Proteoid Root Development of Phosphorus Deficient Lupin is Mimicked by Auxin and Phosphonate |
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| Authors: | Gilbert, Glena A. Knight, J. Diane Vance, Carroll P. Allan, Deborah L. |
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| Affiliation: | Department of Soil, Water, and Climate, University of Minnesota, St. Paul, Minnesota, 55108-6028, USA United States Department of Agriculture-Agricultural Research Service, Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, Minnesota, 55108-6028, USA |
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| Abstract: | White lupin (Lupinus albus L.) develops proteoid (cluster) rootsin response to phosphorus deficiency. Proteoid roots are composedof tight clusters of rootlets that initiate from the pericycleopposite protoxylem poles and emerge from every protoxylem polewithin the proteoid root axis. Auxins are required for lateralroot development, but little is known of their role in proteoidroot formation. Proteoid root numbers were dramatically increasedin P-sufficient (+P) plants by application of the syntheticauxin, naphthalene acetic acid (NAA), to leaves, and were reducedin P-deficient (-P) plants by the presence of auxin transportinhibitors [2,3,5-triiodobenzoic acid (TIBA) and naphthylphthalamicacid (NPA)]. While ethylene concentrations in the root zonewere 1.5-fold higher in -P plants, there was no effect on proteoidroot numbers of the ethylene inhibitors aminoethoxyvinvylglycine(AVG) and silver thiosulphate. Phosphonate, which interfereswith plant perception of internal P concentration, dramaticallyincreased the number of proteoid root segments in +P plants.Activities of phosphoenolpyruvate carboxylase (PEPC), malatedehydrogenase (MDH) and exuded acid phosphatase in proteoidroot segments were not different from +P controls when NAA wasapplied to +P lupin plants, but increased to levels comparableto -P plants in the phosphonate treatment. Addition of TIBAor NPA to -P plants reduced PEPC and MDH activity of -P proteoidroots to levels found in +P or -P normal root tissues, but didnot affect acid phosphatase in root exudates. These resultssuggest that auxin transport from the shoot plays a role inthe formation of proteoid roots during P deficiency. Auxin-stimulatedproteoid root formation is necessary, but not sufficient, tosignal the up-regulation of PEPC and MDH in proteoid root segments.In contrast, phosphonate applied to P-sufficient white lupinelicits the full suite of coordinated responses to P deficiencyCopyright2000 Annals of Botany Company Lupinus albus L., white lupin, proteoid roots, auxin, ethylene, phosphonate, phosphorus deficiency |
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