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Characterization of the blue light‐induced extracellular alkalinization associated with the monovalent anion uptake by Monorapidium braunii. Competition between NO 3 and Cl −
Author(s) -
Witt Federico G.,
Aparicio Pedro J.
Publication year - 1995
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1995.tb00966.x
Subject(s) - extracellular , chemistry , ion , blue light , biophysics , stereochemistry , nuclear chemistry , biochemistry , biology , physics , organic chemistry , optics
The blue light‐elicited monovalent anion‐dependent alkalinization of the medium of Monoraphidium braunü (Legnerová, 202–7d) was characterized for the NO‐ 3 and Cl‐ uptake. The maximal H + uptake rates for these two anions have a similar optimum pH around 8.5, and quite similar K s values for high (38 ü M for Cl‐ and 35ü M for NO‐ 3 ) and low (320 ü M for Cl‐ and 335 ü M for NO‐ 3 ) affinities. The steady H + uptake associated with the uptake and reduction of NO‐ 3 showed a K s of 125 ü M . which in this alga corresponds to the NO‐ 3 reductase (EC 1.6.6.2) K m for NO‐ 3 . The only and striking difference found in the uptake properties of these anions was the delay time between the switching on of the blue light and the start of the alkalinization, which increased from 10 to 90 s as the initial pH decreased from 8.5 to 6.5 in the presence of NO‐ 3 , whereas for Cl‐ uptake this delay time (10s) did not vary in relation to the initial pH. When the NO‐ 3 concentration in the medium was low (100 ü M ), the presence of relatively high concentrations of Cl‐ (3 ü M ), on the one hand, greatly stimulated the maximal alkalinization rates but, on the other, Cl‐ severely reduced the steady NO‐ 3 ‐dependent rate of alkalinization. The data indicate that Cl‐ inhibits competitively NO‐ 3 uptake with a K i of 750 ü M . Moreover, high concentrations of NO‐ 3 (above 5 ü M ) reduced its own maximal, but not the steady, uptake rates. The above results allow us to propose that most of the components of the individual NO‐ 3 and Cl‐ transport systems are under identical light control and, as the competition data suggest, that these two anions may be taken up by the same transport system.