The chemical form and physiological function of nickel in some Iberian Alyssum species [hyperaccumulators of nickel, Alyssum serpyllifolium Desv. subsp. malacitanum, Alyssum serpyllifolium Desv. subsp. lusitanicum, Spain, Portugal]
1981
Brooks, R.R. | Shaw, S. (Massey Univ., Palmerston North (New Zealand). Dept. of Chemistry) | Marfil, A.A.
The form of nickel in leaves of Iberian subspecies of Alyssum serpyllifolium Desv. was investigated. Subsp. lusitanicum T.R. Dudley and P. Silva (from N.E. Portugal) and subsp. malacitanum Rivas Goday (from Southern Spain) were hyperaccumulators of nickel (1000 mu-g/g Ni) whereas their non-accumulating precursor (subsp. serpyllifolium) was not. Nickel existed mainly as a water-soluble polar complex in the vacuoles. Small concentrations of nickel did however exist in cell fractions, particularly in the mitochondria where enzyme systems are located. Gas-liquid chromatography on the purified nickel complexes showed that this element is associated principally with malic and malonic acids which are present in high concentrations in the hyperaccumulators but not in subsp. serpyllifoilum. It is suggested that production of malic acid is a mechanism whereby hyperaccumulators can tolerate unfavourable edaphic factors such as nickel-rich soils. Presence of nickel in the mitochondria can presumably block the citric acid cycle by deactivating malic dehydrogenase leading to build-up of malic acid in the vacuoles which could then absorb excess nickel by a complexing reaction and lead to its diffusion back into the vacuoles from the mitochondria, hence unblocking the citric acid cycle. It is postulated that the chemical evidence suggests that the two hyperaccumulators are not conspecific and that subsp. malacitanum should be promoted ot full specific rank.
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