The Arabidopsis Halophytic RelativeThellungiella halophilaTolerates Nitrogen-Limiting Conditions by Maintaining Growth, Nitrogen Uptake, and Assimilation    

Abstract

A comprehensive knowledge of mechanisms regulating nitrogen (N) use efficiency is required to reduce excessive input of N fertilizers while maintaining acceptable crop yields under limited N supply. Studying plant species that are naturally adapted to low N conditions could facilitate the identification of novel regulatory genes conferring better N use efficiency. Here, we show that Thellungiella halophila, a halophytic relative of Arabidopsis (Arabidopsis thaliana), grows better than Arabidopsis under moderate (1 mM nitrate) and severe (0.4 mM nitrate) N-limiting conditions. Thellungiella exhibited a lower carbon to N ratio than Arabidopsis under N limitation, which was due to Thellungiella plants possessing higher N content, total amino acids, total soluble protein, and lower starch content compared with Arabidopsis. Furthermore, Thellungiella had higher amounts of several metabolites, such as soluble sugars and organic acids, under N-sufficient conditions (4 mM nitrate). Nitrate reductase activity and NR2 gene expression in Thellungiella displayed less of a reduction in response to N limitation than in Arabidopsis. Thellungiella shoot GS1 expression was more induced by low N than in Arabidopsis, while in roots, Thellungiella GS2 expression was maintained under N limitation but was decreased in Arabidopsis. Up-regulation of NRT2.1 and NRT3.1 expression was higher and repression of NRT1.1 was lower in Thellungiella roots under N-limiting conditions compared with Arabidopsis. Differential transporter gene expression was correlated with higher nitrate influx in Thellungiella at low 15 NO 3 2 supply. Taken together, our results suggest that Thellungiella is tolerant to N-limited conditions and could act as a model system to unravel the mechanisms for low N tolerance.

Genome Structures and Halophyte-Specific Gene Expression of the Extremophile Thellungiella parvula in Comparison with Thellungiella salsuginea (Thellungiella halophila) and Arabidopsis

“…salsuginea (salt cress) has been studied as a model halophyte, juxtaposing its physiology and genetic structure to that of Arabidopsis. Suggested mechanisms for tolerance to stress and nutrient-limiting conditions include control over stomatal conductance (Inan et al, 2004), greater discriminatory power of K + -and Na + -transport systems (Volkov et al, 2004;Volkov and Amtmann, 2006), and nitrogen utilization efficiency (Kant et al, 2008). However, a genetic basis of the differences in tolerance could only be deduced by attempts at establishing Arabidopsis-like resources and databases (Inan et al, 2004;Taji et al, 2004Taji et al, , 2008Wang et al, 2004Wang et al, , 2006Gong et al, 2005;Wong et al, 2005;Zhang et al, 2008;Oh et al, 2009).…”

“…In particular, Thellungiella salsuginea, previously known as Thellungiella halophila (Al-Shehbaz and O'Kane, 1995;Amtmann, 2009), has been studied for its extreme salt, cold, and freezing tolerance and for its efficient mobilization of resources in poor or degraded soils (Kant et al, 2008). Another species, Thellungiella parvula, has been reported to have slightly higher salt and drought tolerance, being otherwise comparable to T. salsuginea in cold and freezing response characteristics (Orsini et al, 2010).…”

Plant N Fluxes and Modulation by Nitrogen, Heat and Water Stresses: A Review Based on Comparison of Legumes and Non Legume Plants

“…A low N supply generally leads to decreased root growth, suppression of lateral root initiation, increase in the C/N ratio (ie sucrose-to-nitrate ratio) within the plant, reduction in photosynthesis, and early leaf senescence (Kant et al, 2008;Malamy, 2005;Malamy & Ryan, 2001;Martin et al, 2002;Paul & Driscoll, 1997;Wingler et al, 2006;Zhang, 2007). Several genes of Arabidopsis thaliana involved in root development through hormonal signals and/or nutrient perception were reviewed by Casson & Lindsey (2003).…”

“…To cope with this, plants have evolved a suite of adaptive responses to successfully finish their life cycles to produce offspring, rather than die early and barren due to insufficient N nutrient (Kant et al, 2008;Peng et al, 2007). Several physiological and biochemical changes occur in plants as adaptive responses to N limitation, including an increase in N uptake by high-affinity transporters, remobilization of N from older to younger leaves and www.intechopen.com reproductive parts, a delay of growth and development, a decrease of photosynthesis capacity, and increased anthocyanin accumulation (Peng et al, 2007).…”

Arabidopsis thaliana Tolerates Iron Deficiency more than Thellungiella Salsuginea by Inducing Metabolic Changes at the Root Level

“…Furthermore, A. thaliana and T. salsuginea can be easily transformed and have several other characteristics such as a short life cycle and abundant seed production (Volkov and Amtmann, 2006). In response to abiotic stresses, T. salsuginea (an extremophile plant) appears to show resistance to stress caused by low temperature, drought, high salt and nitrogen deficiency as compared to A. thaliana (Volkov and Amtmann, 2006;Inan et al, 2004;Kant et al, 2008).…”