Short-term supply of elevated phosphate alters the belowground carbon allocation costs and functions of lupin cluster roots and nodules.
The legume Lupinus albus is able to survive under low nutrient conditions due to the presence of two specialized below ground organs for the acquisition of nitrogen and phosphate, respectively.In this regard, cluster roots increase phosphate uptake and root nodules acquire atmospheric N₂via biological nitrogen fixation(BNF). Although these organs normally tolerate low phosphate conditions, very little is known about their physiological and metabolic flexibility during short-term changes in phosphate supply. The aim of this investigation was therefore to determine the physiological and metabolic flexibility of these organs during short-term supply of elevated phosphate nutrition. L. albus was cultivated in sand culture for 4 weeks at 0.1 mM phosphate supply, and then supplied with 2 mM phosphate for 2 weeks. Short-term elevated phosphate supply caused increased allocation of carbon and respiratory costs to nodules, at the expense of cluster root function. This alteration was also reflected in the increase in nodule enzyme activities related to organic acid synthesis, such as Phosphoenol-pyruvate Carboxylase (PEPC), Pyruvate Kinase (PK), Malate Dehydrogenase(NADH-MDH) and Malic Enzyme (ME). In cluster roots, elevated phosphate conditions caused a decline in these organic acid synthesizing enzymes. Phosphate recycling via Acid Phosphatase (APase),declined in nodules with elevated phosphate supply, but increased in cluster roots. Our findings suggest that during short-term elevated phosphate supply, there is a great degree of physiological and metabolic flexibility in lupin nutrient acquiring structures, and that these changes are related to the altered physiology of these organs [corrected].
Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
Rochelle
R
Thuynsma
Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa. Electronic address: alexvalentine@mac.com.
Alex
A
Valentine
Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
Aleysia
A
Kleinert
D018533:Biomass; D002244:Carbon / Q000378:metabolism*; D031297:Lupinus / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism*; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D010710:Phosphates / Q000378:metabolism*; D010788:Photosynthesis; D018517:Plant Roots / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism; D053204:Root Nodules, Plant / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism
D010710:Phosphates; D002244:Carbon; D009584:Nitrogen
Cluster roots; Nodules; Resource allocation; Short-term phosphate supply