title: Excessive sulphur accumulation and ionic storage behaviour identified in species of Acacia (Leguminosae: Mimosoideae).
abstract: OBJECTIVE
  Thiophores, which are typically desert gypsophytes, accumulate high (2-6 % S dry weight) sulphur concentrations and may possess unique tolerance to environmental stress factors, e.g. sulphate/metal toxicity, drought and salinity. Little is known of the prevalence of the behaviour or the associated physiological aspects. The aim of this study was to (a) determine the prevalence of thiophore behaviour in a group of Australian xerophytes; (b) identify elemental uptake/storage characteristics of these thiophores; and (c) determine whether the behaviour is constitutive or environmental.
  
  
  METHODS
  The elemental composition of soils and the foliage of 11 species (seven genera) at a site in the Tanami Desert (NT, Australia) was compared and 13 additional Acacia species from other locations were examined for elevated calcium and sulphur concentrations and calcium-sulphur mineralization, thought to be particular to thiophores.
  
  
  RESULTS
  Acacia bivenosa DC. and 11 closely related species were identified as thiophores that can accumulate high levels of sulphur (up to 3·2 %) and calcium (up to 6.8 %), but no thiophores were identified in other genera occupying the same habitat. This behaviour was observed in several populations from diverse habitats, from samples collected over three decades. It was also observed that these thiophores featured gypsum (CaSO4·2H2O) crystal druses that completely filled cells and vascular systems in their dried phyllode tissues.
  
  
  CONCLUSIONS
  The thiophores studied exhibit a tight coupling between sulphur and calcium uptake and storage, and apparently store these elements as inorganic salts within the cells of their foliage. Thiophore behaviour is a constitutive trait shared by closely related Acacia but is not highly prevalent within, nor exclusive to, xerophytes. Several of the newly identified thiophores occupy coastal or riparian habitats, suggesting that the evolutionary and ecophysiological explanations for this trait do not lie solely in adaptation to arid conditions or gypsiferous soils.
authors.affiliation: CSIRO Mineral Resources, PO Box 1130, Bentley, Western Australia, 6102 and Nathan.Reid@csiro.au.
authors.forename: N
authors.initials: N
authors.lastname: Reid
authors.affiliation: CSIRO Mineral Resources, PO Box 1130, Bentley, Western Australia, 6102 and.
authors.forename: T C
authors.initials: TC
authors.lastname: Robson
authors.affiliation: Gamut Consulting Pty Ltd, Dayboro, Queensland, Australia.
authors.forename: B
authors.initials: B
authors.lastname: Radcliffe
authors.affiliation: CSIRO Mineral Resources, PO Box 1130, Bentley, Western Australia, 6102 and.
authors.forename: M
authors.initials: M
authors.lastname: Verrall
mesh_terms: D000045:Acacia / Q000378:metabolism* / Q000648:ultrastructure; D002118:Calcium / Q000378:metabolism; D003460:Crystallization; D005843:Geography; D007477:Ions; D010802:Phylogeny; D018515:Plant Leaves / Q000378:metabolism / Q000648:ultrastructure; D013045:Species Specificity; D013052:Spectrometry, X-Ray Emission; D013324:Strontium / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism*
chemical_list: D007477:Ions; D013455:Sulfur; D002118:Calcium; D013324:Strontium
keywords: Acacia bivenosa; Acacia robeorum; Biomineralization; calcium regulation; geobotany.; hyperaccumulation; ionic storage; phytoaccumulation; sulphur accumulation; sulphur regulation; thiophore; xerophyte