Poster: Membrane Transport

Abs # 1201: ATP-dependent uptake of salicylic acid 2-O-b-D-glucose by soybean tonoplast membrane vesicles.

Presenter:	Dean, John V, jdean@depaul.edu
Authors	Dean, John V (A)
Affiliations:	(A): DePaul University

Glucosylation and vacuolar sequestration of salicylic acid (SA) are important metabolic events that may allow plant cells to tolerate high levels of endogenously produced SA or regulate the availability and activity of this plant hormone. In soybean, SA is converted primarily to SA 2-O-b-D-glucose (SAG) in the cytoplasm. SAG is then transported into the vacuole for storage. However, this vacuolar transport has never before been investigated. We characterized the vacuolar transport of SAG by measuring the uptake of [¹⁴C]SAG into tonoplast vesicles isolated from etiolated soybean hypocotyls. The uptake of SAG was stimulated 3-fold when MgATP was included in the assay media. The uptake of SA was only stimulated 1.25-fold by the addition of ATP and was 2.2-fold less than the uptake of SAG. ATP-dependent SAG transport was saturable with a K_m of 90 mM and had some specificity for SAG since uptake was not strongly inhibited by the glucose conjugates salicin, esculin, and arbutin and the glutathione conjugate of 1-chloro-2,4-dinitrobenzene. SAG uptake was not stimulated when ATP was replaced by a non-hydrolyzable analog of ATP. The ATP-dependent uptake was inhibited by vanadate (a phosphoryl transition-state analog), but was much less sensitive to inhibition by bafilomycin A₁ (an inhibitor of vacuolar H⁺-ATPase), and dissipation of the pH or the electrical potential differences across the tonoplast membrane. These results provide evidence that the tonoplast transport of SAG in soybean is directly energized by ATP and is independent of the ATP generated transtonoplast H⁺-electrochemical gradient. It is possible that the tonoplast SAG transporter may be a member of the ATP-binding cassette (ABC) transporter family. Supported by a grant from the NSF (IBN-0114131).