Genetic Regulation Mechanism of Cadmium Accumulation and Its Utilization in Rice Breeding.

Cadmium (Cd) is a heavy metal whose pollution in rice fields leads to varying degrees of Cd accumulation in rice. Furthermore, the long-term consumption of Cd-contaminated rice is harmful to human health. Therefore, it is of great theoretical significance and application value to clarify the genetic regulation mechanism of Cd accumulation in rice and cultivate rice varieties with low Cd accumulation for the safe use of Cd-contaminated soils. This review summarizes the effects of Cd on rice growth, yield, and quality; the physiological and molecular mechanisms of Cd absorption in the roots, loading, and transport of Cd in the xylem, the distribution of Cd in nodes, redistribution of Cd in leaves, and accumulation of Cd in the grains; the regulation mechanism of the Cd stress response; and the breeding of rice with low Cd accumulation. Future directions on the genetic regulation of Cd in rice and application are also discussed. This review provides a theoretical basis for studies exploring the genetic regulation of Cd stress in rice. It also offers a basis for formulating effective strategies to reduce the Cd content in rice.

Physiological and Molecular Mechanisms of Plant Responses to Copper Stress.

Copper (Cu) is an essential micronutrient for humans, animals, and plants, and it participates in various morphological, physiological, and biochemical processes. Cu is a cofactor for a variety of enzymes, and it plays an important role in photosynthesis, respiration, the antioxidant system, and signal transduction. Many studies have demonstrated the adverse effects of excess Cu on crop germination, growth, photosynthesis, and antioxidant activity. This review summarizes the biological functions of Cu, the toxicity of excess Cu to plant growth and development, the roles of Cu transport proteins and chaperone proteins, and the transport process of Cu in plants, as well as the mechanisms of detoxification and tolerance of Cu in plants. Future research directions are proposed, which provide guidelines for related research.

Salt Tolerance of Rice Is Enhanced by the SS3 Gene, Which Regulates Ascorbic Acid Synthesis and ROS Scavenging.

Mining the key genes involved in the balance of rice salt tolerance is extremely important for developing salt-tolerant rice varieties. A library of japonica mutants was screened under salinity conditions to identify putative salt stress-responsive genes. We identified a highly salt-sensitive mutant ss3 and used a map-based cloning approach to isolate the gene SS3, which encodes mannose-1-phosphate guanylyltransferase. Under salt treatment, ss3 mutants have decreased ascorbic acid (AsA) content and increased reactive oxygen species (ROS) levels compared with the wild type (WT). Exogenous AsA restored the salt tolerance of ss3 plants, indicating that inhibition of AsA synthesis was an important factor in the salt sensitivity of the mutant. Functional complementation using the WT allele rescued the mutation, and transcription of SS3 was induced by salt stress. Vector SS3p:SS3 was constructed containing the 1086 bp coding sequence of SS3. Under salinity conditions, transgenic seedlings expressing SS3p:SS3 had improved salt tolerance relative to WT, as demonstrated by better growth status, higher chlorophyll content, a lower level of Na+, and a reduced Na+/K+ ratio. Further investigation revealed that several senescence- and autophagy-related genes were expressed at lower levels in salt-stressed transgenic lines compared to WT. These results demonstrate the positive impact of SS3 on salt tolerance in rice through the regulation of AsA synthesis and ROS accumulation, and indicate that SS3 is a valuable target for genetic manipulation.

Spider-Inspired HCCapture: Beware That What You Are Writing on Mobile Devices Is Becoming Prey for Spiders.

On mobile devices, the most important input interface is touchscreen, which can transmit a large amount of sensitive information. Many researchers have proven that sensors can be used as side channels to leak touchscreen interactive information. The research of information leakage in the restricted area has been relatively mature, but in the unrestricted area, still there are two issues to be solved urgently: chirography difference and posture variation. We learn from the way spiders perceive prey through the subtle vibrations of their webs; an unrestricted-area handwriting information speculation framework, called spider-inspired handwriting character capture (spider-inspired HCCapture), is designed. Spider-inspired HCCapture exploits the motion sensor as the side-channel and uses the neural network algorithm to train the recognition model. To alleviate the impact of different handwriting habits, we utilize the generality patterns of characters rather than the patterns of raw sensor signals. Furthermore, each character is disassembled into basic strokes, which are used as recognition features. We also proposed a user-independent posture-aware approach to detect the user's handwriting posture to select a suitable one from some pretrained models for speculation. In addition, the Markov model is introduced into spider-inspired HCCapture, which is used as an enhancement feature when there is a correlation between adjacent characters. In conclusion, spider-inspired HCCapture completes the handwritten character speculation attack without obtaining the victim's information in advance. The experimental results show that the accuracy of spider-inspired HCCapture reaches 96.1%.

Biochar-based molybdenum slow-release fertilizer enhances nitrogen assimilation in Chinese flowering cabbage (Brassica parachinensis).

Low molybdenum (Mo) bioavailability in acidic soil obstructs vegetable nitrogen assimilation and thus increases the health risk of vegetable ingestion due to nitrate accumulation. Constantly providing available Mo in acidic soil is a challenge for decreasing nitrate accumulation in vegetables. In this study, three Mo application methods, including biochar-based Mo slow-release fertilizer (Mo-biochar), seed dressing, and basal application, were investigated to enhance Mo bioavailability in acidic soil and nitrogen assimilation in Chinese flowering cabbage (Brassica parachinensis). The results showed that Mo-biochar constantly and sufficiently supplied Mo nutrients throughout the growing period of Brassica parachinensis, as evidenced by the soil available Mo, plant Mo uptake, and Mo values. The improved Mo supply was attributed to the alleviation of acidic soil (pH from 5.10 to 6.99) and the slow release of Mo adsorbed on biochar. Mo-biochar increased the nitrate reductase (NR) activity by 238.6% and glutamate dehydrogenase activity by 27.5%, indicating an enhancement of the rate-limiting steps of nitrogen assimilation, especially for nitrate reduction and amino acid synthesis. The increase in Mo-containing NR could be directly ascribed to the high level of Mo in Brassica parachinensis. Compared with the control, the nitrate content of Brassica parachinensis decreased by 42.9% due to the nitrate reduction induced by increased NR. Additionally, Mo-biochar was beneficial to vegetable growth and quality. In contrast, the transformation from NO3- to NH4+ was blocked with Mo seed dressing and basal application because of low Mo bioavailability in the soil, resulting in a high nitrate content in Brassica parachinensis. Conclusively, Mo-biochar can slowly release Mo and improve the neutral environment for Mo bioavailability, which is an effective strategy to mitigate the high nitrate accumulation of vegetables planted in acidic soil.

Quantification of nickel and cobalt mobility and accumulation via the phloem in the hyperaccumulator Noccaea caerulescens (Brassicaceae).

Hyperaccumulators have exceptional phloem translocation capability for heavy metals. This study aims at quantifying the mobility and accumulation of Ni and Co via the phloem in the model hyperaccumulator Noccaea caerulescens. "Phloem loading capability (PLC)," which is calculated by the "Metal content in phloem sap/Metal content in leaves," was introduced to evaluate the metal phloem mobility, while "Phloem mobility value (PMV)" was used for the normalization of PLC, which sets the PLC of Sr as PMV 0 and that of Rb as 100. The results showed that the PMVs of Ni and Co were 63 and 47, respectively. And the phloem mobility of Rb, Ni, Co, and Sr could be graded as highly mobile, mobile, intermediate, and immobile accordingly. The phloem stream can supply up to 19.1% and 16.0% of the total Ni and Co accumulated in the young leaves, respectively, while for Rb and Sr, the phloem contributes to 29% and 1.4% of the total Rb or Sr, indicating phloem contribution of certain metal is directly linked with its mobility. The results of this study raise the importance of phloem translocation on metal accumulation in shoots and provide insights on the metal cycling process in hyperaccumulators.

A risk-based approach for the safety analysis of eight trace elements in Chinese flowering cabbage (Brassica parachinensis L.) in China.

BACKGROUND: Most countries set regulatory values for the total trace element (TE) concentrations in soil, although there is growing interest in using a risk-based approach to evaluate the bioavailable TE using dilute salt extractants or other soil parameters, including pH and organic carbon. The present study compares the current regulatory system (based on total TEs and pH) and a risk-based approach using 0.01 mol L-1 CaCl2 to estimate the bioavailable fraction. RESULTS: In total, 150 paired samples of Chinese flowering cabbages (Brassica parachinensis) and their growth soils were collected, and the total and extractable concentrations of chromium (Cr), cadmium (Cd), lead (Pb), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As) and mercury (Hg), as well as soil pH and organic matter content, were measured. No more than 3.33% of the edible parts exceeded Chinese food safety standards, even when growing in soils exceeding the current regulatory thresholds by over 50%. The total soil Cd (1.5 mg kg-1 ), as well as the extractable concentrations of Cd (0.1 mg kg-1 ), Ni (0.03 mg kg-1 ) and Zn (0.1 mg kg-1 ), are the key factors affecting the TE concentrations in B. parachinensis. CONCLUSION: Our findings suggest that the current soil regulatory guidelines for safe production of B. parachinensis are overly strict and conservative. A risk-based approach based on the extractable TE concentrations would provide a better indication for plant uptake of soil TEs and avoid the waste of farmlands that can still produce safe vegetables. Future research should focus on providing crop-specific available TE concentration guidelines to promote effective utilization of farmlands. © 2021 Society of Chemical Industry.

Antimony symplastic and apoplastic absorption, compartmentation, and xylem translocation in Brassica parachinensis L. under antimonate and antimonite.

Antimony (Sb) excess accumulation in edible parts of crops causes potential risks to human health. However, knowledge about the mechanisms of its accumulation within vegetable plants is still not well known. Here, we investigated the physiological processes of Sb involved in symplastic and apoplastic absorption, compartmentation by roots, and translocation in xylem in Brassica parachinensis L. exposed to antimonate (SbV) and antimonite (SbIII) forms. The results showed that plants treated with SbIII emerged to be more toxic than SbV as proved by the lower biomass and the higher concentrations of malonaldehyde (MDA) and hydrogen peroxide (H2O2) in plant tissues, especially at high dosages. The Sb concentration showed more in shoots but less in roots treated with SbV than with SbIII. The total Sb accumulation was higher under the SbV treatment than the SbIII treatment, mainly due to the higher accumulation in shoots. Additionally, the Sb concentration in symplastic flow of roots was higher exposed to SbV than SbIII, while no differences were found for the Sb concentration in apoplastic flow between them. Moreover, the Sb concentration in cell walls of roots was higher exposed to SbIII than SbV, especially at high levels. Furthermore, the Sb concentration in xylem was higher exposed to SbV than SbIII, and a greatly positive correlation was observed between the Sb concentrations in xylem and shoots. Overall, these findings revealed that vegetable plants accumulated more SbV than SbIII in edible parts mainly due to xylem translocation rather than root absorption.

Ammonium nutrition mitigates cadmium toxicity in rice (Oryza sativa L.) through improving antioxidase system and the glutathione-ascorbate cycle efficiency.

Nitrogen (N) forms not only affect cadmium (Cd) accumulation in plants, but also affect plant resistance to Cd toxicity. However, few researches have been reported underlying the mechanism of the relationship between nitrogen forms and plant resistance under Cd exposure. Here, we explored the mechanism on how different NO3-/NH4+ ratios affect antioxidase system and the glutathione-ascorbate cycle under five different ratios of NO3-/NH4+ (1:0, 2:1, 1:1, 1:2, 0:1) and three dosages of Cd exposure (0, 1, 5 µmol L-1 Cd) in rice (Oryza sativa L.). The results showed that high NO3- and high Cd exposure both significantly inhibited tissue growth of rice plants, and this inhibiting trend was mitigated with increasing NH4+ ratios as proved by the increased biomass and the decreased concentrations of malonaldehyde (MDA) and hydrogen peroxide (H2O2), as well as the levels of Cd contents in rice tissues. Additionally, high NH4+ ratios elevated the SOD activities in rice tissues, especially at high Cd treatment. However, other two antioxidases (CAT and APX) were insensitive to changes of NO3-/NH4+ ratios (except the full NO3-). Furthermore, high NH4+ ratios induced increasing of the efficiency of glutathione-ascorbate cycle (GSH-AsA) under two levels of Cd exposure, as evidenced by increasing concentrations of GSH and AsA and the activities of GR and DHAR in rice tissues. Overall, these results revealed that ammonium nutrition caused an enhancement resistance to Cd stress in rice plants was responsible for increasing of partial antioxidase system and the efficiencies of GSH-AsA cycle.

Comparison of foliar silicon and selenium on cadmium absorption, compartmentation, translocation and the antioxidant system in Chinese flowering cabbage.

Silicon (Si) and selenium (Se) are beneficial for many higher plants when grown on stress conditions. However, the mechanisms underlying the differential effects between foliar Si and Se in alleviation of plant toxicity exposed to cadmium (Cd) stress are remained unclear. In this study, we investigated the discrepant mechanisms of foliar Si and Se on Cd absorption and compartmentation by roots, its translocation in xylem, and the antioxidant system within Chinese flowering cabbage (Brassica campestris L. ssp. chinensis var. utilis) under low and high Cd stress. Results showed that plant growth was significantly enhanced by foliar additions of Si or/and Se according to an increased plant tissue biomass at high Cd exposure. In addition, the foliar coupled addition of Si and Se showed little effects on the concentrations of Si or Se in plant tissues in comparison with the single addition of foliar Si or Se respectively. The foliar Si alone or combined with Se markedly reduced the Cd concentrations in plant shoots under two Cd treatments. This might be explained by the lower Cd concentrations in symplast and apoplast and the higher Cd concentrations in cell walls of plant roots, and the lower Cd concentrations in xylem sap. However, no great changes in these values were observed under the treatments of foliar Se alone. Moreover, the foliar additions of Si or/and Se all increased the antioxidant enzyme activities of SOD, CAT and APX in plant tissues, especially at high Cd dosage. No significant differences in the increasing degrees of these three antioxidant enzymes were found between the foliar Si and Se treatments. However, only the foliar Se alone or combined with Si markedly promoted the antioxidant enzyme activities of GR and DHAR in plant tissues. Our findings demonstrate that the alleviation of Cd toxicity by foliar Si maybe mainly responsible for inhibition of Cd absorption and its translocation to plant shoots, reinforcing its compartmentation into root cell walls, whilst enhancing the antioxidant enzyme system may be employed by foliar Se.

Biosorption mechanisms involved in immobilization of soil Pb by Bacillus subtilis DBM in a multi-metal-contaminated soil.

Mechanisms of soil Pb immobilization by Bacillus subtilis DBM, a bacterial strain isolated from a heavy-metal-contaminated soil, were investigated. Adsorption and desorption experiments with living bacterial cells as well as dead cells revealed that both extracellular adsorption and intracellular accumulation were involved in the Pb(2+) removal from the liquid phase. Of the sequestered Pb(II), 8.5% was held by physical entrapment within the cell wall, 43.3% was held by ion-exchange, 9.7% was complexed with cell surface functional groups or precipitated on the cell surface, and 38.5% was intracellularly accumulated. Complexation of Pb(2+) with carboxyl, hydroxyl, carbonyl, amido, and phosphate groups was demonstrated by Fourier transform infrared spectroscopic analysis. Precipitates of Pb5(PO4)3OH, Pb5(PO4)3Cl and Pb10(PO4)6(OH)2 that formed on the cell surface during the biosorption process were identified by X-ray diffraction analysis. Transmission electron microscopy-energy dispersive spectroscopic analysis confirmed the presence of the Pb(II) precipitates and that Pb(II) could be sequestered both extracellularly and intracellularly. Incubation with B. subtilis DBM significantly decreased the amount of the weak-acid-soluble Pb fraction in a heavy-metal-contaminated soil, resulting in a reduction in Pb bioavailability, but increased the amount of its organic-matter-bound fraction by 71%. The ability of B. subtilis DBM to reduce the bioavailability of soil Pb makes it potentially useful for bacteria-assisted phytostabilization of multi-heavy-metal-contaminated soil.

Comparison of the concentrations of metal elements and isotopes of lead found in rice and rice bran.

Very few studies have investigated the difference in the distribution of metal elements between rice and rice bran samples. In this study, the concentrations of 27 metal elements (Li, Be, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Ag, Cd, Cs, Ba, Tl, Pb, and U) in 56 polished rice and their corresponding bran samples were determined. A significant difference in concentrations of all elements except Ag and Cd was found between rice and bran (P < 0.05), with bran/rice ratios of 1.21 to 36.3. High concentrations of metal elements, especially that of the heavy metal Cr, in bran samples present a potential safety issue for bran products, such as food and feed containing bran. Pb isotope ((204)Pb, (206)Pb, (207)Pb, and (208)Pb) ratios also were determined. The (206)Pb/(207)Pb and (208)Pb/(207)Pb ratios in bran were generally higher than those in rice (P < 0.0001), and rice and bran samples were distinctly different from each other, indicating that Pb isotope composition is an effective for discriminating between bran and rice samples.