Plant response to nitrate starvation is determined by N storage capacity matched by nitrate uptake capacity in two Arabidopsis genotypes

Abstract

In a low-input agricultural context, plants facing temporal nutrient deficiencies need to be efficient. By comparing the effects of NO(3)(-)-starvation in two lines of Arabidopsis thaliana (RIL282 and 432 from the Bay-0xShahdara population), this study aimed to screen the physiological mechanisms allowing one genotype to withstand NO(3)(-)-deprivation better than another and to rate the relative importance of processes such as nitrate uptake, storage, and recycling. These two lines, chosen because of their contrasted shoot N contents for identical shoot biomass under N-replete conditions, underwent a 10 d nitrate starvation after 28 d of culture at 5 mM NO(3)(-). It was demonstrated that line 432 coped better with NO(3)(-)-starvation, producing higher shoot and root biomass and sustaining maximal growth for a longer time. However, both lines exhibited similar features under NO(3)(-)-starvation conditions. In particular, the nitrate pool underwent the same drastic and early depletion, whereas the protein pool was increased to a similar extent. Nitrate remobilization rate was identical too. It was proportional to nitrate content in both shoots and roots, but it was higher in roots. One difference emerged: line 432 had a higher nitrate content at the beginning of the starvation phase. This suggests that to overcome NO(3)(-)-starvation, line 432 did not directly rely on the N pool composition, nor on nitrate remobilization efficiency, but on higher nitrate storage capacities prior to NO(3)(-)-starvation. Moreover, the higher resistance of 432 corresponded to a higher nitrate uptake capacity and a 2-9-fold higher expression of AtNRT1.1, AtNRT2.1, and AtNRT2.4 genes, suggesting that the corresponding nitrate transporters may be preferentially involved under fluctuating N supply conditions.

The Arabidopsis Nitrate Transporter NRT1.7, Expressed in Phloem, Is Responsible for Source-to-Sink Remobilization of Nitrate

“…Mutants of nrt1.7 defective in this process had retarded growth when the plants encountered long-term severe nitrogen deficiency during vegetative growth, indicating that internal nitrate remobilization between leaves was important for plants to cope with nitrogen deficiency and the importance of enhanced NUE for maximum growth. Consistent with this, by comparing nitrogen contents and growth of two Arabidopsis lines in response to nitrogen starvation, Richard-Molard et al (2008) found that the line with higher nitrate storage capacity prior to nitrate starvation coped better with nitrate starvation. Our study of NRT1.7 (A) Schematic map of the nrt1.7-1 and nrt1.7-2 mutants.…”

“…However, significant amounts of the nitrate taken into plants can be stored in vacuoles and recirculated after storage (Rossato et al, 2001). A study by Richard-Molard et al (2008) showed that an Arabidopsis thaliana line that exhibited higher nitrate storage capacities coped better with nitrate starvation. In addition, quantitative trait locus (QTL) analysis of maize and barley (Hordeum vulgare) also showed that increased productivity or grain protein content is probably associated with their ability to accumulate higher amounts of nitrate in their leaves during vegetative growth and then to efficiently remobilize the stored nitrate during grain filling (Hirel et al, 2001;Mickelson et al, 2003).…”

Impact of the Genetic–Environment Interaction on the Dynamic of Nitrogen Pools in Arabidopsis

“…One possibility is that amino acids would be interconverted to increase the synthesis of amino acids dedicated to transport, such as glutamine and asparagine. It has also been proposed by Richard-Molard et al [15] that the initial size of the N storage pool is crucial for the capacity of plants to cope with nitrate starvation, unlike the remobilization dynamics and the composition of the internal N pool [14]. The reduction of growth and photosynthesis, the remobilization of N from old, mature organs to actively growing ones, and the accumulation of abundant anthocyanins, have also been observed in N-starved plants [17].…”

“…The phenotypic description of Arabidopsis Recombinant Inbred Lines (RIL) built-up to study the plant response to low and high N supplies [12], identified multiple sources of physiological variation, such as those leading to the variations of shoot biomass, nitrogen percentage and free amino-acids content [13]. Several studies showed decreases in total N%, in NO 3 reserves and in total free amino-acids content in plants grown on low regimes [14][15][16], while soluble proteins content remains unchanged in rosettes [10]. On the other hand, rubisco degradation releases numerous free amino acids available for phloem loading and other interconversions in N depleted plants [2].…”

Plasticity of the Arabidopsis Root System under Nutrient Deficiencies

“…In fact, most studies describe the effect of nutrient deficiencies on root growth and development only in terms of root biomass or total root length (Hermans and Verbruggen, 2005;Hermans et al, 2006;Richard-Molard et al, 2008;Jung et al, 2009;Cailliatte et al, 2010). Thus, important features of the root system are not comprehensible from these rather basic measurements.…”