Screening and evaluation of bamboo shoots: Comparing the content of trace elements from 100 species.

Hundreds of bamboo shoots have been reported to be edible, but the accumulation of trace elements and hazardous elements in bamboo shoots is poorly understood. Here, 100 bamboo species have been evaluated by screening elements including B, Fe, Mn, Cu, Zn, Cd, Pb and As in bamboo shoots using different assessment systems. Bamboo shoots displayed different morphological characteristics, and large differences were found in the concentration of elements. Most bamboo shoots were rich in Fe and Zn and low concentrations of hazardous elements, but the concentration of Cd and Pb exceeded the maximum permissible limits of tuber vegetables in some bamboo species. Different bamboo shoots were ranked differently in the four assessment systems, and the comprehensive evaluation assigned final scores to all 100 bamboo shoots. This study provides valuable recommendations for selecting high-quality bamboo shoots that are rich in trace elements nutrition while minimizing the potential for hazardous element accumulation.

Salylic acid minimize cadmium accumulation in rice through regulating the fixation capacity of the cell wall to cadmium.

Although salylic acid (SA) has been linked to how plants react to cadmium (Cd) stress, the exact mechanism is still unknown. The endogenous SA concentration in the rice (Oryza sativa L.) roots was enhanced by Cd stress in the current investigation, and exogenous SA reduced the hemicellulose content in root cell wall, which in turn inhibited its Cd binding capacity. What's more, exogenous SA also decreased the transcription level of genes such as Natural Resistance-Associated Macrophage Protein 5 (OsNRAMP5) and a major facilitator superfamily gene-OsCd1 that responsible for root Cd absorption. Finally, less Cd was accumulated in the rice as a result of the higher expression of Heavy Metal ATPase 3 (OsHMA3), Cation/Ca exchanger 2 (OsCCX2) and Pleiotropic Drug Resistance 9 (OsPDR9/OsABCG36) that were responsible for separating Cd into vacuole and getting Cd out of cells, respectively. In contrast, mutant with low SA level accumulated more Cd. Additionally, SA enhanced endogenous nitric oxide (NO) levels, and its alleviatory effects were mimicked by a NO donor, sodium nitroprusside (SNP). In conclusion, SA enhanced rice's Cd resistance through regulating the binding capacity of the cell wall to Cd, a pathway that might dependent on the NO accumulation.

A comparative evaluation of chemical composition and nutritional value of bamboo rice and major cereals reveals the potential utility of bamboo rice as functional food.

Bamboo rice refers to the edible seeds collected from bamboo plants, but the nutritional and chemical compositions of bamboo rice are unknown. Here, we evaluated the nutritional value of two types of bamboo seeds by comparing them to rice and wheat. The fiber, protein, and microelement contents were much higher in bamboo seeds than in rice and wheat seeds. The flavonoids content was 5- and 10-folds higher in Moso bamboo seeds than in rice and wheat seeds, respectively. Amino acid profiles exhibited that most of amino acids were abundant in bamboo seeds compared to rice and wheat seeds. While water-soluble B vitamins and fatty acids in bamboo seeds were similar to those in rice and wheat seeds. Accordingly, rice and wheat may thus be substituted by bamboo rice which is a potentially functional food. Its high flavonoid content may be further exploited by the food industry.

The potential of bamboo seeds for natural biofortification of dietary zinc and iron.

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 by using an in vitro digestion protocol. Our evaluations revealed that values of bioaccessibility and bioavailability of iron were 25 and 21 mg kg-1 in bamboo seeds which were 1.6- and 1.7- fold higher than in rice, respectively. Also, values of bioaccessibility and bioavailability of zinc were 20 and 13 mg kg-1 in bamboo seeds which 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, phytic acid concentration in bamboo seeds was only 0.42 times higher than in rice. By contrast, the tannins concentration in bamboo seeds was 2.2 times higher than in rice. Cellular localization results showed that iron and zinc were mainly concentrated in the embryo and the aleurone layer. These results clearly suggest that Moso bamboo seeds are rich in iron and zinc and have potential as a food for iron and zinc biofortification.

Physiological and transcriptomic characterization of cadmium toxicity in Moso bamboo (Phyllostachys edulis), a non-timber forest species.

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.

Boron uptake in rice is regulated post-translationally via a clathrin-independent pathway.

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.

Fine regulation system for distribution of boron to different tissues in rice.

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.

A transcription factor OsbHLH156 regulates Strategy II iron acquisition through localising IRO2 to the nucleus in rice.

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.

Effective reduction of cadmium accumulation in rice grain by expressing OsHMA3 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.

Preferential Distribution of Boron to Developing Tissues Is Mediated by the Intrinsic Protein OsNIP3.

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.

The Key to Mn Homeostasis in Plants: Regulation of Mn Transporters.

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.

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.

Aluminium alleviates manganese toxicity to rice by decreasing root symplastic Mn uptake and reducing availability to shoots of Mn stored in roots.

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.