Transport activity of rice sucrose transporters OsSUT1 and OsSUT5.
Expression in Xenopus oocytes and electrophysiology was used to test for transport activity of the five sucrose transporter (SUT) homologs from rice. Expression of OsSUT1 and OsSUT5 resulted in sucrose-dependent currents that were analyzed by two-electrode voltage clamping. We examined the transport kinetics, substrate specificity and pH dependence of sucrose transport and K(0.5) for sucrose. OsSUT1 showed similar features to those of other type II SUTs from monocots examined previously, with a K(0.5) value of 7.50 mM at pH 5.6. In contrast, OsSUT5 had a higher substrate affinity (K(0.5) = 2.32 mM at pH 5.6), less substrate specificity and less pH dependence compared with all type II SUTs tested to date. Regulation of the rice SUTs, as well as ZmSUT1 from maize and HvSUT1 from barley, by reduced (GSH) and oxidized (GSSG) forms of glutathione was tested. GSSG and GSH were found to have no significant effect on the activity of sucrose transporters when expressed in Xenopus oocytes. In conclusion, differences in transport activity between OsSUT1 and OsSUT5 indicate that type II SUTs have a range of transport activities that are tuned to their function in the plant.
Sun
Ye
Y
Department of Plant Biology, University of Minnesota, 250 Biological Sciences Center, St. Paul, MN 55108 USA.
Reinders
Anke
A
LaFleur
Kathryn R
KR
Mori
Toko
T
Ward
John M
JM
D000222:Adaptation, Physiological; D000818:Animals; D050260:Carbohydrate Metabolism / Q000502:physiology*; D019143:Evolution, Molecular; D005978:Glutathione / Q000378:metabolism; D001467:Hordeum / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D012275:Oryza / Q000378:metabolism*; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology; D018408:Patch-Clamp Techniques; D010802:Phylogeny; D010940:Plant Proteins / Q000378:metabolism*; D013045:Species Specificity; D013395:Sucrose / Q000378:metabolism*; D014982:Xenopus laevis; D003313:Zea mays / Q000378:metabolism
D009004:Monosaccharide Transport Proteins; D010940:Plant Proteins; D013395:Sucrose; D005978:Glutathione