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Short-Term Response of Cytosolic N O 3 − to Inorganic Carbon Increase in Posidonia oceanica Leaf Cells

Published version
Peer-reviewed

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Authors

Rubio, Lourdes 
García-Pérez, Delia 
Davies, Julia M. 
Fernández, José A. 

Abstract

The concentration of CO2 in the atmosphere has increased over the past 200 years and is expected to continue rising in the next 50 years at a rate of 3 ppm·year−1. This increase has led to a decrease in seawater pH that has changed inorganic carbon chemical speciation, increasing the dissolved HC O 3 − . Posidonia oceanica is a marine angiosperm that uses HC O 3 − as an inorganic carbon source for photosynthesis. An important side effect of the direct uptake of HC O 3 − is the diminution of cytosolic Cl− (Cl−c) in mesophyll leaf cells due to the efflux through anion channels and, probably, to intracellular compartmentalization. Since anion channels are also permeable to N O 3 − we hypothesize that high HC O 3 − , or even CO2, would also promote a decrease of cytosolic N O 3 − ( N O 3 − c ). In this work we have used N O 3 − - and Cl−-selective microelectrodes for the continuous monitoring of the cytosolic concentration of both anions in P. oceanica leaf cells. Under light conditions, mesophyll leaf cells showed a N O 3 − c of 5.7 ± 0.2 mM, which rose up to 7.2 ± 0.6 mM after 30 min in the dark. The enrichment of natural seawater (NSW) with 3 mM NaHCO3 caused both a N O 3 − c decrease of 1 ± 0.04 mM and a Cl c − decrease of 3.5 ± 0.1 mM. The saturation of NSW with 1000 ppm CO2 also produced a diminution of the N O 3 − c , but lower (0.4 ± 0.07 mM). These results indicate that the rise of dissolved inorganic carbon ( HC O 3 − or CO2) in NSW would have an effect on the cytosolic anion homeostasis mechanisms in P. oceanica leaf cells. In the presence of 0.1 mM ethoxyzolamide, the plasma membrane-permeable carbonic anhydrase inhibitor, the CO2-induced cytosolic N O 3 − diminution was much lower (0.1 ± 0.08 mM), pointing to HC O 3 − as the inorganic carbon species that causes the cytosolic N O 3 − leak. The incubation of P. oceanica leaf pieces in 3 mM HC O 3 − -enriched NSW triggered a short-term external N O 3 − net concentration increase consistent with the N O 3 − c leak. As a consequence, the cytosolic N O 3 − diminution induced in high inorganic carbon could result in both the decrease of metabolic N flux and the concomitant biomass N impoverishment in P. oceanica and, probably, in other aquatic plants.

Description

Keywords

Plant Science, cytosolic NO3 −, elevated inorganic carbon, NO3 − efflux, anion channels, intracellular nitrate-selective microelectrodes, seagrasses

Journal Title

Frontiers in Plant Science

Conference Name

Journal ISSN

1664-462X

Volume Title

11

Publisher

Frontiers Media S.A.