In vivo transport of three radioactive [18F]-fluorinated deoxysucrose analogs by the maize sucrose transporter ZmSUT1

Abstract

Sucrose transporter (SUT) proteins translocate sucrose across cell membranes; however, mechanistic aspects of sucrose binding by SUTs are not well resolved. Specific hydroxyl groups in sucrose participate in hydrogen bonding with SUT proteins. We previously reported that substituting a radioactive fluorine-18 [18F] at the C-6′ position within the fructosyl moiety of sucrose did not affect sucrose transport by the maize (Zea mays) ZmSUT1 protein. To determine how 18F substitution of hydroxyl groups at two other positions within sucrose, the C-1′ in the fructosyl moiety or the C-6 in the glucosyl moiety, impact sucrose transport, we synthesized 1′-[F18]fluoro-1′-deoxysucrose and 6-[F18]fluoro-6-deoxysucrose ([18F]FDS) analogs. Each [18F]FDS derivative was independently introduced into wild-type or sut1 mutant plants, which are defective in sucrose phloem loading. All three (1′-, 6′-, and 6-) [18F]FDS derivatives were efficiently and equally translocated, similarly to carbon-14 [14C]-labeled sucrose. Hence, individually replacing the hydroxyl groups at these positions within sucrose does not interfere with substrate recognition, binding, or membrane transport processes, and hydroxyl groups at these three positions are not essential for hydrogen bonding between sucrose and ZmSUT1. [18F]FDS imaging afforded several advantages compared to [14C]-sucrose detection. We calculated that 1′-[18F]FDS was transported at approximately a rate of 0.90 ± 0.15 m.h-1 in wild-type leaves, and at 0.68 ± 0.25 m.h-1 in sut1 mutant leaves. Collectively, our data indicated that [18F]FDS analogs are valuable tools to probe sucrose-SUT interactions and to monitor sucrose transport in plants.