Browsing by Subject "Ammonium iron"

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Iron and ammonium sensing differentially modulate root plasticity in Arabidopsis thaliana
(2010) Lima, Joni Esrom; von Wirén, Nicolaus
Modulation of root system architecture by plants has an impact on water, nutrient acquisition and anchorage during plant development. In a given environment, root plasticity is a favorable feature to react according to abiotic and biotic factors. Under nutrient limited conditions, the root plasticity is essential for a better soil volume exploitation. This response can vary according to the plant species and the given environment in which they evolved. Moreover, nutrient mobility in the soil plays an important role for the response of plants to nutrient limitation. Thus, root plasticity is a nutrient-specific response during plant development. In fact research on the effect of nutrient availability on root system architecture is scarce. Furthermore, the mechanism how plants sense nutrients and the signaling upon nutrient availability remains a challenge. Therefore, identification of which nutrient can affect the root system architecture and investigating the molecular components involved in the signaling pathway is certainly relevant for agronomical practices. The first part of the present work aimed to identify how the root architecture is affected by iron (Fe) supply. Due to the low mobility of Fe in soils, the morphological response of lateral roots from Arabidopsis plants to localized Fe supply and its regulation were investigated. Increasing Fe concentrations in a homogenous or localized supply on separated agar plates enhanced lateral root number in a similar manner. Lateral root length, however, was twofold higher under localized relative to homogenous Fe supply. With further increasing Fe concentrations lateral root length was repressed even though shoot growth was unaffected. In the Fe uptake-defective mutant irt1, the formation of lateral roots required higher local Fe supplies, which restored wild type levels only with respect to the number but not to the length of lateral roots. Moreover, IRT1 transcript levels were strongly enhanced under localized Fe supply. In the frd3-1 mutant, which is defective in root-to-shoot translocation of Fe, lateral root development was similar to wild type plants although frd3-1 shoots were Fe deficient. These results show a differential regulation of lateral root initiation and elongation in response to localized Fe supply and that lateral root elongation is under control of a local rather than a systemic regulatory loop involving the high-affinity Fe transporter IRT1. In the second part of the thesis, a remarkable and an unknown feature of root morphology dependent on localized ammonium supply is described. Arabidopsis plants were able to increase lateral root initiation and higher-order lateral root branching. Since ammonium-stimulated lateral root number or density decreased after ammonium or glutamine supply to a separate root fraction and did not correlate with cumulative uptake of 15N-labeled ammonium, lateral root branching was not purely due to a nutritional effect but most likely a sensing event. Moreover, a detailed investigation has shown that ammonium and nitrate co-ordinate root morphology in an additive and complementary way. By a genetic approach, the ammonium-induced lateral root branching was demonstrated to be dependent on AMT1;3 activity in the root.