Flow injection analysis (FIA) and high-performance liquid chromatography double-focusing sector field inductively coupled plasma mass spectrometry (HPLC-DF-ICP-MS) were used for total arsenic determination and arsenic speciation of xylem sap of cucumber plants (Cucumis sativus L.) grown in hydroponics containing 2 micromol dm(-3) arsenate or arsenite, respectively. Arsenite [As(III)], arsenate [As(V)] and dimethylarsinic acid (DMA) were identified in the sap of the plants. Arsenite was the predominant arsenic species in the xylem saps regardless of the type of arsenic treatment, and the following concentration order was determined: As(III) > As(V) > DMA. The amount of total As, calculated taking into consideration the mass of xylem sap collected, was almost equal for both treatments. Arsenite was taken up more easily by cucumber than arsenate. Partial oxidation of arsenite to arsenate (<10% in 48 h) was observed in the case of arsenite-containing nutrient solutions, which may explain the detection of arsenate in the saps of plants treated with arsenite.

In intact plants, Cd-induced Fe deficiency is thought to play a role in the toxic effects of Cd on photosynthesis. To investigate the contribution of the Cd-induced Fe deficiency to Cd stress symptoms we studied the composition and organization changes of thylakoid pigment-protein complexes by twodimensional Blue Native-SDS gel electrophoresis and mass spectrometry, in parallel to functional changes, using Beta vulgaris plants grown in hydroponics. Plants were treated by withdrawing of Fe or with 10 µM CdCl2 for 10 days. Both metal stresses caused a marked decline in leaf chlorophyll concentration and chloroplast Fe content, as well as a loss in photosystem I (PSI) and light harvesting complex II (LHCII) particles. Furthermore, organizational changes of the photosynthetic apparatus were found, including a decrease in the ratio of the PSII mega-/supercomplexes and an increase in the monomeric form of the LHCII antennae, with the extent of these changes being similar under both stresses. This supports that Fe deficiency responses have a major role in the responses of plants under Cd stress. In the Fe-deficient thylakoids, an increase in the ratio of PSI supercomplexes and degrading PSII particles was more pronounced, together with a higher zeaxanthin content. Under Cd stress, a stronger inhibition of PSII activity and enhancement of thermal dissipation of the inactive PSII complexes were observed. The differences detected under the two metal stresses lead to the conclusion that both local Fe deficiency in chloroplasts and other direct or indirect inhibitory effects of Cd are behind the response mechanisms of plants grown under Cd stress. Our results appreciably contribute to the sparse structural information on thylakoid complexes affected by Cd toxicity and Fe deficiency. EÖTVÖS LORÁND UNIVERSITY INSTITUTE OF BIOLOGY DEPARTMENTAll previously published work cited in the manuscript has been fully acknowledged.I am looking forward to hearing from you at your earliest convenience.With best regards, Yours faithfully, Brigitta BasaHighlights:-Cd-induced chloroplast Fe deficiency is a prime trigger for thylakoid acclimation to Cd excess.-Both Cd stress and Fe deficiency induce PSII supercomplex and LHCII disassembly.-Thermal dissipation by inactive PSII complexes is markedly induced by Cd stress.-The amounts of PSI supercomplexes and zeaxanthin rise with Fe deficiency.-Cyclic electron flow and zeaxanthin are likely to be energy quenchers under low Fe.

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Effects of 10 microM cadmium (supplied as Cd nitrate) on the utilization and allocation of iron (Fe) were investigated in poplar (Populus alba L.) plants grown in nutrient solution with Fe(III)-EDTA or Fe(III)-citrate as the Fe source. The effects of Cd were also compared with those of Fe deprivation. The accumulation of Fe in roots was 10-fold higher in plants grown with Fe-citrate than with Fe-EDTA. Cadmium decreased leaf chlorophyll concentrations and photosynthetic rates, and these decreases were more marked in plants grown with Fe-citrate than with Fe-EDTA. In both Fe treatments, addition of Cd caused large increases in root and shoot apoplasmic and non-apoplasmic Cd contents and increases in root Fe content; however, Cd decreased shoot Fe content, especially in plants grown with Fe-citrate. New leaves of plants grown with Fe-citrate had small cellular (non-apoplasmic) Fe pools, whereas these pools were large in new leaves of plants grown with Fe-EDTA. Non-apoplasmic Cd pools in new leaves were smaller in plants grown with Fe-citrate than with Fe-EDTA, indicating that inactivation of non-apoplasmic Cd pools is facilitated more by Fe-EDTA than by Fe-citrate. In the presence of Cd, Fe-EDTA was also superior to Fe-citrate in maintaining an adequate Fe supply to poplar shoots. Differences in plant responses to Fe-EDTA and Fe-citrate may reflect differences in long-distance transport of Fe rather than in acquisition of Fe by roots.

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Main conclusion The accumulation of NiCo following the termination of the accumulation of iron in chloroplast suggests that NiCo is not solely involved in iron uptake processes of chloroplasts.Abstract Chloroplast iron (Fe) uptake is thought to be operated by a complex containing permease in chloroplast 1 (PIC1) and nickel-cobalt transporter (NiCo) proteins, whereas the role of other Fe homeostasis-related transporters such as multiple antibiotic resistance protein 1 (MAR1) is less characterized. Although pieces of information exist on the regulation of chloroplast Fe uptake, including the effect of plant Fe homeostasis, the whole system has not been revealed in detail yet. Thus, we aimed to follow leaf development-scale changes in the chloroplast Fe uptake components PIC1, NiCo and MAR1 under deficient, optimal and supraoptimal Fe nutrition using Brassica napus as model. Fe deficiency decreased both the photosynthetic activity and the Fe content of plastids. Supraoptimal Fe nutrition caused neither Fe accumulation in chloroplasts nor any toxic effects, thus only fully saturated the need for Fe in the leaves. In parallel with the increasing Fe supply of plants and ageing of the leaves, the expression of BnPIC1 was tendentiously repressed. Though transcript and protein amount of BnNiCo tendentiously increased during leaf development, it was even markedly upregulated in ageing leaves. The relative transcript amount of BnMAR1 increased mainly in ageing leaves facing Fe deficiency. Taken together chloroplast physiology, Fe content and transcript amount data, the exclusive participation of NiCo in the chloroplast Fe uptake is not supported. Saturation of the Fe requirement of chloroplasts seems to be linked to the delay of decomposing the photosynthetic apparatus and keeping chloroplast Fe homeostasis in a rather constant status together with a supressed Fe uptake machinery.

Prevention of iron chlorosis with Fe synthetic chelates is a widespread agronomical practice but implies high costs and environmental risks. Blood meal is one of the main fertilizers allowed to be used in organic farming. Through this work a novel blood meal fertilizer was audited. Measurements such as FTIR, Raman, electron paramagnetic resonance, and Mössbauer spectroscopy, UV-visible properties, stability against pH, and batch experiments were performed to characterize and assess the reactivity on soil constituents and agronomic soils. The spectroscopy findings give clear indications that Fe is in the ferric oxidation state, is hexacoordinated, and has a low-spin form suggesting a similar structure to hemin and hematin. A spectrophotometric method at 400 nm was validated to quantify blood meal concentration at low electrolyte concentrations. Batch experiments demonstrated high reactivity of blood meal fertilizer with soil constituents, mainly in the presence of calcium, where aggregation processes are predominant, and its ability to take Fe from synthetic Fe (hydr)oxides. The beneficial profile of blood meal by a providing nitrogen source together with the capability to keep the Fe bound to porphyrin organic compounds makes it a good candidate to be used as Fe fertilizer in organic farming.

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