Nitrate reductase regulation in wheat seedlings by exogenous nitrate: A possible role in tolerance to salt stress

Background

Soil salinity is a major abiotic stress causing severe damage to plants. Thus, proper management approaches need to be developed to lessen the detrimental effect of salinity on crop growth and productivity.

Aims

This study was conducted to investigate the putative role of nitrate (NO₃⁻) and nitrate reductase (NR) in mitigating the adverse effects of salt stress on the growth of durum wheat seedlings.

Methods

Nitrogen nutrition has been modified, in the presence of 100 mM NaCl, either by increasing the NO₃⁻ availability, the deprivation of NO₃⁻ or by the addition of sodium tungstate—an inhibitor of NR—in the culture medium.

Results

Obtained results showed that, in the presence of 2.5 mM NO₃⁻, salt stress significantly decreased all studied growth traits (biomass production, relative growth rate, and water content). This was associated with a noteworthy reduction in total chlorophyll pigment, total carbohydrates, and protein contents. Concomitantly, NR activity was remarkably decreased. However, proline and malondialdehyde (MDA) were significantly accumulated. In the absence of NO₃⁻ as well as in the presence of tungstate, NR activities were noticeably reduced, and wheat seedling growth was further disturbed in comparison to salt-stressed seedlings grown under 2.5 mM NO₃⁻. Increasing the NO₃⁻ availability to 7.5 mM significantly restricted Cl⁻ uptake, markedly increased root and leaf NR activities, and alleviated salt stress–induced seedling growth inhibition as compared to salt-stressed seedlings grown under 2.5 mM NO₃⁻. Such effects were associated with an increase in leaf chlorophyll and protein concentrations and in root and leaf carbohydrate concentrations. Nevertheless, MDA concentrations were sharply decreased.

Conclusions

This study provides strong arguments highlighting the potential role of NO₃⁻ reduction in mitigating the adverse effects of salt stress on the growth of wheat plants at the early seedling stage. The enhancement of the NR activity through increasing the NO₃⁻ availability may, therefore, represent a potential strategy to overcome the salinity-mediated impairment of wheat seedlings to some extent.