Nitrate-sensitive ATPase activity and proton pumping in guard cell protoplasts of Commelina

Journal article

ATPase activity was measured in crude homogenates of guard cell protoplasts of Commelina communis L. using a linked enzyme assay. A low level of azide-sensitive ATPase activity was detected with a pH optimum of 6.8. This activity was stimulated by 0.01% (v/v) Triton X-100, and the pH optimum shifted to pH 7.4. Nitrate-sensitive ATPase activity was measured in the presence of azide and showed a pH optimum around pH 8.0. Proton pumping activity in a mixed population of vesicles from GCP was monitored using fluorescence quenching of quinacrine. Mg-ATP dependent proton pumping was observed at pH 8.0, but not at pH 6.6. The activity at pH 8.0 was inhibited by nitrate and DCCD but not vanadate. These data indicate that activity of the tonoplast proton pump was being measured. There was, however, no evidence for a tonoplast cation (K⁺)/proton antiporter under these assay conditions as potassium did not reduce the initial rate of pH gradient formation or increase the rate of collapse of a pre-formed gradient after inhibition of the pump.

Authors: Fricker, M; Willmer, C

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Journal of Experimental Botany
• Volume: 41
• Issue: 223
• Pages: 193-198
• Publication date: 1990-02-01
• DOI: 10.1093/jxb/41.2.193
• EISSN: 1460-2431
• ISSN: 0022-0957
• Keywords: guard cell protoplasts; proton pump; Commelina; tonoplast ATPase