| Description: | Plants that hyperaccumulate nickel account for over three-quarters of all known species of metal hyperaccumulators, yet almost nothing is known about the molecular processes that allow these plants to accumulate this ion to concentrations exceeding 1% of their dry biomass. As with the zinc hyperaccumulator species Thlaspi caerulescens , Alyssum lesbiacum (Brassicaceae) is relatively small and slow growing. Identification and characterisation of genes involved in Ni hyperaccumulation in this species would be of use in developing plants to clean up Ni-contaminated soils (a process known as phytoremediation). It would also reveal much about the underlying mechanisms of metal ion homeostasis and trafficking in plant cells. Very little is currently known about Ni homeostasis in plants other than its requirement as a component of the enzyme urease, and no Ni-responsive genes have been identified to date in any eukaryote.Previous studies have shown that A. lesbiacum can survive in hydroponic culture with Ni concentrations in excess of 1 mM. Exposure to Ni leads to a linear increase in xylem histidine concentrations over a range of Ni concentrations. When exogenous histidine was supplied to the root medium of A. montanum (a non-hyperaccumulator), it ameliorated the toxic effect of Ni and increased Ni flux through the xylem. This suggests that histidine plays a central role in Ni detoxification (probably in the cell cytoplasm), and transport from root to shoot. However, the molecular basis of this response has still not been elucidated. The majority of Ni in the leaf tissue is water extractable, suggesting that much of it is stored in the vacuole. Yet no tonoplast (or other) membrane Ni transporters have been identified to date.We propose to identify Ni-responsive genes in A. lesbiacum by comparing 3-week-old hydroponically grown plants exposed to either 0 mM (control) or 0.3 mM NiSO4 for 6 hours prior to harvesting and RNA extraction. Arabidopsis microarrays should be an excellent means of identifying changes in the expression of conserved genes in closely related species of Brassicaceae. Data from the 13 genes cloned so far in our laboratory from A. lesbiacum indicates high sequence identity between the coding regions of homologous genes in the two species (range 87 to 93%). |
NASCArrays Information at The BAR
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