Molecular regulation of nitrate and ammonium response in maize roots

Nitrogen (N) is fundamental for plant growth and development, since it represents an essential component of DNA, RNA, proteins and other metabolic components. Thus, nitrogen can be considered the most requested mineral nutrient in plants. Soil does not have sufficient N in available forms to support production levels, for this reason the application of nitrogen fertilization plays a key role in crop productivity. Only about 50% of the total N is harvested in the grain, and the remainder is lost from the plant-soil system, causing adverse impacts on environment and human health. Therefore, in order to increase the sustainability of agriculture and to reduce the environmental damage, improving nitrogen use efficiency (NUE) of crops represents a crucial point for reducing the N fertilizer application by ensuring high yields. However, the NUE molecular pathway components that act in plant response to nitrogen availability are still only partially characterized. The nitrogen uptake and assimilation by plants can essentially occur in two forms: nitrate (NO3-) and ammonium (NH4+). Concerning nitrate, besides its role as a nutrient, it acts also as a signalling molecule since it is involved in the modulation of expression of several genes linked to plant development. The understanding of the molecular mechanisms at the base of root architecture adjustment in response to N fluctuations in soil seems to be necessary to enhance the ability of plants to capture the applied N fertilizer. In the present study, in order to discriminate between the specific effects of nitrate from those more generally attributed to nitrogen, root morphology and gene expression analyses 6 were conducted, particularly on 2 days-old maize seedlings growth for 24 hours in a N deprived solution and then transferred for additional 24 hours to nitrate or ammonium supplied medium.