A comparison of structure, development and function in cluster roots of Lupinus albus L. under phosphate and iron stress

Cluster roots are adaptations for nutrient acquisition, found throughout th e world in many different plant families and habitats. They arise from chan ges in root initiation, meristem maintenance and physiology. In Lupinus alb us cluster roots form under low internal plant phosphate and low internal p lant iron levels. In this study, we compare morphology, structure and physi ology of cluster roots formed under -P and -Fe conditions. -Fe cluster root s had a lower density of shorter rootlets than -P roots, and were yellow in colour, probably because of increased phenolics due to down-regulation of peroxidase. Rootlet length and width was reduced in -Fe conditions. The cha nge in exudation of citrate, over time, of -P and -Fe cluster roots shared identical temporal dynamics, with an exudative burst occurring in day 3. Ho wever, the -Fe cluster roots displayed much higher rates of exudation than the -P cluster roots. Results are discussed within the context of structura l and functional control.