Ecological and phytochemical studies on nickel accumulating plants from the Pacific Basin region : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University
The distribution of species and genera contained in the floras of the Pacific Basin region is discussed. The outstanding feature of these floras is the high degree of specific endemism.
A survey of the 53 species of Flacourtiaceae known in New Caledonia was successful in identifying a tital of 19 nickel hyperaccumulating species. The seven previously recorded in the Homalium genus were re-identified using fresh material and a further ten were located in the Xylosma genus with one in each of Casearia and Lasiochlamys. A similar survey of the Phyllanthus revealed a further ten hyperaccululating species out of the 51 studied. It was also possible to characterise and identify a number of species from their nickel and/or cobalt contents. This was particularly true for the taxonomically-difficult section Heteroglochidion.
It appears that many nickel accululating plants are exclusive to ultrabasic substrates and as well as being able to tolerate high concentrations of the non-essential heavy metals they are also able to withstand extremely low levels of the essential elements. Pot trials showed that a strong relationship existed between soil and leaf nickel concentrations in Psychotria douarrei. Elemental concentrations were determined in several specimens of Rinorea bengalensis growing over a wide variety of substrates throughout the Pacific Basin region. It appears that soil conditions determine the extent to which an element is accumulated. Statistical considerations suggested a dependency on the organic constituents in the plant for the translocation of nickel.
The nature of nickel complexes in several hyperaccumulating plants was investigated using gel filtration, ion exchange chromatroraphy, high pressure liquid chromatography and gas-liquid chromatography - mass spectrometry. Aquo, citrate and malate complexes of nickel were identified. Gel-filtration, electrophoretic and spectrophotometric comparisons with synthetic compounds suggested a 1:1 nickel/organic acid ratio exists in vivo. All species studied contained aquo and citrate complexes, but Psychotria douarrei and Phyllanthus serpentinus also have a large portion of their nickel bound in a malate complex. Possible factors determining the formation of a particular nickel complex are considered as is a possible pathway for the translocation of such a complex within the plant.