Electron microscopical observations of leaf ferritin from iron-treated Xanthium plants: Localization and diversity in the organelle

Seckbach, Joseph

doi:10.1016/s0022-5320(72)80007-8

Cited by 35 publications

(38 citation statements)

References 25 publications

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“…Ferritin iron, which is easily reduced by dithionite, is not released to a significant degree during the first 7 min after dithionite addition, when more than 90% of the rapidly removable iron pool has been released. Since ferritin is located exclusively in the plastids (27), this experiment shows that dithionite does not reach the inside of the plastids during the first 7 min of incubation. However, with the consideration that, quantitatively, ferritin is the most important form of iron storage in the cell (7), and that the bulk of K+ ions leaking into solution after 10 min incubation must come from the vacuoles, we conclude that the potentially most important spaces for dithionite-sensitive iron, the vacuoles and the plastids, are not reached by the reductant during the period used for the extraction of free space iron.…”

Section: Discussionmentioning

confidence: 69%

Free Space Iron Pools in Roots

Bienfait¹,

Briel²,

Mesland-Mul³

1985

Plant Physiol.

281

108

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A rapid and simple method for the determination of a ferric iron pool in the free space of roots is described. Formation of this pool depended on the source of iron in the nutrient solution. During growth in water culture at pH 5 to 6 with Fe-ethylenediaminetetraacetate, a free space pool of 500 to 1000 nanomoles Fe per gram fresh weight was formed in the roots of bean (Phaselus vullgaris L. var. Prelude), maize (Zea mays L. var. Capella), and chlorophytum (Chlorophytum comosum IThunb. Jacques). No si nt pool (less than 100 nanomoles per gram fresh weight) was formed with ferrioxamine. Upon impending Fe deficiency, bean and chlorophytum were able to mobilize this pool. Fe-deficient bean plants mobilized iron from the free space iron pool of another plant in the same vessel.Iron uptake by plants is fastest when iron is present in the ferrous form (10). In anaerobic soils, high concentrations of ferrous ions may lead to iron toxicity by excessive iron uptake. Plants may limit iron uptake under those conditions by oxidation of ferrous ions with oxygen which is transported from the shoot via aerenchyma (12). Iron in aerobic soils is mainly present as the ferric ion in precipitates (14) or in soluble chelates (22). Dicotyledonous plants may enhance their capacity for iron uptake in response to a developing deficiency, by increasing their ability to reduce ferric chelates at the root surface (10). The uptake of iron by roots is therefore a result of several processes which may occur simultaneously: (a) reduction of ferric chelates in the rhizosphere by excreted reducing compounds (20) Crude Cell Wall Preparations. Root systems were washed in 0.5 mM CaSO4 for 10 to 15 min, frozen in liquid N2, and milled with an iron-free mortar and pestle. The resulting powder was suspended in 0.5 mM CaSO4, and the material precipitating at 500g was collected. This washing procedure was repeated at least three times, after which the final precipitate was suspended in 0.5 mM CaSO4, 10 mM Mes (pH 5.5).Determination of Apoplasmic Iron. A plant was transferred from nutrient solution to a beaker with 0.5 mm CaSO4 under vigorous aeration. After 10 to 15 min, the plant was placed with its root system in a wide 40-ml tube with 21 ml 10 mm Mes, 0.5 mM Ca(NO3)2, 1.5 mM 2,2'-bipyridyl (pH 5.5) at 25°C. Nitrogen was bubbled through the solution and the tube was covered with a cotton plug to prevent entry of oxygen by turbulence. After 5 min under N2, 1 ml 250 mm Na2S204 was added from a syringe.The A520 of the solution (A520 of 1 mM Fe[bipyridyl]3 = 8.650) was followed on 2-ml samples. The first sample was taken just before addition ofdithionite. The reaction was stopped, routinely after 10 min, by transferring the plant to a beaker with 0.5 L vigorously aerated 0.5 mM CaSO4. The plant could then be used for other determinations, or be put back on nutrient solution for further culture.Reducible iron in crude cell wall preparations was determined in the same way as described for intact roots, but samples taken from the incubation suspens...

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Section: Discussionmentioning

confidence: 69%

Free Space Iron Pools in Roots

Bienfait¹,

Briel²,

Mesland-Mul³

1985

Plant Physiol.

281

108

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“…Since the electron-dense iron cores of ferritin can also be detected by EM (Seckbach, 1982), we tried to characterize the iron/phosphorus-particles in the mutant leaves by comparison with a known plant ferritin as a reference. Plant ferritin is an iron storage protein that accumulates in seeds (Sczekan and Joshi, 1987;Briat et al, 1989), in leaves during senescence (Barton, 1970), or after iron overload (Seckbach, 1972(Seckbach, ,1982van der Mark and van den Briel, 1985). It is located mainly in plastids but also in xylem (Robards and Robinson, 1968) and in phloem (Behnke, 1977).…”

Section: Discussionmentioning

confidence: 99%

Subcellular Localization and Characterization of Excessive Iron in the Nicotianamine-less Tomato Mutant chloronerva

1995

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To understand the function of the Fe2+-complexing compound nicotianamine (NA) in the iron metabolism of plants we have localized iron and other elements in the NA-containing tomato wild type (Lycopersicon esculentum) and its NA-free mutant chloronerva by quantitative x-ray microanalysis. Comparison of element composition of the rhizodermal cell walls indicated that the wild type accumulated considerable amounts of iron and phosphorus in the cell wall, whereas in the mutant iron and phosphorus were detected in the cytoplasm and vacuoles of the rhizodermis. In mutant leaves containing high iron concentrations in the symplast, electron-dense inclusions were detected in chloroplasts and phloem. Such particles, consisting mainly of iron and phosphorus, were never found in the wild type and were very rarely detected in young chlorotic mutant leaves or after treatment of the mutant with NA. For further characterization the electron-dense inclusions in mutant leaves were isolated and compared by sodium dodecyl sulfate-gel electrophoresis and immunoblotting to ferritin from iron-loaded Phaseolus vulgaris leaves. Antibodies raised against purified Phaseolus leaf ferritin were used. Neither in mutant nor in wild type (iron loaded and control) was ferritin protein detected. These results suggest that the electron-dense inclusions in mutant leaves are not identical with ferritin. It is concluded that NA is necessary to complex ferrous iron in a soluble and available form within the cells. In the absence of NA the precipitation of excessive iron in the form of insoluble ferric phosphate compounds could protect the cells from iron overload.

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“…These purified ferritin grains show the electron dense iron core 6-7 nm in diameter of each moleculemany of them show iron micellar substructure (encircled). After Seckbach, 1972b. FERRETING OUT THE SECRETS OF PLANT FERRITIN 371 various cellular organelles, e.g., mitochondria, nucleus, lyzosome and in cytoplasmic vesicles (see Seckbach, 1968).…”

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confidence: 99%

“…Studies fron that period show that iron-chlorotic plants deposit increasing amounts of ferritin after they have been transferred to nutrient solutions supplemented with higher concentrations of iron (Seckbach, 1968(Seckbach, , 1969(Seckbach, , 1971(Seckbach, , 1972(Seckbach, , 1972a. Such manipulation, termed plant "iron treatment," has also been perforned with mammalian systems with similar results of ferritin increase in cells (see Drysdale and Shafritz, 1975;Bomford et al, 1981).…”

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confidence: 99%