植物硒生理及与重金属交互的研究进展

硒是一种重要的微量元素,在低浓度时对生物有益,但高浓度时呈现与重金属类似的毒性。植物作为人体硒摄入的主要来源,其硒代谢对于植物硒积累乃至人体硒营养水平十分重要。研究植物硒吸收、代谢和积累机理能指导富硒粮食的生产,是解决人体硒摄入不足/超量问题的有效途径。本文在阐述土壤硒含量、形态、生物有效性及分布的基础上,综述了植物对硒的吸收、代谢机理的研究进展,并讨论了农业生物强化以及遗传育种生物强化等两种硒生物强化的实践方法,以及利用硒生物强化缓解重金属毒性减少积累;最后,提出了植物硒代谢及硒生物强化研究的前沿问题,以期为改善人体硒营养水平提高人体健康状况提供理论和实践依据。     

硒在高等植物中的生理作用

就高等植物对硒的吸收和转化以及硒在植物体内的分布和某些生理作用进行了概述。     

土壤硒及其与植物硒营养的关系

综述了土壤中Se的形态分布、有效性及其与植物关系研究方面的进展。论述了不同形态的Se在土壤中分布情况、对植物的有效性与土壤pH值、化学及矿物学组成、吸附表面、氧化还原状态等物理化学性质的关系;Se在植物中的富集、转化及其对植物的抗氧化、促进生长、提高产量和质量等各种生物学效应;并在此基础上对Se的应用前景做了展望。     

微生物硒代谢机制研究进展

硒(Se)是人与动物生命必需的微量元素,在医学保健和工业制造方面有着广泛的应用。硒在环境中有四种价态,包括硒酸盐Se O42-(+6)、亚硒酸盐Se O32-(+4)、单质硒Se0(0)和硒化物Se2-(-2)。微生物在硒的形态转化中扮演了重要的角色,影响着环境中硒的生物地球化学循环。本文主要从自然界中硒的循环以及微生物与硒代谢机制两个方面阐述微生物对硒的生物地球化学循环的重要性。     

植物叶片对硒的吸收与转运

以花生为供试植物的叶面施硒试验结果表明,叶片能够吸收利用Ｓｅ（ＩＶ）和Ｓｅ（ＶＩ）两种价态的外源硒,并将所吸收的硒主要转运至花生种子中去。叶片对硒的吸收转运能力受施硒量、施硒时间和硒的价态等因素的影响,叶片对Ｓｅ（ＶＩ）的吸收能力约是Ｓｅ（ＩＶ）的３倍,吸收量与施硒量成正比,在花针期施用有利于叶片的吸收利用和转运．     

硒在植物生命活动中的作用

简要叙述了微量元素硒在植物体内的吸收、运输、存在形态、生理功能及其与其他元素的相互作用，并就增加植物体内的硒含量提出了一些设想。     

Selenium uptake, translocation and speciation in wheat supplied with selenate or selenite

Selenite can be a dominant form of selenium (Se) in aerobic soils; however, unlike selenate, the mechanism of selenite uptake by plants remains unclear. Uptake, translocation and Se speciation in wheat (Triticum aestivum) supplied with selenate or selenite, or both, were investigated in hydroponic experiments. The kinetics of selenite influx was determined in short-term (30 min) experiments. Selenium speciation in the water-extractable fraction of roots and shoots was determined by HPLC-ICPMS. Plants absorbed similar amounts of Se within 1 d when supplied with selenite or selenate. Selenate and selenite uptake were enhanced in sulphur-starved and phosphorus-starved plants, respectively. Phosphate markedly increased K(m) of the selenite influx. Selenate and selenite uptake were both metabolically dependent. Selenite was rapidly converted to organic forms in roots, with limited translocation to shoots. Selenomethionine, selenomethionine Se-oxide, Se-methyl-selenocysteine and several other unidentified Se species were detected in the root extracts and xylem sap from selenite-treated plants. Selenate was highly mobile in xylem transport, but little was assimilated to organic forms in 1 d. The presence of selenite decreased selenate uptake and xylem transport. Selenite uptake is an active process likely mediated, at least partly, by phosphate transporters. Selenite and selenate differ greatly in the ease of assimilation and xylem transport.     

水稻对硒吸收、分布及硒与硅共施效应

水稻幼苗根吸收的７５Ｓｅ在顶叶分布较多,以下各对依次减少,但根内积累更多。当Ｙｏｓｈｉｄａ营养液加入０．１和０．３ｕｇ／ｍｌ亚硒酸钠,根吸收３２Ｐ多,幼苗长高并生根;但经０．６ｕｇ／ｍｌ处理后幼苗生长受抑制,叶片失绿。加Ｓｉ可抑制Ｓｅ高浓度使叶片变黄。在同样加Ｓｅ处理中,加Ｓｉ的株高、根长、叶绿素含量和叶片可溶性蛋白含量以及对３２Ｐ吸收量和幼苗地上部分布量均高于不加Ｓｉ的处理,并随着Ｓｅ浓度的增加而增高,而当Ｓｅ浓度过高时则下降。加Ｓｉ促进１４Ｃ－同化物分布在稻穗。     

Selenium addition alters mercury uptake,bioavailability in the rhizosphere and root anatomy of rice (Oryza sativa)

Background and Aims

Mercury (Hg) is an extremely toxic pollutant, especially in the form of methylmercury (MeHg), whereas selenium (Se) is an essential trace element in the human diet. This study aimed to ascertain whether addition of Se can produce rice with enriched Se and lowered Hg content when growing in Hg-contaminated paddy fields and, if so, to determine the possible mechanisms behind these effects.

Methods

Two cultivars of rice (Oryza sativa, japonica and indica) were grown in either hydroponic solutions or soil rhizobags with different Se and Hg treatments. Concentrations of total Hg, MeHg and Se were determined in the roots, shoots and brown rice, together with Hg uptake kinetics and Hg bioavailability in the soil. Root anatonmy was also studied.

Key Results

The high Se treatment (5 μg g^–1) significantly increased brown rice yield by 48 % and total Se content by 2·8-fold, and decreased total Hg and MeHg by 47 and 55 %, respectively, compared with the control treatments. The high Se treatment also markedly reduced ‘water-soluble’ Hg and MeHg concentrations in the rhizosphere soil, decreased the uptake capacity of Hg by roots and enhanced the development of apoplastic barriers in the root endodermis.

Conclusions

Addition of Se to Hg-contaminated soil can help produce brown rice that is simultaneously enriched in Se and contains less total Hg and MeHg. The lowered accumulation of total Hg and MeHg appears to be the result of reduced bioavailability of Hg and production of MeHg in the rhizosphere, suppression of uptake of Hg into the root cells and an enhancement of the development of apoplastic barriers in the endodermis of the roots.     

Selenium and sulfur accumulation and soil selenium dissipation in planting of four herbaceous plant species in soil contaminated with drainage sediment rich in both selenium and sulfur

Four selenium (Se) nonaccumulator plant species, including a forage grass species, Tall Fescue (Festuca arundinacea Schreb.), a forage legume species, Alfalfa (Medicago sativa L.), a wetland species, Rush (Juncus tenuis Wild.), and a dry-land alkaline soil species, Saltgrass (Distichlis spicata L.), were grown in soil contaminated by agricultural drainage sediment having elevated levels of Se and sulfur (S). The above-ground plant tissues were consecutively harvested five times and examined for Se and S accumulation. Plant tissue Se concentrations ranged from 23.0 mg kg-1 to 8.3 mg kg-1. Tissue S concentrations ranged from 3239 mg kg-1 to 7034 mg kg-1. Both tissue Se and S concentrations were significantly different between harvests, species, and species/harvest interactions. Total Se accumulation by the plant biomass harvested ranged from 0.3 to 1.3 mg per soil column and total S accumulations ranged from 87.5 to 321.1 mg per soil column. The reduction in the percentage of total soil Se after 24 weeks growth of the plant species ranged from 12.0% in the Tall Fescue planting to 17.3% in the Rush planting. Over 90% of the soil Se losses were unidentified losses and leaching of Se was prevented. The accumulations of Se and S in the plant biomass were very small compared with the total soil Se and S losses, but substantial amounts of total soil Se (12.0 to 15.0%) and S (28.0 to 50.9%) inventories were dissipated by the growing and harvesting of the plants. The soil S concentration was several hundred times higher than the soil Se concentration, but Se accumulation by the plants and Se dissipation from the soil were not impaired by the high level of soil sulfur. For natural grassland habitat restoration, such as at the Kesterson Wildlife Refuge in the Central Valley of California, or for restoration of large-scale Se contaminated agricultural lands, Se nonaccumulator plant species are favorable candidates, because the possibility of introducing Se toxicity into the food chain can be minimized.     

硒与叶酸在抗病毒治疗中的作用及其在植物中的应用前景分析

2020年,科学家在新型冠状病毒肺炎的治疗过程中发现,治疗效果与患者体内的硒和叶酸水平有一定相关性。这说明提高人体内硒和叶酸含量的膳食方案,可以有效地增加人体免疫能力来应对病毒性疾病的冲击。通过膳食保障人体硒和叶酸的摄入是植物营养强化的主要任务之一,但目前硒和叶酸的复合营养强化工作鲜见报道。综述了硒和叶酸这两种微量营养素在抗病毒治疗中的机制、以及硒和叶酸在植物中的应用前景,为提升营养品质、创制富含硒和叶酸的营养强化植物提供理论支撑。     

Oxygen uptake through water during early life in Channa punctatus (Bloch) (Pisces; Ophicephaliformes)

Oxygen uptake in relation to body size during the early life of the fish Channa punctatus shows a significant two-component curve: one related to the fully aquatic phase and the other to the bimodal phase of respiration. The onset of the air-breathing habit around the 18–20th day after hatching brings about a 45% drop in O₂ uptake through the gill/skin in water.     

植物对盐分空间不均匀分布的形态和生理响应研究进展

盐胁迫是干旱、半干旱地区以及灌溉土地主要的非生物胁迫,是影响农业生产的主要不利环境因子之一。随集约化灌溉农业的发展、水资源的缺乏、气候干旱带来的蒸发量的增加,土壤及地下水盐渍化程度不断增加。自然界中,土壤盐分在时空上呈不均匀分布。关于植物对均匀盐胁迫的响应研究报到较多,然而植物对不均匀盐胁迫的响应研究报道较少。分析了国内外植物适应不均匀盐胁迫的研究案例,从植物地上部分生长、地下部分生长、水分调节、光合作用以及离子调控等方面阐述植物适应盐分不均匀分布的生理机制,并提出展望。     

Copper in plant species in a copper gradient in Catalonia (North East Spain) and their potential for phytoremediation

The accumulation of Cu in roots and shoots of 32 plant species growing on soils with a wide range of Cu concentrations (30–18 500 g g^–1 total soil Cu) located in Collserola Mountain (Barcelona, Spain) was analysed. High Cu availability decreased the species diversity in the Hyparrhenietum hirto-pubescentis, the natural plant association at the study sites. Shoot and root Cu concentrations in relation to extractable soil Cu concentrations were used for the evaluation of the Cu resistance strategy in the different species. Saturation of Cu accumulation in roots was observed in most species. Hyparrhenia hirta was the most efficient shoot excluder, while the linear increase of shoot Cu with the Cu soil concentration exhibited the highest slope in Hirschfeldia incana. Most species accumulated more Cu in roots than in shoots. High shoot/root Cu ratios were only found in the highly Cu-resistant Hirschfeldia incana, in the resistant or moderately resistant Spartium junceum and Reseda sp. (R. lutea and R. phyteuma), and in the much less resistant Ononis natrix. Only two species, Hirschfeldia incana and Sedum sediforme were able to support the extreme Cu-toxicity conditions on soils with 5000–16 800 g g^–1 extractable Cu. Among the grass species tested Hyparrhenia hirta was the most Cu-resistant species (up to 1950 g g^–1 extractable soil Cu). The potential usefulness of these pseudometallophytes for phytoremediation of Cu-contaminated soils is discussed.     

Selenium supplementation of infant formula: uptake and retention of various forms of selenium in suckling rats

Formula-fed infants often have lower serum selenium levels than breast-fed infants. Although no deleterious effects have been correlated to this finding, supplementation of formula with selenium is considered. In this study, we investigated the uptake and retention by suckling rat pups of ⁷⁵Se from selenite, selenate, and selenomethionine added to infant formula. The molecular distribution of ⁷⁵Se in liver, kidney, intestine, and plasma was followed by gel-filtration chromatography on Superose 12. ⁷⁵Se-uptake was most rapid from selenomethionine (70% at 1 hr), followed by selenate (51%) and selenite (29%). This difference was explained by a higher retention of ⁷⁵Se in the stomach and small intestinal wall of pups given selenite supplement. Plasma distribution of ⁷⁵Se as studied by gel filtration was also different, with a higher proportion of ⁷⁵Se from selenomethionine being protein-bound than from selenite or selenate. Similarly, a larger proportion of ⁷⁵Se from selenomethionine became protein-bound in the liver than from selenite or selenate. In conclusion, although whole body retention after 24–48 hr was similar, the metabolic fate of selenium varies considerably with the form of selenium added to formula. Further studies are needed to study the long-term consequences of selenium accumulated in different body compartments.