Abstract
Nitrogen nutrition in plants is a key determinant in crop productivity. The availability of nitrogen nutrients in the soil, both inorganic (nitrate and ammonium) and organic (urea and free amino acids), highly differs and influences plant physiology, growth, metabolism, and root morphology. Deciphering this multifaceted scenario is mandatory to improve the agricultural sustainability. In root cells, specific proteins located at the plasma membrane play key roles in the transport and sensing of nitrogen forms. This review outlines the current knowledge regarding the biochemical and physiological aspects behind the uptake of the individual nitrogen forms, their reciprocal interactions, the influences on root system architecture, and the relations with other proteins sustaining fundamental plasma membrane functionalities, such as aquaporins and H+-ATPase. This topic is explored starting from the information achieved in the model plant Arabidopsis and moving to crops in agricultural soils. Moreover, the main contributions provided by proteomics are described in order to highlight the goals and pitfalls of this approach and to get new hints for future studies.
Highlights
Nitrogen (N) is the most abundant mineral element present in plant tissues, in which it constitutes about 1 to 5% of total dry matter [1]
First indications were provided by a phosphoproteomic study aimed at the characterization of the early changes induced by NO3 − or NH4 + resupply to Arabidopsis seedlings, based on the phosphopeptide enrichment by the titanium dioxide methodology
Considering this framework, it is highly conceivable that these transporters have complementary roles in amino acid uptake from the soil, with individual contributions probably varying during plant development and growth conditions
Summary
Nitrogen (N) is the most abundant mineral element present in plant tissues, in which it constitutes about 1 to 5% of total dry matter [1]. N is present as inorganic forms, such as nitrate (NO3 − ) and ammonium (NH4 + ), and as organic forms, mainly consisting of urea, free amino acids, and short peptides The accessibility of these resources by roots varies considerably through space and time, due to soil heterogeneity and to dynamic microbial conversions, two aspects in turn affected by agronomic practices and environmental conditions [4]. The major adaptations to N availability consist of the changes in uptake activity and in the modulation of the root system architecture (RSA), both of which are related to the ability of N forms to act as nutrients and/or regulatory signals for plant growth and metabolism (Figure 1). Deciphering how the root membrane proteome changes in response to different N sources could provide new knowledge useful to enhance agriculture sustainability
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