The Role of Node Restriction on Cadmium Accumulation in the Brown Rice of 12 Chinese Rice (Oryza sativa L.) Cultivars

Application of Lanthanum at the Heading Stage Effectively Suppresses Cadmium Accumulation in Wheat Grains by Downregulating the Expression of TaZIP7 to Increase Cadmium Retention in Nodes

Reducing cadmium (Cd) accumulation in wheat is an effective way to decrease the potential threats of Cd to human health. The application of lanthanum (La) in agricultural fields is eliciting extensive attention due to its beneficial effects on improving yields and inhibiting Cd accumulation in edible parts of crops. However, the potential mechanism of La-restricted Cd accumulation in crop grains is not entirely understood. Here, we investigated the effects of La and Cd accumulation in wheat grains by implementing application at the shooting and heading stages. Some associated mechanisms were explored. Results showed that La application at the shooting and heading stages considerably promoted the thousand-grain weight. La application at the shooting and heading stages increased Cd accumulation in the first node beneath the panicle (N1) but reduced Cd levels in the other tissues. La application at the heading stage exerted greater effects on Cd storage in N1 while reducing Cd concentrations in the other tissues compared with La application at the shooting stage. La addition substantially decreased the translocation of Cd from the lower nodes to the upper internodes, but increased Cd translocation from the lower internodes to the upper nodes. The expression of TaZIP7 in N1 was downregulated by La treatment. These results suggest that the effective reduction in Cd in wheat grains by La application at the heading stage is probably a consequence of the successful promotion of Cd storage in nodes by downregulating the expression of TaZIP7 during the grain-filling stage, thereby hindering the redirection Cd from nodes to grains.

Cadmium distribution in rice: Understanding the role of plant nodes and growth stages

Cadmium (Cd) contamination in farmland poses a significant threat to food security in staple crops, especially rice. Using a mix of hydroponic and soil culture methods, stable isotope tracers, and advanced analytical techniques, this study elucidated the mechanisms of Cd uptake, translocation, and accumulation in rice throughout different growth stages. Despite a notable linear correlation between soil DTPA (diethylene-triaminepentaacetic acid)-Cd and the total Cd concentration of rice, our findings showed that the influence of soil Cd level on the proportion of Cd in grain was negligible. The study highlighted the dynamic response of Cd distribution within plant nodes to changes in DTPA-extractable Cd. Heading stage (HS) and mature stage (MS) were critical for Cd uptake and upward transport in rice, and the contribution of Cd absorption in brown rice was 28.61% and 40.16%, respectively. Moreover, the distribution of Cd in nodes showed how important nodes are for controlling and redistributing Cd in rice. In the HS, the lower node had a function in re-transporting, whereas in the MS, there was a considerable redistribution of Cd in the upper node. These insights can help us understand rice Cd dynamics and develop agronomic techniques and rice cultivars that minimize Cd accumulation.

Trade-offs of reproductive growth and Cd remobilization regulated Cd accumulation in wheat grains (Triticum aestivum L.)

Minimization of cadmium (Cd) accumulation in wheat grain (Triticum aestivum L.) is an important way to prevent Cd hazards to humans. However, little is known about the mechanisms of varietal variation of Cd accumulation in wheat grain. This study explores the physiological mechanisms of Cd bioaccumulation through field and hydroponic experiments on two wheat varieties of low-Cd-accumulating variety (L-6331) and high-Cd-accumulating variety (H-6049). Field study showed that average Cd accumulative rates in spikes of H-6049 were 1.57-fold of L-6331 after flowering, ultimately grain-Cd of H-6049 was 1.70-fold of L-6331 in Cd-contaminated farmland. The hydroponic experiment further confirmed that more vegetative tissues of L-6331 were involved in the remobilization of Cd, which jointly mitigated the process of Cd loaded to grains when leaf-cutting conducted after Cd stress. Additionally, the L1 and N1 of L-6331 play an especially important role in regulating Cd remobilization, and the larger EVB areas in N1 have the morphological feature that facilitates the transfer of Cd to L1. Overall results implied that low-Cd-accumulating variety initiated more trade-offs of reproductive growth and Cd remobilizatoin under Cd-stress after flowering compared with high-Cd-accumulating variety, and provided new insights into the processes of Cd loaded into wheat grains among different varieties.

Uptake and translocation of cadmium and trace metals in common rice varieties at different growth stages

Rice (Oryza sativa) is an important nutritional grain for the majority of Asian countries, but it is also a major source of cadmium (Cd) accumulation. A pot experiment was carried out to investigate the Cd uptake and translocation of high Cd (IR-50) and low Cd (White Ponni) rice cultivars in Cd-contaminated soils. The findings revealed that Cd impacts on rice development and growth differed depending on rice cultivars. Soil Cd levels in the seedling stage exceeded the critical levels (3-6 mg kg-1) only 5.0 mg kg-1 Cd treatment for the IR-50 (7.47 mg kg-1). At higher Cd treatments (1.0 and 5.0 mg kg-1), morphometric characteristics and yield of grains showed a declining and increasing trend in both rice varieties, respectively. The accumulation of Cd was higher in soil and roots during seedling and tillering stages, whereas in booting and maturity stages increased in stems and leaves in IR-50 and WP rice varieties. Cd levels in rice grains above the maximum allowable limit (0.4 mg kg-1) only in IR-50 (0.51 mg kg-1) rice cultivar at maturity stage. The EF of Cd were classified as minor enrichment to 'moderate enrichment' in both rice cultivars. TF values exhibited > 1 in booting and maturity stages in both rice cultivars at higher Cd treatments. The study concluded that the IR-50 rice variety exhibited increased Cd intake and transported to various parts of rice plants, particularly grains. The findings indicate that WP rice cultivar is more resistant to Cd toxicity, reducing health hazards for persons who preferred the staple food rice.

Effect of silicon spraying on rice photosynthesis and antioxidant defense system on cadmium accumulation

Cadmium (Cd) pollution is a serious threat to food safety and human health. Minimizing Cd uptake and enhancing Cd tolerance in plants are vital to improve crop yield and reduce hazardous effects to humans. In this study, we designed three Cd concentration stress treatments (Cd1: 0.20 mg·kg-1, Cd2: 0.60 mg·kg-1, and Cd3: 1.60 mg·kg-1) and two foliar silicon (Si) treatments (CK: no spraying of any material, and Si: foliar Si spraying) to conduct pot experiments on soil Cd stress. The results showed that spraying Si on the leaves reduced the Cd content in brown rice by 4.79-42.14%. Si application increased net photosynthetic rate (Pn) by 1.77-4.08%, stomatal conductance (Gs) by 5.27-23.43%, transpiration rate (Tr) by 2.99-20.50% and intercellular carbon dioxide (CO2) concentration (Ci) by 6.55-8.84%. Foliar spraying of Si significantly increased the activities of superoxide dismutase (SOD) and peroxidase (POD) in rice leaves by 9.84-14.09% and 4.69-53.09%, respectively, and reduced the content of malondialdehyde (MDA) by 7.83-48.72%. In summary, foliar Si spraying protects the photosynthesis and antioxidant system of rice canopy leaves, and is an effective method to reduce the Cd content in brown rice.

Mechanisms of chloride to promote the uptake and accumulation of cadmium in rice (Oryza sativa L.)

Cadmium (Cd) contamination in rice ecosystems posed a critical challenge to global food security and environmental health. This study aimed to unveil the key mechanisms trough hydroponic experiments by which chloride (Cl-) promoted the absorption and accumulation of cadmium (Cd) in rice plants. The findings elucidated that the addition of Cl- increased Cd uptake by rice roots (5.1 % ∼ 61 %), acting both directly by enhancing root morphology and indirectly through regulating of the main transporter genes of Cd. The study unveiled that Cl- addition significantly improves Cd bioavailability in roots, which was discernible through the augmentation of Cd concentration and proportion in subcellular fractions, coupled with elevated energy values in key cellular components. Moreover, Cl- addition further augmented the intricate process of Cd transport from roots to shoots (16.1- 86.7 %), which was mainly attributed to the underexpression of OsHMA3 and the decrease in the formation of sulfuhydryl substances. This research provides a comprehensive understanding of the complex mechanisms governing Cd dynamics in rice plants in the presence of Cl-. By elucidating these processes, our findings not only contribute to fundamental knowledge in plant metal uptake but also hold promising implications for mitigating Cd contamination in rice cultivation systems.

Insights into growth stages and genotypes in airborne Pb accumulation in Oryza sativa L. grains: Utilizing isotope fingerprinting alongside a model study

Atmospheric exposure is an important pathway of accumulation of lead (Pb) in Oryza sativa L. grains. In this study, source contributions of soil, early atmospheric exposure, and late atmospheric exposure, along with their bioaccumulation ratios were examined both in the pot and field experiments using stable Pb isotope fingerprinting technology combined with a three-compartment accumulation model. Furthermore, genotype differences in airborne Pb accumulation among four field-grown rice cultivars were investigated using the partial least squares path model (PLS-PM) linking rice Pb accumulation to agronomic traits. The findings revealed that during the late growth period, the air-foliar-grain transfer of Pb was crucial for rice Pb accumulation. Approximately 69-82% of the Pb found in polished rice was contributed by atmospheric source, with more than 80% accumulating during the late growth stage. The air accumulation ratios of rice grains were genotype-specific and estimated to be 0.364-1.062 m3/g during the late growth. Notably, grain size exhibited the highest standardized total effects on the airborne Pb concentrations in the polished rice, followed by leaf Pb and the upward translocation efficiency of Pb. The present study indicates that mitigating the health risks associated with Pb in rice can be achieved by controlling atmospheric Pb levels during the late growth stage and choosing Japonica inbred varieties characterized by large grain size.

Co-foliar application of zinc and nano-silicon to rice helps in reducing cadmium exposure risk: Investigations through in-vitro digestion with human cell line bioavailability assay

Foliar application of zinc (Zn) or silicon nanoparticles (Si-NPs) may exert regulatory effects on cadmium (Cd) accumulation in rice grains, however, their impact on Cd bioavailability during human rice consumption remains elusive. This study comprehensively investigated the application of Zn with or without Si-NPs in reducing Cd accumulation in rice grains as well to exactly evaluate the potential risk of Cd exposure resulting from the rice consumption by employing field experiment as well laboratory bioaccessibility and bioavailability assay. Sole Zn (ZnSO4) or in combination with Si (ZnSO4 +Si and ZnO+Si) efficiently lowered the Cd concentration in rice grains. However, the impact of bioaccessible (0.1215-0.1623 mg kg-1) and bioavailable Cd (0.0245-0.0393 mg kg-1) during simulated human rice consumption depicted inconsistent trend. The straw HCl-extractable fraction of Cd (FHCl-Cd) exhibited a significant correlation with total, bioaccessible, and bioavailable Cd in grains, indicating the critical role of FHCl-Cd in Cd accumulation and translocation from grains to human. Additionally, foliar spraying of Zn+Si raised the nutritional value of rice grains, leading to increased protein content and reduced phytic acid concentration. Overall, this study demonstrates the potential of foliar application of ZnSO4 +Si in mitigating the Cd levels in rice grains and associated health risks upon consumption.

Effects of different phosphorus fertilizers on cadmium absorption and accumulation in rice under low-phosphorus and rich-cadmium soil

Rice is the main food crops with the higher capacity for cadmium (Cd) uptake, necessitating the urgent need for remediation measures to address Cd in paddy soil. Reasonable agronomic methods are convenient and favorable for fixing the issue. In this study, a pot experiment was employed to evaluate the effects of two foliar (NaH2PO4, SDP; KH2PO4, PDP) and two solid phosphate fertilizers (double-superphosphate, DSP; calcium-magnesium phosphate, CMP) on uptake and remobilization of Cd in rice plants under the low-P and rich-Cd soil. The results revealed that these four phosphorus fertilizer significantly down-regulated the relative expression of OsNRAMP5 involved in Cd absorption, while up-regulated OsPCS1 expression and increased distribution of Cd into the cell wall in roots. Furthermore, phosphorus fertilizer resulted in a significant decrease in the relative expression of OsLCT1 in stems and OsLCD in leaves, decreased the transfer factor of Cd from shoots to grains, and ulterior reduced the Cd accumulation in three protein components of globulin, albumin, and glutelin, making the average Cd concentration of brown rice decreased by 82.96%. These results comprehensively indicate that in situations with similar soil backgrounds, the recommended application of solid CMP and foliar PDP can alleviate the toxicity of Cd by reducing its absorption and remobilization.

New insights into the key role of node I in thallium accumulation in seed of coix (Coix lacryma-jobi L.)

The mechanisms underlying the distribution of many toxic metal(loid)s in shoots and metal(loid) transport to grains have been well documented in the quest for food safety but there remains a lack of knowledge on thallium (Tl) accumulation in food crops. Here, field investigations combined with a glasshouse pot experiment were conducted to investigate the characteristics of Tl distribution and accumulation in coix, a major food crop in south Guizhou province, China, and the role of node I in restricting Tl transport to the seed. Fourteen percent of coix seed samples collected from the Lanmuchang Tl-As-Hg mine contained higher Tl concentrations than the recommended limit for foods and feedstuffs in Germany (0.5 mg kg-1), with the highest exceedance rate of the metal(loid)s determined, when grown in soils surrounding the mine with a very high Tl concentration of 0.07-89.5 mg kg-1 and a general low pH of 4.19-6.48. Thallium concentrations were higher in coix nodes than in internodes, followed by roots and grains. The Tl translocation factors from node I to grains were 0.01-0.21 and were the lowest of any translocation factors between different tissues. Node I is therefore the key tissue restricting Tl transport to coix grains. Thallium was localized mainly in the diffuse vascular bundles (DVBs) in node I. The co-localization of Tl and sulfur in the DVBs and Tl contamination-induced phytochelatin (PC) accumulation indicate that Tl storage in the DVBs involving complexation with PCs in node I is an important process in Tl accumulation in coix grains. Moreover, the area of DVBs in node I increased with increasing soil Tl pollution level, providing more channels for Tl transport to the panicles and grains and thereby acting as a key factor restricting Tl transport to the grains. These results provide new insights into the key role of node I in Tl accumulation in coix grains and indicate key points to minimize Tl accumulation in grains for food safety.

Selenate reduced wheat grain cadmium accumulation by inhibiting cadmium absorption and increasing root cadmium retention

Selenium (Se) fertilizer has been recently used to reduce cadmium (Cd) accumulation in plant. A pot culture was performed to analyze Cd uptake, translocation, and distribution in wheat plants during the reproductive growth period in a Cd-contaminated soil after selenate was applied to the soil, and a hydroponic culture was carried out to investigate the effects of selenate application on Cd2+ influx, subcellular Cd distribution, and Cd accumulation in wheat seedlings. Results showed that selenate application had no significant effect on DTPA-Cd and Cd fraction in soil. The application of selenate greatly inhibited the whole-plant Cd absorption by 14%-23%. In addition, selenate prompted the retention of Cd in root by increasing the Cd distribution in the vacuole, which reduced the root-to-shoot Cd translocation by 18%-53%. The application of selenate increased the Cd concentration in nodes, inhibited Cd remobilization from nutritive organs to grain, and ultimately reduced Cd accumulation in wheat grain. Further, heading to grain filling was the key growth stage for exogenous selenate to regulate grain Cd accumulation. In summary, soil selenate application is an effective method to reduce grain Cd concentration in wheat, which provided scientific basis for remediation of Cd-contaminated soil.

Foliar zinc reduced Cd accumulation in grains by inhibiting Cd mobility in the xylem and increasing Cd retention ability in roots1

Cadmium (Cd) pollution endangers the safe utilization of paddy soils, and foliar zinc (Zn) can reduce the toxic effects of Cd. However, little is known about the effects of foliar Zn application on the transport and immobilization of Cd in key rice tissues and the physiological state of rice plants. A pot experiment was conducted to explore the effects of spraying 0.2% and 0.4% Zn (ZnSO4) during the early grain-filling stage on Cd transport in rice, photosynthesis, glutathione (GSH) levels, Cd concentrations in xylem sap, and the expression of Zn transporter genes. The results showed that grain Cd concentrations in the 0.2% Zn and 0.4% Zn treatments were 24% and 31% lower, respectively, than those of the control treatments at maturity. Compared with the control treatments, the 0.4% Zn treatment increased Cd by 60%, 69%, 23%, and 22% in husks, rachises, first internodes, and roots, respectively. Application of Zn reduced xylem Cd content by up to 26% and downregulated transporter genes (OSZIP12, OSZIP4, and OSZIP7a) in flag leaves. Foliar Zn increased Cd bioaccumulation in roots while decreasing Cd bioaccumulation in grains. Zn reduced GSH concentration in flag leaves and stems, inhibiting photosynthesis (intercellular CO2 concentration, transpiration rate). Taken together, foliar Zn can reduce the expression of Zn transporter genes and the mobility of Cd in the xylem, promoting the fixation of Cd in husks, rachises, first internodes, and roots, ultimately reducing Cd concentration in rice grains.

Phenotypic and genetic dissection of the contents of important metallic elements in hybrid rice grown in cadmium-contaminated paddy fields

Rice (Oryza sativa L.) is a staple food that feeds over half of the world's population, and the contents of metallic elements in rice grain play important roles in human nutrition. In this study, the contents of important metallic elements were determined by ICP-OES, and included cadmium (Cd), zinc (Zn), manganese (Mn), copper (Cu), iron (Fe), nickel (Ni), calcium (Ca), and magnesium (Mg) in brown rice, in the first node from the top (Node 1), in the second node from the top (Node 2), and in roots of 55 hybrids and their parental lines. The heritability of metallic element contents (MECs), the general combining ability (GCA) for MEC, and the correlation between MECs in different organs/tissues of hybrids were also analyzed. The results indicated that: (1) there was a positive correlation between the contents of Cd and Zn in nodes and roots, but a negative correlation between the contents of Cd and Zn in brown rice of the hybrids(2) the GCA for MECs can be used to evaluate the ability of the parental lines to improve the metal contents in brown rice of the hybrids(3) the contents of Cd, Zn, Ca, and Mg in brown rice were mainly affected by additive genetic effects(4) the restorer lines R2292 and R2265 can be used to cultivate hybrids with high Zn and low Cd contents in the brown rice.

Silicon inhibits the upward transport of Cd in the first internode of different rice varieties in a Cd stressed farm land

Silicon spraying on leaves can reduce the accumulation of cadmium (Cd) in rice grain. However, it has been found that not all rice varieties decrease in Cd content after silicon (Si) application. A field study was conducted to check the performance of Si on the accumulation and transport of Cd in four rice varieties. TY390 and YXY2, having 51.5%- 60.6% Cd content of grain was inhibited by foliar Si, were classified as CRS varieties; BXY9978 and YXYLS, having Cd content of grain is nonresponsive with Si, were classified as CNS varieties. The Cd contents were mainly accumulated in stem, especially in the first stem node. While foliar Si reported no changes in the Cd content of first node in four different rice varieties. Comparing the correlation between Si and Cd contents in the above part of the first internode of CRS and CNS, as well as the relative expression of Cd transport genes in the first internode suggested that first internode was the key site to effect Cd transport through Si application, and OsZIP7 is a key Cd transporter protein responsive to Si, leading to different response of Cd transport and accmulation between the CRS and the CNS varieties of rice.

Characterizing the remobilization flux of cadmium from pre-anthesis vegetative pools in rice during grain filling using an improved stable isotope labeling method

A clear understanding of the allocation of Cd to grains is essential to manage the level of Cd in cereal diets effectively. Yet, debate remains over whether and how the pre-anthesis pools contribute to grain Cd accumulation, resulting in uncertainty regarding the need to control plant Cd uptake during vegetative growth. To this end, rice seedlings were exposed to ¹¹¹Cd labeled solution until tillering, transplanted to unlabeled soils, and grown under open-air conditions. The remobilization of Cd derived from pre-anthesis vegetative pools was studied through the fluxes of ¹¹¹Cd-enriched label among organs during grain filling. The ¹¹¹Cd label was continuously allocated to the grain after anthesis. The lower leaves remobilized the Cd label during the earlier stage of grain development, which was allocated almost equally to the grains and husks + rachis. During the final stage, the Cd label was strongly remobilized from the roots and, less importantly, the internodes, which was strongly allocated to the nodes and, to a less extent, the grains. The results show that the pre-anthesis vegetative pools are an important source of Cd in rice grains. The lower leaves, internodes, and roots are the source organs, whereas the husks + rachis and nodes are the sinks competing with the grain for the remobilized Cd. This study provides insight into understanding the ecophysiological mechanism of Cd remobilization and setting agronomic measures for lowering grain Cd levels.

Mechanisms of lead uptake and accumulation in wheat grains based on atmospheric deposition-soil sources

Lead (Pb) accumulation in wheat grains depends on two aspects: i) Pb uptake by the roots and shoots, and ii) the translocation of organ Pb into the grain. However, the underlying mechanism of the uptake and transport of Pb in wheat remains unclear. This study explored this mechanism by establishing field leaf-cutting comparison treatments. Interestingly, as the organ with the highest Pb concentration, only 20.40 % of the root's relative contribution to grain Pb. The relative contributions of the spike, flag leaf, second leaf, and third leaf to grain Pb were 33.13 %, 23.57 %, 13.21 %, and 9.69 %, respectively, which was opposite to their Pb concentration distribution trends. According to Pb isotope analysis, it was found leaf-cutting treatments reduced the proportion of atmospheric Pb in grain, and grain Pb predominantly comes from atmospheric deposition (79.60 %). Furthermore, from the bottom to the top, the concentration of Pb in internodes decreased gradually, and the proportions of Pb originating from soil in the nodes also decreased, revealing that wheat nodes hindered the translocation of Pb from roots and leaves to the grain. Therefore, the hindering effect of nodes on the migration of soil Pb in wheat resulted in atmospheric Pb having a more convenient pathway to the grain than soil Pb, and further leading grain Pb accumulation primarily depended on the contribution of the flag leaf and spike.

Cadmium mobility and health risk assessment in the soil-rice-human system using in vitro biaccessibility and in vivo bioavailability assay: Two year field experiment

Humans are mainly exposed to cadmium (Cd) due to the rice consumption, however there exist considerable differences across rice cultivars in terms of Cd absorption and accumulation in the grains, and subsequent release after digestion (bioaccessibility), as well as uptake by Caco-2 cells of humans (bioavailability). This study comprised of field and lab simulation trials where in the field, firstly 39 mid-rice cultivars were screened for their phytoremediation potential coupled with safe production in relation to uptake and translocation of Cd. Lower Cd concentrations (˂0.2 mg kg^-1) in polished rice of 74 % cultivars were ascribed to the increased root to straw translocation indicating that straw may acquire higher accumulation of Cd. Furthermore, the ionomic profile demonstrated that the spatial distribution of metals in different rice organs corresponds to the plant growth morphology. In the second year, in vitro-in vivo assay model was employed to assess the bioaccessibility and bioavailability of Cd in polished rice and to further estimate the daily Cd intake by humans through rice grains. The results of bioaccessibility and bioavailability assays and daily estimated Cd intake presented the corresponding values of 39.02-59.76 %, 8.69-24.26 %, and 0.0185-0.9713 μg kg^-1 body weight day^-1, respectively. There exists a strong connection between total Cd and bioaccessible Cd to humans (R² = 0.94, P < 0.01). Polynomial fitting (R² = 0.91, P < 0.01) showed a better statistically significant correlation between total Cd contents and bioavailable levels, suggesting that in vitro-in vivo assays should be considered in future studies. The results of field experiments and in vitro-in vivo assays recommended the Tianyouhuazhan (MR-29), Heliangyou1hao (MR-17), and Yongyou15 (MR-1) as suitable mid-rice cultivars for the phytoremediation of slightly Cd contaminated soils coupled with rice agro-production due to their high nutritional value and low total and bioavailable Cd for human.

Nodes play a major role in cadmium (Cd) storage and redistribution in low-Cd-accumulating rice (Oryza sativa L.) cultivars

Rice cadmium (Cd) contamination is one of the critical agricultural issues. Breeding of low-Cd-accumulating cultivar is an effective approach to reduce Cd bioaccumulation in rice. To investigate the molecular mechanism underlying Cd transport in rice, the functions of nodes in Cd transport are explored. The results show that different nodes have different functions of Cd transport in the rice plant and the physiological structure of the first node under panicle (N1) determine the Cd accumulation in the brown rice. The upper nodes can redistribute the Cd transport in aboveground tissues. The expressions of Cd-efflux transporter genes (OsLCT1 and OsHMA2) located on the plasma-membrane are the main factors affecting the Cd transport form node to brown rice, which are more depended on the node functions but not the node Cd concentrations. Lower expressions of OsLCT1 and OsHMA2 in N1 result in lower Cd transport from node to brown rice. The size of vascular-bundle (VB) areas in the junctional node with the flag leaf can determine the expression of OsHMA2 and the expression of OsLCT1 positively correlated with the Cd transport ability of first node (N1). The expressions of OsVIT2 and OsABCC1 cannot allow Cd to be immobilized into the vacuoles in node. The VB structure and Cd transporter gene expression level of N1 proved that the Cd concentration of N1 can be used as an important indicator for screening low-Cd-accumulating cultivars. The major implication is that selecting or breeding cultivars with lower Cd accumulations in N1 could be an effective strategy to reduce Cd accumulation in rice grains.

The Relative Contributions of Different Wheat Leaves to the Grain Cadmium Accumulation

In the context of increasing atmospheric particles pollution, wheat cadmium (Cd) pollution caused by atmospheric deposition in agro-ecosystems has attracted increasing attention. However, the relative contribution of different wheat leaves-to-grain Cd accumulation is still unclear. We assessed the roles of different wheat leaves on grain Cd accumulation with field-comparative experiments during the filling stage. Results show that wheat leaves can direct uptake atmospheric Cd through stomata, and the flag leaf exhibited a higher Cd concentration compared to other leaves. The relative contribution of the leaves-to-grain Cd accumulation decreased gradually during the grain-filling period, from 34.44% reaching 14.48%, indicating that the early grain-filling period is the critical period for leaf Cd contributions. Moreover, the relative contribution of flag leaves (7.27%) to grain Cd accumulation was larger than that of the sum of other leaves (7.21%) at maturity. Therefore, the flag leaf is the key leaf involved in grain Cd accumulation, and controlling the transport of Cd from leaves to grains at the early filling period, particularly flag leaf, could help to ensure wheat grain safety, thus ensuring the safety of food production.

Screening of low-Cd accumulating early rice cultivars coupled with phytoremediation and agro-production: Bioavailability and bioaccessibility tests

Previous studies have focused on total cadmium (Cd) accumulation in rice or its transformation in soil, but only a few have examined the entire soil-rice-human system. This study investigated the Cd bioaccessibility and bioavailability for humans from grains of early rice cultivars grown in a Cd-polluted field and further combined with multi-traits to discover and evaluate the optimum safe production and phytoremediation potential cultivars. The results revealed that Cd concentration in polished rice was <0.20 mg kg^-1 in 79 % of early rice cultivars, implying that Cd levels in rice might be reduced by cultivar selection. Furthermore, the higher values of root to straw translocation factor indicates the maximal accumulation of Cd in straw and with highest soil to straw accumulation factor (>1.0) in 66.67 % of cultivars. However, bioaccessibility and bioavailability varied greatly among cultivars with corresponding values ranging from 5.68 to 7.67 % and 1.87 to 5.71 ng g^-1, respectively. Despite the fact that polynomial fitting revealed a statistically significant relationship between Cd content in polished rice and bioavailable Cd in humans (R² = 0.718, P = 0.025), poor goodness of fit for bioaccessibility, bioavailability, and toxicity varied even within low-Cd accumulating cultivars. As a result of multi trait analysis and bioavailability, Zhuliangyou4024 (ER-9), Lingliangyou211 (ER-3), and Yonxian15 (ER-28) were found to be the three best early rice cultivars with higher essential nutrients, less total and bioavailable Cd, and relative high phytoremediation potential and are suitable for healthy rice production and soil remediation.

Synchrotron X-ray Fluorescence Technique Identifies Contribution of Node Iron and Zinc Accumulations to the Grain of Wheat

Increasing iron (Fe) and zinc (Zn) concentrations in crop grains with high yield is an effective measure to ensure food supply and alleviate mineral malnutrition in humans. Micronutrient concentrations in grains depend on not only their availability in soils but also their uptake in roots and translocation to shoots and grains. In this three-year field study, we investigated genotypic variation in Fe and Zn uptake and translocation within six wheat cultivars and examined in detail Fe and Zn distributions in various tissues of two cultivars with similar high yield but different grain Fe and Zn concentrations using synchrotron micro-X-ray fluorescence. Results revealed that root Fe and Zn concentrations were 11 and 44% greater in high-nutrient (HN) than in low-nutrient (LN) concentration cultivar. Although both cultivars accumulated similar amounts of Fe in shoots, HN cultivar had greater accumulation of Fe in grain and greater accumulation of Zn in both shoots and grain. Grain Zn concentration was positively correlated with shoot Zn accumulation, and grain Fe concentration was positively correlated with the ability to translocate Fe from leaves/stem to grains. In the first nodes of shoots, HN cultivar had 482% greater Fe and 36% greater Zn concentrations in the enlarged vascular bundle (EVB) than LN cultivar. In top nodes, HN cultivar had 225 and 116% greater Fe and Zn concentrations in the transit vascular bundle and 77 and 71% greater in the EVB when compared to LN cultivar. HN cultivar also had a greater ability to allocate Fe and Zn to the grain than LN cultivar. In conclusion, HN cultivar had greater capacity of Fe and Zn acquirement by roots and translocation and partitioning from shoots into grains. Screening wheat cultivars for larger Fe and Zn concentrations in shoot nodes could be a novel strategy for breeding crops with greater grain Fe and Zn concentrations.

Effects of Cd uptake, translocation and redistribution in different hybrid rice varieties on grain Cd concentration

In order to identify the key transport process that determines the Cd concentration in brown rice, this study used 21 hybrid rice varieties as experimental materials and conducted field experiments in Qiyang (cadmium-contaminated site) and Yongding (low-cadmium site). Cd concentrations in 8 organs were measured, and bioconcentration factors and transfer factor were further calculated. The results showed that the Cd concentrations of the organs related to the xylem transport were as follows: root > node > stem > leaf sheath > leaf. In the phloem, the Cd concentrations were as follows: rachis > brown rice > rice husk. And the results of the correlation analysis found that Cd concentration between brown rice and root showed a significant positive correlation in Cd-contaminated site, but no significant correlation in low-cadmium site. Meanwhile, at both experimental sites, the Cd concentration of brown rice showed the most significant correlation with the phloem transfer factor from leaf and leaf sheath to brown rice. Principal Component Analysis (PCA) and stepwise regression analysis likewise found that Cd concentration in leaf and leaf sheath and their phloem transport of Cd to brown rice were significantly and positively correlated with Cd concentration in brown rice. The above results showed that the transport of leaf and leaf sheath to brown rice was a key process, and played a more important role in the accumulation of cadmium in brown rice than in root.

Airborne lead: A vital factor influencing rice lead accumulation in China

Traditionally, lead (Pb) in rice grains has been thought to be mostly derived from soil, and the contribution of aerosol Pb remains so far unknown. Based on a meta-analysis, we surprisingly found rice Pb content decreased proportionally with urban atmospheric Pb concentrations in major rice-growing provinces in China during 2001-2015, suggestive of the strong influence of long-range Pb transport on agricultural environment. With the combination of field survey, field experiment, as well as a predictive model, we confirmed high contribution of atmospheric exposure to rice grain Pb in China. We for the first time developed a predictive mathematical model which revealed that aerosol Pb accumulation ratios of rice grains were related to both grain weight and accumulation types. We successfully predicted the national-scale rice Pb in China on the basis of the public data of urban PM_2.5 from 19 rice-growing provinces and proposed a seasonal atmospheric Pb limit of 0.20 µg m^-3 based on the safe threshold level of Pb in rice, which was much lower than the current limit of 1 µg m^-3 set in China.

Cadmium accumulation and migration of 3 peppers varieties in yellow and limestone soils under geochemical anomaly

The high geological background of heavy metal cadmium (Cd) in geochemical anomaly areas in Southwest China and the anthropogenic pollution superposition effect in some typical areas due to mining exploitation have attracted special attention for several decades. The accumulation and migration of Cd in the farmland soil-crop system was worth discussing. In this study, the representative yellow soil and limestone soil in Guizhou Province, as well as three types of pepper (Capsicum annuum L.) were selected to investigate Cd accumulation and migration regulation from soil to plants using pot tests at different Cd concentration levels. For red cluster pepper, line pepper and hybrid pepper, the accumulation capacity of Cd in various parts was similar as follows: Cd_root > Cd_stem ≈ Cd_leaf > Cd_fruit. The differences in the Cd concentration between pepper varieties were as follows: Cd in line pepper roots was higher than that in red cluster pepper and hybrid pepper, but for leaves and fruits, the Cd concentration of red cluster pepper was higher than the others. A higher accumulation and lower transport capacity of Cd in yellow soil as well as a lower accumulation and higher transport capacity of Cd in limestone soil were achieved based on the results of enrichment coefficients and transport coefficients in yellow soil. The red pepper Cd concentration was higher than that of the other two types. The accumulation and transformation of Cd for peppers in yellow soil is more significant (p < 0.05), which results in a higher risk of migration through the food chain.

Biochar and exogenous calcium assisted alleviation of Pb phytotoxicity in water spinach (Ipomoea aquatica Forsk) cultivated in Pb-spiked soil

The consumption of vegetables grown in Pb-polluted soils causes serious threats to human health around the globe. In this study, we evaluated the Pb toxicity alleviation in water spinach grown of pot experiments in Pb-spiked soil treated with biochar and exogenous calcium. The results showed that both biochar and exogenous calcium alleviated Pb stress in water spinach, which was mainly manifested on its improved soil health and increased growth and decreased Pb uptake. Incorporation of 3% biochar significantly reduced CaCl₂ extracted Pb by 53.6% and decreased Pb accumulation in roots (67.1%) and shoots (80.8%). Our also findings indicated that Pb detoxification mechanism of biochar and exogenous calcium was totally different, while they can induce a synergistic impact on water spinach Pb stress alleviation. The combination of biochar and exogenous calcium in Pb-contaminated soil remediation may complement each other and reduce Pb entry into the human body through vegetables.

Effects of silkworm excrement and water management on the accumulation of Cd and As in different varieties of rice and an assessment of their health risk

Rice (Oryza sativa L.) consumption represents a major route for the exposure to cadmium (Cd) and arsenic (As) in many countries. Two varieties of rice that were grown in soils contaminated with Cd and As were evaluated for the accumulation of these toxins in rice grains and the risks of exposure of local residents to Cd and As when treated with different amounts of silkworm excrement and types of water management. Silkworm excrement, water management and the variety of rice significantly affected the accumulation of Cd and As in rice. The combination of multiple measures can be more effective at reducing heavy metals than the use of single measure, i.e., silkworm excrement management, water management, and the selection of low accumulation variety. The use of a variety that accumulates low amounts of Cd combined with 1% silkworm excrement management can effectively increase the soil pH and electrical conductivity (EC) and decrease the contents of soil available Cd and the transfer coefficients of Cd in rice, subsequently reducing the concentrations of Cd in rice grains and lowering the health risks of the intake of Cd. Similarly, the use of a conventional rice variety combined with alternating periods of drying and wetting in the three weeks before and after the heading stage decreased the contents of soil available As and the transfer coefficient of As in rice, subsequently reducing the accumulation of As in the grains and lowering the health risk of the intake of As. The significantly lower concentrations of Cd and As in rice grains and the risk of intake of Cd and As from rice was observed using a conventional rice variety combined with alternating drying-wetting in the three weeks before and after the heading stage and 1% silkworm excrement management. Thus, the combination of multiple measures in the coexistence of Cd and As in contaminated soils can be a promising strategy to avoid serious health risks and ensure the safety of food for local residents.

Foliar application of anthocyanin extract regulates cadmium accumulation and distribution in rice (Oryza sativa L.) at tillering and booting stages

Anthocyanin extract has been applied in agricultural production and enhanced tolerance of plants to adverse effects of Cd stress. Rice was subjected to different concentration of Cd and blueberry anthocyanin, and the effects on rice growth, antioxidative defense, Cd distribution in rice tissues, FTIR and TEM characterization of rice leaves were examined to explain the Cd reductions in rice grains and the protective mechanisms by blueberry anthocyanin. Foliar spray of blueberry anthocyanin at tillering and booting stages was effective for reducing Cd concentration in rice grains and increasing the rice yield, anthocyanin and Cd concentration of rice leaves under 1.0 and 10.0 mg/kg Cd stress. The Cd concentration in rice grains was less than the China national standard of Cd for rice grains (0.2 mg/kg) after surface spraying by 5.0-12.5 g/L blueberry anthocyanin under 1.0 mg/kg Cd stress, while 7.5 g/L spray concentration was the best choice. Blueberry anthocyanin spraying prevents Cd from being transferred from leaves to rice grains mainly by fixation of Cd in soluble and organelle fractions at the tillering and booting stages, and reduces H2O2 and MDA accumulation in rice leaves to decrease Cd toxicity. Combined with FTIR and TEM characterization of rice leaves, the results indicated that surface spraying of 7.5 g/L blueberry anthocyanin under 1.0 mg/kg Cd stress could effectively relieve Cd oxidative damage, and form chelates with Cd ions to immobilize Cd in rice leaves. Hence, blueberry anthocyanin could be used as a foliar resistance control agent to reduce Cd accumulation in rice grains through chelate compound synthesis and decrease Cd toxicity by preventing membrane lipid peroxidation and H2O2 accumulation.

Polymer-coated manganese fertilizer and its combination with lime reduces cadmium accumulation in brown rice (Oryza sativa L.)

Manganese (Mn) has the potential to reduce cadmium (Cd) uptake by rice; however, the efficiency depends on its soil availability. Therefore, this study designed a slow-release Mn fertilizer by employing a polyacrylate coating. Pot trials were conducted to study the effects of coated-Mn and uncoated-Mn alone or in combination with lime on the dynamics of soil dissolved-Mn and available Cd, and the transportation of Mn and Cd within rice. The results showed that coated-Mn declined the release of Mn until the 7th day of application; however, it consistently supplied more dissolved-Mn than uncoated-Mn. As a result, coated-Mn induced a greater Cd reduction (45.8%) in brown rice than uncoated-Mn (9.7%). The total Cd of rice and its proportion in brown rice were greatly reduced by coated-Mn, indicating the inhibition of root uptake and interior transport of Cd. Additionally, lime addition prominently increased the soil pH and decreased the CaCl₂-extractable Cd (90.1-93.9%). However, since lime reduced the soil dissolved-Mn, downregulated the OsHMA3 expression and upregulated the OsNramp5 expression, brown rice Cd was reduced by only 43.0%. The combined addition of lime and coated-Mn alleviated the liming effect on soil Mn and gene expression in roots, thereby reducing brown rice Cd by 71.5%.

Iron and copper micronutrients influences cadmium accumulation in rice grains by altering its transport and allocation

Cadmium (Cd) contamination in rice paddy fields constitutes a serious health issue in some parts of China. Here we study the potential for remediation of Cd contaminated alkaline paddy soil with low iron (Fe) and high copper (Cu) background by altering the concentrations of Fe and Cu in the growing media, which has been only seldom considered. We assessed how these two micronutrients (Cu and Fe) affect the absorption and transport of Cd in rice. Adding Cu significantly increased rice biomass and grain yield by reducing root Cd influx and Cd upward transport which, consequently, lowered Cd concentrations in roots, culms and leaves. However, excessive Cu also promoted a relatively higher Cd allocation in grains, especially under Fe deficiency, likely because Cu significantly increased the proportion of bioavailable Cd in leaves. Contrastingly, Fe did not alleviate the toxic effects of Cd on rice growth and yield, but it significantly reduced Cd transfer towards grains, which might be attributed to a sharp decrease in the proportion of bioavailable Cd in leaves. Our results demonstrated that Cd remediation may be achieved through altering Fe and Cu inputs, such that Cd accumulation in rice grains is reduced.

Foliar application of Zn reduces Cd accumulation in grains of late rice by regulating the antioxidant system, enhancing Cd chelation onto cell wall of leaves, and inhibiting Cd translocation in rice

Paddy soil contaminated by cadmium (Cd) has attracted worldwide attention, while foliar spraying of zinc (Zn) could be considered a cost-effective and practical agronomic measure for reducing Cd accumulation in rice grain. However, the effects due to foliar spraying of Zn on different cultivars, as well as the mechanism of subsequent processes taking place are not fully understood up to now. To go a step ahead, a field experiment was conducted with the aim of studying the capability of foliar application of Zn (0.4% ZnSO₄) to reduce Cd concentration in grain in five late rice cultivars (here named JLYHZ, FYY272, JY284, CLY7 and LXY130), and the antioxidant activities and subcellular distribution of Cd in the leaves. The results indicate that foliar Zn application significantly decreased grain yield in JY284, CLY7 and JLYHZ, compared to controls. In addition, foliar application of Zn significantly decreased Cd concentration in grain of the five rice cultivars, while increased Zn concentration. The effect of foliar application of Zn on transport coefficients of Cd varied greatly for the different rice cultivars. Foliar application of Zn significantly decreased the malondialdehyde (MDA) concentration in rice leaves, and increased peroxidase (POD) activity. Also, it changed the distribution of Cd in the soluble fraction in leaves (expressed as proportion), which was significantly decreased, and the proportion of Cd in the cell wall increased. The structural equation model (SEM) revealed the positive effects of flag leaf Cd, first node Cd, old leaf Cd, and root Cd concentration on grain Cd concentration. Flag leaf Cd had the highest standardized total effects on grain Cd concentration, followed by old leaf Cd. These results indicated that foliar application of Zn was effective in reducing grain Cd concentration of late rice by enhancing antioxidant activities and Cd chelation onto cell wall of leaves, and reducing Cd concentrations in leaves.

Cadmium stress in paddy fields: Effects of soil conditions and remediation strategies

Cadmium (Cd) toxicity in paddy soil and accumulation in rice plants and grains have got global concern due to its health effects. This review highlights the effects of soil factors including soil organic matter, soil pH, redox potential, and soil microbes which influencing Cd uptake by rice plant. Therefore, a comprehensive review of innovative and environmentally friendly management practices for managing Cd stress in rice is lacking. Thus, this review discusses the effect of Cd toxicity in rice and describes management strategies to offset its effects. Moreover, future research thrusts to reduce its uptake by rice has also been highlighted. Through phytoremediation, Cd may be extracted and stabilized in the soil while through microbes Cd can be sequestrated inside the microbial bodies. Increased Cd uptake in hyperaccumulator plants to remediate and convert the toxic form of Cd into non-toxic forms. While in chemical remediation, Cd can be washed out, immobilized and stabilized in the soil through chemical amendments. The organic amendments may help through an increase in soil pH, adsorption in its functional groups, the formation of complexations, and the conversion of exchangeable to residual forms. Developing rice genotypes with restricted Cd uptake and reduced accumulation in grain through conventional and marker-assisted breeding are fundamental keys for safe rice production. In this regard, the use of molecular techniques including identification of QTLs, CRISPR/Cas9, and functional genomics may be quite helpful.

Crucial roles of cadmium retention in nodeⅡ for restraining cadmium transport from straw to ear at reproductive period in a grain low-cadmium rice line (Oryza sativa L.)

Using an ideal parental line to breed hybrid rice with low cadmium (Cd) accumulation in grain is an environmental-friendly approach to reduce the risk of Cd contamination in field. A grain low-Cd rice line YaHui2816 has stably low Cd in grain but strong Cd accumulation in straw, revealing specific pattern of its straw-grain Cd remobilization is beneficial to effectively breed hybrid rice for safe production as well as phytoremediation. In this study, a pot experiment was conducted to investigate Cd partitioning of YaHui2816 at different stages by comparison with a common rice C268A. The Cd from lower nodes and leaves was restricted in nodeⅡ, this Cd retention led to weak Cd transport from straw to ear in YaHui2816. Cd concentration in nodeⅡ of YaHui2816 was 1.56-fold and 7.36-fold higher than C268A at filling and mature stages. Thus, glutathione (GSH) and phytochelatin (PC) concentration, PC synthase (OsPCS1), GSH S-Transferase (OsGST) and Cd-remobilization associated genes were measured at filling stage. OsHMA2 and OsCCX2 were up-regulated in nodeⅡ of YaHui2816, relative expression of them were significantly higher than C268A. PCs participated in Cd remobilization process, remarkable PC increase in nodeⅡ of YaHui2816 was found in response to Cd treatment under regulation of OsPCS1 and OsGST of which PC₂ was dominant form. Taken as a whole, the Cd retention in nodeⅡ of YaHui2816 acts as a 'firewall' to restrain Cd transport to grain. This work provides more insight to understand possible function of alleles for reducing Cd concentration in grain as well as strengthening Cd accumulation in straw of YaHui2816.

Effects of zinc application on cadmium (Cd) accumulation and plant growth through modulation of the antioxidant system and translocation of Cd in low- and high-Cd wheat cultivars

Cadmium (Cd) contamination is a big challenge for managing food supply and safety around the world. Reduction of the bioaccumulation of cadmium (Cd) in wheat is an important way to minimize Cd hazards to human health. This study compared and highlighted the effects of soil and foliar applications of Zn on Cd accumulation and toxicity in cultivars with high Cd accumulation (high-Cd wheat) and low Cd accumulation (low-Cd wheat). Both foliar and soil Zn applications provided effective strategies for reducing wheat grain Cd concentrations in the high-Cd wheat by 26-49% and 25-52%, respectively, and these also significantly reduced the concentrations in wheat stems and leaves. Foliar and soil Zn applications significantly reduced Cd in leaves and stems of the low-Cd wheat but had no effects on grain Cd. Both soil and foliar Zn applications significantly alleviated Cd toxicity by regulation of Cd transport genes, as reflected by the increased grain yield and antioxidant enzyme activity in the wheat tissues. Gene expression in response to zinc application differed in the two wheat cultivars. Down-regulation of the influx transporter (TaNramp5) and upregulation of the efflux transporters (TaTM20 and TaHMA3) in the high-Cd wheat may have contributed to the Zn-dependent Cd alleviation and enhanced its tolerance to Cd toxicity. Additionally, foliar Zn applications down-regulated the leaf TaHMA2 expression that reduced root Cd translocation to shoots, while soil Zn applications down-regulated the root TaLCT1 expression, which contributed to the reduction of root Cd concentrations. Soil (99 kg ZnSO₄·7H₂O ha^-1) and foliar (0.36 kg ZnSO₄·7H₂O ha^-1) Zn applications can effectively decrease the Cd in grains and guarantee food safety and yield, simultaneously. The presented results provide a new insight into the mechanisms of, and strategies for, using Zn for the Cd reduction in wheat.

Effects of node restriction on cadmium accumulation in eight Chinese wheat (Triticum turgidum) cultivars

Minimization of cadmium (Cd) accumulation in wheat is an effective method to prevent Cd-related health risks to humans. To understand the underlying mechanisms of restricting Cd transport, the role of nodes in Cd restriction was studied in eight Chinese wheat cultivars. The Cd accumulation differed significantly among the cultivars. The grain Cd concentrations were mainly dependent on the Cd concentrations in the roots and shoots. The Cd transport in the shoots controlled the wheat grain Cd accumulations. Nodes in the wheat stem have distinct functions in the transfer, distribution, and restriction of Cd. The node connected to the panicle showed the lowest translocation factors. The area of the vascular bundles, especially the diffuse vascular bundles, in the junctional node with the flag leaf was the key factor in restricting Cd transfer to the wheat grain. There was a significant relation between these areas and the grain Cd concentrations. The conclusion of this study is that screening or breeding cultivars with low Cd concentrations in the roots or with smaller areas of diffuse vascular bundles in the junctional nodes with the flag leaf is an effective strategy to decrease Cd concentration in wheat grains.

Toxic effect of three imidazole ionic liquids on two terrestrial plants

To determine the toxic effect of three imidazole ionic liquids (IILs) in terrestrial monocotyledonous and dicotyledonous plants, three IILs (1-butyl-3-methylimidazole tetrafluoroborate, 1-butyl-3-methylimidazole hexafluorophosphate, and butyl-3-methylimidazolium bi-[(trifluoromethyl)sulfonyl]imide) were investigated using rice and capsicum as target toxicity models. In hydroponic experiments, increasing the concentration of the IILs led to a decrease in the seed germination rate, a decrease in the reduced stem and root lengths, and an increase in the inhibition rate of the stem and root lengths; in addition, as the concentration increased, the reducing sugar content of rice and capsicum seedling leaves and roots first increased and then decreased, while permeability of the cell membranes of the stems and roots of the two plants also gradually increased. In terms of the effects on these indices in rice, the ranking of these three IIL anions was [TF2N]- > [PF6]- > [BF4]-; in terms of the effects on capsicum, the sequence was [BF4]- > [TF2N]- > [PF6]-. These findings provide a theoretical reference for the next step in the synthesis and the use of green ionic liquids.

Goethite-modified biochar ameliorates the growth of rice (Oryza sativa L.) plants by suppressing Cd and As-induced oxidative stress in Cd and As co-contaminated paddy soil

Co-contamination of soils with cadmium (Cd) and arsenic (As) in rice growing areas is a serious threat to environment and human health. Increase in soil Cd and As levels curtail the growth and development of rice plants by causing oxidative stress and reduction in photosynthetic activity. Therefore, it is necessary to formulate and evaluate different strategies for minimizing the Cd and As uptake in rice plant. We modified biochar (BC) with goethite and assessed the effects of goethite-modified biochar (GB) application on mitigating Cd and As stress in rice plant. Although BC supply to rice plants enhanced their performance in contaminated soil but application of different GB levels i.e.1.5% GB to the soil resulted in prominent improvements in physiological and biochemical attributes of rice plants grown in Cd and As co-contaminated paddy soil. It was observed that soil amendment with GB increased the plant growth, biomass, photosynthetic pigments, gas exchange attribute of rice plant and suppressed the oxidative stress in rice leaves and roots by increased antioxidant enzymes activities. Supplementing the soil with 1.5% GB incremented the iron plaque (Fe-plaque) formation and enhanced the Cd and As sequestration by Fe-plaque. Application of GB (1.5%) significantly improved the Fe content of Fe-plaque by 68.7%. Maximum Cd (1.57 mg kg^-1) and As (0.85 mg kg^-1) sequestration by Fe-plaque was observed with 1.5% GB treatment. Compared to the control, 1.5% GB treatment application prominently reduced the Cd content in the rice roots and shoots by 42.9%, and 56.7%, respectively and As content in the rice roots and shoots declined by 32.2%, 46.6%, respectively, compared to the control. These findings demonstrate that amending the soil with 1.5% GB can be a potential remediation strategy for checking Cd and As accumulation, reducing oxidative stress and increasing the growth of rice plant.

Effects of external Mn2+ activities on OsNRAMP5 expression level and Cd accumulation in indica rice

Manganese (Mn) transporter OsNRAMP5 was widely reported to regulate cadmium (Cd) uptake in rice. However, the relationship between OsNRAMP5 expression level and Cd accumulation, impacts of external ion activities on OsNRAMP5 expression level and Cd accumulation are still unclear. Investigations of the relationship between OsNRAMP5 expression level and Cd accumulation in three indica rice genotypes were conducted under various external Mn²⁺ activities ranging from Mn deficiency to toxicity in EGTA-buffered nutrient solution. Results in this work indicated that OsNRAMP5 expression level in roots significantly up-regulated at Mn phytotoxicity compared to that at Mn deficiency, which may stimulate by the increasing uptake of Mn. Our work also demonstrated that root Cd concentration of all the tested rice decreased notably when external Mn²⁺ activity reached the level of toxicity. This may explain by the increasing competition between the excess Mn²⁺ and Cd²⁺ as well as the disorder of element absorption caused by root damage at Mn toxicity. Our work also revealed that the relationship between OsNRAMP5 expression level in roots and Cd accumulation in roots was insignificant for all the tested genotypes. Besides, OsNRAMP5 expression level in roots seemed more related to root Mn accumulation. The fact that function of OsNRAMP5 mainly focuses on Mn uptake, together with the fact that many transporter genes involved in Cd uptake might result in the insignificant correlation between OsNRAMP5 expression level and Cd accumulation in roots. At last, multi-level regulating and processing of the process from gene expression to protein translation might account for the inconsistent relationship between root OsNRAMP5 expression level and Cd accumulation in roots.

Differences in cadmium accumulation between indica and japonica rice cultivars in the reproductive stage

Excessive cadmium (Cd) in rice grains is of great concern worldwide, particularly in southern China where heavy metal pollution in the soil is widespread. Much work has been done regarding the key genes responsible for Cd absorption, transport, and accumulation in rice, but little is known about the differences of Cd accumulation between indica and japonica rice cultivars during the reproductive stage. Furthermore, physiological parameters, such as nonstructural carbohydrate content, involved in Cd accumulation have not been fully elucidated. We studied several indica and japonica cultivars under three different Cd treatment levels and harvested them at different periods after heading. Differences in Cd accumulation between subspecies mainly were generated during the reproductive stage. An increase in the Cd pollution level caused the average absorption rate of Cd in the aerial parts of the indica cultivars in the reproductive stage to be 6.17, 4.52, and 3.89 times greater than that of the japonica cultivars across the three Cd treatments. The contribution of Cd absorption by shoots to Cd accumulation at the pre- or postheading stages was 33.8% and 66.2% in indica, and 44.9% and 55.1% in japonica. We found a significant negative correlation between Cd content in the rice grains and the content of nonstructural carbohydrates in the sheath (P < 0.05). Cd translocation from sheath to grain occurred along with sugar transfer in the indica cultivars. The Cd content of the indica cultivar grain was 1.84-4.14 times higher than that of the japonica cultivars (P < 0.05). The japonica cultivars thus met the cereal Cd limits of China (0.2 mg kg^-1) under low and moderate soil Cd pollution. These findings are helpful for the selection of proper cultivars and field management practices to alleviate Cd exposure risk in rice production.

Calcium acetate-induced reduction of cadmium accumulation in Oryza sativa: Expression of auto-inhibited calcium-ATPase and cadmium transporters

Calcium (Ca) signalling has an essential role in regulating plant responses to various abiotic stresses. This study applied Ca in various forms (Ca acetate and CaCl₂ ) and concentrations to reduce cadmium (Cd) concentration in rice and propose a possible mechanism through which Ca acts to control the Cd concentration in rice. The results showed that supplementation of Cd-contaminated soil with Ca acetate reduced the Cd concentration in rice after exposure for 7 days in both hydroponic and soil conditions. The possible involvement of the auto-inhibited Ca²⁺ -ATPase gene (ACA) might act to control the primary signal of the Cd stress response. The messages from ACA3 and ACA13 tended to up-regulate the low-affinity cation transporter (OsLCT1) and down-regulate Cd uptake and the Cd translocation transporter, including the genes, natural resistance-associated macrophage protein 5 (Nramp5) and Zn/Cd-transporting ATPase 2 (HMA2), which resulted in a reduction in the Cd concentration in rice. After cultivation for 120 days, the application of Ca acetate into Cd-contaminated soil inhibited Cd uptake of rice. Increasing the Ca acetate concentration in the soil lowered the Cd concentration in rice shoots and grains. Moreover, Ca acetate maintained rice productivity and quality whereas both aspects decreased under Cd stress.

Accumulation and distribution of arsenic and cadmium in winter wheat (Triticum aestivum L.) at different developmental stages

Arsenic (As) and cadmium (Cd) are known to be toxic to humans, and elevated concentrations have been documented in food crops worldwide. However, little is known regarding their uptake, translocation, and distribution in wheat plants during plant development. A series of experiments were conducted to investigate the spatial distribution and dynamics of As and Cd in two wheat cultivars (cv. JN12 and JM85; the latter is a low grain Cd accumulator) at different developmental stages. Root concentrations of As decreased by 84%, and those of Cd by 67%, from tillering to maturity. In contrast, As concentrations in the stems increased 3.1-fold. A significant decrease in root As accumulation was observed at the mature stage, whereas root Cd accumulation decreased largely at the elongation stage. The concentrations of Cd in all leaves and As in new leaves increased as plant growth advanced. However, As concentrations in old leaves decreased significantly from grain filling to maturity. In both cultivars, the upward transfer toward younger parts of shoots was greater in the case of Cd than of As. The remobilization of As and Cd from stems and roots differed between the two cultivars. Arsenic concentrations in rachis, glumes, and grain in JM85 were significantly higher than those in JN12, whereas As concentrations in roots and stems did not differ between the cultivars. Grain Cd was significantly higher in JN12 than in JM85, but Cd concentrations in rachis and glumes were similar between the cultivars. The difference in grain Cd concentration between the two cultivars depended on root and stem Cd remobilization and redistribution from rachis to glumes and grain; in contrast, accumulation of As in grain was influenced by As remobilization from the leaves and stem to the spike.

Distribution and chemical forms of cadmium in Coptis chinensis Franch. determined by laser ablation ICP-MS, cell fractionation, and sequential extraction

Coptis chinensis Franch., is a widely used medicinal plant in China. This plant is often contaminated by cadmium (Cd) and render health risk to human consumers. Understanding distribution of Cd and its chemical forms is important to evaluate accumulation of the metal and its detoxification mechanisms in this plant. Since few studies have focused on this aspect, we used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to spatially locate Cd in rhizome cross-sections, and ICP-MS to analyze the Cd subcellular distribution and the chemical forms of Cd in different tissues. Rhizome bioimaging results showed that Cd was distributed predominantly within the periderm, cortex, pith, and root trace vascular bundle. The LA-ICP-MS results suggested that Ca²⁺ channels might be a pathway for Cd entry into the plant. Subcellular distribution data indicated that most of Cd was associated with the cell wall (41.8-77.1%) and the soluble fraction (14.4-52.7%) in all tissues. Analysis of chemical forms revealed that majority Cd existed in less mobile and less toxic forms in all tissues, and P could convert to insoluble phosphate with Cd to moderate Cd toxicity. The new understanding of Cd accumulation and detoxification might provide novel strategies for reducing the levels of Cd in C. chinensis Franch., thereby mitigating its potential transfer to humans and providing a theoretical basis for evaluating the Cd status in other medicinal plants. Further, our findings might provide a basis for establishing a reasonable Cd limit level of traditional Chinese medicinal materials.

Effectiveness of simultaneous foliar application of Zn and Mn or P to reduce Cd concentration in rice grains: a field study

Excess cadmium (Cd) in agricultural soils can be taken up by rice plants and concentrated in the grain, presenting a human health risk. In this study, we field tested the effects of three foliar treatments (zinc (Zn) alone, or combined with manganese (ZnMn) or phosphorus (ZnP)) on the Cd concentration and grain yield of six rice cultivars (C Liangyou 7, Fengyuanyou 272, Xiangwanxian 12, Tianyouhuazhan, Xiangwanxian 13, and Jinyou 284) at the grain filling stage. Our results showed that rice yield and Cd, Zn, Mn, P, and K concentrations were significantly different among the cultivars (p < 0.05); for example, Jinyou 284 recorded lower Cd levels than any other cultivar. Application of Zn, ZnMn, and ZnP had no significant effect on rice yield and Mn, P, and K concentrations for all cultivars. Compared with the control, Cd concentrations after treatment with Zn, ZnMn, and ZnP decreased by 19.03-32.55%, 36.63-55.78% (p < 0.05), and 25.72-49.10%, respectively, while Zn concentrations increased by 11.02-29.38%, 10.63-32.67%, and 11.97-36.82%, respectively. There was a significant negative correlation between Cd and Zn concentrations (p < 0.01). All three treatments increased Zn and reduced Cd concentration in rice grains, though ZnMn was most effective. Therefore, cultivar selection and Zn fertilizer application are effective strategies to minimize Cd concentration in rice grains. However, the lowest result still exceeded the Chinese Cd safety limit (0.2 mg Cd kg^-1) by a factor of 2.6, demonstrating that additional effective measures should be simultaneously used to further reduce the accumulation of Cd in rice grains.

A tillering application of zinc fertilizer based on basal stabilization reduces Cd accumulation in rice (Oryza sativa L.)

Cadmium (Cd) contamination in paddy fields has received extensive attention throughout the world, especially in China. In this study, treatments of a lime application with or without zinc sulfate as basal fertilizer, a basal or tillering application of zinc sulfate, and basal stabilization using lime combined with a tillering application of zinc sulfate were designed in a field trial to investigate their contributions to the uptake and translocation of Cd in rice plants. The results showed that basal stabilization using lime significantly decreased brown rice Cd by 42%; the CaCl₂-extractable Cd in the soil was decreased by 46-51%, but the phytoavailability of Zn in the soil was also inhibited. The basal or tillering application of zinc sulfate significantly inhibited the upward transport of Cd (from the root to the shoot) while having no significant impact on CaCl₂-extractable Cd; consequently, the concentration of Cd in the brown rice was reduced by only 17-25%. Compared with the lime application alone, the basal application of lime together with zinc sulfate did not further reduce the Cd in brown rice. However, basal stabilization using lime combined with the tillering application of zinc decreased the Cd in brown rice by 73%, which was attributed to the reduced CaCl₂-extractable Cd and the competitive effect of Zn on Cd, in which the inhibition of the upward transport of Cd inside the root played an important role. Two field verification tests conducted during the next year also demonstrated that this combined method significantly decreased the level of Cd in brown rice.

Association Study Reveals Genetic Loci Responsible for Arsenic, Cadmium and Lead Accumulation in Rice Grain in Contaminated Farmlands

Accumulation of toxic heavy metals and metalloids (THMMs) in crop grain remarkably affects food safety and human health. Reducing the content of THMMs in grain requires the identification and manipulation of the genes regulating their accumulation. This study aimed to determine the genetic variations affecting grain THMM accumulation in rice by using association mapping. We used 276 accessions with 416 K single nucleotide polymorphisms (SNPs) and performed genome-wide association analysis of grain THMM concentrations in rice grown in heavily multi-contaminated farmlands. We detected 22, 17, and 21 quantitative trait loci (QTLs) for grain arsenic, cadmium, and lead concentrations, respectively. Both inter- and intra-subpopulation variants accounted for these QTLs. Most QTLs contained no known THMM-related genes and represented unidentified novel genes. We examined the candidate genes in qGAS1, a QTL for grain arsenic concentration with the best P-value detected for the entire population. We speculated that a transport protein of the multidrug and toxin extrusion family could be the candidate gene for this QTL. Our study suggested that the genetic regulation of grain THMM accumulation is very complex and largely unknown. The QTLs and SNPs identified in this study might help in the identification of new genes regulating THMM accumulation and aid in marker-assisted breeding of rice with low grain THMM content.

Topdressing iron fertilizer coupled with pre-immobilization in acidic paddy fields reduced cadmium uptake by rice (Oryza sativa L.)

Soil cadmium (Cd) contamination has become a serious problem in China. This study was conducted to test the effects of basal application of hydrated lime and iron fertilizer alone or together and topdressing of iron fertilizer at the tillering stage alone or coupled with basal application of hydrated lime, on reducing the accumulation of Cd in brown rice grown in an acidic paddy field slightly contaminated with Cd. The results showed that Cd in brown rice (BR-Cd) was dependent on not only the pH increase and CaCl₂-extractable Cd reduction in the soil due to lime amendment but also Cd sequestration by the iron plaque on root surfaces. However, lime significantly decreased the amounts of Fe and Cd in the iron plaque on the surface of rice root. Topdressing of ferrous sulfate at the tillering stage resulted in the highest Fe and Cd sequestration in the iron plaque. Compared with the control (0.71 mg kg^-1 BR-Cd), the basal application of lime and ferrous sulfate alone or together reduced BR-Cd by 45.8%, 18.3%, and 53.1%, respectively; topdressing of ferrous sulfate alone reduced BR-Cd by 23.6%, and topdressing of ferrous sulfate at the tillering stage coupled with basal application of lime yielded the lowest BR-Cd level with a 74.6% reduction. This result was further confirmed by field experiments at two sites in the following year.