title: Putting the P in Ptilotus: a phosphorus-accumulating herb native to Australia.
abstract: OBJECTIVE
  Ptilotus polystachyus (green mulla mulla; ptilotus) is a short-lived perennial herb that occurs widely in Australia in arid and semi-arid regions with nutrient poor soils. As this species shows potential for domestication, its response to addition of phosphorus (P) and nitrogen (N) was compared to a variety of the domesticated exotic perennial pasture herb Cichorium intybus (chicory), 'Puna'.
  
  
  METHODS
  Pots were filled with 3 kg of an extremely nutrient-deficient sterilized field soil that contained 3 mg kg(-1) mineral N and 2 mg kg(-1) bicarbonate-extractable P. The growth and P and N accumulation of ptilotus and chicory in response to seven rates of readily available phosphorus (0-300 mg P pot(-1)) and nitrogen (N) (0-270 mg N pot(-1)) was examined.
  
  
  RESULTS
  Ptilotus grew extremely well under low P conditions: shoot dry weights were 23, 6 and 1.7 times greater than for chicory at the three lowest levels of P addition, 0, 15 and 30 mg P pot(-1), respectively. Ptilotus could not downregulate P uptake. Concentrations of P in shoots approached 4% of dry weight and cryo-scanning electron microscopy and X-ray microanalysis showed 35-196 mM of P in cell vacuoles in a range of tissues from young leaves. Ptilotus had a remarkable tolerance of high P concentrations in shoots. While chicory exhibited symptoms of P toxicity at the highest rate of P addition (300 mg P pot(-1)), no symptoms were present for ptilotus. The two species responded in a similar manner to addition of N.
  
  
  CONCLUSIONS
  In comparison to chicory, ptilotus demonstrated an impressive ability to grow well under conditions of low and high P availability. Further study of the mechanisms of P uptake and tolerance in ptilotus is warranted.
authors.affiliation: School of Plant Biology, The University of Western Australia M081, 35 Stirling Hwy, Crawley, WA, 6009, Australia. megan.ryan@uwa.edu.au
authors.forename: M H
authors.initials: MH
authors.lastname: Ryan
authors.forename: S
authors.initials: S
authors.lastname: Ehrenberg
authors.forename: R G
authors.initials: RG
authors.lastname: Bennett
authors.forename: M
authors.initials: M
authors.lastname: Tibbett
mesh_terms: D027703:Amaranthaceae / Q000378:metabolism*; D001315:Australia; D010758:Phosphorus / Q000378:metabolism*
chemical_list: D010758:Phosphorus