Short-Term Response of Cytosolic to Inorganic Carbon Increase in Leaf Cells.

The concentration of CO 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. This increase has led to a decrease in seawater pH that has changed inorganic carbon chemical speciation, increasing the dissolved . is a marine angiosperm that uses as an inorganic carbon source for photosynthesis. An important side effect of the direct uptake of is the diminution of cytosolic Cl (Clc) in mesophyll leaf cells due to the efflux through anion channels and, probably, to intracellular compartmentalization. Since anion channels are also permeable to we hypothesize that high , or even CO, would also promote a decrease of cytosolic ( ). In this work we have used - and Cl-selective microelectrodes for the continuous monitoring of the cytosolic concentration of both anions in leaf cells. Under light conditions, mesophyll leaf cells showed a 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 NaHCO caused both a decrease of 1 ± 0.04 mM and a decrease of 3.5 ± 0.1 mM. The saturation of NSW with 1000 ppm CO also produced a diminution of the , but lower (0.4 ± 0.07 mM). These results indicate that the rise of dissolved inorganic carbon ( or CO) in NSW would have an effect on the cytosolic anion homeostasis mechanisms in leaf cells. In the presence of 0.1 mM ethoxyzolamide, the plasma membrane-permeable carbonic anhydrase inhibitor, the CO-induced cytosolic diminution was much lower (0.1 ± 0.08 mM), pointing to as the inorganic carbon species that causes the cytosolic leak. The incubation of leaf pieces in 3 mM -enriched NSW triggered a short-term external net concentration increase consistent with the leak. As a consequence, the cytosolic diminution induced in high inorganic carbon could result in both the decrease of metabolic N flux and the concomitant biomass N impoverishment in and, probably, in other aquatic plants.