Synthetic and analytical studies of phytochelations, the metal(loid)-binding peptides of terrestrial plants

• Main Author: Wood, Barry Alan
• Published: University of Aberdeen 2011
• Subjects: 547.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540437

This thesis describes research based around phytochelatins (PCs), plant peptides synthesised during the influx of metal(loid)s such as arsenic.  Development of synthetic strategies for production of PCs and a bromine-based thiol tag were pursued.  The role of PCs in the arsenic translocation system in plants was monitored firstly by statistical analysis, then by monitoring arsenic translocation of <i>L-</i>BSO-poisoned and mutant plants. Whilst protected PC₂ was synthesised in good yield, subsequent isolation of deprotected PC₂ was not achieved via SEC or RP chromatography.  Statistical analysis showed that differential transport of iAs(V) and DMA(V) <i>in planta </i>between two plant groups was not due to PC/As(III)-PC speciation difference, but this was far from conclusive.  Plants exposed to iAs(V) and the <i>PC synthase </i>inhibitor <i>L</i>-BSO showed increased arsenic translocation with decreasing As(III)-PC levels, but the trend was not statistically significant.  Analysis of <i>Arabidopsis thaliana </i>mutants with differing PC levels confirmed that arsenic translocation increased with reduced PC and As(III)-PC complex levels.  HR-ICP-MS quantified unbound PC species on <i>m/z</i> 32 (S⁺), whilst HR-ESI-MS identified the (GS)₃-As(III) complex for the first time <i>in vivo</i>.  Whilst significant levels of iAs(III) and PC₂ exist within seaweeds, no As(III)-PC complex formation was observed.  This indicates a transient role, if any, for PCs during the <i>in vivo </i>detoxification of arsenic within seaweeds.  The development of a thiol tag based upon a polybrominated-pyrrole moiety was unsuccessful, owing to the greater-than-anticipated complexity of the chemistry exhibited by pyrrole.