Selenium Biofortification and Antioxidant Activity in Lettuce Plants Fed with Selenate and Selenite

Selenium biofortification and antioxidant activity in lettuce plants fed with selenate and selenite

S.J. Ramos1,2, V. Faquin2, L.R.G. Guilherme2, E.M. Castro3, F.W. Ávila2, G.S. Carvalho2, C.E.A. Bastos2, C. Oliveira3

1Robert W. Holley Center for Agriculture and Health, Cornell University, Ithaca, New York, USA 2Soil Science Department, Federal University of Lavras, Lavras, Brazil 3Biology Department, Federal University of Lavras, Lavras, Brazil

ABSTRACT

Selenium is an important element associated with enhancement of antioxidant activity in plants, microorganisms, animals, and humans. In Brazil, the information on Se in agricultural crops is lacking, though there are indications that low levels of Se are consumed by the population. The experiment was conducted under greenhouse conditions with pots containing 3 l of nutritive solution in a completely randomized factorial design, with seven Se concentrations (0, 2, 4, 8, 16, 32, and 64 µmol/l) and two forms of Se (sodium selenate – Na2SeO4 and sodium selenite – Na2SeO3), with six replicates. The application of Se as selenate at low concentrations is more appropriate for lettuce biofortification because it favors shoot biomass growth and Se levels in the shoot biomass. Selenium in both forms had two effects on lettuce plant metabolism: at low doses it acted as an antioxidant and enhanced plant growth, whereas at higher levels it reduced yield.

Keywords: selenate; selenite; antioxidant enzymes; biofortification

Selenium (Se) is an important element for human biofortification programs, use of selenate is recom- and animal nutrition, due to its roles on a series mended over selenite (Ríos et al. 2008). of biochemical reactions enhancing antioxidant The antioxidative effect of Se was related to an activity (Rayman 2002). In contrast, Se was not improved GSH-Px and SOD activity and a de- considered essential for plants (Terry et al. 2000, creased lipid peroxidation in Se treated plants, Kápolna et al. 2009). Nevertheless, several studies like ryegrass (Hartikainen et al. 2000), lettuce (Xue reported the beneficial effects of Se, because it et al. 2001) and soybean (Djanaguiraman et al. increases the antioxidant activity in plants, lead- 2005). Moreover, Cartes et al. (2005) determined ing to better plant yield (Hartikainen et al. 2000, that selenite was more efficient that selenate in Lyons et al. 2009). promoting enzymatic activity. Plants recycle Se within the food chain. Thus, bio- Even though there are reports of low Se con- fortification of agricultural crops with Se, by means sumption by the Brazilian population, studies on of adding Se along with fertilizers, is a useful tech- Se fortification of crop plants are scarce (Ferreira nique to increase the consumption of Se by animals et al. 2002, Maihara et al. 2004). Since lettuce is and man (Chen et al. 2002, Ríos et al. 2008, White the most consumed leafy plant in Brazil and many and Broadley 2009, Broadley et al. 2010). Inorganic parts of the world (Luz et al. 2008, Li et al. 2010), Se forms differ in terms of absorption and mobility this crop can be preferred in Se biofortification within plants; selenate is more easily transported to programs, as an efficient way of increasing intake shoots, while selenite tends to accumulate in plant of this element by the population. So in the present roots (Zhang et al. 2003). For this reason, in some Se work the effect of the biofortification of different

Supported by the National Council of Scientific and Technological Development (CNPq-Brazil), and by the Foundation to Support Research of Minas Gerais State (FAPEMIG-Brazil).

584 PLANT SOIL ENVIRON., 56, 2010 (12): 584–588 Se forms on the yield and antioxidant systems in and Fridovich 1987). A 5 ml reaction mixture, con- lettuce plants has been studied. taining 50 mmol/l Na2CO3 (pH 10.0), 13 mmol/l methionine, 0.025% (v/v) Triton X-100, 63 µmol/l NBT, 1.3 mmol/l riboflavin, and an appropri- MATERIALS AND METHODS ate quantity of enzyme extract was used. The reaction mixtures were illuminated for 15 min Plant materials and experimental design. at photosynthetic photon flux density (PPFD) of Lettuce (Lactuca sativa L. cv. Vera) was planted 380 µmol/m2/s. Non-illuminated mixtures were in expanded polystyrene trays containing 128 com- used to correct for background absorbance. One partments filled with vermiculite and irrigated with unit of SOD activity was defined as the amount of distilled water in the first five days. Seedlings were enzyme required to inhibit 50% of NBT reduction irrigated with the 0.5N Hoagland nutrient solution as monitored at 560 nm. till 15 days. After that, seedlings with uniform Catalase (EC 1.11.1.6) activity was tested by seedling vigour were selected and transplanted to observing H2O2 consumption at 240 nm for 5 min 3 l pots containing 0.5N Hoagland nutrient solution (Rao et al. 1997). Reaction mixture (3 ml total vol- with different concentrations of Se. ume) contained 25 mmol/l Tris-acetate buffer (pH The experimental design was a completely ran- 7.0), 0.8 mmol/l EDTA-Na, and 20 mmol/l H2O2, domized factorial 7 × 2, in which the main factor and the enzyme assay was carried out at 25°C. was Se concentration in seven levels (0, 2, 4, 8, 16, For the malondialdehyde (MDA) assay, 0.5 g of 32 and 64 µmol/l) and the other factor was Se form lettuce leaf was homogenized in 5 ml of 50 mmol/l

(sodium selenate – Na2SeO4, and sodium selenite buffer solution (containing 0.07% NaH2PO4·2 H2O – Na2SeO3·5 H2O, both from Sigma-Aldrich), with and 1.6% Na2HPO4·12 H2O), ground with a cooled six replicates, totaling 84 plots. Each experimental mortar and pestle, and centrifuged at 22 000 × g for unit was made up of one plant per pot. 30 min (4°C). MDA concentration was calculated Throughout the experimental period, the nu- using the extinction coefficient of 155 mmol/l/cm tritive solution underwent constant aeration and (Fu and Huang 2001). pH was monitored daily and kept at 6.0 ± 0.2 by Selenium measurement. In this step, 500 mg addition of 0.1 mol/l NaOH or HCl. The solution of dried powder of plant materials was added was changed whenever the initial electrical con- with 10 ml of concentrated p.a. HNO3 to Teflon ductivity dropped more than 30%. After 25 days PTFE flasks and digested at 0.76 MPa for 10 min of Se exposure, plants were harvested, and divided in a microwave oven (CEM, model Mars 5, CEM into shoots and roots. Corporation, Matthews, NC, USA). After cool- During harvest, three replicates with five leaves ing to room temperature, the extract was filtered each from the middle part of the plant were im- (Whatman number 40 filter) and diluted by adding mediately wrapped in aluminum foil, submerged 5 ml of bi-distilled water. in liquid nitrogen and were stored in a freezer, at Total Se in the extracts was determined in a –80°C, for enzyme assay. The remaining plants PerkinElmer Analyst 800 atomic absorption spec- (replicates) were dried in a forced-air drying oven trophotometer with electrothermal atomization by at 65–70°C until constant mass of the root and (pyrolytic) graphite furnace with transversal heating shoot samples was achieved. and automatic sampler. A hollow cathode Se bulb was Antioxidant enzymes activity and lipid per- employed as a radiation source, operating at 6.0 mA, oxidation measurement. In order to estimate with a 196.0 nm wavelength, and a 2.0 nm gap. The the superoxide dismutase and catalase enzyme matrix modifier consisted of a solution containing activities, frozen tissue was homogenized in a 0.005 mg Pd + 0.003 mg Mg(NO3)2; argon (95% pure) cooled 0.1 mol/l Tris-HCl buffer at pH 7.8 contain- was used as an inert gas in the graphite furnace. In ing 1 mmol/l EDTA, 1 mmol/l dithiothreitol and these conditions, pre-treatment temperature was 5 ml of 4% polyvinyl pyrrolidone per gram of fresh 1300°C and an atomization temperature was 1900°C. weight. The homogenate was filtered through Readings were carried out by peak absorption area, a nylon mesh and centrifuged at 22 000 × g for using a 5 s atomization time, taken out of the re- 30 min at 4°C. The supernatant was used to meas- spective blanks of each sample digestion battery. ure enzyme activity. Certified reference material (tomato leaf material, Superoxide dismutase (EC 1.15.1.1) activity was NIST 1573a) were included in each batch of samples assayed by monitoring photochemical inhibition for quality control, and the recovery percentages of nitroblue tetrazolium (NBT) reduction (Beyer varied from 89.4 to 93.2%.

PLANT SOIL ENVIRON., 56, 2010 (12): 584–588 585 All data were subjected to a simple ANOVA at 95% tion in both Se forms. The difference between confidence, using Sisvar 4.6 software (Build 6.1) and selenate and selenite is due to the high affinity the graphs were done on Sigma Plot (version 11.0). between sulfate transporters and selenate, which facilitates its absorption and translocation (Zhang et al. 2003). As for the selenite absorption pro- RESULTS AND DISCUSSION cesses, little is known (Rosen and Liu 2009). There are indications that selenite transport by cellular Figure 1A shows that Se affected shoot biomass simplasm actively takes place and that phosphate production, with an increase of 5.67 and 3.69% by transporters act in the process, at least partially selenate and selenite, respectively, at low concen- (Hopper and Parker 1999, Li et al. 2008). In ad- trations of up to 8 and 4 µmol/l. However, further dition, when selenite is absorbed by plants, it is increase in Se concentrations reduced shoot bio- rapidly converted to organic forms of Se in roots, mass production. Our results are in agreement which have low mobility in xylem (Li et al. 2008). with Fargašová (2003) who observed an inhibitory Leaf Se concentration increased with an increase effect of Se on the mustard growth. In general, in Se concentration in the nutrient medium (Figure the biomass production was higher when selenate 1C). These results corroborate with those obtained was supplied to the nutrient solution than sel- in other works, which reported that increasing doses enite (Figure 1A). Previous studies showed that of Se in medium culture can cause a significant selenate and selenite provide distinct responses increase6 of Se content in agricultural crops (Ducsay in Se translocation6 (Zhang et al. 2003). Figure 1B et al. 2009, Broadley et al. 2010). Considering that shows that Se translocation was higher when sup- Brazilian5 per capita consumption of fresh lettuce

plied as5 selenate. When lettuce received lower Se leaves) is 33.3 g/day (Yuri et al. 2005), and that the -1 4 A concentrations) (2, 4, and 8 µmol/l), approximately recommended consumption of Se for adults is 70%-1 of 4the elementA applied as selenate and 50% 50–70 µg/day (US Department of Agriculture 2001), 3 as selenite were found in the shoots. When the the (g plant Se content obtained in this experiment with 3 plants(g plant were treated with higher concentration selenate without compromising production, met 2 Y = 4.98 - 0.053x + 0.211x0.5 R2 = 0.98* Shoot dry matter yield matter dry Shoot of Se, there was a small reduction in transloca- only ca. 5% of the recommended human0.5 Se2 intake 2 Y = 4.98 - 0.053x + 0.211x0.5 R2 = 0.98* Y = 4.96 - 0.069x + 0.234x R = 0.97* Shoot dry matter yield matter dry Shoot 0.5 2 1 (A) Y = 4.96 - 0.069x + 0.234x R = 0.97* (B) 61 100100 100 B 5 B 8080 80 ) Se in plant)x100 -1 4 6060 4 A -1

Se in plant)x100 60 -1 (g/plant) 3 4040 (g plant 3 Se translocation

40 translocationSe Shoot dry yield matter 0.50.5 2 2 20 YY = = 9.26 9.26 – - 3.0213.021xx ++ 31.1331.13xx0.50.5 R R2 2= = 0.92* 0.92*

Se translocationSe 2 YY = = 4.98 4.98 – - 0.053 0.053xx + + 0.211 0.211xx R R = =0.98* 0.98* 20 Shoot dry matter yield matter dry Shoot 2 0.50.5 2 2 0.50.5 22 20 YYY = = =4.96 4.96 9.26 – - -0.0690.069x 3.021xx + ++ 0.234 0.234x31.13xx 0.5 R RR 2= == 0.98* 0.97*0.92* YY = = 6.55 6.55 – - 2.3412.341xx ++ 23.5123.51xx R R = = 0.90* 0.90* 0.5 2 0 1 Y = 6.55 - 2.341x + 23.51x R = 0.90* (mg Se in shoot/mg Se × 100 in plant) 0

1 mg shoot in Se (mg 0 0 2 4 8 16 32 64 (C) 100 24 2

(mg Se in shoot mg shoot in Se (mg Y = -0.672 + 0.363x R = 0.99* [Se] (μmol/l)2 24 2 solution 24 B YY = = –0.672-0.672 + 0.363x0.363x R2 == 0.99*0.99* 20 Y = 0.102 + 0.174x R = 0.98* 80 2 20 YY = = 0.102 0.102 + + 0.174 0.174xx R = 0.98* 16 C DW) -1 Se in plant)x100 6016 C -1 DW) 12 -1 12 40 8 (mg Se kg Se (mg Se translocationSe 8

(mg Se/kg DW) 8 20 0.5 2 4 Shoot Se concentration concentration Shoot Se (mg Se kg Se (mg Y = 9.26 - 3.021x + 31.13x R = 0.92* Shoot Se concentration 4 4 Y = 6.55 - 2.341x + 23.51x0.5 R2 = 0.90* Shoot Se concentration concentration Shoot Se 0 0 0 Figure 1. Shoot024 8biomass 16 (A), Se 32 translocation (B) and64 (mg Se in shoot mg shoot in Se (mg 0 24 2 shoot Se concentration (C) in lettuce plants treated with 0240 2 4 88 Y = 1616 -0.672 + 0.363x 32 32 R = 0.99* 6464 [Se] (µmol L-1) 2 different concentrations andsolution forms of Se (● selenite; 20 Y = [Se]0.102 + 0.174x(µmol R L =-1 )0.98* [Se]solutionsolution (μmol/l) ○ selenate) *P < 0.05 16 C DW) -1 586 12 PLANT SOIL ENVIRON., 56, 2010 (12): 584–588

8 (mg Se kg Se (mg 4 Shoot Se concentration concentration Shoot Se 0 024 8 16 32 64 [Se] (µmol L-1) solution 2,4 A 2,4 2,2 2,2 A 2,0 FW) FW) -1

2,0 g 1,8 -1 FW) FW) -1

SOD 1,6

g 1,8 -1

SOD 1,6 1,4 Y = 1.354 - 0.032x + 0.297x0.5 R2 = 0.91* 1,4 (Unit min 1,2 0.5 2 Y = 1.354 - 0.032x + 0.297x0.5 R2 = 0.91* Y = 1.226 - 0.027x + 0.309x R = 0.88* (Unit min (A) 1,2 Y = 1.226 - 0.027x + 0.309x0.5 R2 = 0.88* (B) 1,0 1,02,42.4 22 22 A B 2,22.2 FW) B -1 20 FW)

2,0 kg -1 202.0 FW) FW) -1 18

-1 18 kg

g 1,8 -1 181.8 -1 min /min/kg FW) SOD 2 2 16 CAT 16 CAT SOD

1,6 O O

min 1.6 2 2 2 16 CAT O

(Unit/min/g FW)(Unit/min/g 14 2 1,4 0.5 2 14 1.4 YY = = 1.354 1.354 – - 0.0320.032xx ++ 0.2970.297xx 0.5 R R 2= = 0.91* 0.91*

(Unit min 14 0.52 2 2 1,2 Y = 1.226 – 0.027x + 0.309x0.50.5 R2 2= 0.88* 12 YY = = 17.31 17.31 – + 0.276 0.276xx + - 0.005 0.005xx R R = 0.84*= 0.84* 1.2 Y = 1.226 - 0.027x +2 0.309x2 R = 0.88* (mmol H 12 0.50.5 2 2 Y = 17.31 + 0.276x - 0.005x R = 0.84* H (mmol Y = = 16.81 16.81 – - 0.2710.271xx + + 1.965 1.965xx R R = =0.88* 0.87* 12 0.5 2 (mmol H (mmol 1,01.0 Y = 16.81 - 0.271x + 1.965x R = 0.87* 10 1022 (C) B 50 0 2 4 8 16 32 64

FW) 5050 C [Se] (μmol/l)

-1 20 C 45 solution

kg 4545 -1 18 FW) 40 -1 FW) 40

-1 40 min

2 16 CAT 35

O 3535 2 30

14 TBARS

TBARS 30

TBARS 30 2 2 12 Y = 17.31 + 0.276x - 0.005x R = 0.84* 25 0.5 2 2525 0.5 2 0.50.5 22 Y = 26.60 + 0.527x - 1.539x R = 0.92* (mmol H (mmol Y = 16.81Y = 26.60- 0.271x + 0.527 + 1.965xx – 1.539 R x = 0.87* R = 0.92* (mmol MDA/kg FW)(mmol MDA/kg Y = 26.60 + 0.527x - 1.539x R = 0.92* 2 Figure kg MDA (mmol 2. Activity of superoxide dismutase (SOD) 2 (mmol MDA kg MDA (mmol 2 20 Y = 25.95 + 0.1729x R = 0.91* 202010 YY = =25.95 25.95 + +0.1729 0.1729xx R R = = 0.91* 0.91* (A), catalase (CAT) (B) and lipid peroxidation 15 151550 (TBARS) (C) in lettuce plants treated with differ- 0048 224 C 8 1616 32 6464 0482 16 32 ● 64 45 ent concentrations and forms of Se-1 ( selenite; -1 ○ [Se] (µmol L ) [Se][Se]solutionsolution (µmol (μmol/l) L ) selenate) *P < 0.05 solution FW) 40 -1 (approximately35 230 g FW/week and considering leaf production through the enhanced activity that lettuce30 is composed of 96% water). Thus, the of antioxidants. Similar results were reported in presentTBARS study suggests a need for further research ryegrass (Hartikainen et al. 2000). 25 on biofortificationY = of26.60 different + 0.527x crops- 1.539x with0.5 R2 Se,= 0.92* in Our results indicate that for biofortification 2 order kg MDA (mmol to20 meet idealY =Se 25.95 consumption + 0.1729x R by = 0.91*Brazilians. program with lettuce the application of Se as se- These results shown in Figure 1 are conform with lenate at low concentrations would be more ben- 15 the earlier048 2result by16 Ríos et al.32 (2008). 64 eficial because it favors shoot biomass growth, Se Figure 2 shows changes[Se] in the (µmol activity L-1 of) SOD, CAT translocation, and Se levels in the shoot biomass. and lipid peroxidation insolution lettuce leaves treated with an increasing concentrations of Se, either as selenate or selenite. SOD activity was maximum at Se con- Acknowledgement centrations of 32.9 and 22.1 µmol/l, for selenate and selenite, respectively (Figure 2A). As for CAT, the To Dr. Yuri Lopes Zinn (Federal University of Lavras) maximum activity was detected at concentrations of and Dr. Li Li (Robert W. Holley Center for Agriculture 12.3 and 20.8 µmol/l (Figure 2B). During oxidative and Health, USDA/Cornell University, USA) for proof stress, excess reactive oxygen species (ROS) produc- reading the manuscript. S.J. Ramos thanks National tion causes membrane damage that eventually leads Council of Scientific and Technological Development to cell death (Das et al. 1992, Montillet et al. 2005). (CNPq-Brazil), for granting the doctorate scholar- In our experiment, increased lipid peroxidation at ships (regular and sandwich program). higher Se concentrations indicated the occurrence of oxidative stress (Figure 2C). This might be one of the reasons for lowering lettuce production at higher REFERENCES Se concentrations (Figure 1A). To protect against ROS, plants have antioxidant enzymes such as SOD Beyer W.F., Fridovich I. (1987): Assaying for superoxide dismutase and CAT, as well as a wide array of non-enzymatic activity: some large consequences of minor changes in conditions. antioxidants (Mittler 2002). Analytical Biochemistry, 161: 559–566. Se induced increase in SOD and CAT activity at Broadley M.R., Alcock J., Alford J., Cartwright P., Foot I., Fairweather- low concentrations, but probably enhanced lettuce Tait S.J., Hart D.J., Hurst R., Knott P., Mcgrath S.P., Meacham M.C.,

PLANT SOIL ENVIRON., 56, 2010 (12): 584–588 587 Norman K., Mowat H., Scott P., Stroud J.L., Tovey M., Tucker hydroponic lettuce and the human health. Ciência Rural, 38: M., White P.J., Young S.D., Zhao F.J. (2010): Selenium biofor- 2388–2394. (In Portuguese) tification of high-yielding winter wheat (Triticum aestivum L.) Lyons G.H., Genc Y., Soole K., Stangoulis J.C.R., Liu F., Graham by liquid or granular Se fertilisation. Plant and Soil, 332: 5–18. R.D. (2009): Selenium increases seed production in Brassica. Cartes P., Gianfreda L., Mora M.L. (2005): Uptake of selenium Plant and Soil, 318: 73–80 and its antioxidant activity in ryegrass when applied as selenate Maihara V.A., Gonzaga I.B., Silva V.L., Fávaro D.I.T., Vasconcellos and selenite forms. Plant and Soil, 276: 359–367. M.B.A., Cozzolino S.M.F. (2004): Daily dietary selenium intake Chen L., Yang F., Xu J., Yun H., Hu Q., Zhang Y., Pan G. (2002): of selected Brazilian population groups. Journal of Radioana- Determination of selenium concentration of rice in China and lytical and Nuclear Chemistry, 259: 465–468. effect of fertilization of selenite and selenate on Se content of Mittler R. (2002): Oxidative stress, antioxidants and stress toler- rice. Journal Agricultural Food and Chemistry, 50: 5128–5130. ance. Trends and Plant Science, 7: 405–410. Das N., Misra M., Misra A.N. (1992): Sodium chloride salt stresss Montillet J.L., Chamnogpol S., Rustérucci C., Dat J., Van De Cotte induced metabolic changes in pearl millet callus: oxidases. B., Agnel J.P., Triantaphylides C. (2005): Fatty acid hypersensi-

Proceedings of National Academy of Sciences, India, Section tive and H2O2 in the execution of hypersensitive cell death in B, 62: 263–268. tobacco leaves. Plant Physiology, 138: 1516–1526. Djanaguiraman M., Durga D.D., Shanker A.K., Sheeba J.A., Rao M.V., Paliyath C., Ormrod D.P., Murr D.P., Watkins C.B.

Bangarusamy U. (2005): Selenium – an antioxidative protect- (1997): Influence of salicylic acid on H2O2 production, oxida-

ant in soybean during senescence. Plant and Soil, 272: 77–86. tive stress and H2O2-metabolizing enzymes: salicylic acid-

Ducsay L., Ložek O., Varga L. (2009): The influence of selenium mediated oxidative damage requires H2O2. Plant Physiology, soil application on its content in spring wheat. Plant, Soil and 115: 137–149. Environmental, 55: 80–84. Rayman M.P. (2002): The argument for increasing selenium intake. Fargašová A. (2003): Toxicity comparison of some possible toxic Proceedings of the Nutrition Society, 61: 203–215. metals (Cd, Cu, Pb, Se, Zn) on young seedlings of Sinapis alba Ríos J.J., Rosales M.A., Blasco B., Cervilha L., Romero L., Ruiz L. Plant, Soil and Environmental, 50: 33–38. J.M. (2008): Biofortification of Se and induction of the an- Ferreira K.S., Gomes J.C., Bellato C.R., Jordão C.P. (2002): Se- tioxidant capacity in lettuce plants. Scientia Horticulturae, lenium content of Brazilian foods. Revista Panamericana de 116: 248–255. Salud Pública, 11: 172–177. (In Portuguese) Rosen B.P., Liu Z. (2009): Transport pathways for arsenic and se- Fu J.M., Huang B.R. (2001): Involvement of antioxidants and lipid lenium: a minireview. Environment International, 35: 512–515. peroxidation in the adaptation of two cool-season grasses to Terry N., Zayed A.M., Souza M.P., Tarun A.S. (2000): Selenium localized drought stress. Environmental and Experimental in higher plants. Annual Review of Plant Physiology and Plant Botany, 45: 105–114. Molecular Biology, 51: 401–432. Hartikainen H., Xue T., Piironen V. (2000): Selenium as an antioxi�- US Department of Agriculture (2001): Dietary reference intakes: dant and pro-oxidant in ryegrass. Plant and Soil, 225: 193–200. elements. Available at http://www.iom.edu/Global/News%20 Hopper J.L., Parker D.R. (1999): Plant availability of selenite and Announcements/~/media/48FAAA2FD9E74D95BBDA2236E selenate as influenced by the competing ions phosphate and 7387B49.ashx (Accessed 29 January 2010) sulfate. Plant and Soil, 210: 199–207. White P.J., Broadley M.R. (2009): Biofortification of crops with Kápolna E., Hillestrom P.R., Laursen K.H., Husted S., Larsen E.H. seven mineral elements often lacking in human diets-iron, (2009): Effect of foliar application of selenium on its uptake zinc, copper, calcium, magnesium, selenium and iodine. New and speciation in carrot. Food Chemistry, 115: 1357–1363. Phytologist, 182: 49–84. Li H., McGrath S., Zhao F. (2008): Selenium uptake, translocation Xue T., Hartikainen H., Piironen V. (2001): Antioxidative and and speciation in wheat supplied with selenate or selenite. New growth-promoting effect of selenium on senescing lettuce. Phytologist, 178: 92–102. Plant and Soil, 237: 55–61. Li Z., Zhao X., Sandhu A.K., Gu L. (2010): Effects of exogenous Yuri J.E., Souza R.J., Resende G.M., Mota J.H. (2005): Comporta- abscisic acid on yield, antioxidant capacities, and phytochemical mento de cultivares de alface americana em Santo Antônio do contents of greenhouse grown lettuces. Journal of Agricultural Amparo. Horticultura Brasileira, 23: 870–874. (In Portuguese) and Food Chemistry, 58: 6503–6509. Zhang Y., Pan G., Chen J., Hu Q. (2003): Uptake and transport of Luz G.L., Medeiros S.L.P., Manfron P.A., Amaral A.D., Muller selenite and selenate by soybean seedlings of two genotypes. L., Torrez M.G., Mentges L.A. (2008): The nitrate issue in Plant and Soil, 253: 437–443.

Received on May 8, 2010

Corresponding author:

Sílvio Júnio Ramos, Cornell University, Robert W. Holley Center for Agriculture and Health, USDA-ARS, Ithaca 14853, New York, USA Federal University of Lavras, Soil Science Department, Lavras-MG 37200-000, Brazil phone: + 1 607 793 1280, phone/fax: + 55 35 3829 1258, 3829 1252, e-mail: [email protected]

588 PLANT SOIL ENVIRON., 56, 2010 (12): 584–588