Nitrogen modulation of legume root architecture signaling pathways involves phytohormones and small regulatory molecules

Abstract

Nitrogen, particularly nitrate is an important yield determinant for crops. However, current agricultural practice with excessive fertilizer usage has detrimental effects on the environment. Therefore, legumes have been suggested as a sustainable alternative for replenishing soil nitrogen. Legumes can uniquely form nitrogen-fixing nodules through symbiotic interaction with specialized soil bacteria. Legumes possess a highly plastic root system which modulates its architecture according to the nitrogen availability in the soil. Understanding how legumes regulate root development in response to nitrogen availability is an important step to improving root architecture. The nitrogen-mediated root development pathway starts with sensing soil nitrogen level followed by subsequent signal transduction pathways involving phytohormones, microRNAs and regulatory peptides that collectively modulate the growth and shape of the root system. This review focuses on the current understanding of nitrogen-mediated legume root architecture including local and systemic regulations by different N-sources and the modulations by phytohormones and small regulatory molecules.

Effects of Field Inoculation with VAM and Bacteria Consortia on Root Growth and Nutrients Uptake in Common Wheat

“…In this trial, in the absence of inoculation, the reduction in root length density with increased amounts of chemical fertilizer is in agreement with many reports in the literature [49][50][51], suggesting that root growth impairment can occur at extremely high and extremely low N supply [52]. Despite species-specific regulation, an excess of nitrogen can reduce lateral root formation through hormone-mediated mechanisms related to reduced shoot-to-root auxin transport [53], and ethylene accumulation at the root level [54]. Azotobacter is capable of synthetizing biologically active substances, particularly auxins, that directly affect root growth and morphology [41], and many PGPRs lower root ethylene levels through production of the ACC-deaminase enzyme [55,56] and toxins, like rhizobitoxine, capable of inhibiting ethylene synthesis [35].…”

Urea Addition Promotes the Metabolism and Utilization of Nitrogen in Cucumber

“…Nitrogen (N) is an important phytonutrient that is usually required in large amounts, and its deficiency generally limits plant growth and development [3,4]. Thus, N functions as a signaling element that sustains plant growth and development, particularly under stressful conditions [5,6]. Deficient or excessive amounts of N have a significant negative impact on vegetables [3,7], suggesting that changing the forms of nitrogen supply without changing the molar amount of nitrogen is a very important pathway that influences the growth of plants.…”

Ethylene and the Regulation of Physiological and Morphological Responses to Nutrient Deficiencies

“…More recently, a role for ethylene has been extended to other deficiencies, such as K (Shin and Schachtman, 2004;Jung et al, 2009;Kim et al, 2012), S (Maruyama-Nakashita et al, 2006;Wawrzy nska et al, 2010;Moniuszko et al, 2013), and B (Martín-Rejano et al, 2011). Ethylene has also been implicated in both N deficiency and excess Mohd-Radzman et al, 2013;Zheng et al, 2013), and its participation in Mg deficiency has been suggested (Hermans et al, 2010).…”

“…For information relating ethylene to other aspects of plant mineral nutrition, such as N 2 fixation and responses to excess of nitrate or essential heavy metals, the reader is referred to other reviews (for review, see Maksymiec, 2007;Mohd-Radzman et al, 2013;Steffens, 2014).…”

“…In general, ethylene production increases under different nutrient deficiencies. Additionally, ethylene production can increase upon excess of some nutrients, like nitrate Mohd-Radzman et al, 2013) or essential heavy metals (Maksymiec, 2007). In 1999, Romera et al (1999) showed that Fe-deficient roots of several dicots produced more ethylene than the Fe-sufficient ones, even before the plants showed any other symptom of deficiency (which could lead to tissue necrosis and thereby, stimulation of wound ethylene; Lynch and Brown, 1997).…”