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Effects of Pb and Cd on Cucumber Depending on the Fe-Complex in the Culture Solution

Summary Modifying effects of EDTA and citrate as Fe(III)-complexes on Pb-and Cd-toxicity were investigated with cucumber ( Cucumis sativus L.) grown in culture solution. Pb and Cd were applied in lO μM concentration. Pb and Cd inhibited the growth of plants with Fe-citrate but with Fe-EDTA only Cd did. Chlorophyll content of Cd-treated plants-independently on the Fe-complex-was very low similarly to the iron deficient plants. Pb is proved to inhibit the chlorophyll accumulation only in plants supplied with Fe-citrate. Photosynthetic activity of 6-week-old plants was characterized by in vivo CO 2 fixation. The highest activities were observed in the middle (third-fourth) leaf storeys, and decreased in the lower and higher leaf storeys. Cd caused more than 50 % inhibition of the photosynthetic activity when applied with Fe-EDTA. With Fe-citrate, the inhibition exceeded 90 %. The photosynthetic activities in the Pb-treated plants were not significantly different from the control plants. The amount of chlorophyll containing complexes, especially that of PS I was highly affected by Cd particularly in the lower leaves. The results correlate with 59 Fe translocation into the shoot. Fe translocation was stimulated by Pb in the presence of Fe-EDTA but it was inhibited in the presence of Fe-citrate. Cd completely inhibited Fe translocation from the root to the shoot with both chelators. It is concluded that strong iron deficiency has a great but not exclusive role in the observed symptoms, and that the quality of the chelator strongly influences the effects of these polluting metals.

Lead uptake, distribution, and remobilization in cucumber

Abstract Mobility and distribution of lead (Pb) were investigated in cucumber (Cucumis sativus L.) grown in solution culture. Based on the observation that Pb uptake is influenced by the chemical form of iron (Fe) (complexed or ionic) in the solution, Fe distribution was also determined. Iron concentration was even in the stem (separated to internodes) and petioles but slightly increased at the shoot tip while Pb concentration decreased upwards. In the leaves Fe concentration decreased upwards (whereas in the control it increased a little at the youngest leaves) while Pb concentration increased to the largest leaves then decreased towards the shoot tip. It is suggested that the distribution of Pb in cucumber is passive process and it accumulates in the apoplast while Fe distribution is determined by the requirements of synthetic processes in young or photosynthesizing tissues. Lead probably lowers Fe transport into the symplast in the leaves causing slight chlorosis at the youngest leaves. In the plants t...

Relationship between Changes in Ion Content of Leaves and Chlorophyll-Protein Composition in Cucumber under Cd and Pb Stress

Hydroponically cultured cucumber plants supplied with 4 μᴍ Fe chelated either with EDTA or citrate and treated with Cd (10 μᴍ) and Pb (10, 50 μᴍ) from their one- or fourleaf stage were grown up to five-week-old age. The decrease in the chlorophyll content was the most pronounced in plants treated with Cd from a younger age, and in the case of Fecitrate. The chlorophyll a/b ratio of Cd stressed plants was also significantly lowered. In later treated plants the accumulation of chlorophyll was inhibited and the chlorophyll a/b ratio decreased only in the vigorously growing young leaves. Pb treatment had only a slight effect on both parameters. The changes in the chlorophyll-protein pattern of thylakoids were strongly related to their chlorophyll content but the response of each complex was different. Cd reduced the amount of chlorophyll containing complexes in the order of photosystem I > light-harvesting complex II > photosystem Il-core, while light-harvesting complex II appeared somewhat more sensitive than photosystem I in Pb treated plants. In accordance, a decline or blue shift of the long wavelength fluorescence emission band of chloroplasts was observed referring to disturbances also in photosystem I antenna assembly. The accumulation of chlorophyll and chlorophyll-proteins did not show close relationship to the heavy metal content of leaves which was the highest in the first of the intensively expanding leaves in the time of the treatment. The extraordinary sensitivity of photosystem I, and the relative stability of photosystem II under Cd treatment were similar to the case found in iron deficient plants. However, the pattern of chlorophyll content of leaf storeys of Cd treated plants rather followed the changes in their Mn content

Effect of lead, nickel and vanadium contamination on organic acid transport in xylem sap of cucumber

Abstract Three organic acids (citric, fumaric and malic) of the Krebs cycle were measured by the reversed-phase high performance liquid chromatography (RP-HPLC) technique in the xylem saps of cucumber plants grown in (i) control nutrient solutions containing iron as Fe(III)-ethylene-diamine-tetraacetate (Fe(III)-EDTA), Fe(III)-citrate or FeCl 3 and (ii) in nutrient solutions contaminated with nickel, lead or vanadium in a concentration of 10 −5 M. Simultaneously, the heavy metal content of the xylem sap samples was determined by total reflection X-ray fluorescence spectrometry (TXRF). In the presence of lead or nickel contamination the transport of the organic acids became higher by factor 1.1–2.3 compared to the control plants when Fe(III)-citrate or Fe(III)-chloride was added to the nutrient solutions. In the case of plants growing in Fe(III)-EDTA containing solutions, however, the transport of the organic acids decreased by 30–40%. The effect of vanadium on the transport of organic acids was considerably smaller. Generally, the deviation in the organic acid transport between the contaminated and the control plants was proportional to the heavy metal transport in the xylem in the sequence Ni>Pb>V.

Study of interaction of iron and lead during their uptake process in wheat roots by total-reflection X-ray fluorescence spectrometry

Microwave assisted acidic digestion and total-reflection X-ray fluorescence spectrometry (TXRF) was used for the determination of lead and iron in wheat roots cultured in CaSO4 solution, and treated with Pb(NO3)2 and Fe(III)-citrate or Fe(III)-EDTA under controlled conditions, respectively. It was established that lead has a stimulation effect on the iron uptake in the presence of Fe(III)-citrate. The lead uptake, however, is hardly influenced by iron independently from the complex forming agents applied. To check the stability of the accumulated iron and lead constituents, some of the roots were washed with various solutions and the removable iron and lead were also measured by TXRF. These experiments indicate that the presence of lead results in higher stability of iron constituents in the root; however, iron does not have any effect on the lead constituents, the stabilities of which increase in the order Pb-citrate < Pb-(cell wall) < Pb-EDTA.

Effect of lead treatment on the distribution of essential elements in cucumber

Abstract Changes in the fresh and dry weight of leaf blades, petioles, internodes, and their ion concentrations as well as rates of root exudation were investigated in cucumber grown in hydroponic culture and treated with physiological concentrations of lead (Pb). The growth of flowering cucumber supplied with FeCl3 shows a typical bell‐shaped curve derived from leaf dry weights, where the 4th, 5th, and 6th leaves are the largest ones. Lead inhibited growth up to 20% (except the youngest leaves which were stimulated), but did not cause morphological changes. Whereas root growth was also retarded by about 20%, exudation was inhibited to 50%, that is, the root resistance to water transport was increased by Pb. In spite of that the dry matter yield of internodes and petioles hardly reached 10 and 5% of that of leaf blades, respectively, their calcium (Ca), magnesium (Mg), and zinc (Zn) concentrations were almost the same. Similarly, the concentrations of these metals in the specific leaf blades are equal despite their different growth characteristics but the concentration of Mn is independent of the growth of the examined tissues. Lead was the only cation to accumulate in the largest leaves. The inhibitory effect of Pb on ion uptake was proportional to the growth inhibition of the tissues except manganese (Mn), the accumulation of which was stimulated by Pb in all the analyzed tissues and copper (Cu) which increased only in the internodes. We could not explain the extremely different ion distributions observed during the growth of cucumber. However, it is evident that the measurement of ion concentrations at whole shoot level is not enough to characterize ion interactions because only some ions accumulate at the same rate as tissues grow. These ions maintain stable concentration levels in shoot parts whereas others decrease or increase independently from growth.

Application of total-reflection X-ray fluorescence spectrometry and high-performance liquid chromatography for the chemical characterization of xylem saps of nickel contaminated cucumber plants

Abstract Total-reflection X-ray fluorescence (TXRF) spectrometry, reversed-phase (RP) and size–exclusion (SE) high-performance liquid chromatography (HPLC) methods were applied for the characterization of low-volume xylem sap of control and nickel contaminated cucumber plants growing in hydroponics containing urea as the sole nitrogen source. In these saps collected for 1 h, Ca, K, Fe, Mn, Ni, Zn, as well as malic, citric and fumaric acids were determined. The SEC measurements showed that macromolecules were not detectable in the samples. Nickel contamination had minimum impact on the organic acid transport, however, the transport of Zn, K and Fe was reduced by 50, 22 and 11%, respectively. This observation supports the results of our earlier experiments when nitrate ions were used as the sole nitrogen form. At the same time, the fresh root weight and the volume of the collected xylem sap increased by 36 and 85%, respectively. Therefore, nickel addition seemed to decrease the urea toxicity of the plants. By pooling the eluting fractions of the SEC column, which were 10-fold concentrated by freeze-drying, the series of the resulted samples were analyzed by the TXRF spectrometry and RP-HPLC. The three organic acids could be identified in only one of the fractions, which contained Fe and, in the case of the contaminated plants, Ni in detectable concentration. However, considerable parts of these two elements and Mn, as well as practically the total amounts of Cu may be transported by unidentified organic compounds in the xylem.

Heavy metal accumulation and tolerance of energy grass (Elymus elongatus subsp. ponticus cv. Szarvasi-1) grown in hydroponic culture

Phytoremediation is a plant based, cost effective technology to detoxify or stabilise contaminated soils. Fast growing, high biomass, perennial plants may be used not only in phytoremediation but also in energy production. Szarvasi-1 energy grass (Elymus elongatus subsp. ponticus cv. Szarvasi-1), a good candidate for this combined application, was grown in nutrient solution in order to assess its Cd, Cu, Ni, Pb and Zn accumulation and tolerance. Its shoot metal accumulation showed the order Pb < Ni < Cu ∼ Cd < Zn. In parallel with this, Pb and Ni had no or very little influence on the growth, dry matter content, chlorophyll concentration and transpiration of the plants. Cu and Cd treatment resulted in significant decreases in all these parameters that can be attributed to Fe plaque formation in the roots suggested by markedly increased Fe and Cu accumulation. This came together with decreased shoot and root Mn concentrations in both treatments while shoot Cu and Zn concentrations decreased under Cd and Cu exposure, respectively. Zn treatment had no effect or even slightly stimulated the plants. This may be due to a slight stimulation of Fe translocation and a very efficient detoxification mechanism. Based on the average 300 mg kg⁻¹ (dry mass) Zn concentration which is 0.03% of the shoot dry mass the variety is suggested to be classified as Zn accumulator.

Fluorescence Spectroscopy of Iron-Deficient Plants

Iron deficient cucumber (Cucumis sativus L.) plants and such differently supplied with iron were studied by low-temperature fluorescence emission and excitation spectroscopy. Iron deficiency caused a relative decrease and a blue-shift of the 733 nm emission and a decrease or disappearance of the 700 and 707-710 nm excitation bands which are considered to belong to chlorophyll forms of PSI. The process of iron uptake was observed after readdition of iron to previously iron-stressed plants. Iron-deficient plants (with green cotyledon) were treated with the chelator EDTA which treatment resulted in a small increase of the chlorophyll content but the fluorescence spectra of these plants differed from those of plants supplied with iron: they had blue-shifted maxima. The data presented show that fluorescence spectroscopy is a very sensitive and suitable method for studying iron deficiency, observing - indirectly - iron uptake and its utilization in plants.

ARSENATE INDUCES WATER STRESS

The effects of arsenate and arsenite on growth and transpiration were investigated in cucumber plants grown in nutrient solution containing 2, 10, and 100 μM phosphate, respectively. Root and shoot growth decreased by 48–64% compared to the control in all treatments and there was no significant difference between the effects of arsenic As(V) and As(III) except for the lowest phosphate concentration. At 2 μM phosphate As(III) had significantly higher growth inhibition than As(V). The inhibition of transpiration was between 46–68% in all treatments, and As(V) had stronger effect at 10 μM phosphate compared to 100 μM. Arsenic caused fast wilting 2 hours after the commencement of the treatment. However, the formation of adventitious roots prevented the loss of turgor. The hypothesis that aquaporins might be involved in the action of As(V) has been tested by comparison of the effect of As(V) and Hg, the inhibitor of aquaporins. Both treatments resulted in similar inhibition of growth and transpiration, increase in water saturation deficit and decrease in root exudation. Data imply that (i) phosphate reduces arsenate uptake, (ii) arsenate can be at least partially detoxified in cucumber at higher phosphate concentrations, (iii) arsenate may be reduced to arsenite and (iv) As(V) may interfere with the proper functioning of aquaporins.