Sucrose partitioning between vascular bundles and storage parenchyma in the sugarcane stem: a potential role for the ShSUT1 sucrose transporter.
A transporter with homology to the SUT/SUC family of plant sucrose transporters was isolated from a sugarcane (Saccharum hybrid) stem cDNA library. The gene, designated ShSUT1, encodes a protein of 517 amino acids, including 12 predicted membrane-spanning domains and a large central cytoplasmic loop. ShSUT1 was demonstrated to be a functional sucrose transporter by expression in yeast. The estimated K(m) for sucrose of the ShSUT1 transporter was 2 mM at pH 5.5. ShSUT1 was expressed predominantly in mature leaves of sugarcane that were exporting sucrose and in stem internodes that were actively accumulating sucrose. Immunolocalization with a ShSUT1-specific antiserum identified the protein in cells at the periphery of the vascular bundles in the stem. These cells became lignified and suberized as stem development proceeded, forming a barrier to apoplasmic solute movement. However, the movement of the tracer dye, carboxyfluorescein from phloem to storage parenchyma cells suggested that symplasmic connections are present. ShSUT1 may have a role in partitioning of sucrose between the vascular tissue and sites of storage in the parenchyma cells of sugarcane stem internodes.
Rae
Anne L
AL
CSIRO Plant Industry, Queensland Bioscience Precinct, 306 Carmody Road, Qld. 4067, St. Lucia, Australia.
Perroux
Jai M
JM
Grof
Christopher P L
CP
D018506:Gene Expression Regulation, Plant; D015723:Gene Library; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018547:Plant Stems / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D031786:Saccharum / Q000235:genetics / Q000378:metabolism*; D013395:Sucrose / Q000378:metabolism*
D026901:Membrane Transport Proteins; D010940:Plant Proteins; C078729:sucrose transport protein, plant; D013395:Sucrose