para estudiantes y profesores Antonio Briz
2. El Diccionario de Partículas Discursivas del español (DPDE)
Cadmium compounds CdSeO4 and CdSeO3 used for
experiments were prepared according to procedures de- scribed in Kráľová et al.28 Chemicals of analytical purity
used for preparation of Knop nutrient solution were pur- chased from Lachema (Brno, Czech Republic).
Chem. Listy 104, s698s703 (2010) ACP 2010 Súčasný stav a perspektívy analytickej chémie v praxi Posters Cultivation of experimental plants
For cultivation of experimental plants seeds of St. John´s wort (Hypericum perforatum L.) (Research Institute of Agroecology in Michalovce, Slovakia) were used. Six weeks old plants were cultivated in hydroponic solution at controlled conditions (photoperiod 16 h light/8 h dark; irradiation: 80 mol m2 s1 PAR; mean air temperature:
28 °C): control variant in Hoagland solution and metal variants containing studied compounds (12, 24 and 60 mol dm–3, respectively) and the response of plants to metal
treatment were evaluated 7 d after Cd application. Then dry mass of roots and shoots was determined.
The seeds of maize (Zea mays L.), cv. Lucia (FAO 380) were soaked in distilled water for 24 h, then for 3 days germinated in filter paper scroll moistured with distilled water and consequently hydroponically cultivated in Knop nutrient solution under controlled conditions (7 days; photoperiod 16 h day/8 h night; irradiance 80 mol m−2 s−1
PAR; air temperature 25 °C). After 7-day cultivation dry mass of roots and shoots was estimated
The results were evaluated by the multifactorial ANOVA algorithm (P ≤ 0.05) after verification of normality and homogeneity of the variance. The multiple comparisons of means were based on the method of Tukey contrast. Determination of Cd content in plants
Roots of plants used for Cd analysis were thoroughly washed by tap water to remove test solution from the exte- rior of roots. Plants organs were dried at 70 °C and cut to small pieces (< 1 mm). All plants were processed for Cd analysis and the total root and shoot accumulation of Cd was determined. Mineralization of plants was carried out in the PTFE-coated stainless steel pressure vessels ZA-1 (JZD Zahnašovice, Czech Republic). 0.10.5 g of the plant sample was weighted to the vessel and 5.0 cm3 of concen-
trated HNO3 p.a. (Lachema, Czech Republic) was added.
Vessel was closed and heated in the oven at 160 °C for 6 h. After this procedure the solution was diluted to 25 cm3
with redistilled water and stored in a 50 cm3 polyethylene
(PE) bottle. Cadmium contents were determined using the flame atomic absorption spectrometry method (AAS Perkin-Elmer Model 1100, at 228.8 nm with deuterium background correction). Standard reference Cd stock solu- tion (1 g dm−3, Merck, Germany) and the certified stan-
dard reference materials NCS DC 73350 Poplar Leaves (China) and NCS DC 733 49 Bush Branches and Leaves (China) were used to quality assurance of the results. The detection limit of cadmium was 2 g dm−3. The detection
limit corresponding to three times the standard deviation of the blank was 2 g dm−3. The precision expressed by
relative standard deviation (RSD) for five successive de- terminations varied in the range from 1 % to 3 %.
Results and discussion
The dependence of root and shoot dry mass of St. John´s wort and maize plants treated with CdSeO4 and
CdSeO3 is presented in Fig. 1. The phytotoxic effect of
the highest applied concentration of studied compounds (60 mol dm3) was manifested by desiccated leaves and
leaf fall of St. John´s wort plants what was reflected in great reduction of shoot dry mass. The leaves of these experimental plants were yellow or brownish. Significant reduction of the formation of lateral roots of maize plants was observed mainly for the treatment with 60 mol dm3
CdSeO4 and CdSeO3, whereby the leaves of plants culti-
vated in the presence of 60 mol dm3 CdSeO
4 exhibited
symptoms of chlorosis. Due to the supply of studied com- pounds dry mass of shoots was affected to a greater extent than root dry mass. The reduction of plant biomass by Cd toxicity could be the direct consequence of the inhibition of chlorophyll synthesis29 and photosynthesis30.
The dependence of cadmium content in roots and shoots of experimental plants treated with is CdSeO4 and
CdSeO3 is shown in Fig. 2. Selenite treatment resulted in
significantly lower Cd accumulation in plant organs of John´s wort and maize plants than that of selenate. This is in agreement with the results of several authors27,28, 31.32.
In the studied concentration range (0–60 mol dm3) Cd
content in roots and shoots of John´s wort (Fig. 2: I, II) and in shoots of maize (Fig. 2: IV) increased linearly with increasing CdSeO4 and CdSeO3 concentration in hydro-
ponics. On the other hand, in roots of maize (Fig. 2: III) the increase of supplemented Cd led to gradual satura- tion of root tissue with this metal. Cadmium bioaccumulat- ing capacity of roots of John´s wort was much higher than that of maize roots, whereby Cd accumulation in shoots of both experimental plant species was similar (slightly higher Cd shoot concentration was determined for maize). Higher Cd bioaccumulating capacity of H. perforatum roots could be connected with effective synthesis of phyto- chelatins due to metal stress. This detoxification mecha- nism utilizes complexation of phytochelatins with Cd and storage of these metal complexes in root vacuoles. Ligands participating in complexing heavy metals in vacuoles may be also metal chaperones, organic acids such as citric, malic and malonic acids or even histidine, nicotianamine and phytates3336. The great difference in bioaccumulating capacity of plant roots related to Cd can be also affected by different age of tested plant species (7 week old plants of H. perforatum) and 10 d old maize seedlings) as well as different tolerance of tested plant species with respect to Cd stress. High tolerance of H. perforatum to Cd was pre- viously confirmed37,38. Similarly, some authors reported
relative high tolerance of some maize variants to Cd stress39,40. It is necessary to stress that higher shoot con-
centrations of cadmium suggest higher Cd mobility (root to shoot transfer) within the plant.
Bioaccumulation factor (BAF) expresses the ratio of the metal concentration in the biological material (in mol
or g g1 dry mass) to the metal concentration in external
solution (in mol or g dm3). After supply of both tested
Cd compounds the roots of St. John´s wort accumulated much more Cd than maize roots (Fig. 3) and the corre- sponding BAF values determined for roots varied in the range from 378 to 441 (CdSeO4) and from 182 to 198
(CdSeO3), respectively. The BAF values estimated for
shoots were 17.120.2 (CdSeO4) and 2.84.1 (CdSeO3).
Higher accumulation of Cd in maize plant organs due to CdSeO4 application was reflected in the corresponding
BAF values determined for roots as well as shoots, which were approximately twofold in comparison with those estimated after CdSeO3 treatment. In comparison with St.
John´s wort lower BAF values related to plant roots were determined for maize plants: these BAF values varied from 69.3 to 213.1 for CdSeO4 and from 35.2 to 114.8 for
CdSeO3 treatment. The corresponding BAF values related
to maize shoots were estimated as follows: 28.057.9 for CdSeO4 and 11.526.0 for CdSeO3 treatment.
The translocation factor (TF) corresponds to the ratio of accumulated Cd amount in shoots and roots and thus it depends also on the actual dry mass of these plant organs, similarly as the portion from the total accumulated metal
amount by the plant occurring in the shoots. TF values related to Cd in maize plants treated with compounds con- taining selenium in different oxidation state varied in the range from 0.828 to 1.049 (CdSeO4) and from 0.484 to
0.836 (CdSeO3), respectively. Significantly lower TF val-
ues were determined for St. John´s wort plants: 0.104 0.121 for CdSeO4 and 0.0580.070 for CdSeO3 treatment.
In maize plants portion from the total accumulated metal amount by the plant occurring in the shoots was about 43 % in the whole studied concentration range (12 60 mol dm3) for both tested compounds (CdSeO
4
a CdSeO3). On the other hand, in St. John´s wort the val-
ues of this portion were significantly lower: 9.4–10.8 % for CdSeO4 and 5.4–6.5 % for CdSeO3 application. The Cd
portion accumulated in shoots of V. radiata (with respect to total Cd amount accumulated by plants) was approxi- mately twofold higher in the case of CdSeO4 treatment
than after CdSeO3 application41. Similar values were ob-
tained also for Matricaria recutita plants when after appli- cation of 12 mol dm3 CdSeO
4 this portion reached
50.3 % for cv. Goral and 37,65 % for cv. Lutea, whereby at application of 12 mol dm3 CdSeO
3 the corresponding
portion was only 32,6 % and 16.6, respectively28,32. Never-
Fig. 1. Dependence of root (A) and shoot (B) dry mass of St. John´s wort and maize plants on the concentration of CdSeO4 (I) and CdSeO3 (II). Mean ± S.E; S.E.- standard error
1 2 3 4 0 20 40 60 80 100 dry m a ss [ m g] c [mol dm-3] I II 0 12 24 60 ST. JOHN'S WORT A 1 2 3 4 0 100 200 300 400 I II dry mass [m g ] c [mol dm-3] 0 12 24 60 ST. JOHN'S WORT B 1 2 3 4 0 10 20 30 40 50 dr y m a ss [m g] c [mol dm-3 ] I II 0 12 24 60 MAIZE A 1 2 3 4 0 25 50 75 100 125 150 175 dr y m a ss [m g] c [mol dm-3 ] I II 0 12 24 60 MAIZE B
Chem. Listy 104, s698s703 (2010) ACP 2010 Súčasný stav a perspektívy analytickej chémie v praxi Posters
theless, M. recutita plants are considered to be significant Cd accumulators38,42. Experiments with Pisum sativum L.
showed that due to CdSeO4 treatment up to 38 % of Cd
and 89 % of Se from the total accumulated metal amount by pea plants was accumulated in the shoots whereas these values for CdSeO3 reached only 18 % for both Cd and Se
(ref.27).
The above results confirmed high effectiveness of maize plants (cv. Lucia) to accumulate Cd in their shoots. It is necessary to stress that despite of bioavailability of both selenate and selenite, plants absorb preferentially selenate which will be converted to organic compounds43.
Shanker et al. 31 studied uptake and translocation of Cd
absorbed by roots of mung bean treated with selenate and selenite and irrigated by solution containing 2 g cm3 Cd.
The authors observed statistically significant reduction of
Cd uptake with increasing selenite and selenate concentra- tion whereby selenite application resulted in more effec- tive reduction of Cd uptake. This is connected with the fact that the less mobile selenite after being reduced to selenide tends to form Cd-Se complex, which appears to be un- available for the plants. The more mobile anion selenate is available for Cd-Se formation only after following a more complicated redox processes involving Se(VI) in SeO42−,
Se(IV) in SeO32−, and Se(0) species. Reduced Cd accumu-
lation in maize shoots in the presence of sodium selenate (VI) and sodium selenite(IV) was confirmed by Shanker et al.26. Landberg a Greger25 studied the effects of Se(IV) and
Se(VI) on Cd uptake in pea and wheat plants and found that selenite caused approximately threefold increase of Cd root concentration whereas application of selenate in- creased Cd shoot concentration by 50 %.
0 10 20 30 40 50 60 0 500 1000 1500 2000 2500 3000 Cd c on tent [m g kg -1 d. m .] c [mol dm-3] I III II IV CdSeO4 0 10 20 30 40 50 60 0 250 500 750 1000 1250 1500 C d c ontent [m g k g -1 d.m .] c [mol dm-3] I III IV II CdSeO3
Fig. 2. Dependence of cadmium content in roots (I) and shoots (II) of St. John´s wort as well as roots (III) and shoots (IV) of maize
plants on CdSeO4 and CdSeO3 concentration; d.m.- dry mass
1 2 3 0 100 200 300 400 500 BAF c [mol dm-3] I II III IV CdSeO4 12 24 60 0 1 2 3 50 100 150 200 250 BAF c [mol dm-3] I II III IV 12 24 60 CdSeO3
Fig. 3. Dependence of bioaccumulation factors (BAF) related to Cd determined for roots (I) and shoots (II) of St. John´s wort as
Conclusion
Flame atomic absorption spectroscopy was used for monitoring cadmium translocation within St. John´s wort and maize plants treated with cadmium selenate and se- lenite. It was found that Cd accumulation in plant roots was higher than its accumulation in the shoots. Selenium oxidation state significantly affected effectiveness of cad- mium uptake and accumulation by plants. Cd content in plant organs of experimental plant species treated with selenate was significantly higher than in plants treated with selenite. Roots of St. John´s wort exhibited higher Cd bioaccumulating capacity than maize roots, however Cd bioaccumulating ability of shoots was comparable. In the young maize plants portion from the total accumulated metal amount by the plant occurring in the shoots was about 43 % in the whole studied concentration range (1260 mol dm3) for both tested compounds (CdSeO
4
a CdSeO3). Therefore it is necessary to monitor metal con-
centrations in maize grown on the polluted fields whether Cd content in biomass do not exceed the limits of toxicity for animal feed. Similar monitoring is important also for St. John´s wort plants, above ground part of which is util- ized for phytotherapeutic purposes.
This study was financially supported by Scientific Grant Agency of the Ministry of Education of Slovak Re- public and the Slovak Academy of Sciences under the con- tract No. VEGA 1/0272/08 and by Sanofi Aventis Pharma Slovakia. The authors thank Assoc. Prof. Iveta Ondrejkovi- čová from Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava for prepara- tion of the studied compounds.
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