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

In a low-input agricultural context, plants facing temporal nutrient deficiencies need to be efficient. By comparing the effects of NO3--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 NO3--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 NO3-. It was demonstrated that line 432 coped better with NO3--starvation, producing higher shoot and root biomass and sustaining maximal growth for a longer time. However, both lines exhibited similar features under NO3--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 NO3--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 NO3--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.