Characterization of a Developmental Root Response Caused by External Ammonium Supply in Lotus japonicus      

Abstract

Plants respond to changes of nutrient availability in the soil by modulating their root system developmental plan. This response is mediated by systemic changes of the nutritional status and/or by local perception of specific signals. The effect of nitrate on Arabidopsis (Arabidopsis thaliana) root development represents a paradigm of these responses, and nitrate transporters are involved both in local and systemic control. Ammonium (NH 4 + ) represents an important nitrogen (N) source for plants, although toxicity symptoms are often associated with high NH 4 + concentration when this is present as the only N source. The reason for these effects is still controversial, and mechanisms associating ammonium supply and plant developmental programs are completely unknown. We determined in Lotus japonicus the range of ammonium concentration that significantly inhibits the elongation of primary and lateral roots without affecting the biomass of the shoot. The comparison of the growth phenotypes in different N conditions indicated the specificity of the ammonium effect, suggesting that this was not mediated by assimilatory negative feedback mechanisms. In the range of inhibitory NH 4 + conditions, only the LjAMT1;3 gene, among the members of the LjAMT1 family, showed a strong increased transcription that was reflected by an enlarged topology of expression. Remarkably, the short-root phenotype was phenocopied in transgenic lines by LjAMT1;3 overexpression independently of ammonium supply, and the same phenotype was not induced by another AMT1 member. These data describe a new plant mechanism to cope with environmental changes, giving preliminary information on putative actors involved in this specific ammonium-induced response.

Effects of externally supplied protein on root morphology and biomass allocation in Arabidopsis

“…At high concentrations, BSA inhibited root development, similar to the effects of IN e.g 40,. glutamate (>50 μM), glycine (10 mM N), serine and valine (3 mM N)243641.…”

Ammonium Inhibits Primary Root Growth by Reducing the Length of Meristem and Elongation Zone and Decreasing Elemental Expansion Rate in the Root Apex in Arabidopsis thaliana

“…Root growth inhibition by ammonium in arabidopsis has also been shown to be mediated by the root tip and linked with a significant ammonium efflux at the elongation zone [7]. In Lotus japonicas, 20 mM ammonium significantly represses root growth without affecting shoot biomass or amino acid content, as compared to treatment with 20 mM Gln [8]. These findings suggest that ammonium inhibits root growth by perceived as a signal rather than by an assimilatory negative feedback mechanism.…”

The diatom molecular toolkit to handle nitrogen uptake

“…The high-affinity transporter NRT2.1 has been also proposed as a NO 3 − sensor also involved in the regulation of lateral root formation under N-limiting conditions (Little et al, 2005). As for NPF and NRT2 proteins, a signaling role has been also proposed for specific AMT1 members such as AtAMT1;3 that seems to play a role in the control of lateral root branching (Lima et al, 2010;Rogato et al, 2010). An intriguing hypothesis is that transceptor roles are also shared by diatom transporters as many data suggest in diatoms the existence of specific acclimation mechanisms for energy balance under fluctuating environmental conditions (Allen et al, 2011).…”