Rates of Selenium Volatilization among Crop Species (original) (raw)
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Agricultural and Food Science, 2008
The effect of Selenium (Se) supplementation at five levels of 0 (control), 5, 10, 15, 20 ìM in plants supplied with one of four concentrations of sulphur (S) including 0.05, 0.25, 0.5 and 1.0 mM was investigated in two varieties of Brassica oleracea (cabbage and kohlrabi) and alfalfa (Medicago sativa L.) in a hydroponic experiment. In severely S deficient plants (0.05 mM), Se acted as a toxic element, alfalfa was the most susceptible plant that died at this treatment. However, in plants supplied with near adequate (0.5 mM) or adequate (1.0 mM) S, Se acted as a growth promoting element. The most pronounced stimulation of growth was observed in cabbage and the lowest in alfalfa. Increasing S concentration in the medium, reduced Se uptake and transport. In contrast, S uptake and transport increased in response to Se addition. Se volatilization was higher in alfalfa than cabbage and kohlrabi when expressed on unit shoot dry weight or leaf area basis, but not when expressed per plant. Re...
Journal of Plant Nutrition, 2014
The effects of selenium (Se) (VI) soil fertilization with 2 μg Se L −1 or foliar spraying twice with 20 mg Se L −1 in the form of sodium (Na) selenate on the physiological and biochemical characteristics of cabbage plants were studied. The ability of the plants to take up Se and translocate it to different parts of the plants was also studied. Despite the high concentration of Se in the foliar solution, there was no effect on photosynthesis, transpiration rate, photochemical efficiency of PSII, or electron transport system activity. The amount of chlorophyll and antocyanins were unchanged. At harvest, the concentration of Se in control plants was lower than 100 ng Se g −1 dry weight (DW), while plants treated with 20 mg Se L −1 contained 5500 ng Se g −1. Selenium enriched cabbage could be used in human nutrition. The tolerance of cabbage to Se could be explained by the formation of insoluble compounds that are not available for the plant.
Frontiers of Agriculture in China, 2009
A greenhouse experiment was conducted to study the accumulation of selenium by some vegetable crops commonly grown in the Indian Punjab. Eleven vegetable crops were raised in an alkaline clay loam soil treated with different levels of selenate-Se, i.e., 0, 1.25, 2.5 and 5.0 mg·kg−1 soil. Dry matter yield of both edible and inedible portions of different vegetable crops decreased with increasing Se level in soil except potato (Solanum tuberosum), radish (Raphanus sativus) and cauliflower (Brassica oleracea var. botrytis) which recorded 10%–21% increase in inedible dry matter at 1.25 mg·kg−1 Se soil. Application of 5 mg·kg−1 selenate-Se soil resulted in complete mortality in the case of radish, turnip (Brassica rapa) and brinjal (Solanum melongena). Some vegetable crops including tomato (Lycopersicum esculentum), cauliflower and pea (Pisum sativum), though, survived the toxic effect at the highest concentration of Se yet did not bear any fruit. Potato and spinach (Spinacea oleracea) proved to be highly tolerant crops. Selenium concentration in the edible as well as inedible portions of all the vegetables increased with an increase in the level of applied Se. Selenium accumulation in the edible portion of vegetable crops in the no-Se control ranged from 2.2 to 4.9 mg·kg−1 Se dry weight. At 1.25 mg·kg−1 Se soil, the edible portion of radish accumulated the greatest concentration of Se (38 mg·kg−1 Se dry weight) with that of onion (Allium cepa) bulb the lowest (9 mg·kg−1 Se dry weight). Inedible portions of vegetables accumulated Se 2–5 times more than that absorbed by edible portions. Total Se uptake by edible portions of different vegetables was the greatest at 1.25 mg·kg−1 Se soil, ranging from 7 to 485 μg·pot−1. The results suggest that vegetable crops vary in their sensitivity to the presence of selenate-Se in soil. Vegetative portions were several times richer in Se than other parts of vegetable crops.
Rate-limiting steps in selenium assimilation and volatilization by Indian mustard
Plant …, 1998
To determine the rate-limiting steps in Se volatilization from selenate and selenite, time-and concentration-dependent kinetics of Se accumulation and volatilization were studied in Indian mustard (Brassica juncea). Time-dependent kinetic studies showed that selenate was taken up 2-fold faster than selenite. Selenate was rapidly translocated to the shoot, away from the root, the site of volatilization, whereas only approximately 10% of the selenite was translocated. For both selenate-and selenite-supplied plants, Se accumulation and volatilization increased linearly with external Se concentration up to 20 M; volatilization rates were also linearly correlated with root Se concentrations. Se-volatilization rates were 2-to 3-fold higher from plants supplied with selenite compared with selenate. Se speciation by x-ray absorption spectroscopy revealed that selenite-supplied plants accumulated organic Se, most likely selenomethionine, whereas selenate-supplied plants accumulated selenate. Our data suggest that Se volatilization from selenate is limited by the rate of selenate reduction, as well as by the availability of Se in roots, as influenced by uptake and translocation. Se volatilization from selenite may be limited by selenite uptake and by the conversion of selenomethionine to dimethylselenide.
Annual Review of Plant Physiology and Plant Molecular Biology, 2000
Plants vary considerably in their physiological response to selenium (Se). Some plant species growing on seleniferous soils are Se tolerant and accumulate very high concentrations of Se (Se accumulators), but most plants are Se nonaccumulators and are Se-sensitive. This review summarizes knowledge of the physiology and biochemistry of both types of plants, particularly with regard to Se uptake and transport, biochemical pathways of assimilation, volatilization and incorporation into proteins, and mechanisms of toxicity and tolerance. Molecular approaches are providing new insights into the role of sulfate transporters and sulfur assimilation enzymes in selenate uptake and metabolism, as well as the question of Se essentiality in plants. Recent advances in our understanding of the plant's ability to metabolize Se into volatile Se forms (phytovolatilization) are discussed, along with the application of phytoremediation for the cleanup of Se contaminated environments.
Plant and Soil, 2005
Critical levels of selenium in raya (Brassica juncea Czern L.), maize (Zea mays L.), wheat (Triticum aestivum L.) and rice (Oryza sativa L.) were worked out by growing these crops in an alkaline silty loam soil treated with different levels of selenite-Se ranging from 1 to 25 lg g )1 soil. Significant decrease in dry matter yield was observed above a level of 5 lg Se g )1 soil in raya and maize; 4 lg Se g )1 soil in wheat and 10 lg Se g )1 soil in rice shoots. The critical level of Se in plants above which significant decrease in yield would occur was found to be 104.8 lg g )1 in raya, 76.9 lg g )1 in maize, 41.5 lg g )1 in rice and 18.9 lg g )1 in wheat shoots. Significant coefficients of correlation were observed between Se content above the critical level and dry matter yield of raya as well as rice (r = )0.99, P £ 0.01), wheat (r = )0.97, P £ 0.01) and maize ((r = )0.96, P £ 0.01). A synergistic relationship was observed between S and Se content of raya (r = 0.96, P £ 0.01), wheat (r = 0.89, P £ 0.01), rice (r = 0.85, P £ 0.01) and maize (r = 0.84, P £ 0.01). Raya, maize and rice absorbed Se in levels toxic for animal consumption (i.e. >5 mg Se kg )1 ) when the soil was treated with more than 1.5 lg Se g )1 . In case of wheat, application of Se more than 3 lg g )1 soil resulted in production of toxic plants.
The plants grown in seleniferous soils constitute a major source of toxic selenium levels in the food chain of animals and human beings. Greenhouse and field experiments were conducted to study selenium concentrations of weeds, forages and cereals grown on seleniferous soils located between 31.0417°to 31.2175°N and 76.1363°to 76.4147°E in northwestern India. Eleven winter season (November-April) weed plants were grown in the greenhouse in a soil treated with different levels of selenate-Se. Selenium concentrations of weed plants increased progressively with the levels of selenate-Se in soil. The highest Se concentration was recorded by Silene gallica (246 mgkg − 1 ) and the lowest by Avena ludoviciana (47 mgkg − 1 ) at 2.5 mg Sekg − 1 soil. A. ludoviciana and Spergula arvensis proved highly tolerant to the presence of 1.25 and 2.5 mg selenate-Sekg − 1 soil and the remaining weeds were sensitive to Se. Dry matter yield of Se-sensitive weed plants was 25 to 62% of the yield in the no-Se control at 1.25 mg selenate-Sekg − 1 and 6 to 40% at 2.5 mg selenate-Se kg − 1 soil. Other symptoms like change in leaf colour and size, burning of leaf tips and margins, and delayed flowering were also observed due to Se. Dry matter yield of Se-sensitive weed plants expressed as percentage of yield in the no-Se control at both the Se levels was inversely correlated with their Se content (r = −0.731, p b 0.01, N = 17). Among the weed plants grown in seleniferous soils under field situations, Mentha longifolia accumulated the highest Se (365 mgkg − 1 ) and Phalaris minor the lowest (34 mgkg − 1 ). Among agricultural crops grown on a naturally contaminated soil in the greenhouse, Se concentrations were the highest for oilseed crops (19-29 mg kg − 1 ), followed by legumes (6-13 mg kg − 1 ) and cereals (2-18 mg kg − 1 ). Helianthus annuus among the oilseed crops, A. ludoviciana among the winter season weeds, M. longifolia among the summer season (May-October) weeds and Cirsium arvense among the perennial weeds can be used for phytoremediation of seleniferous soils as these accumulate the highest amounts of Se.
Selenium in the Soil-Plant Environment: A Review
International Journal of Applied Agricultural Sciences
Selenium (Se) exhibits a "double-edged" behavior in animal and human nutrition. It is a micronutrient required in low concentrations by animals and humans, but toxic at high concentrations. Selenium deficiency has been associated with cancer and other health problems. Selenium requirements are commonly met through soils and plants such as wheat, rice, vegetables and maize in many countries. Selenium concentration in the soil generally ranges from 0.01-2.0 mg kg-1 but seleniferous soils usually contain more than 5 mg kg-1. Seleniferous soils have been reported in Ireland, China, India and USA. Weathering of parent rocks and atmospheric deposition of volcanic plumes are natural processes increasing Se levels in the environment. Anthropogenic sources of Se include irrigation, fertilizer use, sewage sludge and farmyard manure applications, coal combustion and crude oil processing, mining, smelting and waste incineration. Mobility of Se in the soil-plant system largely depends on its speciation and bioavailability in soil which is controlled by pH and redox potential. Plant uptake of Se varies with plant species and Se bioavailability in the soil. The uptake, translocation, transformation, metabolism, and functions of Se within the plant are further discussed in the paper. The release of Se in soils and subsequent uptake by plants has implications for meeting Se requirements in animals and humans.
Selenium and agricultural crops
African Journal of Agricultural Research, 2017
Higher plants have different capacities to accumulate and tolerate selenium, referred to as accumulative and non-accumulative plants. Selenium-accumulators plants may contain hundreds of times more selenium than non-accumulators even when grown in the same soil, or can also grow in soils with low and medium selenium reserves; while selenium non-accumulator plants present low accumulation and tolerance to high selenium levels in the culture medium. Several studies have demonstrated the protective role of selenium in relation to oxidative stress in plants. Depending on the dose used, Se can activate certain enzymes such as superoxide dismutase, glutathione reductase and glutathione peroxidase. These enzymes are activated in the presence of Se, reducing the rate of lipid peroxidation and formation of hydrogen peroxide in plant tissue cells, which results in reduced senescence. Symptoms of selenium toxicity include reduced growth, chlorosis of leaves and pink coloration of the roots, yellowing of leaves and black spots. Studies provide evidence on a beneficial role of Se in plants and for environmental phytoremediation. However more research is needed to consolidate the beneficial effects of Se in plants.