxicity and accumulation in rice (Oryza sativa) by using two mutants (lsi1 and lsi2) defective in Si uptake and their wild types (WTs). Root elongation was decreased with increasing external Cd concentrations in both WTs and mutants, but Si did not show an alleviative effect on Cd toxicity in all lines. By contrast, the Cd concentration in both the shoots and roots was decreased by Si in the WTs, but not in the mutants. Furthermore, Si supply resulted in a decreased Cd concentration in the root cell sap and xylem sap in the WTs, but not in the mutants. Pre-treatment with Si also decreased Cd accumulation in the WTs, but not in the mutants. Silicon slightly decreased Cd accumulation in the cell wall of the roots. The expression level of OsNramp5 and OsHMA2 was down-regulated by Si in the WTs, but not in the mutants. These results indicate that the Si-decreased Cd accumulation was caused by down-regulating transporter genes involved in Cd uptake and translocation in rice.

Plants only require small amounts of manganese (Mn) for healthy growth, but Mn concentrations in soil solution vary from sub-micromolar to hundreds of micromolar across the growth period. Therefore, plants must deal with large Mn concentration fluctuations, but the molecular mechanisms underlying how plants cope with low and high Mn concentrations are poorly understood. In this Opinion we discuss the role of Mn transporters in the uptake, distribution, and detoxification of Mn in response to changes in Mn concentrations through their regulation at the transcriptional and protein levels, mainly focusing on rice, an Mn-tolerant and −accumulating species. We also propose mechanisms involved in the hyperaccumulation of Mn and future prospects for studying this specific trait.