Acquisition and transport of phosphorus in the Australian koala fern Caustis blakei (Cyperaceae), a role for specialised dauciform roots.

Cameron Playsted
Australian Flora Foundation Young Scientist awards at the 6th Australian Horticultural Conference 2004,  and at the 7th Australian Native Flower Conference 2005

Abstract (from the 2005 Conference, which includes and extends the presentation given in 2004)

Cameron W.S. Playsted1,2, Margaret E. Johnston1,3, Carl M. Ramage2,6, David G. Edwards4, Susan Hamilton5, Hans Lambers7.

The University of Queensland;1School of Agronomy and Horticulture, 2 Agricultural Molecular Biotechnology Laboratory, 3Centre for Native Floriculture; 4School of Land and Food Sciences; 5School of Molecular and Microbial Sciences.

Primary Industries Research Victoria;6Department of Primary Industries, Plant Biotechnology Centre, R.L Reid Building, LaTrobe University, Victoria.

The University of Western Australia; 7School of Plant Biology.

Attempts to domesticate Australian native plants into conventional nursery production systems have been hampered by the sensitivity of a number of species to the essential element phosphorus (P). The response of P sensitive species appears to be a consequence of the adaptations of some Australian plants to soils with low levels of available P. Initial experiments determined the P requirements of the Australian native plants Caustis and waxflower in order to compare them with the crop species tomato (Lycopersicon esculentum L.). Results show that Caustis is sensitive to P levels well below the optimum for most species, at solution concentrations of 10 uM. Under these conditions, P toxicity symptoms become evident with most plants becoming unmarketable. In contrast, under P limiting conditions Caustis appears to have a highly efficient P uptake capacity. Observed low-P adaptations include an increased root to shoot ratio and the formation of dauciform roots at very low solution P concentrations < 1 uM. Dauciform roots are short swollen lateral roots, which are particularly hairy (Davies et al., 1973; Lamont, 1974, 1982). It is hypothesised that dauciform roots may enhance the acquisition of sparingly soluble minerals, similar to the well known cluster roots of white lupin and many proteaceous species (Davies et al., 1973; Lambers et al 2003). Our research has identified the role of dauciform roots of Caustis in the exudation of carboxylates as a response to P deficiency. In addition, molecular analysis of two putative high affinity phosphate transporter genes cloned from Caustis roots is being performed to elucidate their role in P uptake, particularly in dauciform roots.