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The fusicoccin‐stimulated phosphorylation of a 33 KDa polypeptide in cells of Acer pseudoplatanus as influenced by extracellular and intracellular pH
Author(s) -
TOGNOLI L.,
BASSO BARBARA
Publication year - 1987
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/1365-3040.ep11602262
Subject(s) - fusicoccin , phosphorylation , acer pseudoplatanus , extracellular , chemistry , intracellular , isobutyric acid , biochemistry , intracellular ph , efflux , protein phosphorylation , biophysics , stimulation , cytoplasm , iodoacetic acid , atpase , protein kinase a , biology , enzyme , neuroscience
In a previous study, it was shown that the fungal toxin fusicoccin (FC) is able to stimulate the in vivo phosphorylation of a 33 KDalton polypeptide (33 KP) independently of protein synthesis. Here we show that the stimulation by FC of both proton efflux and 33 KP phosphorylation are strongly enhanced when the external medium contains K + or Na + , suggesting that the two phenomena are related. The stimulatory effect of FC is higher in unbuffered than in buffered media; moreover, in the absence of FC, 33 KP is more phosphorylated at an acidic than at a basic pH of the medium, suggesting that the effect of FC may depend, to a certain extent, on the acidification of the free space caused by FC‐promoted proton efflux. Treatments reported to alter the intracellular pH influence 33 KP phosphorylation even more strongly than the external pH does. The acidifying agents isobutyric acid and trimethylacetic acid decrease 33 KP phosphorylation, while the alkalinizing agents, ammonia and procaine, increase it. FC partially counteracts the inhibition by the weak acids, whereas the stimulatory effect of FC is not additive with that of the weak bases. The results indicate that 33 KP phosphorylation senses both the external and internal pH. The stimulatory effect of cytoplasm‐alkalinizing treatments, which mimics that of FC, agrees with the reported capacity of FC to cause cytoplasmic alkalinization, following activation of the plasmalemma proton pump.