Hydrogen peroxide mediates cadmium accumulation in the root of a high cadmium-accumulating rice (Oryza sativa L.) line.

Hydrogen peroxide (H2O2) is a vital signaling molecule in response to cadmium (Cd) stress in plants. However, the role of H2O2 on Cd accumulation in root of different Cd-accumulating rice lines remains unclear. Exogenous H2O2 and 4-hydroxy-TEMPO (H2O2 scavenger) were applied to investigate the physiological and molecular mechanisms of H2O2 on Cd accumulation in the root of a high Cd-accumulating rice line Lu527-8 through hydroponic experiments. Interestingly, it was found Cd concentration in the root of Lu527-8 increased significantly when exposed to exogenous H2O2, while reduced significantly when exposed to 4-hydroxy-TEMPO under Cd stress, proving the role of H2O2 in regulating Cd accumulation in Lu527-8. Lu527-8 showed more Cd and H2O2 accumulation in the roots, along with more Cd accumulation in cell wall and soluble fraction, than the normal rice line Lu527-4. In particular, more pectin accumulation, especially low demethylated pectin, was observed in the root of Lu527-8 when exposed to exogenous H2O2 under Cd stress, resulting in more negative functional groups with greater capacity to binding Cd in the root cell wall of Lu527-8. It indicated that H2O2-induced cell wall modification and vacuolar compartmentalization contributes greatly to more Cd accumulation in the root of the high Cd-accumulating rice line.

Aggregate-associated carbon compositions explain the variation of carbon sequestration in soils after long-term planting of different tea varieties.

Strategies to increase carbon (C) sequestration in tea plantation soils are pertinent to mitigating global climate change, but little is known about the variation in C sequestration in soils planted with different tea varieties. In the current study, we collected 0-20 and 20-40 cm layer soil samples from a tea plantation planted with four tea varieties (Chuancha No.3 (CC3), Chuanmu No. 217 (CM217), Chuannong Huangyazao (CN), and C. sinensis 'Fuding Dabaicha' (FD)). Soil organic carbon (SOC) stock and composition in the bulk soil and aggregate fractions, as well as the SOC stability index (SI), were investigated. Both SOC stock and composition in the bulk soil or aggregate fractions were variable among the soils after planting different tea varieties. Overall, the highest SOC stock (0-40 cm) was observed in FD soil, followed by CN, CC3, and CM217 soil. This difference was dominated by the SOC stock associated with macroaggregates, and the highest macroaggregate-associated SOC stock was detected in FD soil in both soil layers. Moreover, FD soil showed the highest proportion of macroaggregates in both soil layers, accumulated the greatest recalcitrant organic carbon (ROC) and further contributed to the highest SI values of SOC associated with most aggregate fractions. In contrast, CN topsoil (0-20 cm) accumulated the greatest labile organic carbon (LOC) in most aggregate fractions, which had a positive correlation with the amount of C return by pruning litter. Ultimately, long-term planting of FD promoted macroaggregate formation, and ROC accumulation in aggregates greatly contributed to maintaining high C sequestration in the tea plantation soils and showed a high potential for future C budgets; in contrast, the tea plantation soil planted with CN could be a potential C source because of high C return.

Evaluation for phosphorus accumulation and removal capability of nine species in the Polygonaceae to excavate amphibious superstars used for phosphorus-phytoextraction.

Reducing excessive phosphorus (P) from both soils and eutrophic waters is attractive to achieve environmental P balance, and P-phytoextraction by amphibious plants with great biomass and P uptake is an amazing method, as already reported for P-accumulating plant, Polygonum hydropiper. However, it is still unknown how widespread high P tolerance and great P accumulation is among species in the Polygonaceae, and if there are new amphibious superstars used for P-phytoextraction. We used six Polygonum species and three non-Polygonum species to compare P accumulation and removal capability in hydroponics and soils with different P treatments. In high P hydroponics, all species showed superiority in growth and P accumulation without P toxicity, except for F. multiflora. In high P soils, all species showed much better growth performance with green leaves at 8 weeks, with shoot biomass being 3.60-29.49 g plant-1. At 8 weeks, Polygonum species displayed obviously higher shoot P accumulation (31.32-152.37 mg plant-1), P extraction ratio (3.16%-15.36%), maximum potential P removal (13.89-67.59 kg ha-1), and much lower plant effective number (7-32) than non-Polygonum species under high P soils. Besides, P. lapathifolium, P. divaricatum and P. orientale ranked the top three in growth with P concentration more than 10 mg g-1 dry weight in hydroponics and showed dominant advantage in P accumulation and P removal from high P soils. Through the cluster analysis, P. lapathifolium was always separated into a class, and P. divaricatum and P. orientale more likely clustered together. It is therefore that P. lapathifolium, P. divaricatum and P. orientale are tolerant to high P and attractive in P accumulation and P removal from high P waters and soils, and thus can be used as new amphibious superstars for P-phytoextraction, particularly P. lapathifolium.

Hydrogen peroxide contributes to cadmium binding on root cell wall pectin of cadmium-safe rice line (Oryza sativa L.).

Cell wall pectin is essential for cadmium (Cd) accumulation in rice roots and hydrogen peroxide (H2O2) plays an important role as a signaling molecule in cell wall modification. The role of H2O2 in Cd binding in cell wall pectin is unclear. D62B, a Cd-safe rice line, was found to show a greater Cd binding capacity in the root cell wall than a high Cd-accumulating rice line of Wujin4B. In this study, we further investigated the mechanism of the role of H2O2 in Cd binding in root cell wall pectin of D62B compared with Wujin4B. Cd treatment significantly increased the H2O2 concentration and pectin methyl esterase (PME) activity in the roots of D62B and Wujin4B by 22.45-42.44% and 12.15-15.07%, respectively. The H2O2 concentration and PME activity significantly decreased in the roots of both rice lines when H2O2 was scavenged by 4-hydroxy-Tempo. The PME activity of D62B was higher than that of Wujin4B. The concentrations of high and low methyl-esterified pectin in the roots of D62B significantly increased when exposed to Cd alone but significantly decreased when exposed to Cd and exogenous 4-hydroxy-Tempo. No significant difference was detected in Wujin4B. Exogenous 4-hydroxy-Tempo significantly decreased the Cd concentration in the cell wall pectin in both rice lines. The modification of H2O2 in Cd binding was further explored by adding H2O2. The maximum Cd adsorption amounts on the root cell walls of both rice lines were improved by exogenous H2O2·H2O2 treatment significantly influenced the relative peak area of the main functional groups (hydroxyl, carboxyl), and the groups intensely shifted after Cd adsorption in the root cell wall of D62B, while there was no significant difference in Wujin4B. In conclusion, Cd stress stimulated the production of H2O2, thus promoting pectin biosynthesis and demethylation and releasing relative functional groups involved in Cd binding on cell wall pectin, which is beneficial for Cd retention in the roots of Cd-safe rice line.

Sufficient nitrogen promoted high phosphorus tolerance and phosphorus-accumulating capability of Polygonum hydropiper in relation to changes of phytohormones and phenols.

Nitrogen (N) application is efficient to enhance phosphorus (P)-phytoextraction efficiency of P-accumulating plants. However, there is little available information on growth, P uptake and physiological changes of P-accumulating plants in high P media with different N application, and that whether the improved growth or P uptake is related with changes of phytohormones and phenols. This study investigated growth, P-accumulating capability, phytohormones and phenols of a mining ecotype (ME) and a non-mining ecotype (NME) of Polygonum hydropiper in high P media (400 mg L-1) with sufficient N (SN, 50 mg L-1) and low N (LN, 12.5 mg L-1) supply. SN supply greatly increased tissue biomass, P-accumulating capability of P. hydropiper in high P media, and the ME showed higher P bioaccumulation coefficient, and tissue P accumulation than the NME. The greatest tissue biomass and P accumulation was found at 5 weeks. At 5 weeks, SN supply greatly decreased concentrations of indole-3-acetic acid (IAA), zeatin, abscisic acid (ABA), total phenolic and flavonoid in tissues of P. hydropiper, compared with LN supply. The ME produced lower concentrations of IAA, zeatin, ABA, total phenolic and flavonoid than the NME in leaf and stem in high P media with N supply. Significantly negative correlations were found between IAA, zeatin, ABA, flavonoid concentrations and biomass as well as P accumulation in leaf. Thus, SN supply promoted high P tolerance and P-accumulating capability of the ME in relation to modulating phytohormones and phenols to suitable concentrations, ultimately improving P-phytoextraction ability.

Accumulation of phosphorus and calcium in different cells protects the phosphorus-hyperaccumulator Ptilotus exaltatus from phosphorus toxicity in high-phosphorus soils.

Ptilotus exaltatus accumulates phosphorus (P) to > 40 mg g-1 without toxicity symptoms, while Kennedia prostrata is intolerant of increased P supply. What physiological mechanisms underlie this difference and protect P. exaltatus from P toxicity? Ptilotus exaltatus and K. prostrata were grown in a sandy soil with low-P, high-P and P-pulse treatments. Both species hyperaccumulated P (>20 mg g-1) under high-P and P-pulse treatments; shoot dry weight was unchanged for P. exaltatus, but decreased by >50% for K. prostrata. Under high-P, in young fully-expanded leaves, both species accumulated P predominantly as inorganic P. However, P. exaltatus preferentially allocated P to mesophyll cells and stored calcium (Ca) as occasional crystals in specific lower mesophyll cells, separate from P, while K. prostrata preferentially allocated P to epidermal and spongy mesophyll cells, but co-located P and Ca in palisade mesophyll cells where granules with high [P] and [Ca] were evident. Mesophyll cellular [P] correlated positively with [potassium] for both species, and negatively with [sulfur] for P. exaltatus. Thus, P. exaltatus tolerated a very high leaf [inorganic P] (17 mg g-1), associated with P and Ca allocation to different cell types and formation of Ca crystals, thereby avoiding deleterious precipitation of Ca3(PO4)2. It also showed enhanced [potassium] and decreased [sulfur] to balance high cellular [P]. Phosphorus toxicity in K. prostrata arose from co-location of Ca and P in palisade mesophyll cells. This study advances understanding of leaf physiological mechanisms for high P tolerance in a P-hyperaccumulator and indicates P. exaltatus as a promising candidate for P-phytoextraction.

Changes in P accumulation, tissue P fractions and acid phosphatase activity of Pilea sinofasciata in poultry manure-impacted soil.

Pilea sinofasciata is a promising phytoextraction material to remove excess phosphorus (P) from manure-impacted soil. However, little information is available on its physiological response to animal manure treatments. Here, P accumulation, tissue P fractions and acid phosphatase activity were investigated in a mining ecotype (ME) and a non-mining ecotype (NME) of P. sinofasciata at different poultry manure (PM) treatments (0, 25, 50, 75, 100 and 125 g kg-1). Biomass and P accumulation of the ME increased up to 50 g kg-1, after which they significantly decreased; while P accumulation of the NME increased up to 100 g kg-1. But, shoot and root P accumulation of the ME were significantly higher than those of the NME at all PM treatments, showing 1.13-2.92 and 1.11-2.89 times higher values, respectively. Inorganic P and nucleic P dominated in tissues of both ecotypes. Besides, the ME maintained higher concentrations of inorganic P and ester P in leaves and ester P, nucleic P and residual P in roots than the NME. Acid phosphatase activity in leaves and roots increased by increasing PM treatments, except in root at 125 g kg-1. Acid phosphatase activity in leaves of the ME was positively correlated with concentrations of inorganic P, ester P and nucleic P, while that of the NME only correlated with inorganic P concentration. Probably, the optimized P fractions allocation and higher tissue acid phosphatase allow the ME to grow well and efficiently accumulate P in PM-impacted soil.

Subcellular distribution and chemical form of phosphorus involved in alleviating phosphorus toxicity of the phosphorus-accumulator Polygonum hydropiper.

Polygonum hydropiper is a dominant plant species in Shifang phosphorus (P) mine area and is a promising P-accumulator used for P-phytoextraction. To date, little information is available on the physiological response involved in alleviating P toxicity of P. hydropiper under high P. A pot experiment was carried out to investigate growth, P subcellular distribution, chemical forms in two ecotypes of P. hydropiper under high levels (1, 4, and 8 mmol P L-1) of inorganic P (Pi) and organic P (Po), supplied as KH2PO4 and myo-inositol hexaphosphoric acid dodecasodium salt, respectively. The mining ecotype (ME) showed a greater ability to tolerate high P than the non-mining ecotype (NME), as shown by its superior growth with undamaged leaf anatomical structure. The ME showed 1.3-2.2 times greater shoot P accumulation than the NME. More than 93% of P accumulated in tissue cell wall and soluble fraction. The increasing P treatments increased all tissue P forms, especially Pi form. The ME showed significantly higher ester P, nucleic P and insoluble P in tissues than the NME at 8 mmol L-1; however, it demonstrated lower Pi, expect for roots at 5 weeks. The percentages of Pi and nucleic P in roots of the ME were higher than other P forms, and the percentages of nucleic P dominated in the leaves. Probably, the combination of preferential distribution of P in cell wall and soluble fraction in tissues and storage of P in low activity as nucleic P in leaves allows the ME to adapt high P.

P accumulation and physiological responses to different high P regimes in Polygonum hydropiper for understanding a P-phytoremediation strategy.

Phosphorus (P) accumulators used for phytoremediation vary in their potential to acquire P from different high P regimes. Growth and P accumulation in Polygonum hydropiper were both dependent on an increasing level of IHP (1-8 mM P) and on a prolonged growth period (3-9 weeks), and those of the mining ecotype (ME) were higher than the non-mining ecotype (NME). Biomass increments in root, stem, and leaf of both ecotypes were significantly greater in IHP relative to other organic P (Po) sources (G1P, AMP, ATP), but lower than those in inorganic P (Pi) treatment (KH2PO4). P accumulation in the ME exceeded the NME from different P regimes. The ME demonstrated higher root activity compared to the NME grown in various P sources. Acid phosphatase (Apase) and phytase activities in root extracts of both ecotypes grown in IHP were comparable to that in Pi, or even higher in IHP. Higher secreted Apase and phytase activities were detected in the ME treated with different P sources relative to the NME. Therefore, the ME demonstrates higher P-uptake efficiency and it is a potential material for phytoextraction from P contaminated areas, irrespective of Pi or Po contamination.

Influence of swine manure on growth, P uptake and activities of acid phosphatase and phytase of Polygonum hydropiper.

Excessive application of animal manure to the farmland results in enrichment of P in the soil. Phytoremediation is a promising strategy for extracting excess P from manure impacted soil. P uptake characteristics of a mining ecotype (ME) and a non-mining ecotype (NME) of Polygonum hydropiper were investigated in this study by adopting soil culture containing various concentrations of swine manure (0-200 g swine manure kg(-1) soil). A peak value in the biomass of P. hydropiper was determined in 100 g kg(-1) soil. Significant increase of P content in tissues of two ecotypes was noticed with an increase in swine manure concentration. Maximum P accumulation in shoots and roots was observed at the concentration of 100 g kg(-1) soil, however, the ME accumulated more P as compared to the NME. The ME showed a lower plant effective number and a higher P extraction ratio compared to the NME. Both acid phosphatase and phytase activities of P. hydropiper were obviously enhanced under swine manure impacted soil compared with control, while those of ME higher than the NMEs. Therefore, the two ecotypes of P. hydropiper can accumulate P from soil amended with swine manure and establishes the foundation for phytoremediation.