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Background and aims: Water spinach readily uptakes cadmium (Cd), posing a risk to human health. Selecting low-Cd cultivars is a promising mitigation strategy, but its extensive utilization is limited without a clear understanding of the critical plant factors determining Cd accumulation. This study aimed to elucidate the effects and interactions of the radial oxygen loss (ROL) and iron (Fe) plaque on the Cd accumulation in different water spinach cultivars and the underlying mechanisms. Methods: A pot and four hydroponic experiments using ten water spinach cultivars were conducted with different aeration, Fe supply, and Cd stress treatments. Results: The Cd accumulation of different cultivars was determined by both root uptake and root-to-shoot transport. There were 4.0-, 3.8- and 6.3-fold differences among different cultivars in ROL, Fe plaque, and shoot Cd accumulation, respectively. Rhizosphere and root Fe plaque reduced root Cd uptake and were regulated by Fe supply and ROL. Increased ROL under stagnant conditions enhanced Fe plaque and induced its redistribution along root axes. Root Cd retention through compartmentalization and chelation inhibited root-to-shoot Cd translocation. Conclusion: The Fe plaque, ROL, and root Cd retention formed an interactive system to decrease the Cd uptake and accumulation in water spinach. Low-Cd cultivars exhibited higher ROL, greater Fe plaque and more effective root Cd retention, and responded to stagnant conditions with greater ROL increases and more enhanced Fe deposition on root surfaces. This study provides new insights into the Cd accumulation mechanisms in water spinach and a theoretical basis for selecting low-Cd cultivars. [ABSTRACT FROM AUTHOR]

Background and aims: Large areas of paddy fields have been contaminated by cadmium (Cd) in both China and worldwide, resulting in excessive Cd accumulation in rice grains. Here, we investigated the effects of cultivars, water regimes, and growth stages on Cd accumulation in rice with different radial oxygen loss (ROL). Methods: Two groups of experiments were conducted: pot trials with soil-added Cd and solution-added agar using 20 rice cultivars and a rhizobag trial with Cd-contaminated soil and pot trial with solution-added agar under flooded and non-flooded water regimes with three growth stages and two cultivars. Results: Different rice cultivars exhibited different porosity, Cd tolerance, and Cd accumulation in grains, which were significantly correlated with ROL. Cd concentration in shoots was significantly lower under the flooded (0.13–1.01, mean 0.56 mg kg−1) than non-flooded regime (0.68–1.39, mean 0.97 mg kg−1). The low Cd-accumulating cultivar showed higher rates of ROL, higher Cd combined with Fe plaque formation, and lower Cd bioavailability in the rhizosphere soil than the high-Cd accumulating cultivar. Conclusions: Rice cultivars grown under flooded regimes effectively reduced Cd accumulation in edible parts, and the later stage was crucial for reducing Cd accumulation. Low Cd-accumulating cultivars generally exhibited a higher ability to reduce Cd bioavailability in the rhizosphere soil. [ABSTRACT FROM AUTHOR]

Background and aims: Rice grains contaminated by mercury (Hg) and methylmercury (MeHg) pose risks to human health. This study evaluated the relative importance of genotype, environment and genotype-environment interactions on the accumulation of total Hg (THg) and MeHg in brown rice.Methods: A pot trial with four rice genotypes and 10 Hg-contaminated paddy soils was conducted under greenhouse conditions. The effects of genotype, environment and genotype-environment interactions on brown rice THg and MeHg accumulation were assessed by an Additive Main Effects and Multiplicative Interaction (AMMI) model.Results: THg and MeHg concentrations in brown rice ranged from 20.5 to 75.5 μg kg−1 and 2.24 to 54.7 μg kg−1, respectively. The AMMI model indicated that genotype explained 41.1 and 19.6%, environment described 40.6 and 55.8%, and the genotype-environment interaction explained 11.9 and 20.0% of the variation in brown rice THg and MeHg levels, respectively. Brown rice THg positively correlated with water-soluble Hg and total potassium, but negatively correlated with total sulphur, iron, total organic carbon and nickel in soils. Brown rice MeHg negatively correlated with soil pH and selenium.Conclusion: THg accumulation in brown rice was mainly affected by both genotype and environment, whereas MeHg accumulation was largely determined by environment. [ABSTRACT FROM AUTHOR]

Background and aims: Rice contaminated by mercury [Hg, especially methylmercury (MeHg)] has given rise to great concern in recent years. This study investigated variations in ecophysiological features (anatomy, organic acid secretions, Fe plaque formation) of rice roots and their effects on the uptake and accumulation of total mercury (THg) and MeHg by rice plants. Methods: The development of apoplastic barriers in roots of four rice cultivars was observed by a hydroponic experiment while the concentrations of five organic acids, Fe and THg in Fe plaque were determined using a rhizobag trial with different Hg treatments. Results: Cultivars with low Hg accumulation tended to develop strong apoplastic barriers in endodermis, secrete less organic acids and form more Fe plaque on root surfaces and in rhizosphere. Fe concentrations were positively correlated with THg concentrations in rhizosphere's Fe plaque (R = 0.60, P < 0.01), whereas the latter was negatively correlated with bioavailable Hg concentrations in rhizosphere (R = 0.40, P < 0.01). Conclusions: Organic acids and Fe plaque formation of rice roots play important roles in Hg uptake and accumulation. The development of apoplastic barriers in root restricts Hg uptake but the significance of suberin deposition on Hg uptake needs further investigations. [ABSTRACT FROM AUTHOR]

Background and aims: Water spinach is a common leafy vegetable in Asia, with a strong ability to accumulate cadmium (Cd) in its edible parts. The aims of this study were to investigate the effects of cultivar variation and water management on Cd accumulation in this plant. Methods: Three experiments were conducted: a soil pot trial with 32 cultivars, a rhizobox trial with 4 cultivars under flooded and non-flooded conditions and an uptake kinetics trial with 2 cultivars. Results: There were significant differences in Cd accumulation between the different cultivars, and Cd concentrations in shoots were significantly lower in the flooded (0.25-1.4, mean 0.90 mg kg DW) than in the non-flooded (1.9-4.7, 3.2 mg kg) treatments. Cultivars with a low Cd accumulation had a lower Cd bioavailability and mobility in the rhizosphere soil, higher Cd combined with Fe plaque on roots, lower Cd uptake capacity by roots, and lower Cd transfer factors than those with a high Cd accumulation. Conclusions: Water spinach grown under anaerobic conditions effectively reduces Cd accumulation in edible parts. Low Cd-accumulating cultivars tend to possess a high ability to reduce Cd bioavailability in rhizosphere soil, as well as decrease Cd uptake, and translocation from root to shoot. [ABSTRACT FROM AUTHOR]

Background and Aims: Mercury (Hg) pollution in paddy fields and rice has aroused great concern in recent years. This study investigated the dynamic changes of radial oxygen loss (ROL) and Fe plaque formation on roots, and their effects on Hg accumulation in rice plants. Methods: A rhizobag experiment was conducted to study temporal variations and correlations between ROL (amounts and rates), Fe plaque formation, total Hg (THg) and methylmercury (MeHg) in plant tissues and in plaque of four rice cultivars during six growth stages. Results: ROL amounts and Fe plaque formation increased from tillering to reproductive stages, then ROL amounts gradually decreased until maturation stage, whereas Fe plaque remained relatively stable. ROL rates continued to decline during the entire growth period. Both ROL amounts and Fe concentrations in plaque were positively correlated with THg concentrations in the plaque, whereas negatively correlated with THg in straw and brown rice. However, there were no significant relationships between ROL, Fe in plaque and MeHg in plaque and in plant tissues. Conclusions: ROL has great effects on THg but not MeHg accumulation in rice plants. Rice cultivars with higher ROLs tend to have a greater ability to reduce THg accumulation in brown rice. [ABSTRACT FROM AUTHOR]

Background and Aims: Metal (e.g. Cd and Pb) pollution in agricultural soils and crops have aroused considerable attention in recent years. This study aimed to evaluate the effects of ROL and Fe plaque on Cd and Pb accumulation and distribution in the rice plant. Methods: A rhizobag experiment was employed to investigate the correlations among radial oxygen loss (ROL), Fe plaque formation and uptake and distribution of Cd and Pb in 25 rice cultivars. Results: Large differences between the cultivars were found in rates of ROL (1.55 to 6.88 mmol O kg root d.w. h), Fe plaque formation (Fe: 6,117-48,167 mg kg; Mn: 127-1,089 mg kg), heavy metals in shoot (Cd: 0.13-0.35 mg kg; Pb: 4.8-8.1 mg kg) and root tissues (Cd: 1.1-3.5 mg kg; Pb: 45-199 mg kg), and in Fe plaque (Cd: 0.54-2.6 mg kg; Pb: 102-708 mg kg). Rates of ROL were positively correlated with Fe plaque formation and metal deposition on root surfaces, but negatively correlated with metal transfer factors of root/plaque and distributions in shoot and root tissues. Conclusions: ROL-induced Fe plaque promotes metal deposition on to root surfaces, leading to a limitation of Cd and Pb transfer and distribution in rice plant tissues. [ABSTRACT FROM AUTHOR]

Background and aims: Wetland plants have been widely used in constructed wetlands for the clean-up of metal-contaminated waters. This study investigated the relationship between rate of radial oxygen loss (ROL), root porosity, Zn uptake and tolerance, Fe plaque formation in wetland plants. Methods: A hydroponic experiment and a pot trial with Zn-contaminated soil were conducted to apply different Zn level treatments to various emergent wetland plants. Results: Significant differences were found between plants in their root porosities, rates of ROL, Zn uptake and Zn tolerance indices in the hydroponic experiment, and concentrations of Fe and Mn on roots and in the rhizosphere in the pot trial. There were significant positive correlations between root porosities, ROL rates, Zn tolerance, Zn, Fe and Mn concentrations on roots and in the rhizosphere. Wetland plants with higher root porosities and ROL tended to have more Fe plaque, higher Zn concentrations on roots and in their rhizospheres, and were more tolerant of Zn toxicity. Conclusions: Our results suggest that ROL and root porosity play very important roles in Fe plaque formation, Zn uptake and tolerance, and are useful criteria for selecting wetland plants for the phytoremediation of Zn-contaminated waters and soils/sediments. [ABSTRACT FROM AUTHOR]

Purpose: Mangrove wetlands have experienced significant contaminant input such as copper (Cu), aggravated by rapid urban development. This study aimed to investigate the possible function of root permeability in metal detoxification. Methods: Pot trials were conducted to evaluate the responses of root permeability in relation to metal (Cu) exposure in seedlings of two mangroves: Bruguiera gymnorrhiza and Rhizophora stylosa. Results: Copper inhibited plant growth and root permeability of the two species significantly (due to decreases in root porosity, thickening of exodermis and increases in lignification), leading to a significant reduction in radial oxygen loss (ROL). A negative correlation between soil Cu and ROL from root tip was also observed. The observed metal uptake by excised roots further indicated that increased lignification would directly prevent excessive Cu from further entering into the roots. Conclusions: In summary, the two mangroves reacted to Cu by producing an impermeable barrier in roots. Such an inducible barrier to ROL is likely to be an adaptive strategy against Cu toxicity. This study reveals new evidence of a structural adaptive strategy for metal tolerance by mangrove plants. [ABSTRACT FROM AUTHOR]