Convergent patterns of tissue-level distribution of elements in different tropical woody nickel hyperaccumulator species from Borneo Island

Abstract The Malaysian state of Sabah on the Island of Borneo has recently emerged as a global hotspot of nickel hyperaccumulator plants. This study focuses on the tissue-level distribution of nickel and other physiologically relevant elements in hyperaccumulator plants with distinct phylogenetical affinities. The roots, old stems, young stems and leaves of Flacourtia kinabaluensis (Salicaceae), Actephila alanbakeri (Phyllanthaceae), Psychotria sarmentosa (Rubiaceae) and young stems and leaves of Glochidion brunneum (Phyllanthaceae) were studied using nuclear microprobe (micro-PIXE and micro-BS) analysis. The tissue-level distribution of nickel found in these species has the same overall pattern as in most other hyperaccumulator plants studied previously, with substantial enrichment in the epidermal cells and in the phloem. This study also revealed enrichment of potassium in the spongy and palisade mesophyll of the studied species. Calcium, chlorine, manganese and cobalt were found to be enriched in the phloem and also concentrated in the epidermis and cortex of the studied species. Although hyperaccumulation ostensibly evolved numerous times independently, the basic mechanisms inferred from tissue elemental localization are convergent in these tropical woody species from Borneo Island

Iron and ferritin accumulate in separate cellular locations in Phaseolus seeds

<p>Abstract</p> <p>Background</p> <p>Iron is an important micronutrient for all living organisms. Almost 25% of the world population is affected by iron deficiency, a leading cause of anemia. In plants, iron deficiency leads to chlorosis and reduced yield. Both animals and plants may suffer from iron deficiency when their diet or environment lacks bioavailable iron. A sustainable way to reduce iron malnutrition in humans is to develop staple crops with increased content of bioavailable iron. Knowledge of where and how iron accumulates in seeds of crop plants will increase the understanding of plant iron metabolism and will assist in the production of staples with increased bioavailable iron.</p> <p>Results</p> <p>Here we reveal the distribution of iron in seeds of three <it>Phaseolus </it>species including thirteen genotypes of <it>P. vulgaris</it>, <it>P. coccineus</it>, and <it>P. lunatus</it>. We showed that high concentrations of iron accumulate in cells surrounding the provascular tissue of <it>P. vulgaris </it>and <it>P. coccineus </it>seeds. Using the Perls' Prussian blue method, we were able to detect iron in the cytoplasm of epidermal cells, cells near the epidermis, and cells surrounding the provascular tissue. In contrast, the protein ferritin that has been suggested as the major iron storage protein in legumes was only detected in the amyloplasts of the seed embryo. Using the non-destructive micro-PIXE (Particle Induced X-ray Emission) technique we show that the tissue in the proximity of the provascular bundles holds up to 500 μg g^-1of iron, depending on the genotype. In contrast to <it>P. vulgaris </it>and <it>P. coccineus</it>, we did not observe iron accumulation in the cells surrounding the provascular tissues of <it>P. lunatus </it>cotyledons. A novel iron-rich genotype, NUA35, with a high concentration of iron both in the seed coat and cotyledons was bred from a cross between an Andean and a Mesoamerican genotype.</p> <p>Conclusions</p> <p>The presented results emphasize the importance of complementing research in model organisms with analysis in crop plants and they suggest that iron distribution criteria should be integrated into selection strategies for bean biofortification.</p

\u3ci\u3eSenecio Conrathii\u3c/i\u3e N.E.Br. (Asteraceae), a New Hyperaccumulator of Nickel from Serpentinite Outcrops of the Barberton Greenstone Belt, South Africa

Five nickel hyperaccumulators belonging to the Asteraceae are known from ultramafic outcrops in South Africa. Phytoremediation applications of the known hyperaccumulators in the Asteraceae, such as the indigenous Berkheya coddii Roessler, are well reported and necessitate further exploration to find additional species with such traits. This study targeted the most frequently occurring species of the Asteraceae on eight randomly selected serpentinite outcrops of the Barberton Greenstone Belt. Twenty species were sampled, including 12 that were tested for nickel accumulation for the first time. Although the majority of the species were excluders, the known hyperaccumulators Berkheya nivea N.E.Br. and B. zeyheri (Sond. & Harv.) Oliv. & Hiern subsp. rehmannii (Thell.) Roessler var. rogersiana (Thell.) Roessler hyperaccumulated nickel in the leaves at expected levels. A new hyperaccumulator of nickel was discovered, Senecio conrathii N.E.Br., which accumulated the element in its leaves at 1695 ± 637 µg g−1 on soil with a total and exchangeable nickel content of 503 mg kg−1 and 0.095 µg g−1, respectively. This makes it the third known species in the Senecioneae of South Africa to hyperaccumulate nickel after Senecio anomalochrous Hilliard and Senecio coronatus (Thunb.) Harv., albeit it being a weak accumulator compared with the latter. Seven tribes in the Asteraceae have now been screened for hyperaccumulation in South Africa, with hyperaccumulators only recorded for the Arctoteae and Senecioneae. This suggests that further exploration for hyperaccumulators should focus on these tribes as they comprise all six species (of 68 Asteraceae taxa screened thus far) to hyperaccumulate nickel

The Nuclear Microprobe - a Challenging Tool in Plant Sciences

The nuclear microprobe is a microanalytical tool capable of quantitative studies of elemental distribution at the ppm level with a spatial resolution of the order of 1μm. This sensitivity is adequate for most elements of interest, and the spatial resolution is acceptable for studies of elemental distribution in organs, tissues, and cells. The main techniques used in plant science are particle induced X-ray emission using protons, proton backscattering, scanning transmission ion microscopy, and particle induced gamma-ray emission. Specimen preparation is the most difficult part of analysis, and only cryotechniques are recommended presently for all types of microanalytical studies

Zinc allocation to and within Arabidopsis halleri seeds: Different strategies of metal homeostasis in accessions under divergent selection pressure

Abstract Vegetative tissues of metal(loid)‐hyperaccumulating plants are widely used to study plant metal homeostasis and adaptation to metalliferous soils, but little is known about these mechanisms in their seeds. We explored essential element allocation to Arabidopsis halleri seeds, a species that faces a particular trade‐off between meeting nutrient requirements and minimizing toxicity risks. Combining advanced elemental mapping (micro‐particle induced X‐ray emission) with chemical analyses of plant and soil material, we investigated natural variation in Zn allocation to A. halleri seeds from non‐metalliferous and metalliferous locations. We also assessed the tissue‐level distribution and concentration of other nutrients to identify possible disorders in seed homeostasis. Unexpectedly, the highest Zn concentration was found in seeds of a non‐metalliferous lowland location, whereas concentrations were relatively low in all other seed samples—including metallicolous ones. The abundance of other nutrients in seeds was unaffected by metalliferous site conditions. Our findings depict contrasting strategies of Zn allocation to A. halleri seeds: increased delivery at lowland non‐metalliferous locations (a likely natural selection toward enhanced Zn‐hyperaccumulation in vegetative tissues) versus limited translocation at metalliferous sites where external Zn concentrations are toxic for non‐tolerant plants. Both strategies are worth exploring further to resolve metal homeostasis mechanisms and their effects on seed development and nutrition