Temporal responses of Arabidopsis root architecture to phosphate starvation:: evidence for the involvement of auxin signalling

The ability of the root system architecture to respond to nutrient availability is a key adaptative behaviour allowing plants to cope with environmental conditions. On the basis of single time point comparisons, the response to phosphate deprivation was previously shown to involve both the primary and lateral roots of Arabidopsis. In this work, the temporal pattern of Arabidopsis root responses to phosphate starvation was investigated. Daily scanning of roots showed that changes in architecture were largely due to the alterations of time-based growth parameters, namely a decrease in the elongation rate of the primary root opposed to an increase in the elongation rate of lateral roots and a decrease in the number of initiated lateral roots. In addition, another identified response was a decrease in the proportion of lateral roots showing early growth arrest. All these changes occurred within a short period of approximately 3 d. In addition, the root morphology comparison with the auxin-resistant mutant axr4, the auxin-treatment of phosphate-starved plants and a limited transcriptome analysis supported the conclusion that auxin signalling was involved in the adaptive response of the root system architecture to phosphate deprivation.