Spatial mapping of phosphorus influx in bean root systems using digital autoradiography

• Published in: Journal of experimental botany 2004-10, Vol.55 (406), p.2269-2280
• Main Authors: Rubio, G, Sorgona, A, Lynch, J.P
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Autoradiography; Autoradiography - methods; Biological and medical sciences; Biological Transport; Digital autoradiography; Economic plant physiology; Fundamental and applied biological sciences. Psychology; mineral nutrition; Nutrient uptake; Phaseolus - growth & development; Phaseolus - metabolism; Phosphates; Phosphors; Phosphorus; Phosphorus - metabolism; Phosphorus Radioisotopes; phosphorus uptake; Plant Leaves - growth & development; Plant roots; Plant Roots - growth & development; Plants; Radioactive decay; Research Papers: Regulation of Growth, Development and Whole Organism Physiology; Root systems; Root tips; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...)
• ISSN: 0022-0957; 1460-2431; 1460-2431
• DOI: 10.1093/jxb/erh246

A novel technique was developed to spatially map the phosphorus net influx capacity in intact root systems. The method is based on digital autoradiography and permits the quantification of phosphorus influx at high spatial resolution (2 mm). Roots of 18-d-old common bean plants were exposed to 32P-labelled orthophosphate, quickly frozen, excised, lyophilized, scanned, and exposed to a storage phosphor screen. Plots of 32P content versus root length (distance from the root tip or from the base of the root) were obtained for three different root classes: basal, basal laterals, and taproot laterals. Radioactivity detected by filmless autoradiography correlated well (r2=0.99) with measurements made by scintillation counting. Basal roots absorbed 2.5 times and 1.9 times more phosphorus than the taproot lateral and basal lateral root classes, respectively, in the first 20 mm from the root apex. External phosphorus markedly affected influx: roots averaged 5, 16, and 34 pmol P min(-1) in the apical 20 mm when exposed to 1, 5, and 10 micromolar P solutions, respectively. The spatial pattern of phosphorus influx along the root axes of the different root classes was rather homogeneous when measured on a root surface area basis. Phosphorus influx in the older segments of basal roots (those next to the hypocotyl) did not differ from the newer segments close to the root apex. However, a heterogeneous pattern was detected for basal roots when measured on a length basis, indicating that both root class and diameter constitute main factors controlling the spatial pattern of net influx.