Submitted to: International Journal of Phytoremediation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/22/2010
Publication Date: 7/15/2010
Citation: Centofanti, T., Tappero, R.V., Davis, A.P., Chaney, R.L. 2010. Chelator-buffered nutrient solution is ineffective in extracting Ni from seeds of Alyssum. International Journal of Phytoremediation. 13:434-440. Interpretive Summary: Nickel hyperaccumulator plants can accumulate over 2% nickel in their shoots and support phytomining of nickel rich soils as a new agricultural crop and opportunity. Research is being conducted to better understand the physiology, chemistry and agronomy of this new crop species to improve the ability of growers to reliably obtain high nickel crops. In previous studies we attempted to determine if this species had a higher internal nickel requirement than other species but were unable to obtain low nickel plants because the seeds supplied such high levels; seeds contained about 9000 mg Ni/kg, whereas normal crop plants contain less than 5 mg Ni/kg. Thus we attempted to remove Ni from the seeds and germinating seedlings by starting them in a chelator buffered nutrient solution which can maintain very low chemical activity of Ni. If the Ni were outside of cells in the seed coats, etc., the chelator should remove the Ni from the seed and lower plant Ni. Germination of several Ni hyperaccumulator species on these solutions did not remove significant Ni from the germinating seedlings. To characterize what happened, we examined the localization of Ni within seeds using X-ray absorption spectrometry and found that essentially all the seed Ni was within the embryo and endosperm, not in the hull or seed coat. These findings show that Alyssum murale has remarkable ability to transport Ni to seeds, and the Ni is stored within the living parts of the seed. Because of the physiology of Ni in these seeds, the only way to obtain low Ni seeds is to grow the plants for several generations on low Ni soils.
Technical Abstract: Hyperaccumulator species of the genera Alyssum can accumulate 100 times more Ni than normal crops and are therefore used for phytomining and phytoextraction of nickel contaminated soils. Basic studies on the physiology and metal uptake mechanisms of these plants are needed to increase efficiency and uptake capacity of nickel (Ni) by hyperaccumulators. Recent attempts to disclose if those hyperaccumulator species require higher Ni level than normal plants failed because of the high Ni content in the seeds (7000-9000 mg/kg). Low Ni seeds (250 mg/kg) obtained by traditional time consuming methods of growing plants for several generations on low Ni soils are currently required to determine Ni requirement for germination and adequate plant growth. In this study we attempted to use chelator buffered nutrient solution to deplete Ni from the seed/seed coat and to obtain low Ni seedlings of Alyssum cultivars to be used in physiology studies. HEDTA-buffered nutrient solution did not deplete Ni from the seeds, perhaps because Ni was mainly localized within the seedling embryonic tissues with greatest Ni enrichment in the cotyledons and hypocotyls. We could not observe any positive correlation between seed fitness and germination capacity with seed Ni content. Investigation of nickel localization in Alyssum seeds using synchrotron X-ray microfluorescence (µ-SXRF) showed that nickel is localized in the embryonic tissues with greatest Ni enrichment observed in the cotyledons and hypocotyl.