Glycosylation of endogenous secondary plant products and abiotic substances such as herbicides increases their water solubility and enables vacuolar deposition of these potentially toxic substances. We characterized and compared the transport mechanisms of two glucosides, isovitexin, a native barley flavonoid C-glucoside and hydroxyprimisulfuron-glucoside, a herbicide glucoside, into barley vacuoles. Uptake of isovitexin is saturable (K m ‫؍‬ 82 M) and stimulated by MgATP 1.3-1.5-fold. ATP-dependent uptake was inhibited by bafilomycin A1, a specific inhibitor of vacuolar H ؉ -ATPase, but not by vanadate. Transport of isovitexin is strongly inhibited after dissipation of the ⌬pH or the ⌬⌿ across the vacuolar membrane. Uptake experiments with the heterologue flavonoid orientin and competition experiments with other phenolic compounds suggest that transport of flavonoid glucosides into barley vacuoles is specific for apigenin derivatives. In contrast, transport of hydroxyprimisulfuron-glucoside is strongly stimulated by MgATP (2.5-3 fold), not sensitive toward bafilomycin, and much less sensitive to dissipation of the ⌬pH, but strongly inhibited by vanadate. Uptake of hydroxyprimisulfuron-glucoside is also stimulated by MgGTP or MgUTP by about 2-fold. Transport of both substrates is not stimulated by ATP or Mg 2؉ alone, ADP, or the nonhydrolyzable ATP analogue 5-adenylyl-␤,␥-imidodiphosphate. Our results suggest that different uptake mechanisms exist in the vacuolar membrane, a ⌬pH-dependent uptake mechanism for specific endogenous flavonoid-glucosides, and a directly energized mechanism for abiotic glucosides, which appears to be the main transport system for these substrates. The herbicide glucoside may therefore be transported by an additional member of the ABC transporters.

In plants potentially toxic compounds are ultimately deposited in the large central vacuole. In this report we show that isolated barley mesophyll vacuoles take up the glucoside conjugate of the herbicide derivate [5-hydroxyphenyl]primisulfuron. Transport is stimulated by Mg-ATP and is distinct from that previously described for glutathione conjugates. Treatment of barley with different herbicide antidotes (safeners) revealed that the safener cloquintocet-mexyl doubles the vacuolar transport activities for both the glutathione and glucoside conjugates. Stimulation of the uptake of the metolachlor-glutathione conjugate was the result of an increased uptake velocity whereas the K,,, remained unaltered, suggesting that the higher activity was due to a higher expression of the transporter. These results indicate that modulation of vacuolar transport activities are an integral part of the detoxification mechanism of plants.

The synthesis of several derivatives of a pesticide and an r-amino acid are described. The process involves three steps, the last one (deprotection of the r-amino acid group) being the most critical. The resulting products preserved their r-amino acid group and were globally neutral. They were tested for their effect on the transport of a neutral amino acid, threonine, and two sugars, sucrose and glucose. Two derivatives markedly and specifically inhibited threonine uptake by leaf tissues of Viciu ,faha L. and phloem loading. Preliminary experiments suggested that the lysine-2,4-D derivative is a competitive inhibitor of threonine uptake. The apparent K , (0.5 mM) was much lower than the apparent K , (3 mM) of the natural substrate.