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

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

Frontiers in plant science (2020-07-17)
Lourdes Rubio, Delia García-Pérez, Julia M Davies, José A Fernández
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.

MATERIALS
Product Number
Brand
Product Description

Supelco
Chloride ionophore I - cocktail A, Selectophore