Maize Source Leaf Adaptation to Nitrogen Deficiency Affects Not Only Nitrogen and Carbon Metabolism But Also Control of Phosphate Homeostasis    

Abstract

Crop plant development is strongly dependent on the availability of nitrogen (N) in the soil and the efficiency of N utilization for biomass production and yield. However, knowledge about molecular responses to N deprivation derives mainly from the study of model species. In this article, the metabolic adaptation of source leaves to low N was analyzed in maize (Zea mays) seedlings by parallel measurements of transcriptome and metabolome profiling. Inbred lines A188 and B73 were cultivated under sufficient (15 mM) or limiting (0.15 mM) nitrate supply for up to 30 d. Limited availability of N caused strong shifts in the metabolite profile of leaves. The transcriptome was less affected by the N stress but showed strong genotype-and age-dependent patterns. N starvation initiated the selective down-regulation of processes involved in nitrate reduction and amino acid assimilation; ammonium assimilation-related transcripts, on the other hand, were not influenced. Carbon assimilation-related transcripts were characterized by high transcriptional coordination and general down-regulation under low-N conditions. N deprivation caused a slight accumulation of starch but also directed increased amounts of carbohydrates into the cell wall and secondary metabolites. The decrease in N availability also resulted in accumulation of phosphate and strong down-regulation of genes usually involved in phosphate starvation response, underlining the great importance of phosphate homeostasis control under stress conditions.

ZD958 is a low-nitrogen-efficient maize hybrid at the seedling stage among five maize and two teosinte lines

“…Under N deficiency, many N transporters and proteins mediating N metabolism have differential expression or accumulation (Yang et al 2011;Liao et al 2012a;Schlüter et al 2012;Garnett et al 2013), although no specific genes mediating N uptake and assimilation were identified with differential expression in rice seedlings at the early stage of N limitation (Lian et al 2006). Here, we found eight genes regulating N assimilation with significant down-regulation at the transcriptional level in the ZD958 root after 12-day N deficiency (Fig.…”

“…Asparagine, featured by a high N/C ratio, serves as an efficient carrier for N transport (Miflin and Lea 1980); asparagine synthetase catalyzes synthesis of asparagine using glutamine as a substrate (Lam et al 1996). ASN2 expression is downregulated in maize source leaves under low N (Schlüter et al 2012). Down-regulation of ASN2 expression in ZD958 and other maize and teosinte roots ( Fig.…”

“…At the molecular level, N deficiency causes genome-wild changes in gene expression and carbon and N metabolism in arabidopsis (Bi et al 2007); however, genes regulating N uptake and assimilation showed no significant difference in N-deficient rice seedlings in contrast to quick changes in expression of genes mediating metabolism, protein synthesis, and transport facilitation (Lian et al 2006). In maize, N deficiency causes a series of changes in gene expression and protein accumulation directly affecting N uptake and metabolism, amino acid transport, and protein metabolism (Yang et al 2011;Liao et al 2012a;Schlüter et al 2012Schlüter et al , 2013Garnett et al 2013;Humbert et al 2013). However, little is known about how hybrid maize, especially dominant hybrids in the field, respond to N limitation at physiological and molecular levels, and whether they have similar or contrasting responses compared with inbred lines and wild maize?…”

Nitrogen Stress Affects the Turnover and Size of Nitrogen Pools Supplying Leaf Growth in a Grass

“…N fertilizer supply has multiple direct and indirect effects on plant N metabolism (Stitt et al, 2002;Schlüter et al, 2012). In particular, it modifies the N content of newly produced leaves, leaf longevity/senescence, and the dynamics of light distribution inside expanding canopies (Evans, 1983(Evans, , 1989Moreau et al, 2012).…”

Hydroponic culturing upregulates sucrose and glutamine metabolism by enhancing their utilization via intermediates of aerobic pathway in wheat

“…Plants treated with NH 4 Cl, as exclusive nitrogen source, showed lower level of 388 Kaur and asthir: Sucrose and Glutamine Metabolism in Wheat Cereal Research Communications 44, 2016 total sugars than those treated with NO 3 -. The rapid assimilation of NH 4 + in glutamine led to a consumption of carbon skeletons, causing depletion of the foliar starch and sucrose (Ikram et al 2012;Schluter et al 2012), likewise Britto and Kronzucker (2002) concluded that the consumption of fixed carbon during the assimilation of NH 4 + could appreciably reduce sugars results in increases amino acids.…”