Abstract
Sucrose transporters play a pivotal role for this process. To understand the uptake of sucrose in plant cells we investigated the intercellular localization of tobacco sucrose transporter (NtSUT) orthologs, nameley NtSUT2 and NtSUT4 found in tobacco EST database. Microsomes prepred from tobacco BY-2 cells were separated by a sucrose density gradient centrifugation and used to analyze the distribution of these proteins by immunoblotting. Distribution pattern of NtSUT2 protein suggested that this protein is localized in the Golgi apparatus. In contrast, NtSUT4 was cofractionated with a marker protein of vacuolar membrane (VM). We next expressed the GFP or RFP fusion of these proteins in tobacco cells. The florescence of tagged NtSUT2 co-localized with that of a marker for trans-Golgi network, SYP41-YFP. The tagged NtSUT4 showed the same distribution with SYP21-YFP, which is localized with vacuolar membrane. We next found that both endogenous and tagged sucrose transporters were degraded under several nutrient-staved conditions. The degradation of NtSUT2 in sucrose-starved condition was prevented in the presence of autophagy inhibitors, E64 and 3-methyladenine, respectively.
