Section 9
Chapter 8,213

Bafilomycin inhibits vacuolar pH regulation in a fresh water charophyte, Chara corallina

Okazaki, Y.; Tazawa, M.; Moriyama, Y.; Iwasaki, N.

Botanica Acta 105(6): 421-426


ISSN/ISBN: 0932-8629
Accession: 008212347

Bafilomycin A-1, known as an inhibitor of vacuolar type H+-ATPase, was used to study involvement of the vacuolar ATP-dependent H+-pump in the vacuolar pH regulation in a fresh water charophyte, Chara corallina. When bafilomycin A-1 (100 nM) was externally given to intact cells, the vacuolar pH (about 5) was not affected. Internodal cells were then pretreated with 100 nM bafilomycin for 1-2 h and the vacuolar sap was replaced with a weakly buffered solution of pH 7.4. The readjustment of the modified vacuolar pH in bafilomycin-treated cells was significantly retarded compared with that in untreated cells. Next, bafilomycin A-1 was directly introduced into the vacuole by vacuolar perfusion with the artificial cell sap of pH 7.4. At 100 nM bafilomycin A-1, the decrease in the vacuolar pH was significantly inhibited. When cell sap was replaced with the artificial cell sap containing no buffer (pH 5.2-5.5), the vacuolar pH increased in the presence of vacuolar bafilomycin, suggesting that the PP-i-dependent H+ pumping alone was not sufficient for the pH regulation of Chara vacuoles. Intracellular bafilomycin A-1 had no effect on the plasma membrane potential of tonoplast-free cells, which is evidence that it does not affect the electrogenic H+-pump in the plasma membrane. Bafilomycin A-1 inhibited the ATP-dependent H+ transport of tonoplast vesicles but not the PP-i-dependent H+ transport. The ATPase activity of tonoplast vesicles was also inhibited by bafilomycin A-1.

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