Uptake of salicylic acid 2‐O‐β‐D‐glucose into soybean tonoplast vesicles by an ATP‐binding cassette transporter‐type mechanism

Abstract

In soybean (Glycine max L.), salicylic acid (SA) is converted primarily to SA 2-O-beta-d-glucose (SAG) in the cytoplasm and then accumulates exclusively in the vacuole. However, the mechanism involved in the vacuolar transport of SAG has not been investigated. The vacuolar transport of SAG was characterized by measuring the uptake of [(14)C]SAG into tonoplast vesicles isolated from etiolated soybean hypocotyls. The uptake of SAG was stimulated about six-fold when MgATP was included in the assay media. In contrast, the uptake of SA was only stimulated 1.25-fold by the addition of MgATP and was 2.2-fold less than the uptake of SAG providing an indication that the vacuolar uptake of SA is promoted by glucosylation. The ATP-dependent uptake of SAG was inhibited by increasing concentrations of vanadate (64% inhibition in the presence of 500 microM) but was not very sensitive to inhibition by bafilomycin A(1) (a specific inhibitor of vacuolar H(+)-ATPase; EC 3.6.1.3), and dissipation of the transtonoplast H(+)-electrochemical gradient. The SAG uptake exhibited Michaelis-Menten-type saturation kinetics with a K(m) value of 90 microM for SAG. SAG uptake was inhibited 60% by beta-estradiol 17-(beta-d-glucuronide), but glutathione conjugates and uncharged glucose conjugates were only slightly inhibitory. Based on the characteristics of SAG uptake into soybean tonoplast vesicles it is likely that this uptake occurs through an ATP-binding cassette transporter-type mechanism. However, this vacuolar uptake mechanism is not universal since the uptake of SAG by red beet (Beta vulgaris L) tonoplast vesicles appears to involve an H(+)-antiport mechanism.

Involvement of a Soybean ATP-Binding Cassette-Type Transporter in the Secretion of Genistein, a Signal Flavonoid in Legume-Rhizobium Symbiosis

“…5,C and D). These values are consistent with those observed for other ABC-type transporters involved in the transport of low-M r organic compounds (Senior et al, 1995;Klein et al, 2000;Frangne et al, 2002;Dean and Mills, 2004;Sauna et al, 2004).…”

Salicylic Acid Biosynthesis and Metabolism

“…Similar to tobacco (Dean et al, 2005) and soybean (Dean et al, 2003;Dean and Mills, 2004), SAG in Arabidopsis is thought to be produced in the cytosol and then (actively) transported into the vacuole as a non-toxic storage form of SA (Figure 3). Transport of SAG into the vacuole also ensures there is no end-product inhibition of the cytosolic glucosyltransferase, and can thus increase yield.…”

Vacuolar Transport of Abscisic Acid Glucosyl Ester Is Mediated by ATP-Binding Cassette and Proton-Antiport Mechanisms in Arabidopsis

“…Moreover, the vacuolar import mechanism of particular Glc conjugates was found to be species or tissue specific. Salicylic acid glucoside is transported into vacuoles from tobacco (Nicotiana tabacum) culture cells by protondependent transport mechanisms and into vacuoles from soybean (Glycine max) hypocotyls by ABC-type transport mechanisms (Dean and Mills, 2004;Dean et al, 2005). The glucoside of coniferyl alcohol was shown to be transported into endomembrane-enriched vesicles isolated from differentiating xylem of poplar (Populus spp.)…”