Role of selenium in mitigation of cadmium toxicity in pepper grown in hydroponic condition

Selenium (Se) is an essential element for humans but is not considered as essential for plants. However, its beneficial role in improving plant growth and stress tolerances is well established. In order to study the role of Se in cadmium (Cd) toxicity in pepper (Capsicum frutescens cv. Suryankhi Cluster), this experiment was carried out in greenhouse conditions. Treatments comprised Cd [0, 0.25, and 0.5 mM cadmium chloride (CdCl₂)] and Se [0, 3, and 7 µM sodium selenite (Na₂SeO₃)] with three replications. The result showed that Cd decreased chlorophyll a, chlorophyll b, and carotenoids, whereas Se supplementation diminished Cd toxicity on photosynthetic pigment. Selenium at 7 µM significantly increased the leaf area in the plants grown at 0.25 mM Cd. The application of Se at 3 µM with 0.25 mM Cd and Se at 3 µM and Se at 7 µM with 0.5 mM Cd increased the activity of catalase (CAT). Selenium at 7 µM decreased the proline content of pepper leaves exposed to Cd at 0.5 mM (30%). Selenium significantly enhanced the antioxidant activity of leaves, which was diminished by Cd toxicity. In general, Se has a beneficial effect on plant growth and is an antioxidant enzyme of pepper cv. Suryankhi Cluster under Cd stress and non-stress conditions.     

Selenium uptake response among selected wheat (Triticum aestivum) varieties and relationship with soil selenium fractions

Some South Dakota soils contain high levels of available selenium (Se) for crop uptake. A field study was conducted to determine if any popular wheat (Triticum aestivum) varieties demonstrate differential Se uptake. A total of 280 samples including eight winter wheat and ten spring wheat varieties were analyzed for grain Se concentration and uptake for two growing years. Soil samples were sequentially fractionated into (1) plant available (0.1?M KH₂PO₄ extractable) and (2) conditionally available (4?M HCl extractable) pools and analyzed separately for total Se. Selenium concentration in wheat grain had a wide variability and the mean value over two years was 0.63?µg?Se?g^?1. Grain Se concentration and Se uptake were not significantly different by wheat varieties tested in this study. Grain Se concentration was significantly correlated with soil Se levels, soil pH, and orthophosphate-P content within a location, but grain Se concentration was strongly influenced by geographical location in which different amounts of soil Se bioavailability occurred.     

Influence of Selenium on Cadmium Toxicity in Cucumber (Cucumis sativus cv. 4200) at an Early Growth Stage in a Hydroponic System

An experiment was established to assess the ability of selenium (Se) to reduce cadmium (Cd) toxicity when tomato was grown hydroponically. A factorial experiment was arranged in a completely randomized design with six replicates in cucumber (Cucumis sativus cv. 4200). The Se was applied at four levels [0 mg L^–1 (Se0), 2 mg L^–1 Se (Se1), 4 mg L^–1 Se (Se2), and 6 mg L^–1 Se (Se3)], whereas Cd was applied at three levels [0 µM Cd (Cd0), 5 µM Cd (Cd1), and 7 µM Cd (Cd2)]. The Se improved the dry weight of roots even when plants were exposed to Cd. Treatment Se1 improved the dry weight of shoots in Cd1 and Cd2. Treatments Se1 and Se2 improved photosynthesis in Cd1. Treatment Se1 significantly improved stomatal conductance in Cd2 at all levels of Se relative to Cd2. The greatest Cd concentration in leaves was observed in Cd2 × Se0 and while Se concentration in solution increased in response to Se1, Se2, and Se3. The greatest Se level reduced Cd uptake the most. Growth and photosynthetic attributes can be negatively affected by Cd, but Se has the ability to buffer, or improve, several attributes.     

Effects of selenium on some morphological and physiological traits of tomato plants grown under hydroponic condition

A hydroponic experiment was conducted based on completely randomized design (CRD) to study the effects of Selenium (Se) on tomato (Lycopersicum esculentum L), cv. Foria with three replications. Treatments included 3, 5, 7, and 10 µM sodium selenite (Na₂SeO₃) and 0 as control. The results showed that selenium (Se) at 7 µM was beneficial to photosynthesis pigments. The highest relative water content was resulted from the 3 µM Se treatment. The membrane stability index was decreased with increasing Se concentration up to 10 µM Se. An increase in peroxidase (POD) activity occurred at the 3 µM Se level, and the catalase (CAT) activity was 80% higher than the control at the 7 µM Se level. In general, the highest root volume, leaf numbers, carotenoids content, and CAT activity were found at the 5 µM Se level, and Chlorophyll content increased at the 7 and 10 µM Se levels.     

The effect of nickel supply on bulb yield,urease and glutamine synthetase activity and concentrations of urea,amino acids and nitrogen of urea-fed onion plants

The role of nickel (Ni) on urea metabolism of certain plants has been documented, but little is known regarding the growth and physiological response of onion to Ni nutrition, particularly when urea is used as nitrogen source. In this research study, we investigated the effects of Ni on urea metabolism and growth of two onion cultivars (Allium cepa L., cvs. Dorrcheh and Cebolla Valenciana) supplied with urea as nitrogen source. Three levels of Ni (0, 25, and 50 µM) were used in the form of NiCl₂ or Ni-histidine [Ni(His)₂] complex. Addition of Ni positively affected nitrogen metabolism in onion plants fed with urea and thus was correlated with increase of the bulb yield. Regardless of the plant cultivar and the applied Ni source [NiCl₂ or Ni(His)₂ complex], an increase in urease activity and reduction in bulb urea concentration was observed by Ni nutrition. An increase in hydrolysis of urea and production of NH₄⁺ in the presence of Ni was correlated with higher concentration of the total amino acids (AAs) and nitrogen in onion bulbs. The efficiency of Ni(His)₂ complex in improving Ni uptake and increasing activity of urease and glutamine synthetase, two enzymes involved in urea metabolism, was in general greater than NiCl₂. Accordingly, higher concentration of AAs was measured in the onion plants supplied with Ni(His)₂ complex than those supplied with NiCl₂.     

Relationship between Selenium and Sulfur Assimilation and Resultant Interaction on Quality Parameters in Onion

The relationship between selenium (Se) and sulfur (S) uptake and their interaction on the pungency and quercetin contents of onion was investigated in a sand culture trial under polyhouse conditions. The results indicated that application of Se with increasing rates produced an antagonistic effect on S assimilation. An amount of 20 kg Se ha^–1 drastically reduced the S content in onion bulbs. Further, the pungency and quercetin concentration also declined. Foliar application of Se at 1.0 ppm resulted in production of bulbs with lower levels of pungency and quercetin. Though Se is essential from a health point, its application up to 10 kg ha^–1 was sufficient for enriching onions without much effect on the other essential bulb quality parameters.     

Biofortification of wheat cultivars with selenium

ABSTRACT

Biofortification experiments with three winter wheat cultivars treated with sodium selenate through foliar- and soil-fertilisation were conducted at two locations in Croatia and Serbia in two consecutive years to increase the selenium (Se) concentration in bread-making wheat grain. The treatments were: (a) 5?g?ha^?1 Se foliar-, (b) 10?g?ha^?1 Se foliar- and (c) 10?g?ha^?1 Se in soil surface-application and they were compared with (d) control. Both Se foliar- and soil-fertilisation increased the Se concentration in grains from 2.6- to 4.6-fold. The concentration in grain was highest with Se foliar-fertilisation of 10?g?ha^?1 and it was increased by 29–32?µg Se kg^?1 dry weight for each gram of Se applied per ha. The wheat cultivars differed in grain yield and Se uptake (g?ha^?1 Se). However, on average, there were no differences between wheat cultivars with respect to Se grain concentrations. Agronomic use efficiency (by grain) was significantly higher for Se foliar- (19%) than for soil-fertilisation (13%). It can be concluded that agronomic biofortification of winter wheat can be effective in increasing Se grain concentration, where the efficiency depends on the rate of Se applied, application method and local environmental conditions rather than on cultivar differences.     

Uptake and remobilization of selenium in Brassica napus L. plants supplied with selenate or selenium‐enriched plant residues

Selenium (Se) biofortification via crops is one of the best strategies to elevate the daily Se intake in areas where soil Se levels are low. However, Se fertilizer recovery (SeFR) is low and most of the Se taken up accumulates in non‐harvested plant parts and returns to the soil with plant residues. A pot experiment with soil was undertaken to study the efficiency of inorganic Se (Na₂SeO₄) and Se‐enriched plant residues for biofortification, as well as to identify the bottlenecks in Se utilization by Brassica napus L. The soil was fertilized with Na₂SeO₄ (0 and 7 µg Se kg^?1) or with Se in stem or leaf residues (0 and 7 µg Se kg^?1). A treatment with autoclaved soil was included (0 and 7 µg kg^?1 as Na₂SeO₄) to unravel the impact of microbial activity on Se uptake. The Se‐enriched plant residues produced a lower Se uptake efficiency (SeUPE) and SeFR than did inorganic Se, and soil autoclaving enhanced Se accumulation in the plants. The time required for decomposition seems to preclude crop residues as an alternative source of Se. Furthermore, B. napus had a limited capacity to accumulate Se in seeds. The study shows that the bottlenecks in Se biofortification appear to be its low bioavailability in soil and poor loading from the silique walls to seeds. Thus, improved Se translocation to seeds would be a useful breeding goal in B. napus to increase SeFR.     

Ameliorative effect of selenium on tomato plants grown under salinity stress

The ability of selenium (Se) to counteract salt inhibitory effects in crop plants, especially in tomato, is still poorly documented. In order to examine the impact of Se addition on the growth, some biochemical parameters related to osmotic adjustment and antioxidant defense of salt-stressed tomato, a two-factorial experiment was conducted in a greenhouse. The plants were supplied with NaCl (0, 25, or 50 mM) and Se (0, 5, or 10 μM), individually or simultaneously. The results showed that salinity had a deleterious impact on plant biomass and physiological parameters studied. The application of Se alleviated this adverse effect by improving the integrity of cell membranes and by increasing leaf relative water content under stress conditions. Moreover, the application of 10 μM Se significantly increased the photosynthetic pigments concentration under salt stress. Salt stress also caused an inhibition of catalase activity, but its activity was restored in the presence of Se. The free radical scavenging activity significantly increased in plants subjected to 25 mM NaCl and supplied with 5 µM Se, compared to NaCl-alone treatment. Both physiological and biochemical results indicate that 10 µM Se treatment can increase plant performance under salt stress, especially under high NaCl concentration.

Abbreviations: CAT: catalase; Chl: chlorophyll; DPPH: 2,2-diphenyl-1-picrylhydrazyl; DW: dry weight; FW: fresh weight; POD: peroxidase; REL: relative electrolyte leakage; RWC: relative water content; free radical scavenging activity (FRSA); TW: turgid weight     

The impact of selenium application on enzymatic and non-enzymatic antioxidant systems in Zea mays roots treated with combined osmotic and heat stress

Selenium (Se), regarded as an antioxidant, has been found beneficial for plants growing under stressed conditions. To investigate whether the Se application helps to improve stress tolerance, sodium selenite (Na₂SeO₃ · 5H₂O, 5–15 μM) was hydroponically applied to Zea mays variety OSSK-713-roots under heat and/or PEG-induced osmotic stress (25% PEG-6000) for 8 h. The individual/combined stress caused accumulation of reactive oxygen species (ROS). While only superoxide dismutase (SOD) increased with heat stress alone, the activities of SOD, catalase (CAT) and ascorbate peroxidase (APX) increased under PEG exposure. The combination of these stresses resulted in an induction of both SOD and CAT activities. Lipid peroxidation (TBARS) levels were also high in all the stress treatments, especially under the combination treatment. Addition of Se not only improved the activities of SOD, APX and glutathione reductase (GR) in stress-treated roots, but it also changed the activities of monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR). The findings reveal that Se has a positive effect on heat and/or osmotic stress mitigation mainly by regulating the ascorbate-glutathione cycle, especially in PEG-treated plants. Under the combined stress treatment, addition of 5 µM of exogenous Se was most effective.