Signalling cascades integrating light-enhanced nitrate metabolism

Abstract

In higher plants, light is crucial for regulation of nitrate uptake, translocation and assimilation into organic compounds. Part of this metabolism is tightly coupled to photosynthesis because the enzymes involved, nitrite reductase and glutamate synthase, are localized to the chloroplasts and receive reducing power from photosynthetic electron transport. However, important enzymes in nitrate acquisition and reduction are localized to cellular compartments other than chloroplasts and are also up-regulated by light, i.e. transporters in cell and organellar membranes and nitrate reductase in the cytosol. This review describes the different light-dependent signalling cascades regulating nitrate metabolism at the transcriptional as well as post-transcriptional level, and how reactions in different compartments of the cell are co-ordinated. Essential players in this network are phytochrome and HY5 (long hypocotyls 5)/HYH (HY5 homologue)-dependent signalling pathways, the energy-related AMPK (AMP-activated protein kinase) protein kinase homologue SNRK1 (sucrose non-fermenting kinase 1-related kinase), chloroplastic thioredoxins and the prokaryotically originated PII protein. A complex light-dependent network of regulation emerges, which appears to be necessary for optimal nitrogen assimilation and for avoiding the accumulation of toxic intermediates and side products, such as nitrite and reactive oxygen compounds.

Arabidopsis V-ATPase activity at the tonoplast is required for efficient nutrient storage but not for sodium accumulation

“…Nitrate is stored in the vacuole during the night, when nitrate reductase is inactive. Our data suggest that reduced vacuolar uptake capacity can lead to increased cytosolic nitrate levels that in turn stimulate nitrate assimilation, a process that requires a substantial electron flow either via ferredoxin or NAD(P)H (30). The fact that reduced growth of the double mutant can be alleviated by increasing light periods thus likely reflects the metabolic burden imposed by continuous nitrate assimilation.…”

Otimização da análise da atividade da redutase do nitrato e sua caracterização em folhas de cana-de-açúcar

“…(Figuras 1 A e 4 C). A luz é capaz de influenciar tanto a transcrição de RNA mensageiro que codifica a RN, como o controle pós-traducional da enzima (Lillo, 2008). Os baixos níveis de atividade da RN obtidos no início da manhã e no final do dia podem estar ligados a um mecanismo de controle rápido da atividade dessa enzima.…”

“…agropec. bras., Brasília, v.49, n.5, p.384-394, maio 2014 DOI: 10.1590/S0100-204X2014000500008 O desencadeamento da expressão dos genes da RN é induzido pela presença de nitrato, enquanto o nível de expressão é controlado pela luz (Souza et al, 2002;Lillo, 2008), além de responder a outros sinais ligados ao próprio metabolismo do N (teor de glutamina), ao metabolismo do carbono (sacarose e CO 2 ) e à fotossíntese (energia e citocininas) (Crawford et al, 2000;Miller & Cramer, 2004).…”

Molecular Mechanism of 14-3-3 Protein-mediated Inhibition of Plant Nitrate Reductase

“…NR catalyzes the first and rate-limiting step in primary nitrogen metabolism, the cytosolic reduction of nitrate to nitrite (21), using reducing equivalents provided by NADH. NR has a modular structure with an N-terminal molybdenum-containing domain, a b-type cytochrome domain, and a C-terminal FAD domain (see Fig.…”