Specialised 'dauciform' roots of Cyperaceae exhibit convergent physiology with 'proteoid' roots of Proteaceae to challenge phosphate-deficient environments

摘要

The development of modified branch roots, termed 'dauciform' roots, is stimulated at low phosphate supply in the sedge Schoenus unispiculatus Benth. (Cyperaceae). We assessed carboxylate exudation, and internal carboxylate and P concentrations, and O_2-uptake rates during each of four stages of dauciform-root growth and development (i.e. very-young, young, mature and old). We showed that oxygen consumption was fastest (i.e. 9 nmol O_2 g~(-1) FM s~(-1)) and root [P] greatest (i.e. 2.9 mg P g~(-1) DM) when dauciform roots were young and rapidly developing (i.e. 3 to 4 days old). Mature dauciform roots (i.e. 6 to 8 days old) exuded citrate at rates (i.e. 1.7 nmol citrate g~(-1) EM s~(-1)) that were approximately three orders of magnitude faster than that those reported for roots of most species, but were similar to those from mature duster roots. Citrate was the main carboxylate detected in exudates at each stage of dauciform-root development. The internal citrate concentration was greatest (i.e. 22.2 μmol citrate g~(-1) FM) in young dauciform roots, decreasing by more than half in mature dauciform roots, corresponding with the 'burst' of citrate exudation. It is proposed that the form and functioning of dauciform roots is similar to that of proteoid roots in species adapted to harsh environments.