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.     

Photosynthetic Response of Maize Plants Against Cadmium and Paraquat Impact

The effects of cadmium (Cd) and/or paraquat (PQ) toxicity on photosynthesis in maize leaves were examined by measurement of gas exchange and chlorophyll content in hydroponically cultured plants. It was found that growth rate was distinctly influenced only by 100 µM Cd treatment. Chlorophyll a and chlorophyll b decreased along with the increase of Cd concentration, while PQ spraying, alone and combined with Cd, increased chlorophyll a content on the third and seventh experimental days. Generally, carotenoid content increased in response to Cd and PQ and reached the highest levels at 100 µM Cd. Rate of photosynthesis in maize decreased after Cd treatment. CO₂ assimilation was approximately 60% reduced at 50 µM Cd and 70% reduced in the presence of 100 µM Cd. PQ toxicity was partly overcome after the third day of exposure. Transpiration and stomatal conductance in maize leaves decreased on the third day along with Cd concentration and PQ spraying, except for the 25-µM Cd-treated plants. On the tenth day, the 25-µM Cd-treated plants and those from PQ-treated variants showed an increase of transpiration and stomatal conductance. Maize exhibited an ability to accumulate Cd in high quantities, especially in the roots—over 4,500 mg Cd/kg dry weight.     

Root zone selenium reduces cadmium toxicity by modulating tissue-specific growth and metabolism in maize (Zea mays L.)

The effects of selenium (Se) cadmium (Cd) interactions on plant growth and metabolism are not fully clear. In the present study, we assessed whether Se could alleviate the toxic effects of Cd on growth and metabolism of maize. Seeds of maize variety FH-985 were sown in pots filled with sand treated with CdCl₂ (0, 50 and 100 µM) and Se (0, 2 and 4 mg L^?1) through Hoagland’s nutrient solution. Low Se (2 mg L^?1) increased germination percentage and rate, while high Se (4 mg L^?1) increased fresh and dry biomass under Cd stress. Interestingly, all Se concentrations were effective in alleviating the toxic effects of Cd on photosynthetic pigments, whereas higher Se mitigated the Cd-induced oxidative stress and increased flavonoids both in the shoots and roots while phenolics in the roots. The results demonstrated that root zone Se altered tissue-specific primary metabolism in maize. Furthermore, low Se mitigated the Cd-induced decrease in total proteins in the root. Overall, Se-mediated decrease in the oxidative stress in the shoots while increase of secondary metabolites in the roots helped the plants to grow faster at early growth stage and caused increase in the biomass under different Cd regimes.     

Silicon‐induced cadmium resistance in rice (Oryza sativa)

Silicon (Si)‐induced cadmium (Cd) tolerance in rice (Oryza sativa L.) was investigated by analyzing Cd uptake, growth, and physiological parameters. Silicon treatments (0.0, 0.2, or 0.6 mM) were added to 6 d–old seedlings, and Cd treatments (0.0 or 5.0 μM) were added to 20 d–old seedlings. Parameters determined included: maximum net CO₂ assimilation (A_max), stomatal conductance (g_smax), and transpiration (E_max) rates at varying intercellular CO₂ concentrations (C_i). Also measured were chlorophyll fluorescence, growth, and Cd‐uptake parameters. Results showed a Si‐induced inhibition of Cd uptake. However, 0.2 mM or 0.6 mM Si treatment concentrations did not differentially inhibit Cd uptake or differentially alleviate Cd‐induced growth inhibition, despite a significant increase in tissue Si concentration due to 0.6 mM Si treatment compared to 0.2 mM Si treatment. Additionally, photosynthesis and chlorophyll‐fluorescence analysis showed that treatment with Cd significantly inhibited photosynthetic efficiency. Interestingly, the addition of 0.2 mM Si, more so than the addition of 0.6 mM Si, significantly alleviated the inhibitory effects of Cd toxicity on photosynthesis and chlorophyll‐fluorescence parameters. Our results suggest that 0.2 mM Si could be close to an optimum Si‐dose requirement for the alleviation of toxicity symptoms mediated by moderate (5 μM) Cd exposure.     

Uptake and Translocation of Copper in Brassicaceae

Abstract

Ten cvs. of four Brassicaceae species were tested to evaluate their copper (Cu) uptake and translocation. Germination and root length tests indicated that Brassica juncea cv. Aurea and Raphanus sativus cvs. Rimbo and Saxa were the species with the highest germinability and longest roots at Cu concentrations ranging from 25 up to 200 µM. Raphanus sativus cv. Rimbo grown in hydroponic culture at increasing Cu concentrations (from 0.12 up to 40 µM) for 10 days produced a relatively high biomass (17.2 mg plant^?1) at the highest concentration and had a more efficient Cu translocation (17.8%) in comparison with cvs. Aurea and Saxa. The potential of cv. Rimbo for Cu uptake was then followed for 28 days at 5, 10, and 15 µM Cu. In comparison with the control, after 28 days of growth the 15 µM Cu‐treated plants showed a reduction in the tolerance index (?40%) and in the above‐ground dry biomass (?19%). On the contrary, an increase in the below‐ground dry weight was observed (+35%). Copper accumulated during the growth period both in the below‐ and above‐ground parts (about 14 and 4 µg plant^?1 at 10 and 15 µM Cu, respectively), but the translocation decreased from 50 to 30% in the last week at all the concentrations used. In addition, cv. Rimbo grown in a multiple element [cadmium (Cd), chromium (Cr), Cu, lead (Pb), and zinc (Zn)] naturally‐contaminated site accumulated all elements in the above‐ground part in a range from 5 to 62 µg plant^?1.     

The Effect of Cadmium Toxicity and Silicon Supplementation on the Activity of Antioxidative Enzymes and the Concentration of Zinc and Iron in Hydroponically Grown Cucumber

Two cucumber cultivars (Cucumis sativus L.) exposed to three cadmium (Cd) concentrations (0, 1, and 5 μM) were supplemented or un-supplemented with silicon (Si) (1 mM). Exposure to 1 μM Cd had no effect on shoot and root dry mass, whereas exposure to 5 μM Cd significantly reduced plant growth. Addition of Si stimulated the growth of Cd-treated cucumber. Exposure to 5 μM Cd significantly increased shoot Cd concentration and decreased iron (Fe) and zinc (Zn) concentration. Plants supplied with Si had lower Cd and higher Zn and Fe compared with unsupplied plants. Exposure to Cd resulted in a higher production of malondialdehyde (MDA). Si nutrition partly ameliorated lipid peroxidation induced by Cd toxicity. Activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX), and catalase (CAT) decreased, whereas ascorbate peroxidase (APX) activity increased in response to 5 μM Cd. Induction of APX activity might play an important role in the response of cucumber to Cd toxicity.     

硒镉交互作用对西葫芦幼苗生长及抗氧化酶活性的影响

硒能够缓解镉胁迫对植物产生的毒害。为探明硒(Se)和镉(Cd)交互作用对植物的影响,本研究以西葫芦为材料,采用沙培的方式,研究了不同浓度Se(0.5、2.0和4.0 mg·L^-1)与Cd(0.2、0.4和0.6 mg·kg^-1)交互作用对西葫芦幼苗生长和抗氧化酶活性的影响。结果表明,单一Cd胁迫下,随着Cd浓度的增加,其对西葫芦幼苗的生长和抗氧化酶活性具有一定的促进作用。Se与Cd交互作用对西葫芦幼苗生长和抗氧化酶活性的影响与Se和Cd的浓度有关。不同浓度Se与低中浓度Cd(0.2和0.4 mg·kg^-1)交互作用可使Cd胁迫下西葫芦幼苗苗高、鲜重和干重显著增加,与高浓度Cd(0.6 mg·kg^-1)交互作用却抑制了西葫芦幼苗的生长。与单一Cd胁迫相比,不同浓度Se与0.2 mg·kg^-1Cd交互作用可显著提高西葫芦幼苗SOD和POD活性,不同浓度Se与0.4和0.6 mg·kg^-1Cd交互作用抑制了西葫芦幼苗SOD和POD活性,且Cd浓度越高,差异越明显。在高浓度(0.6 mg·kg^-1)Cd胁迫下,Se浓度越高,2种元素的交互作用对西葫芦幼苗生长和抗氧化酶活性产生的抑制作用越大。Cd胁迫下,外源Se可以降低西葫芦幼苗Cd含量,同时提高Se含量。较低浓度的Se能够有效缓解Cd对西葫芦幼苗造成的毒害作用,综合来看,2.0 mg·L^-1Se与Cd的交互作用对西葫芦幼苗的生长和抗氧化酶活性的促进作用最强。本研究表明施加外源Se缓解Cd胁迫对植物的毒害时,应同时考虑Cd的污染程度和施加Se的量,为Cd污染治理提供了一定的参考依据。     

Oxidative stress response in spinach plants induced by cadmium

In this work we studied the effect of cadmium (Cd) (25 μM), in spinach plants (Spinacea oleracea) growing in nutrient solution, for 1, 2 and 7 days. Spinach growing in the contaminated solution showed a decrease in biomass, chlorophyll content and an increase in malondialdehyde (MDA) content, showing that photosynthetic apparatus was affected and lipid peroxidation occurred. The main defence mechanisms against the induced oxidative stress were the activation of catalase, glutathione reductase and guaiacol peroxidase. Glutathione reductase activity suggests that glutathione is involved in the response against Cd toxicity. The uptake of zinc (Zn), potassium (K), iron (Fe) and copper (Cu) was affected, mainly at the higher exposition times. Spinach leaves showed no signs of toxicity and looked healthy although containing up to 35 mg kg^?1 dry weight (DW) of Cd. This can present a food security issue as there is no visible indication of the high amounts of Cd in the edible parts of the plant.     

Effects of sulfur nutrition on photosynthesis in cadmium‐treated barley seedlings

The effects of sulfur (S) nutrition at 0.1 or 1 mM S on cadmium (Cd) toxicity measured by photosynthesis in barley (Hordeum vulgare L. cv. UC 476) seedlings were studied. Eight‐day‐old seedlings were treated with 25 μM Cd by adding cadmium chloride (CdCl₂) to the nutrient solution. Then photosynthetic carboxylation efficiency (ACi curve) and stomatal conductance of the primary and second leaves were measured at four and eight days after Cd treatment. Fluorescence parameters were measured every 24 h for eight days after two days of Cd treatment. At 20 days, plant growth parameters were measured and dry biomass determined. The results showed that ACi was significantly reduced by Cd, but more in the low (0.1 mM) S than in the high (1 mM) S‐treated plants. Stomatal conductance of plants was also decreased by Cd, but more in the low S‐treated plants. Low S‐treated plants exposed to Cd showed an increase in Fo and Fq, and a decrease in Fv/Fm and T_1/2, indicating photoinhibitory damage to PSII. Analysis of the growth parameters showed that Cd decreased plant size and biomass, but the reduction was more severe in the low S‐treated plants. These results support the hypothesis that S is a critical nutritional factor in plants which is important for the reduction of Cd toxicity.     

Differential Tolerance to Lead and Cadmium of Micropropagated <Emphasis Type="Italic">Gypsophila fastigiata</Emphasis> Ecotype

In vitro techniques may provide a suitable tool for effective propagation and conservation of plant species representing various ecological niches. The elaboration of such protocols is also prerequisite for selection of heavy-metal-tolerant plant material that could be afterwards used for restoration or remediation of polluted sites. In this study, culture protocol for Gypsophila fastigiata propagation was developed. The highest multiplication coefficient, which reached 6.5, and the best growth parameters were obtained on modified MS medium supplemented with 1.0 mg L^?1 2iP and 0.2 mg L^?1 IAA. The obtained cultures were treated with different concentrations of lead nitrate (0.1, 0.5, and 1.0 mM Pb(NO₃)₂) or cadmium chloride (0.5, 2.5, and 5.0 μM CdCl₂). The growth parameters, photosynthetic pigments, and phenolic compound content were examined in order to evaluate whether tested metal salts can have an adverse impact on studied culture. It was ascertained that Pb ions induced growth disturbances and contributed to shoot wither. On the contrary, the proliferative shoot cultures were established on media containing Cd ions and the multiplication coefficients and shoot length increased on all media enriched with CdCl₂. Chlorophylls and carotenoid contents were negatively affected by application of 5.0 μM of cadmium; nevertheless, in shoots treated with 2.5 μM CdCl₂, increased accumulation of photosynthetic pigments occurred and their amount was similar to untreated culture. Adaptation to Cd was associated with stimulation of phenolic compound synthesis. Hence, we have reported on unambiguous positive result of in vitro selection procedure to obtain vigorous shoot culture tolerant to cadmium.     

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.     

Evaluation of Toxicity Level of Nickel on Growth,Photosynthetic Efficiency,Antioxidative Enzyme,and Its Accumulation in Cauliflower

A study was conducted to determine the toxicity level of nickel using cauliflower (Brassica oleracea L. var. botrytis) cv. Snowball grown in refined sand with complete nutrient solution for 79 days. At day 80, plants were separated into three lots. One lot was treated as the control (0.0001 mM Ni) while other two lots were supplied with excess nickel (Ni) at 0.1 and 0.5 mM. The toxicity symptoms of Ni appeared as chlorosis of young leaves. No curd was formed at 0.5 mM Ni supply. Excess Ni decreased biomass, chlorophyll, Hill reaction activity, and carbohydrate fraction, and enzyme activities of catalase, peroxidase, and acid phosphatase in leaves. Excess Ni increased concentration of starch, phenol, and nonprotein nitrogen and decreased protein nitrogen in leaves. Increase in Ni supply increased Ni concentration in all parts of cauliflower, whereas the concentration of phosphorus, sulfur, iron, and manganese decreased significantly.     

Foliar application of zinc promotes cadmium absorption by increasing expression of cadmium transporter genes and activities of antioxidative enzymes in winter wheat

Cadmium (Cd) is a deleterious non-essential metal in plants.To elucidate the mechanisms by which zinc (Zn) application alleviates cadmium (Cd)toxicity in wheat,we characterized plant growth,antioxidant system,leaf cell ultrastructure,and Cd transporter gene expression in winter wheat under Cd exposure (50μmol L^-1Cd) with foliar Zn application in a hydroponic experiment.Results showed that Zn addition (Zn+Cd) or pretreatment (pre-Zn+Cd) at 2 g L^-1as Zn SO₄·7H_...     

Effects of Exogenous Glycinebetaine and Trehalose on Cadmium Accumulation and Biological Responses of an Aquatic Plant (Lemna gibba L.)

This study aimed to investigate and compare the effects of exogenous glycinebetaine (GB) and trehalose (TR) on the biological responses of duckweed (Lemna gibba L.) against cadmium (Cd) accumulation. Duckweed samples were exposed to 0.5, 1, and 3 mM of Cd for 6 days in the presence and absence of GB (0.5, 1, 2, and 5 mM) or TR (0.5, 1, 2, and 5 mM). The accumulation of Cd, GB, and TR were investigated, and their influence on the rates of lipid peroxidation, photosynthetic activity, proline content and enzymatic antioxidant performance was examined. Two-way ANOVA showed that exposure to Cd and/or GB or TR caused an increase in Cd accumulation concentration dependently. TR had significant effects on Cd accumulation. The application of 0.5 mM TR increased Cd accumulation, whereas 5 mM decreased Cd accumulation. However, Cd accumulation was not significantly affected by the presence of GB. Cd concentration alone or in combination with GB or TR had a significant effect on lipid peroxidation, photosynthetic activity, proline content, and antioxidant enzyme activities. In addition, statistically significant GB?CCd and TR?CCd interactions were observed. We conclude that both GB and TR play protective roles against Cd stress in aquatic plants. The use of a low level of TR (i.e., 0.5 mM) may be more useful than GB in phytoremediation studies.     

Combined Effect of Short-Term Water Deficit Stress and Aluminum Toxicity on Citrate Secretion from Soybean Roots

Abstract

In order to investigate the combined effect of drought stress and aluminum (Al) toxicity on citrate exudation in soybean, hydroponic cultivation with addition of Al and PEG-6000 was conducted to simulate Al-toxic dry soil. Results showed that 2-day exposure of soybeans to 5.5% (w/v) PEG-6000 or 100 µM AlCl₃ mainly hindered root growth, while combined exposure to PEG and Al (PEG/Al) reduced both root and shoot growth. Photosynthetic rate of first trifoliolate for the Al-tolerant genotype PI 416937 (PI) was not affected by imposition of 5.5% PEG/100 µM AlCl₃ (38–40 h), whereas photosynthetic rate for the Al-sensitive genotype YC was significantly reduced. Based on root fresh weight, Al-induced citrate exudation in the roots of soybean genotypes recovered from pre-treatment with 5.5 or 9% PEG was not altered, but was increased in the plants pretreated with 7% PEG without recovery. After 2 days of recovery from 2-day combined exposure to 5.5% PEG/100 µM AlCl₃, the Al-tolerant PI exuded more citrate than its control, but the Al-sensitive YC exuded significantly less citrate than its corresponding control. Split root experiment revealed that Al-induced citrate exudation in one half of the root system was significantly reduced by exposing the other half of the root system to 0.5 mM CaCl₂ solution containing 9% PEG or 9% PEG/50 µM AlCl₃. However, organic acid secretion was not observed in the half of the root system in the Ca solution when the other part of the root system was exposed to the Ca solution containing 50 µM AlCl₃, 9% PEG or 9% PEG/50 µM AlCl₃. This suggests that no Al- or drought-induced signals such as ABA are involved in the citrate secretion in soybean.     

Selenium in lemon balm plants: Productivity,phytotoxicity and drought alleviation

Since studies on the effects of selenium (Se) supplementation in water-stressed plants have mainly focused on cereal crops, the specific reports regarding Se-mediated adaptation to drought stress in medicinal vegetables are scant. Thus, we investigated the responses of Melissa officinalis to Se supplementation. Selenium contents were increased in leaves and grains by supplemental Se. Selenium foliar application at 1 mg l^?1 could be useful to increase the vegetative and reproductive growth of Se-enriched plants under well-watered conditions but at 20 mg l^?1 led to toxicity and caused damage to shoots. Drought stress significantly inhibited plant growth by chlorophyll degradation and reduced net carbon dioxide (CO₂) assimilation rate. Although Se at 1 mg l^?1 could increase biomass production under well-watered conditions in addition to the stimulation of antioxidant system under water stress, it could not ameliorate the negative effect of drought on productivity.     

Salicylic acid alleviates the toxicity of cadmium on seedling growth,amylases and phosphatases activity in germinating barley seeds

The present study investigated the possible mediator role of salicylic acid (SA) in alleviating cadmium (Cd) toxicity during the germination stage of barley. The exposure of barley seedling to increasing Cd concentrations (25, 50 and 100 µM) during early stages of their establishment, caused a gradual decrease in vigour index, root length, α-amylase, acid phosphatase, alkaline phosphatase activities in endosperms and mitotic index of the root tip. Seed pretreatment with 600 µM SA partially alleviated the negative effects of Cd on germination parameters and increased the hydrolytic enzyme activities and mitotic index. Cadmium treatment increased Cd accumulation in roots. Furthermore, results showed that compared to the cadmium treatment applied alone, SA pretreatment of the seeds did not influenced the Cd concentration in the roots. These results suggest that SA plays a positive role in barley-seed germination and early seedling growth by protecting it against Cd toxicity by moderating its toxic effect on the mobilization of organic reserves.     

Effects of selenium as a beneficial element on growth and photosynthetic attributes of greenhouse cucumber

Selenium (Se) is an essential element for human and livestock with antioxidant and anticancer characteristics. Although Se is not an essential element for plants, it has been reported that it can improve plant growth. This experiment was conducted at the Isfahan University of Technology in winter 2010. The experiment was factorial based on a completely randomized design (CRD) with four replications. Se was added to nutrient solution in four concentrations 2, 4, and 6 mg/L sodium selenite (Na₂SeO₃). Root volume, fresh and dry weights of shoots and roots, number and weight of fruits, chlorophyll content, and photosynthesis traits [photosynthesis rate, stomata internal carbon dioxide (CO₂) concentration, stomata conductance] were measured. Results showed that Se increased root dry weight. Fresh and dry weights of shoot increased in the 2 mg/L Se treatment and decreased at the higher level of Se. Chlorophyll content and photosynthesis rate were not affected by Se. Stomata internal CO₂ concentration and stomata conductance decreased by Se addition. Overall, Se at 2 mg/L application rate was effective in some physiological characteristics of cucumber.     

Distribution and bioavailability of selenium fractions in some seleniferous soils of Punjab,India

Soil-solid phase associations of Se in seleniferous soils of Punjab were investigated by following sequential extraction procedures involving multiple extractions with 0.2 M K2SO4 (2 times), 0.1 M Na2SeO3 (4 times), 0.05 M NH4OH (4 times), 6 M HCl (2 times) and 9 M HNO3 (2 times) vis-a-vis single extractions with 0.25 M KCl, 0.1 M KH2PO4, 4 M HCl and concentrated HCl. Soil samples were equilibrated with 75Se (as Na2SSeO3) @ 9.25 kBq g - 1 soil by incubating at field capacity moisture regime and subjecting to alternate wetting and drying cycles. Following multiple extraction procedure, out of total 75Se added, 8.8 - 26.1% was present in readily available form (0.2 M K2SO4 extractable); 27.6 - 49.0% as isotopically exchangeable (0.1M Na2SeO3 extractable) and 5.3 - 12.0% as organic Se (0.05 M NH4OH extractable). Selenium extractable in K2SO4 was significantly correlated with free iron (r = - 0.774, p < 0.05) and CaCO3 (r = 0.670, p <0.10) content of the soils. Negative relationship was observed between Se uptake by maize (Zea mays L.) and ammonium hydroxide extractable (r = - 0.752, p <0.05) as well as residual Se (r = - 0.726, p <0.05) in soils. Highly positive coefficients of correlation between isotopically exchangeable Se and Se content (r = 0.851, p <0.01) as well as its uptake by maize (r = 0.841, p <0.01) indicated that the isotopically exchangeable form of Se may be considered as an index of bioavailable Se in seleniferous soils of Punjab. None of the fractions defined by following single extraction procedure was correlated with either the soil characteristics or Se uptake by maize plants. Multiple extraction procedure could, thus, better explain the distribution of Se in different fractions and uptake by plants.