Plant and Cell Physiology, 2003, Vol. 44, No. 1 55-61
© 2003 Oxford University Press
Evidence for Nucleotide-Dependent Passive H+ Transport Protein in the Plasma Membrane of Barley Roots
1 Department of Biology, Faculty of Science, Kyushu University, Ropponmatsu 4-2-1, Fukuoka, 810-8560 Japan
2 Department of Biological Sciences, Faculty of Science, Nara Women’s University, Kitauoyanishi-machi, Nara-shi, 630-8506 Japan
Plasma membranes were isolated from barley roots by two-phase partitioning, and octylglucoside-soluble and -insoluble fractions were obtained. The insoluble fractions were reconstituted into liposomes, and the plasma membrane H+-ATPase was shown to participate in MgATP-dependent H+ transport activity. The H+ transport was decreased when the octylglucoside-soluble fraction was reconstituted together with the insoluble fraction. The decrease was not due to inhibition of the H+-ATPase, but rather was likely due to the increased H+ leakage from the proteoliposome. The octylglucoside-soluble fraction was, therefore, reconstituted in the liposomes and the passive H+ transport was determined using the pH jump method. A pH gradient across the membranes was generated by the pH jump, and the gradient was found to be dissipated by passive H+ transport. The H+ transport required ATP, K+, and valinomycin. The H+-transport also occurred when ADP, AMP, GTP, or ATP-
-S was present instead of ATP, and did not occur when the octylglucoside-soluble fraction was boiled before the reconstitution. These findings suggest that nucleotide-dependent H+ transport protein is present in the plasma membrane of root cells.
3 Present address: Zen-noh Agricultural R & D Center 5-1-5, Higashi-Yahata, Hiratsuka, Kanagawa, 254-0016 Japan.
4 Corresponding author: E-mail: kenrcb@mbox.nc.kyushu-u.ac.jp; Fax: 092-726-4758.