Na⁺-Dependent High-Affinity Nitrate, Phosphate and Amino Acids Transport in Leaf Cells of the Seagrass Posidonia oceanica (L.) Delile

• Published in: International journal of molecular sciences 2018-05, Vol.19 (6), p.1570
• Main Authors: Rubio, Lourdes, García-Pérez, Delia, García-Sánchez, María Jesús, Fernández, José A
• Format: Article
• Language: English
• Subjects: Affinity; Alismatales - metabolism; amino acid transport; Amino acids; Amino Acids - metabolism; Biological Transport; Cell Membrane - metabolism; Cell Membrane - physiology; Cytoplasm - metabolism; Cytosolic Na+; Dependence; Depolarization; Grasses; high-affinity transport; Leaves; Marine environment; Membrane potential; Membrane Potentials; Membrane Transport Proteins - metabolism; Mesophyll; Na+-dependent transport systems; Nitrates - metabolism; NO3− uptake; Nutrients; Phosphates - metabolism; Pi uptake; Plant Leaves - metabolism; Plant Proteins - metabolism; Plants; Posidonia; Posidonia oceanica; Saturation; Seagrasses; Seawater; Sodium; Sodium - metabolism; Transport
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms19061570

(L.) Delile is a seagrass, the only group of vascular plants to colonize the marine environment. Seawater is an extreme yet stable environment characterized by high salinity, alkaline pH and low availability of essential nutrients, such as nitrate and phosphate. Classical depletion experiments, membrane potential and cytosolic sodium measurements were used to characterize the high-affinity NO₃ , Pi and amino acids uptake mechanisms in this species. Net uptake rates of both NO₃ and Pi were reduced by more than 70% in the absence of Na⁺. Micromolar concentrations of NO₃ depolarized mesophyll leaf cells plasma membrane. Depolarizations showed saturation kinetics ( = 8.7 ± 1 μM NO₃ ), which were not observed in the absence of Na⁺. NO₃ induced depolarizations at increasing Na⁺ also showed saturation kinetics ( = 7.2 ± 2 mM Na⁺). Cytosolic Na⁺ measured in leaf cells (17 ± 2 mM Na⁺) increased by 0.4 ± 0.2 mM Na⁺ upon the addition of 100 μM NO₃ . Na⁺-dependence was also observed for high-affinity l-ala and l-cys uptake and high-affinity Pi transport. All together, these results strongly suggest that NO₃ , amino acids and Pi uptake in leaf cells are mediated by high-affinity Na⁺-dependent transport systems. This mechanism seems to be a key step in the process of adaptation of seagrasses to the marine environment.