Flax-sesame crop rotation is an effective phytoremediation method for cadmium (Cd)-contaminated farmland. To investigate the effect of drainage on the uptake efficiency of soil Cd by the crops, field experiments were conducted to analyze the migration of Cd, iron (Fe), and manganese (Mn), and the soil microbial community. Compared with conventional drainage, the deep furrow treatment increased the Cd2 + accumulated in the flax and sesame organs by up to 73.9 % and decreased the soil Cd2+ content by 4.7 %-7.7 %. The accumulation of Fe2+/Fe3+ and Mn2+ showed the same trend as that of Cd. In the soil, deep furrow drainage increased the bioavailability of Cd2+, Mn2+ and Fe2+/Fe3+, while decreased the content of Fe-Mn oxide-bound Cd2+ and that of amorphous Fe2+/Fe3+ oxide by up to 13.3 %, indicating that changes in Fe morphology was highly related with the Cd availability. Further sequencing of the soil microbial community found that deep furrow drainage increased the relative abundance of Fe-redox bacteria Acidobacteria, Comamonas, Flavobacterium, Saccharimonadales, and Novosphingobium by up to 45.8 %, 63.7 %, 1204.1 %, 61.2 % and 93.5 % at the mature stage, respectively. And the relative abundance of other siderophore-secreting bacteria, including Lysobacter and Burkholderiales, increased by up to 85.2 % and 41.6 %, respectively. These findings indicated that the activation of key Fe-associated bacteria facilitated ferrolysis, playing a crucial role in enhancing Fe bioavailability and mitigating the immobilization effect of Fe2+/Fe3+ oxides on Cd2+ in soil. The implementation of deep furrow drainage significantly increased soil Cd2+ availability and enhanced Cd2+ uptake efficiency in the flax-sesame rotation system.

Although oilseed crop rotation provides a safe utilization strategy for Cd–contaminated fields, its overall remediation efficiency remains limited. A two–year field experiment was conducted at two sites to investigate the effects of ridge–furrow height under four crop rotation systems on the soil environment and Cd accumulation. High ridges with deep furrows (DF) improved soil drainage and lowered soil moisture, electrical conductivity, pH, and organic matter content. These changes increased the abundance of Acidobacteria and organic–matter–degrading bacteria, thereby enhancing Cd bioavailability. In contrast, low ridges with shallow furrows (SF) facilitated the enrichment of typical anaerobic Fe– and S–reducing bacteria, which promoted Cd immobilization. Compared with SF, DF increased the proportion of available Cd in macroaggregates and Cd²⁺ in soil solution by 29.3 % and 27.3 %, respectively, leading to a 16.8 %–84.8 % increase in Cd accumulation across the four rotation modes. Under DF, rotation mode 4 reduced total and available Cd in topsoil by 18.4 %–20.2 % and 40.5 %–43.2 %, respectively. The structural equation model revealed the influence of ridge–furrow treatments on the transformation process of Cd in the soil–oilseed crop system. Moreover, Cd concentrations in all plant oils (n = 192) consistently remained below 50 μg/kg, which guaranteed the safe and reliable use of oilseed-derived products in industrial applications. Overall, increasing ridge–furrow height effectively enhanced Cd remediation through oilseed crop rotation, but the restoration of soil fertility and its synergy with phytoremediation require further investigation.

Cadmium (Cd) contamination poses a serious threat to rice safety and productivity. This study investigated the potential of malic acid (MA), a key metabolic organic acid, to mitigate Cd toxicity and its genotype-dependent effects on cadmium uptake and essential element homeostasis in rice. Using hydroponic experiments with multiple genotypes, we found that MA application (0.5–1.5 mmol·L−1) significantly reduced Cd accumulation in both roots and shoots, with the most effective reduction (up to 68.0%) achieved at 1.5 mmol·L−1. Notably, genotype X24 was a low-Cd accumulator, while genotypes 20, 58, and 65 were high accumulators. Beyond Cd reduction, this study reveals the profound and genotype-specific modulation of nutrient homeostasis by MA, including consistent suppression of K and enhancement of Ca across genotypes, and highly divergent responses in Mg, Mn, Fe, and Zn accumulation. Furthermore, MA dramatically alleviated Cd-induced inhibition of root morphology, particularly in the high-Cd genotype 58, increasing root length and tip number by 42.8% and 57.8%, respectively. Our results provide novel insights into the genotype-dependent rebalancing of essential elements under MA amendment, highlighting the crucial role of genetic background in plant responses to organic acid treatments. These findings provide a mechanistic basis for developing MA-based foliar conditioners and genotype-specific strategies for managing Cd contamination in rice.

Cadmium (Cd) pollution in paddy soil seriously endangers food safety production. To investigate the effects and microbiological mechanisms of calcium-magnesium-phosphate (CMP) fertilizer application on Cd reduction in rice, field experiments were conducted in Cd-contaminated paddy soil. Compared with conventional compound fertilizer, CMP fertilizer treatments inhibited Cd uptake through plant roots, significantly decreasing Cd content in rice grains from 0.340 to 0.062 mg/kg. Soil pH and total Ca, Mg and P contents increased after CMP fertilizer application, resulting in a further decrease in soil available Cd content from 0.246 to 0.181 mg/kg. Specific extraction analysis recorded a decrease in both available Fe content and the ratio of nitrate to ammonium nitrogen, indicating that the soil Fe-N cycle was affected by the addition of CMP fertilizer. This finding was also recorded using soil bacterial community sequencing, with CMP fertilizer promoting the progress of nitrate-dependent Fe-oxidation driven by Thiobacillus (1.60-2.83%) and subsequent dissimilatory nitrate reduction to ammonium (DNRA) driven by Ignavibacteriae (1.01-1.92%); Fe-reduction driven by Anaeromyxobacter (3.09-2.23%) was also inhibited. Our results indicate that CMP fertilizer application regulates the Fe-N coupling cycle driven by the soil microbial community to benefit remediation of Cd contaminated paddy soil.

Crop straws provide enormous biomass residues applicable for biofuel production and trace metal phytoremediation. However, as lignocellulose recalcitrance determines a costly process with potential secondary waste liberation, genetic modification of plant cell walls is deemed as a promising solution. Although pectin methylation plays an important role for plant cell wall construction and integrity, little is known about its regulation roles on lignocellulose hydrolysis and trace metal elimination. In this study, we initially performed a typical CRISPR/Cas9 gene-editing for site mutations of OsPME31, OsPME34 and OsPME79 in rice, and then determined significantly upgraded pectin methylation degrees in the young seedlings of three distinct site-mutants compared to their wild type. We then examined distinctively improved lignocellulose recalcitrance in three mutants including reduced cellulose levels, crystallinity and polymerization or raised hemicellulose deposition and cellulose accessibility, which led to specifically enlarged biomass porosity either for consistently enhanced biomass enzymatic saccharification under mild alkali pretreatments or for cadmium (Cd) accumulation up to 2.4-fold. Therefore, this study proposed a novel model to elucidate how pectin methylation could play a unique enhancement role for both lignocellulose enzymatic hydrolysis and Cd phytoremediation, providing insights into precise pectin modification for effective biomass utilization and efficient trace metal exclusion.

Microorganisms play an important role in heavy metal bioremediation and soil fertility. The effects of soil inoculation with Pseudomonas sp. W112 on Cd accumulation in wheat were investigated by analyzing the transport, subcellular distribution and speciation of Cd in the soil and plants. Pseudomonas sp. W112 application significantly decreased Cd content in the roots, internode and grains by 10.2%, 29.5% and 33.0%, respectively, and decreased Cd transfer from the basal nodes to internodes by 63.5%. Treatment with strain W112 decreased the inorganic and water-soluble Cd content in the roots and increased the proportion of residual Cd in both the roots and basal nodes. At the subcellular level, the Cd content in the root cell wall and basal node cytosol increased by 19.6% and 61.8%, respectively, indicating that strain W112 improved the ability of the root cell wall and basal node cytosol to fix Cd. In the rhizosphere soil, strain W112 effectively colonized and significantly decreased the exchangeable Cd, carbonate-bound Cd and iron-manganese oxide-bound Cd content by 43.5%, 27.3% and 17.6%, respectively, while it increased the proportion of residual Cd by up to 65.2%. Moreover, a 3.1% and 23.5% increase in the pH and inorganic nitrogen content in the rhizosphere soil, respectively, was recorded. Similarly, soil bacterial community sequencing revealed that inoculating with strain W112 increased the abundance of Pseudomonas, Thauera and Azoarcus, which are associated with inorganic nitrogen metabolism, and decreased that of Acidobacteria, which is indicative of soil alkalinization. Hence, root application of Pseudomonas sp. W112 improved soil nitrogen availability and inhibited Cd accumulation in the wheat grains in a two-stage process: by reducing the Cd availability in the rhizosphere soil and by improving Cd interception and fixation in the wheat roots and basal nodes. Pseudomonas sp. W112 may be a suitable bioremediation agent for restoring Cd-contaminated wheat fields.

In order to evaluate the feasibility of using Burkholderia sp. Y4 as a cadmium （Cd）-reducing bacterial agent in contaminated wheat fields， the changes in the rhizosphere soil microbial community and Cd available state， as well as the content and transport characteristics of Cd in the wheat root， basal node， internode， and grain under the treatment of strain Y4 were tested using microbial high-throughput sequencing， step-by-step extraction， subcellular distribution， and occurrence analyses. The results showed that root application of strain Y4 significantly reduced the root and grain Cd content of wheat by 7.7% and 30.3%， respectively， compared with that in the control treatment. The Cd content and Cd transfer factor results in wheat vegetative organs showed that strain Y4 reduced the Cd transfer factor from basal node to internode by 79.3%， and Cd content in the wheat internode stem also decreased by 50.9%. The study of Cd occurrence morphology showed that strain Y4 treatment increased the proportion of residual Cd in roots and basal ganglia， decreased the contents of inorganic and water-soluble Cd in roots， and increased the content of residual Cd in basal ganglia. Further examination of the subcellular distribution of Cd showed that the Cd content in root cell walls and basal ganglia cell fluid increased by 21.3% and 98.2%， respectively， indicating that the Cd fixation ability of root cell walls and basal ganglia cell fluid was improved by the strain Y4 treatment. In the rhizosphere soil， it was found that the microbial community structure was changed by strain Y4 application. Under the Y4 treatment， the relative abundance of Burkholderia increased from 9.6% to 11.5%， whereas that of Acidobacteriota decreased. Additionally， the relative abundance of Gemmatimonadales， Pseudomonadales， and Chitinophagales were also increased by strain Y4 treatment. At the same time， the application of strain Y4 increased the pH value of rhizosphere soil by 8.3%. The contents of exchangeable Cd， carbonate-bound Cd， and iron-manganese oxide-bound Cd in the soil decreased by 44.4%， 21.7%， and 15.9%， respectively， whereas the proportion of residual Cd reached 53.6%. Root application of strain Y4 increased the contents of nitrate nitrogen and ammonium nitrogen in the soil by 22.0% and 21.4%， respectively， and the contents of alkaline nitrogen also increased to a certain extent. In conclusion， the root application of strain Y4 not only improved soil nitrogen availability but also inhibited Cd transport and accumulation from contaminated soil to wheat grains in a "two-stage" manner by reducing Cd availability in rhizosphere soil and improving Cd interception and fixation capacity of wheat roots and basal nodes. Therefore， Burkholderia Y4 has application potential as a Cd-reducing and growth-promoting agent in wheat.

Malic acid (MA) plays an important role in plant tolerance to toxic metals, but its effect in restricting the transport of harmful metals remains unclear. In this study, japonica rice NPB and its fragile-culm mutant fc8 with low cellulose and thin cell wall were used to investigate the influence of MA on the accumulation of 4 toxic elements (Cd, Pb, Ni, and Cr) and 8 essential elements (K, Mg, Ca, Fe, Mn, Zn, Cu and Mo) in rice. The results showed that fc8 accumulated less toxic elements but more Ca and glutamate in grains and vegetative organs than NPB. After foliar application with MA at rice anthesis stage, the content of Cd, Pb, Ni significantly decreased by 27.9-41.0%, while those of Ca and glutamate significantly increased in both NPB and fc8. Therefore, the ratios between Cd and Ca in grains of NPB (3.4‰) and fc8 (1.5‰) were greatly higher than that in grains of NPB + MA (1.1‰) and fc8+MA (0.8‰) treatments. Meanwhile, the expression of OsCEAS4,7,8,9 for the cellulose synthesis in secondary cell walls were down-regulated and cellulose content in vegetative organs of NPB and fc8 decreased by 16.7-21.1%. However, MA application significantly up-regulated the expression of GLR genes (OsGLR3.1-3.5) and raised the activity of glutamic-oxalacetic transaminease for glutamate synthesis in NPB and fc8. These results indicate that hazard risks of toxic elements in foods can be efficiently reduced through regulating cellulose biosynthesis and GLR channels in plant by combining genetic modification in vivo and malic acid application in vitro.

To explore the roles of malate-aspartic acid metabolism in the processes of cadmium uptake and transport in rice plant， the distribution characteristics of cadmium （Cd） and the change of aspartic acid （Asp） and glutamate （Glu） in different rice organs were examined by adding or spraying different concentrations of malic acid （MA） under Cd stress. The results revealed that adding 0.5–1.5 mmol·L -1 MA significantly inhibited Cd accumulation in the roots and shoots of rice seedlings. The Cd content in the soluble fraction （F3） of root and shoot cells decreased by 60.1%–82.9% and 64.0%–81.0%， respectively. Simultaneously， the content of glutathione， aspartic acid， and glutamate in roots and shoots increased significantly， while the content of PC 2～4 decreased significantly. During the grain-filling period， the activities of malate dehydrogenase and aspartate transaminase （AST） in developing grains increased by 63.0%–96.8 % and 14.6%–22.6%， respectively. After foliar application of 5 mmol·L -1 malic acid three times at anthesis， the content of Asp and Glu in both vegetative organs and rice grains increased significantly. The transport efficiency of Cd from the stem base to the top vegetative organs and rice grains decreased significantly， resulting in a 37.5%–55.4% decrease in rice Cd. These results indicate that promoting the transformation between malate and Asp or Glu in cells can efficiently inhibit the uptake and transport of Cd in the rice plants and significantly reduce the Cd content in top vegetative organs and rice grains.

为探寻叶面喷施2,3-二巯基丁二酸(DMSA)降低水稻幼苗茎叶镉含量的潜在机制,在人工气候室内,采用水培实验方法研究了镉在幼苗不同部位的累积情况及喷施DMSA对镉胁迫的影响.结果表明:随着DMSA喷施浓度增加,茎基镉含量呈显著增加趋势,当DMSA喷施浓度达到1.0 mmol·L-1时茎基镉含量与对照(不喷施DMSA)处理相比显著增加57.3％,同时镉由茎基向地上部的转移效率降低52.7％.在此基础上,探寻了镉在茎基细胞中的赋存形态及镉的亚细胞分布情况,结果表明茎基中难溶态镉含量与对照处理相比显著增加了80.8％,细胞壁中镉含量达到对照处理的2.1倍.进一步对细胞壁各组分镉含量进行测定发现,果胶组分中镉含量随着DMSA喷施浓度增加呈现出显著升高趋势,与对照处理相比最高增加99.5％.此外,喷施DMSA后茎基中总植物螯合素(PCs)和谷胱甘肽(GSH)含量均呈现出显著增加趋势,最高分别达到对照处理组的2.2倍和3.1倍.喷施DMSA显著缓解了镉胁迫,幼苗地上部超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性分别升至对照处理的3.0倍和2.7倍,荧光标记试验表明叶片中过氧化氢含量随DMSA喷施浓度增加呈现显著降低趋势.研究表明,喷施DMSA显著增加了水稻幼苗茎基巯基化合物含量,从而提高了对镉的拦截能力,降低了镉由茎基向幼苗地上部转运效率,使水稻幼苗地上部镉含量显著降低,同时喷施DMSA还可显著缓解幼苗镉胁迫.

The selective permeation of glutamate receptor channels (GLRs) for essential and toxic elements in plant cells is poorly understood. The present study found that the ratios between cadmium (Cd) and 7 essential elements (i.e., K, Mg, Ca, Mn, Fe, Zn and Cu) in grains and vegetative organs increased significantly with the increase of soil Cd levels. Accumulation of Cd resulted in the significant increase of Ca, Mn, Fe and Zn content and the expression levels of Ca channel genes (OsCNGC1,2 and OsOSCA1.1,2.4), while remarkable reduction of glutamate content and expression levels of GLR3.1-3.4 in rice. When planted in the same Cd-polluted soil, mutant fc8 displayed significantly higher content of Ca, Fe, Zn and expression levels of GLR3.1-3.4 than its wild type NPB. On the contrary, the ratios between Cd and essential elements in fc8 were significantly lower than that in NPB. These results indicate that Cd pollution may damage the structural integrity of GLRs by inhibiting glutamate synthesis and expression levels of GLR3.1-3.4, which leads to the increase of ion influx but the decrease of preferential selectivity for Ca2+/ Mn2+/ Fe2+/ Zn2+ over Cd2+ through GLRs in rice cells.

To explore the effects of foliar application of chlorinated amino acetic acid on the transport characteristics of Cd in rice during the flowering stage, a pot experiment was conducted using Xiangzaoxian24 rice. The changes of Cd content in rice grains and various organ species, and essential elements（K, Mg, Ca, Fe, Mn, Zn）and amino acid contents in rice were analyzed. The results show that the application of 0.8 mmol·L -1 chlorinated amino acetic acid at the flowering stage of rice significantly reduced the Cd content in rice and rachis at the mature stage; the Cd content in rice decreased from 0.28 mg·kg -1 to 0.17 mg·kg -1 , reducing by 39.29%. Through the analysis of the cadmium transfer factor between various organs in rice, we found that the application of chlorinated amino acetic acid significantly decreased the transport factor of Cd ions from the rachis to grain, panicle node to panicle neck, and from the second inverted node to the first inverted. Cd decreased significantly due to the decrease in the transport efficiency of the inverted second internode. Additionally, the application of chlorinated amino acetic acid increased the content of Ca in grain and cob, and promoted the transfer of K, Mg and Zn from the inverted node to the rachis. The amino acid analysis results show that the application of 0.8 mmol·L -1 chlorinated amino acetic acid increased the content of aspartic acid and glutamic acid by 28.54% and 22.96%, respectively, and decreased the glycine content by 51.92%. Therefore, the application of chlorinated amino acetic acid during the flowering period of rice is conducive to the synthesis of aspartic acid and glutamic acid in rice, which promotes the transport of K, Mg and Zn, and significantly reduces Cd content by inhibiting the transportation of Cd from vegetative organs to grain. This method may be applied in the production process of Cd-polluted farmland in southern China.

The distributions of heavy metals in paddy fields and rice along river valleys were studied to explore the key factors affecting the accumulation of heavy metals in the upstream terraces and downstream plains. Results from 975 sampling sites showed that elevation, growing season and soil organic matter (OM) had significant effects on the content of Cd and Pb in topsoil and rice. The content of Cd (0.47-0.66 mg kg-1) and Pb (49.9-68.6 mg kg-1) in paddy fields with low elevation (30-60 m) in the downstream plains was significantly higher than the content of Cd (0.29-0.38 mg kg-1) and Pb (43.9-56.3 mg kg-1) in the upstream terraces with high altitude (60-90 m). In the double-rice production area, late rice generally produced grains with higher Cd and Pb content than early rice. Soil Cd was positively increased with the content of OM, especially in the downstream plains. When elevation was used for principal component analysis, plains with low elevation were grouped together with high content of total and soluble Cd, OM and Pb in soil, as well as high content of Cd and Pb in late rice. Altitude is one of the key factors affecting Cd content in rice. Although content of Cr (93.7-138.0 mg kg-1) was significantly higher than that of Cd and Pb in soil, content of Cr was lower than that of Cd in rice. These results indicate that paddy fields with elevation of 30-60 m in the downstream plains had high risk to produce late rice with Cd and Pb content exceeding the food safety standard 0.2 mg kg-1, which may be resulted from the driving force of runoff on soil soluble Cd and Pb from terraces to alluvial plains in river valleys.

Dietary rice is the main source of inorganic arsenic （iAs） with a high carcinogenic risk for the population， therefore developing countermeasures to reduce the arsenic （As） content in rice is of great importance. Here， we investigated the effect of foliar spraying of S-allyl-L-cysteine （SAC） on the total As content in rice grains and nutritive organs during flowering and identified the potential molecular mechanism of SAC using the main rice cultivar "ZhongZao 35" in southern China. The experimental results showed that the As content in grains and roots significantly decreased by 42.3% and 20.6%， respectively， when the SAC spraying concentration reached 0.2 mmol·L -1 ， but significantly increased in flag leaves by 72.4%. Fluorescence staining showed that the H 2 O 2 content in flag reduced significantly， while the SOD and CAT enzyme activities significantly increased by 61.8% and 105.3%， respectively. The genes encoding Lsi6 and Lsi3 transporters in the first rice node were significantly downregulated by 59.8% and 36.3%， respectively， after SAC spraying; thus， significantly reducing the ability of rice to unload As Ⅲ from the vascular stream leading to the expansion of vascular bundle in the flag leaves and load As Ⅲ into the diffused vascular bundle connected to the rice spike. Moreover， it resulted in a significant decrease in the total As content in the grains and a significant increase in the flag leaves. The genes encoding OsPCS1， a phytochelatins-（PCs）-synthesizing enzyme， and OsABCC1， an As Ⅲ transporter in cell vacuole， were significantly upregulated by 57.6% and 61.0% respectively， indicating that SAC spraying increased the ability of flag leaves to synthesize PCs and compartmentalize As Ⅲ into the vacuole， thereby reducing As Ⅲ stress in the leaves. The genes encoding Lsi1， Lsi2， and Lsi3 transporters in rice roots were significantly downregulated by 27.2%， 23.8%， and 29.5%， respectively， indicating that the uptake and transport capacity of As Ⅲ in rice roots was reduced， which further minimized the loading capacity of As Ⅲ into the xylem ducts. In conclusion， spraying SAC reduced As content in grains and roots by regulating the expression of genes encoding As Ⅲ related transporter and alleviated As stress.

The mechanism of reactive oxygen species (ROS) burst in rice cells induced by cadmium (Cd) stress remains poorly understood. The present study shows that the burst of superoxide anions (O2·-) and hydrogen peroxide (H2O2) in roots and shoots led by Cd stress was attributed to the disturbance of citrate (CA) valve and the damage of antioxidant enzyme structure in the rice seedlings. Cd accumulation in cells altered the molecular structure of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) through attacking glutamate (Glu) and other residues, leading to the significant reduction of their activities in clearing O2·- and decomposing H2O2. Citrate supplementation obviously increased the activity of antioxidant enzymes and decreased ∼20-30% of O2·- and H2O2 contents in roots and shoots. Meanwhile, the synthesis of metabolites/ligands such as CA, α-ketoglutarate (α-KG) and Glu as well as the activities of related enzymes in CA valve were remarkably improved. The activities of antioxidant enzymes were protected by CA through forming stable hydrogen-bonds between CA and antioxidant enzymes, and forming the stable chelates between ligands and Cd. These findings indicate that exogenous CA mitigated the toxicity of ROS under Cd stress by the ways of restoring CA valve function to reduce the production of ROS, and improving the stability of enzyme structure to enhance antioxidant enzymes activity.

为了明确水稻营养器官对镉的拦截作用,对3个水稻基因型关键器官的镉积累特性进行了比较研究.盆栽试验结果表明:高镉积累型水稻T优705茎基部(蘖节)、穗轴和籽粒的镉含量及穗轴向籽粒转运镉的比例显著高于低镉积累型水稻朝阳1号B和湘早籼24.稻穗在含镉0.9～4.5μmol·L-1的Hoagland营养液中灌浆时,T优705籽粒基部拦截镉的能力最弱,稻米镉含量(y)和穗轴中的镉含量(x)呈显著线性相关(y=ax+b),穗轴中的镉含量每增加1.0 mg,朝阳1号B、湘早籼24和T优705稻米中的镉含量分别增加0.01、0.11 mg和0.14 mg.在0.9～18.0μmol·L-1的镉溶液中,进入离体叶片的镉离子数量直接决定着叶绿素的衰减速率,镉含量每增加1.0 mg,朝阳1号B和湘早籼24的叶绿素含量降低0.02 mg左右,而T优705的叶绿素含量只降低0.01 mg.在相同的镉胁迫环境中,T优705离体叶片的氧化损伤程度较轻,释放的O-2和H2O2数量显著少于朝阳1号B和湘早籼24.这些结果表明,低镉积累型水稻籽粒基部对镉的拦截能力强,叶片耐镉性差,而高镉积累型水稻籽粒基部对镉的拦截能力弱,叶片耐镉性强;离体稻穗的镉转运特性和离体叶片的耐镉能力可以作为快速筛选低镉积累水稻品种的重要依据.

When rice plants grown in paddy fields with Cd content of 0.3-1.5 mg kg(-1), Cd quantities in mots and straws were 2-7 times higher than that in topsoil. Return of these vegetative organs to topsoil aggravated the ecological risk of Cd pollution. Cd content in rice grains was 0.1-1.3 mg kg(-1), and hazard quotients for local consumers by intake of these rice were 0.7-8.8. Planting low-Cd-accumulating (LCA) cultivar reduced hazard quotients for consumers by intake of rice, but had similar ecological risks as high-accumulating (HCA) cultivars. LCA cultivar had lower Cd content in grains as well as higher efficiency of altering Cd into insoluble forms in flag leaves and upmost nodes than HCA cultivars. Insoluble Cd content in nodes was linearly increased with soil Cd content, companied by significant decline of 4 amino acids with dicarboxyl groups. Glu or Asp can form a cyclic complex with Cd by two O atoms from alpha-COO- and side chain-COO-. These results indicate that roots and straws have high potential to concentrate Cd by forming complexes between amino acids and Cd ions, and Cd-enriched straw return to topsoil may aggravate the ecological risk of Cd contamination.

目的 确定反相高效液相色谱法(reversed-phase high performance liquid chromatography,RP-HPLC)测定稻米氨基酸含量最适柱前衍生化时间.方法 以氨基酸标准品以及稻米氨基酸提取物为对象,对柱前衍生化时间与氨基酸检测结果之间的关系进行研究.结果 邻苯二甲醛(O-phthalaldehyde,OPA)和3-巯基丙酸与氨基酸的衍生化反应进行到15 min时,氨基酸的峰面积达到最大值,不同OPA-氨基酸衍生化产物的稳定性存在很大的差异.在15～300 min的衍生化反应中,酪氨酸和苯丙氨酸衍生物的峰面积保持在非常稳定的水平上;而侧链含有羟基的丝氨酸和苏氨酸对衍生化时间特别敏感,衍生化时间超过15 min后,其衍生物的峰面积开始快速下降;当衍生化时间在15～60 min之内时,15种氨基酸中,只有酪氨酸、苯丙氨酸、精氨酸、谷氨酸、天冬氨酸、赖氨酸、亮氨酸、异亮氨酸和丙氨酸9种氨基酸的衍生物峰的面积下降幅度小于5％.结论 柱前衍生化时间对稻米氨基酸衍生物峰面积的检测值较为敏感,衍生化时间控制在15 min之内能有效减小实验误差.

In order to investigate the effects of Burkholderia sp. Y4 on rice seedlings under cadmium (Cd) stress, seed germination and vermiculite culture experiments were conducted using low Cd-accumulation xiangzaoxian 24 (X24) and high Cd-accumulation Tyou 705 (T705) varieties. The effects of Burkholderia sp. Y4 on rice growth, oxidative damage caused by Cd, and Cd accumulation were studied. Additionally, the Cd2+ flux rates in the elongation zone of rice roots under Burkholderia sp. Y4 application were detected using non-invasive micro-test technology. Burkholderia sp. Y4 alleviated the inhibition effect of Cd on rice seed germination by 13.8%. After inoculation with Burkholderia sp. Y4 for 7 d, the length of rice roots and buds increased by 83.3% and 12.2%, and their dry weight increased by 56.8% and 12.5%, respectively; those in the 10 d Y4 inoculation group increased by 28.6% and 20.0% in length and by 113.2% and 46.0% in dry weight, respectively. Burkholderia sp. Y4 inoculation also alleviated rice oxidative stress damage caused by Cd. The application of strain Y4 significantly reduced the content of the oxidative damage product malondialdehyde (MDA) in the shoots and roots of rice seedlings by 21.5% and 16.9%, respectively. Under Burkholderia sp. Y4 inoculation, the significant changes in antioxidant enzyme SOD and CAT activities caused by Cd stress disappeared in rice roots; those in shoots also decreased from 176.9% and 74.8% to 53.3% and 21.5%, respectively. Conversely, Burkholderia sp. Y4 inhibited Cd uptake by rice seedlings with different genotypes, including the low Cd-accumulation variety X24 and high Cd-accumulation variety T705. The root application of strain Y4 significantly reduced Cd accumulation in the shoots and roots of rice seedlings by 79.2% and 62.7% in T705 and by 57.3% and 24.1% in X24, respectively. The Cd2+ flux rate of high Cd-accumulation variety T705 was significantly higher than that of low Cd-accumulation variety X24. Under Burkholderia sp. Y4 inoculation, the yellow membrane was formed on the root surface of rice seedlings, and the Cd2+ flux rate in the elongation zone of T705 and X24 roots decreased by 36.0% and 35.0% in 3-day-old seedlings, as well as by 44.6% and 24.9% in 10-day-old seedlings, respectively. In conclusion, Burkholderia sp. Y4 inoculation inhibited the toxic effects of Cd on rice seedling growth through alleviating oxidative stress and damage caused by Cd. Furthermore, the root application of Burkholderia sp. Y4 effectively decreased the Cd2+ flux rate in the elongation zone of roots to inhibit the Cd uptake and accumulation in roots and shoots of rice seedlings. This study provides theoretical basis and data support for the application of Burkholderia sp. Y4 as a Cd-reducing and growth-promoting agent for rice in contaminated farmland.

为评估还原型谷胱甘肽(GSH)作为水稻降Cd叶面调理剂的可行性,本研究通过田间试验,检测开花期叶面喷施一次GSH对水稻各器官Cd和矿质元素含量的影响,并结合各元素在水稻不同器官中的分布情况,探究GSH抑制水稻体内Cd转运的作用机制.结果表明:开花期叶面喷施GSH可显著降低水稻籽粒中Cd含量,最高降幅可达76.5％,使稻米Cd含量由0.449 mg·kg-1降至我国食品安全标准(0.2 mg·kg-1)以内,并提高了稻米中K、Mg、Ca和Mn的含量.喷施GSH后水稻各营养器官的Cd含量均显著降低,降幅为68.8％～86.7％;同时,不同器官中K、Mg、Ca、Fe、Mn和Zn的含量也有不同程度的升高或降低.不同相邻器官之间的元素转移系数显示,叶面喷施GSH分别提高了Cd和Zn从第二节间到穗下节的转移系数,增幅可达46.2％和134.4％,降低了Cd和Zn从穗下节到旗叶的转移系数,降幅分别为44.5％和32.2％,并降低了Cd从穗下节继续向上到穗颈的转运系数,降幅可达31.4％.相关性分析发现,不同处理组水稻第二节及以上营养器官中,Zn含量与Cd含量相关系数最高,为0.809,为极强正相关(P<0.001).由此可见,喷施GSH不但降低了水稻各器官中Cd含量,而且能够通过调控穗下节与其相连营养器官——穗颈、第二节间和旗叶之间的Cd转运,提高水稻自身主要Cd阻控器官——穗下节对Cd的拦截能力,进而抑制Cd向籽粒的转运和积累.同时,喷施GSH也提高了水稻穗下节对Zn的固定能力,改变了水稻不同营养器官中6种矿质元素的含量和分布,其中Zn与Cd的相关性最高,并最终提高了稻米中K、Mg、Ca和Mn的含量.