Biogeochemistry of the Human Environment.- The Biosphere.- Soils.- Waters.- Air.- Plants.- Humans.- Biogeochemistry of Trace Elements.- Trace Elements of Group 1 (Previously Group Ia).- Trace Elements of Group 2 (Previously Group IIa).- Trace Elements of Group 3 (Previously Group IIIb).- Trace Elements of Group 4 (Previously Group IVb).- Trace Elements of Group 5 (Previously Group Vb).- Trace Elements of Group 6 (Previously Group VIb).- Trace Elements of Group 7 (Previously Group VIIb).- Trace Elements of Group 8 (Previously Part of Group VIII).- Trace Elements of Group 9 (Previously Part of Group VIII).- Trace Elements of Group 10 (Previously Part of Group VIII).- Trace Elements of Group 11 (Previously Group Ib).- Trace Elements of Group 12 (Previously Group IIb).- Trace Elements of Group 13 (Previously Group IIIa).- Trace Elements of Group 14 (Previously Group IVa).- Trace Elements of Group 15 (Previously Group Va).- Trace Elements of Group 16 (Previously Group VIa).- Trace Elements of Group 17 (Previously Group VIIa).

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Trace Elements From Soil to Human

Summary
The diets of over two-thirds of the world's population lack one or more essential mineral elements. This can be remedied through dietary diversification, mineral supplementation, food fortification, or increasing the concentrations and/or bioavailability of mineral elements in produce (biofortification). This article reviews aspects of soil science, plant physiology and genetics underpinning crop biofortification strategies, as well as agronomic and genetic approaches currently taken to biofortify food crops with the mineral elements most commonly lacking in human diets: iron (Fe), zinc (Zn), copper (Cu), calcium (Ca), magnesium (Mg), iodine (I) and selenium (Se). Two complementary approaches have been successfully adopted to increase the concentrations of bioavailable mineral elements in food crops. First, agronomic approaches optimizing the application of mineral fertilizers and/or improving the solubilization and mobilization of mineral elements in the soil have been implemented. Secondly, crops have been developed with: increased abilities to acquire mineral elements and accumulate them in edible tissues; increased concentrations of ‘promoter’ substances, such as ascorbate, β-carotene and cysteine-rich polypeptides which stimulate the absorption of essential mineral elements by the gut; and reduced concentrations of ‘antinutrients’, such as oxalate, polyphenolics or phytate, which interfere with their absorption. These approaches are addressing mineral malnutrition in humans globally.

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Biofortification of crops with seven mineral elements often lacking in human diets--iron, zinc, copper, calcium, magnesium, selenium and iodine.

The contamination of soils and water with metals has created a major environmental problem, leading to considerable losses in plant productivity and hazardous health effects. Exposure to toxic metals can intensify the production of reactive oxygen species (ROS), which are continuously produced in both unstressed and stressed plants cells. Some of the ROS species are highly toxic and must be detoxified by cellular stress responses, if the plant is to survive and grow. The aim of this review is to assess the mode of action and role of antioxidants in protecting plants from stress caused by the presence of heavy metals in the environment.

Making the life of heavy metal-stressed plants a little easier

Biogeochemistry of selenium and its impact on food chain quality and human health

The chemical and physical resemblance between selenium (Se) and sulfur (S) establishes that both these elements share common metabolic pathways in plants. The presence of isologous Se and S compounds indicates that these elements compete in biochemical processes that affect uptake, translocation and assimilation throughout plant development. Yet, minor but crucial differences in reactivity and other metabolic interactions infer that some biochemical processes involving Se may be excluded from those relating to S. This review examines the current understanding of physiological and biochemical relationships between S and Se metabolism by highlighting their similarities and differences in relation to uptake, transport and assimilation pathways as observed in Se hyperaccumulator and non-accumulator plant species. The exploitation of genetic resources used in bioengineering strategies of plants is illuminating the function of sulfate transporters and key enzymes of the S assimilatory pathway in relation to Se accumulation and final metabolic fate. These strategies are providing the basic framework by which to resolve questions relating to the essentiality of Se in plants and the mechanisms utilized by Se hyperaccumulators to circumvent toxicity. In addition, such approaches may assist in the future application of genetically engineered Se accumulating plants for environmental renewal and human health objectives.

Selenium uptake, translocation, assimilation and metabolic fate in plants.

The effect of selenium (Se) treatments on potato growth and Se, soluble sugar, and starch accumulation was investigated. Potato plants were cultivated in quartz sand without or with sodium selenate (0, 0.075, 0.3 mg Se kg(-1) sand). In young potato plants, Se treatment resulted in higher starch concentrations in upper leaves. The tuber yield of Se-treated potato plants was higher and composed of relatively few but large tubers. At harvest, the starch concentration in tubers did not differ significantly between treatments. The higher Se addition (0.3 mg Se kg(-1)) may have delayed the aging of stolons and roots, which was observed as high concentrations of soluble sugar and starch. Together with the earlier results showing elevated starch concentration in Se-treated lettuce, the findings of this research justify the conclusion that Se has positive effects also on potato carbohydrate accumulation and possibly on yield formation.

Effects of Selenium Treatments on Potato (Solanum tuberosum L.) Growth and Concentrations of Soluble Sugars and Starch

Selenium effects on oxidative stress in potato

Effects of Se fertilization on potato processing quality, possible changes in Se concentration and form in tubers during storage, and retransfer of Se from seed tubers were examined. Potato plants were grown at five selenate (SeO4(2-)) concentrations. Tubers were harvested 16 weeks after planting and were stored at 3-4 degrees C prior to analysis. The results showed that the Se concentration did not decrease during storage for 1-12 months. In tubers, 49-65% of total Se was allocated in protein fraction, which is less than found in plant leaves in a previous study. The next-generation tubers produced by the Se-enriched seed tubers had increased Se concentrations, which evidenced the relocation of Se from the seed tubers. At low levels, Se improved the processing quality of potato tubers by diminishing and retarding their raw darkening. The value of Se-enriched potato tubers as a Se source in the human diet was discussed.

Distribution of selenium in different biochemical fractions and raw darkening degree of potato (Solanum tuberosum L.) tubers supplemented with selenate.

Selenate fertilization is an effective way to secure selenium (Se) nutrition in Se-poor areas but the cycling of the added selenate in the soil-plant system requires further clarification. We examined the Se uptake efficiency of wheat and ryegrass and Se distribution within these plants in two pot experiments. The behaviour of added selenate in a sand soil under wheat was monitored by sequential extractions during a ten-week growing period. In addition, the relationship between Se uptake of ryegrass and the salt extractable and ligand exchangeable Se in a sand and silty clay soil were studied. The added selenate remained mainly salt soluble in the soil throughout the monitoring. Se uptake by wheat comprised 12% of the soluble Se pool in soil and extended over the whole period of growth. In wheat, over 50% of Se accumulated in grains. The Se uptake of ryegrass comprised, on average, 40% of the soil salt soluble Se. In ryegrass, over 80% of the Se accumulated in roots. The distribution pattern of Se in plants can clearly have a major influence on both the Se cycle in soil and the nutritional efficiency of Se fertilization. The simple salt extraction showed fertilization-induced changes in the soluble soil Se pool, whereas the ligand exchangeable Se fraction reflected the difference in the nonlabile Se status between the two soils.

Plant availability of soil selenate additions and selenium distribution within wheat and ryegrass

Winter turnip rape (Brassica rapa spp. oleifera) is an underutilized crop that deserves to be revitalized for use in high-latitude agriculture. Many crop rotations around the world are dependent on the small-grain cereals, and turnip rape as a break crop, with its range of secondary chemicals, helps to suppress weeds, nematodes and pathogenic fungi. It may be used as an energy crop, it can restrict erosion and nutrient leaching while also improving soil structure and fertility, and it requires relatively low inputs. Although winter turnip rape was once the major oil crop in Finland, in the 1970s it was replaced by spring turnip rape, the lower erucic acid and glucosinolate contents of which made it suitable for food and feed uses. Winter hardiness of the crop could be improved, and industrial end uses, such as lubricants for which high erucic acid content is preferred, targeted in the first instance. Breeding progress would be accelerated by a change from the predominantly self-incompatible breed...

https://www.tandfonline.com/doi/pdf/10.1080/09064711003747470

Marja Turakainen

Papers

Effects of Selenium Treatments on Potato (Solanum tuberosum L.) Growth and Concentrations of Soluble Sugars and Starch

Selenium effects on oxidative stress in potato

Distribution of selenium in different biochemical fractions and raw darkening degree of potato (Solanum tuberosum L.) tubers supplemented with selenate.

Plant availability of soil selenate additions and selenium distribution within wheat and ryegrass

Revitalizing the winter turnip rape crop in the northern latitudes