Abstract
Crop plant development is strongly dependent on nitrogen availability in the soil and on the efficiency of its recruitment by roots. For this reason, the understanding of the molecular events underlying root adaptation to nitrogen fluctuations is a primary goal to develop biotechnological tools for sustainable agriculture. However, knowledge about molecular responses to nitrogen availability is derived mainly from the study of model species. Nitric oxide (NO) has been recently proposed to be implicated in plant responses to environmental stresses, but its exact role in the response of plants to nutritional stress is still under evaluation. In this work, the role of NO production by maize roots after nitrate perception was investigated by focusing on the regulation of transcription of genes involved in NO homeostasis and by measuring NO production in roots. Moreover, its involvement in the root growth response to nitrate was also investigated. The results provide evidence that NO is produced by nitrate reductase as an early response to nitrate supply and that the coordinated induction of non-symbiotic haemoglobins (nsHbs) could finely regulate the NO steady state. This mechanism seems to be implicated on the modulation of the root elongation in response to nitrate perception. Moreover, an improved agar-plate system for growing maize seedlings was developed. This system, which allows localized treatments to be performed on specific root portions, gave the opportunity to discern between localized and systemic effects of nitrate supply to roots.
Highlights
Soil nutrient acquisition intensely affects global crop production (Forde and Clarkson, 1999; Robertson and Vitousek, 2009)
Nitrate exerts specific effects on genes involved in Nitric oxide (NO) homeostatic control The expression of a number of previously identified genes (Quaggiotti et al, 2003; Trevisan et al, 2011, 2012), together with that of some new ones (Supplementary Table S1), was measured in roots and leaves of seedlings grown for 5 days in a nutrient solution containing 1 mM nitrate (+NO3–), 1 mM ammonium (+NH4+), or N-deprived (Fig. 3)
In seedlings supplied with 1 mM nitrate for 2 h, the transcripts of all five genes were more distributed between the apical meristem and the transition zone, with a significant increase of accumulation in the transition zone which showed an amount of mRNA for each gene ranging from 20 to 40% of the total
Summary
Soil nutrient acquisition intensely affects global crop production (Forde and Clarkson, 1999; Robertson and Vitousek, 2009). In poor nations drought and low soil fertility cause low yields and food insecurity, while in rich nations intensive fertilization leads to leaching of nutrients and/or greenhouse gas emission (Donner and Kucharik, 2008). The development of new crop cultivars with enhanced soil resource acquisition is an important strategic goal for modern agriculture (Lynch, 1998, 2007; Vance et al, 2003). The macronutrient nitrogen is essential for plant growth and development as it is a component of proteins, nucleic acids, and many cofactors and secondary metabolites. Nitrate is the major source of nitrogen for most plant species (Ahmad et al, 2007; Nischal et al, 2012)
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