Iron deficiency is a major human nutritional problem wherever plant-based diets are common. Using synchrotron x-ray fluorescence microtomography to directly visualize iron in Arabidopsis seeds, we show that iron is localized primarily to the provascular strands of the embryo. This localization is completely abolished when the vacuolar iron uptake transporter VIT1 is disrupted. Vacuolar iron storage is also critical for seedling development because vit1-1 seedlings grow poorly when iron is limiting. We have uncovered a fundamental aspect of seed biology that will ultimately aid the development of nutrient-rich seed, benefiting both human health and agricultural productivity.

https://science.sciencemag.org/content/sci/314/5803/1295.full.pdf

Localization of Iron in Arabidopsis Seed Requires the Vacuolar Membrane Transporter VIT1

Trace elements in the soil-plant interface: Phytoavailability, translocation, and phytoremediation–A review

Th is paper reviews progress in phytoextraction of soil elements and illustrates the key role of hyperaccumulator plant species in useful phytoextraction technologies. Much research has focused on elements which are not practically phytoextracted (Pb); on addition of chelating agents which cause unacceptable contaminant leaching and are cost prohibitive; and on plant species which off er no useful phytoextraction capability (e.g., Brassica juncea Czern). Nickel phytoextraction by Alyssum hyperaccumulator species, which have been developed into a commercial phytomining technology, is discussed in more detail. Nickel is ultimately accumulated in vacuoles of leaf epidermal cells which prevents metal toxicity and provides defense against some insect predators and plant diseases. Constitutive up-regulation of trans-membrane element transporters appears to be the key process that allows these plants to achieve hyperaccumulation. Cadmium phytoextraction is needed for rice soils contaminated by mine wastes and smelter emissions with 100-fold more soil Zn than Cd. Although many plant species can accumulate high levels of Cd in the absence of Zn, when Cd/Zn > 100, only Th laspi caerulescens from southern France has demonstrated the ability to phytoextract useful amounts of Cd. Production of element-enriched biomass with value as ore or fertilizer or improved food (Se) or feed supplement may off set costs of phytoextraction crop production. Transgenic phytoextraction plants have been achieved for Hg, but not for other elements. Although several researchers have been attempting to clone all genes required for eff ective hyperaccumulation of several elements, success appears years away; such demonstrations will be needed to prove we have identifi ed all necessary processes in hyperaccumulation.

/pdf/improved-understanding-of-hyperaccumulation-yields-4frv030xn4.pdf

Improved Understanding of Hyperaccumulation Yields Commercial Phytoextraction and Phytomining Technologies

Nickel even though recognized as a trace element, its metabolism is very decisive for certain enzyme activities, maintaining proper cellular redox state and various other biochemical, physiological and growth responses. Study of the aspects related with uptake, transport and distributive localization of Ni is very important in various cellular metabolic processes particularly under increased nitrogen metabolism. This review article, in core, encompasses the dual behavior of Ni in plants emphasizing its systemic partitioning, essentiality and ill effects. However, the core mechanism of molecules involved and the successive physiological conditions required starting from the soil absorption, neutralization and toxicity generated is still elusive, and varies among the plants.

Nickel: An Overview of Uptake, Essentiality and Toxicity in Plants

Synchrotron-based X-ray fluorescence (S-XRF) was utilized to locate arsenic (As) in polished (white) and unpolished (brown) rice grains from the United States, China, and Bangladesh. In white rice As was generally dispersed throughout the grain, the bulk of which constitutes the endosperm. In brown rice As was found to be preferentially localized at the surface, in the region corresponding to the pericarp and aleurone layer. Copper, iron, manganese, and zinc localization followed that of arsenic in brown rice, while the location for cadmium and nickel was distinctly different, showing relatively even distribution throughout the endosperm. The localization of As in the outer grain of brown rice was confirmed by laser ablation ICP-MS. Arsenic speciation of all grains using spatially resolved X-ray absorption near edge structure (micro-XANES) and bulk extraction followed by anion exchange HPLC-ICP-MS revealed the presence of mainly inorganic As and dimethylarsinic acid (DMA). However, the two techniques indicated different proportions of inorganic:organic As species. A wider survey of whole grain speciation of white (n=39) and brown (n=45) rice samples from numerous sources (field collected, supermarket survey, and pot trials) showed that brown rice had a higher proportion of inorganic arsenic present than white rice. Furthermore, the percentage of DMA present in the grain increased along with total grain arsenic.

Speciation and Localization of Arsenic in White and Brown Rice Grains

This paper shows that synchrotron-based fluorescence and absorption-edge computed microtomographies (CMT) are well-suited for determining the compartmentalization and concentration of metals in hyperaccumulating plant tissues. Fluorescence CMT of intact leaf, stem, and root samples revealed that Ni concentrated in stem and leaf dermal tissues and, together with Mn, in distinct regions associated with the Ca-rich trichomes on the leaf surface of the nickel hyperaccumulator Alyssum murale “Kotodesh”. Metal enrichment was also observed within the vascular system of the finer roots, stem, and leaves but absent from the coarser root, which had a well-correlated metal coating. Absorption-edge CMT showed the three-dimensional distribution of the highest metal concentrations and verified that epidermal localization and Ni and Mn co-localization at the trichome base are phenomena that occurred throughout the entire leaf and may contribute significantly to metal detoxification and storage. Ni was also observed in t...

Rufus L. Chaney

Papers

Application of quantitative fluorescence and absorption-edge computed microtomography to image metal compartmentalization in Alyssum murale.