Nitrogen assimilation and photorespiration become more efficient under chloride nutrition as a beneficial macronutrient

Abstract

Chloride (Cl−) and nitrate (NO3−) are closely related anions involved in plant growth. Their similar physical and chemical properties make them to interact in cellular processes like electrical balance and osmoregulation. Since both anions share transport mechanisms, Cl− has been considered to antagonize NO3− uptake and accumulation in plants. However, we have recently demonstrated that Cl− provided at beneficial macronutrient levels improves nitrogen (N) use efficiency (NUE). Biochemical mechanisms by which beneficial Cl− nutrition improves NUE in plants are poorly understood. First, we determined that Cl− nutrition at beneficial macronutrient levels did not impair the NO3− uptake efficiency, maintaining similar NO3− content in the root and in the xylem sap. Second, leaf NO3− content was significantly reduced by the treatment of 6 mM Cl− in parallel with an increase in NO3− utilization and NUE. To verify whether Cl− nutrition reduces leaf NO3− accumulation by inducing its assimilation, we analysed the content of N forms and the activity of different enzymes and genes involved in N metabolism. Chloride supply increased transcript accumulation and activity of most enzymes involved in NO3− assimilation into amino acids, along with a greater accumulation of organic N (mostly proteins). A reduced glycine/serine ratio and a greater ammonium accumulation pointed to a higher activity of the photorespiration pathway in leaves of Cl−-treated plants. Chloride, in turn, promoted higher transcript levels of genes encoding enzymes of the photorespiration pathway. Accordingly, microscopy observations suggested strong interactions between different cellular organelles involved in photorespiration. Therefore, in this work we demonstrate for the first time that the greater NO3− utilization and NUE induced by beneficial Cl− nutrition is mainly due to the stimulation of NO3− assimilation and photorespiration, possibly favouring the production of ammonia, reductants and intermediates that optimize C-N re-utilization and plant growth. This work demonstrates new Cl− functions and remarks on its relevance as a potential tool to manipulate NUE in plants.

Linking the key physiological functions of essential micronutrients to their deficiency symptoms in plants

“…Chlorine (Cl) is classified as a micronutrient, although tissue concentrations are typically in the macronutrient range (>1000 lg g À1 DM), with significant stimulation of biomass production often observed when concentrations are well above 1000 lg g À1 DM (Kopsell & Kopsell, 2015). Cl is assigned with a wide range of beneficial functions in plants, including turgor and osmoregulation, biomass productivity, quality attributes, nitrogen use efficiency, water use efficiency and drought resistance, as well as serving an essential function in the oxygen-evolving complex (OEC) of photosystem II (PSII) (Wege et al, 2017;Franco-Navarro et al, 2019;Raven, 2020;Colmenero-Flores, 2023;Peinado-Torrubia et al, 2023). Vinyard et al (2019) showed that Cl plays an important role in the photoassembly of the OEC by tuning the affinity of various amino acid residues for manganese (Mn).…”

Genome-Wide Identification and Characterization of Long Non-Coding RNAs in Roots of Rice Seedlings under Nitrogen Deficiency

“…Between 2020 and 2035, the global demand for rice is expected to rise from 763 million tons to 852 million tons, necessitating increased production. Nitrogen (N) is a crucial macronutrient for plants, and its availability is a major factor in determining plant growth and production [2]. In fact, N availability is often the major factor limiting crop yields in nutrient-poor soils [3].…”