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Medium Acidification by Maize Root Tips and its Inhibition by Heavy Water
Author(s) -
Kotyk A.,
FischerSchliebs E.,
Lüttge U.
Publication year - 1991
Publication title -
botanica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 0932-8629
DOI - 10.1111/j.1438-8677.1991.tb00255.x
Subject(s) - fusicoccin , chemistry , vanadate , bicarbonate , carbonic anhydrase , dissociation (chemistry) , atpase , inorganic chemistry , biophysics , medicinal chemistry , biochemistry , enzyme , biology , organic chemistry
Acidification of external solution by maize root tips can apparently proceed by two mechanisms. The first, significant only above pH 6, does not require the presence of salts in the medium and appears to be due to respiratory CO 2 release with subsequent hydration and dissociation into H + + HCO − 3 . The second, much more efficient process, requires permeant ions and proceeds to well below pH 4 under mediation by the plasma membrane H + ‐ATPase. While the first process is affected by acetazolamide (an inhibitor of carbonate dehydratase), the second is blocked by vanadate, erythrosin B, diethylstilbestrol and miconazole, and is strikingly stimulated by fusicoccin. Both mechanisms are markedly inhibited by heavy water, the first by up to 80% with an ID 50 of 18–25% D 2 O, the second up to 91%, with an ID 50 of 20–30% D 2 O. The inhibition of the acidification by ATPase can be relieved by replacing D 2 O with H 2 O, indicating that the effect of D 2 O is kinetic rather than on covalently‐bound hydrogen atoms. Apparently the H + ‐ATPase uses H + (or possibly H 3 O + ) as substrate which binds to a rather specific site where it cannot be functionally replaced by D + or D 3 O + .