Comparison of cytology and distribution of nickel in roots of Ni-hyperaccumulating and non-hyperaccumulating genotypes of Senecio coronatus

Abstract

Two genotypes of Senecio coronatus (Thunb.) Harv. (Asteraceae) growing on ultramaWc outcrops were identiWed previously: a Ni hyperaccumulator and a non-hyperaccumulator. The aim of the present study was to investigate the cytology of the roots of both genotypes, their Ni content and tissue distribution, and to ascertain whether there was a cytological basis for the diVerential uptake of Ni. Light and Xuorescence microscopy together with histochemical methods were used to study root cytology. X-ray microanalysis by means of a nuclear microprobe-particle-induced X-ray emission (PIXE) and proton backscattering (BS) techniques-was utilized to determine the concentration and distribution of Ni and other elements. Average concentration of Ni and distribution in roots diVered signiWcantly between hyperaccumulating and non-hyperaccumulating genotypes. Ni amount in the hyperaccumulating genotype was ca. 60 times higher in the older part of the root (1,760 g g ¡1 ) and ca. 10 times higher (314 g g ¡1 ) in the younger root hair region in comparison with the equivalent parts of the non-accumulating genotype where Ni amounts were 30 g g ¡1 . Ni distribution pattern was also diVerent in both cases. Cytological diVerences were observed in the inner cortical region and exodermis of the roots. Distinct groups of specialized cells with an organelle-rich cytoplasm that produced copious numbers of spherical bodies occurred in the inner cortical region of the hyperaccumulator. Such distinct cell groups were absent from the inner cortex of the non-hyperaccumulator. Cortical cells here had a thin parietal cytoplasmic layer and produced fewer spherical bodies. In both genotypes the spherical structures were extruded from the cytoplasm into air spaces between the cells where they coalesced to form amorphous deposits, signiWcantly larger and more abundant in the hyperaccumulator. Histochemical tests identiWed these deposits as a mixture of lipids, alkaloids and terpenoids. Specialized cells present in the inner cortex of the hyperaccumulating genotype demonstrated signiWcant relative Ni depletion in comparison with the adjacent inner cortex and phloem. Casparian bands were identiWed in exodermal cell walls of both genotypes but the bands Xuoresced more intensely in the non-accumulator suggesting diVerences in chemical composition and probably also a more eYcient apoplastic barrier. This feature was correlated with the observed Ni distribution pattern. The highest Ni enrichment in the hyperaccumulating genotype occurred in the outer cortex; 20 times more than in the adjacent epidermis/exodermis in older portions of roots and 3 times more than in the epidermis/exodermis in younger root hair regions. In contrast, in the Wojciech Przybyiowicz on leave from the

Root Ultrastructure ofSenecio coronatusGenotypes Differing in Ni Uptake

“…The non-hyperaccumulating genotype in the present study may be adopting a similar strategy probably because of a lack of tolerance for excess Ni. Another ultrastructural difference between the genotypes was the presence of a greater number of spherical bodies and more intercellular-accumulated material in the Ni-hyperaccumulator compared to the non-hyperaccumulator. Although histochemical tests are not defi nitive, the positive staining of spherical bodies and intercellular-accumulated material with Wagner and Dragendorff reagents indicates that they are alkaloids, in concurrence with the results of our previous study (Mesjasz-Przyby owicz et al 2007). Alkaloids are a diverse group of low molecular weight nitrogen-containing compounds that are derived mostly from amino acids (Facchini and De Luca 2008).…”

“…The purpose of the present investigation was to examine this aspect, as well as ultrastructural aspects of the genesis, transport, and storage of an alkaloid known to be synthesized in roots of species of Senecio. This study also extends our previous work (Mesjasz-Przyby owicz et al 2007) in which root cytology at the light microscope level and elemental distribution using a nuclear microprobe were examined in both genotypes of S. coronatus growing on ultramafi c outcrops.…”

Immunohistochemical localization of caffeine in young Camellia sinensis (L.) O. Kuntze (tea) leaves

“…The alkaloid ancistroheynine A was found in the tip of the shoot and leaf midrib of Liana Ancistrocladus heyneanus and ancistrocladine was found in the branch root of the plant by FT-Raman investigations (Urlaub et al 1997). Many more articles are published describing the localization of different alkaloids with different techniques (Verzár -Petri 1975;Yoder and Mahlberg 1976;Furr and Mahlberg 1981;Neumann et al 1983;Platt and Thomson 1992;Bringmann et al 1996;Mösli Waldhauser and Baumann 1996;Meininger et al 1997;Cai et al 1999;Corsi and Bottega 1999;Bottega et al 2004;Pasqua et al 2004;Alcantara et al 2005;Frosch et al 2006Frosch et al , 2007aNikolakaki and Christodoulakis 2006;Mesjasz -Przybyiowicz et al 2007;Liang et al 2009;Moraes et al 2009;Argyropoulou et al 2010;Christodoulakis et al 2010). …”

In Situ Distribution and Speciation of Toxic Copper, Nickel, and Zinc in Hydrated Roots of Cowpea

“…In contrast, studies have shown Cu to be toxic at concentrations ,10 mM (Kopittke et al, 2010). Further, the use of freeze-or oven-dried plant materials, such as by Sahi et al (2007), Baklanov et al (2009), Mesjasz-Przybyłowicz et al (2007), Sarret et al (2002), Terzano et al (2008), and Straczek et al (2008), is not ideal given the potential influence of drying on sample integrity directly affecting metal speciation and distribution. Finally, although metals are known to induce toxicities within minutes or hours of exposure (Blamey et al, 2004, most studies determine metal speciation after comparatively long periods of exposure (often days or weeks).…”