Studies on spatial distribution of nickel in leaves and stems of the metal hyperaccumulator Stackhousia tryonii Bailey using nuclear microprobe (micro-PIXE) and EDXS techniques

Abstract

Stackhousia tryonii Bailey is one of the three nickel hyperaccumulators reported from Australia. It is a rare, herbaceous plant that accumulates (Ni) both in leaf and stem tissues. Localisation of Ni in leaf and stem tissues of S. tryonii was studied using two micro-analytical techniques, energy dispersive X-ray spectrometry (EDXS) and micro-proton-induced X-ray emission spectrometry (micro-PIXE). Dimethylglyoxime complexation of Ni was also visualised by bright- and dark-field microscopy, but this technique was considered to create artefacts in the distribution of Ni. Energy dispersive X-ray spectrometric analysis indicated that guard cells possessed a lower Ni concentration than epidermal cells, and that epidermal cells and vascular tissue contained higher levels of Ni than mesophyll, as reported for other Ni hyperaccumulators. The highest Ni concentration was recorded (PIXE quantitative point analysis) in the epidermal cells and vascular tissue (5400 μg g–1 DW), approximately double that recorded in palisade cells (2500 μg g–1 DW). However, concentrations were variable within these tissues, explaining, in part, the similarity between average Ni concentrations of these tissues (as estimated by region selection mode). Stem tissues showed a similar distribution pattern as leaves, with relatively low Ni concentration in the pith (central) region. The majority of Ni (73–85% for leaves; 80–92% for stem) was extracted from freeze-dried sections by water extraction, suggesting that this metal is present in a highly soluble and mobile form in the leaf and stem tissues of S. tryonii.

Arbuscular Mycorrhiza in Metal Hyperaccumulating Plants

“…Within the xylem, the metals are transported as stable complexes bound either to free His (as His-Ni and His-Zn complexes), to nicotianamine, organic acids (Krämer et al 1996;Küper et al 2004;Pilon-Smits 2005) or S-ligands (Cd) (Küper et al 2004). Within the leaves, metals are usually accumulated along the path of the transpiration stream, in epidermal and vascular tissues and to a lesser extent in palisade and spongy mesophyll, indicating metal accumulation away from photosynthetically active tissues (Seregin and Ivanov 2001;Bhatia et al 2004;Cosio et al 2005;Wójcik et al 2005). Zn was proven to be localized in large vacuolated epidermal cells (Frey et al 2000).…”

Nickel in the Environment and Its Role in the Metabolism of Plants and Cyanobacteria

“…When vacuolar sequestration is the major detoxifi cation mechanism, nickel tolerance is often associated with elevated nickel accumulation; an extreme form of this sequestration is found in hyperaccumulator plants (see Section 4). In most heavy-metal-tolerant plants, the vacuolar sequestration occurs mainly in nonphotosynthetic cells of the epidermis, reducing toxicity to the heavy metal sensitive photosynthetic apparatus [95,[136][137][138][139].…”

“…Hyperaccumulators generally seem to sequester nickel in the vacuole [95,183,184], which is the ideal storage compartment for toxic substances since it is physiologically inactive. Most hyperaccumulator plants have been found to accumulate nickel in the epidermis [95,139,[183][184][185], which makes sense for two reasons. First, the epidermis is the tissue ingested fi rst by a tissue-chewing herbivore, so the epidermal storage is most effi cient for anti-herbivore defence.…”

Transient Influx of Nickel in Root Mitochondria Modulates Organic Acid and Reactive Oxygen Species Production in Nickel Hyperaccumulator Alyssum murale

“…Cellular or tissue compartmentalization and sequestration of nickel has been studied widely (4,6,7,(13)(14)(15)(16)(17)(18), however, few studies focus on organelle distribution of nickel (4,7,8). These studies converge on vacuolar distribution of nickel, whereas its effect on other cellular organelles was not defined.…”