Related Experiment Video
Updated: May 26, 2026

An Induction System for Clustered Stomata by Sugar Solution Immersion Treatment in Arabidopsis thaliana Seedlings
Published on: February 15, 2019
Sucrose efflux mediated by SWEET proteins as a key step for phloem transport
Li-Qing Chen1, Xiao-Qing Qu, Bi-Huei Hou
1Carnegie Institution for Science, 260 Panama Street, Stanford, CA 94305, USA.
Abstract:
Plants transport fixed carbon predominantly as sucrose, which is produced in mesophyll cells and imported into phloem cells for translocation throughout the plant. It is not known how sucrose migrates from sites of synthesis in the mesophyll to the phloem, or which cells mediate efflux into the apoplasm as a prerequisite for phloem loading by the SUT sucrose-H(+) (proton) cotransporters. Using optical sucrose sensors, we identified a subfamily of SWEET sucrose efflux transporters. AtSWEET11 and 12 localize to the plasma membrane of the phloem. Mutant plants carrying insertions in AtSWEET11 and 12 are defective in phloem loading, thus revealing a two-step mechanism of SWEET-mediated export from parenchyma cells feeding H(+)-coupled import into the sieve element-companion cell complex. We discuss how restriction of intercellular transport to the interface of adjacent phloem cells may be an effective mechanism to limit the availability of photosynthetic carbon in the leaf apoplasm in order to prevent pathogen infections.
Related Concept Videos
Phloem and Sugar Transport
Secondary Active Transport
Secondary Active Transport
Secondary Active Transport
Membrane Proteins
Glucose Transporters
Facilitated diffusion-glucose transporters (GLUTs) are encoded by the solute-linked carrier (SLC) family 2, subfamily A gene family, or SLC2A. The 14 GLUT protein members are distributed into three classes:

