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Title: Sucrose accumulation in sweet sorghum stems occurs by apoplasmic phloem unloading and does not involve differential Sucrose transporter expression

Abstract

Background: Sorghum (Sorghum bicolor L. Moench) cultivars store non-structural carbohydrates predominantly as either starch in seeds (grain sorghums) or sugars in stems (sweet sorghums). Previous research determined that sucrose accumulation in sweet sorghum stems was not correlated with the activities of enzymes functioning in sucrose metabolism, and that an apoplasmic transport step may be involved in stem sucrose accumulation. However, the sucrose unloading pathway from stem phloem to storage parenchyma cells remains unelucidated. Sucrose transporters (SUTs) transport sucrose across membranes, and have been proposed to function in sucrose partitioning differences between sweet and grain sorghums. The purpose of this study was to characterize the key differences in carbohydrate accumulation between a sweet and a grain sorghum, to define the path sucrose may follow for accumulation in sorghum stems, and to determine the roles played by sorghum SUTs in stem sucrose accumulation. Results: Dye tracer studies to determine the sucrose transport route revealed that, for both the sweet sorghum cultivar Wray and grain sorghum cultivar Macia, the phloem in the stem veins was symplasmically isolated from surrounding cells, suggesting sucrose was apoplasmically unloaded. Once in the phloem apoplasm, a soluble tracer diffused from the vein to stem parenchyma cell walls, indicatingmore » the lignified mestome sheath encompassing the vein did not prevent apoplasmic flux outside of the vein. To characterize carbohydrate partitioning differences between Wray and Macia, we compared the growth, stem juice volume, solute contents, SbSUTs gene expression, and additional traits. Contrary to previous findings, we detected no significant differences in SbSUTs gene expression within stem tissues. Conclusions: Phloem sieve tubes within sweet and grain sorghum stems are symplasmically isolated from surrounding cells; hence, unloading from the phloem likely occurs apoplasmically, thereby defining the location of the previously postulated step for sucrose transport. Additionally, no changes in SbSUTs gene expression were detected in sweet vs. grain sorghum stems, suggesting alterations in SbSUT transcript levels do not account for the carbohydrate partitioning differences between cultivars. A model illustrating sucrose phloem unloading and movement to stem storage parenchyma, and highlighting roles for sucrose transport proteins in sorghum stems is discussed.« less

Authors:
 [1];  [2];  [3];  [1]
  1. Univ. of Missouri, Columbia, MO (United States). Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center
  2. Univ. of Missouri, Columbia, MO (United States). Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center; Univ. of Missouri, Columbia, MO (United States). Molecular Cytology Core
  3. Univ. of Missouri, Columbia, MO (United States). Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center; Sigma-Aldrich Biotech, Saint Louis, MO (United States)
Publication Date:
Research Org.:
Univ. of Missouri, Columbia, MO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Science Foundation (NSF)
OSTI Identifier:
1494218
Alternate Identifier(s):
OSTI ID: 1441372
Grant/Contract Number:  
SC0006810; IOS-1025976; ᅟ
Resource Type:
Published Article
Journal Name:
BMC Plant Biology
Additional Journal Information:
Journal Volume: 15; Journal Issue: 1; Journal ID: ISSN 1471-2229
Publisher:
BioMed Central
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; Apoplasm; Carbohydrate partitioning; Carboxyfluorescein; Parenchyma; Phloem; Sorghum; Stem; Sucrose; SUT; Symplasm

Citation Formats

Bihmidine, Saadia, Baker, R. Frank, Hoffner, Cassandra, and Braun, David M. Sucrose accumulation in sweet sorghum stems occurs by apoplasmic phloem unloading and does not involve differential Sucrose transporter expression. United States: N. p., 2015. Web. doi:10.1186/s12870-015-0572-8.
Bihmidine, Saadia, Baker, R. Frank, Hoffner, Cassandra, & Braun, David M. Sucrose accumulation in sweet sorghum stems occurs by apoplasmic phloem unloading and does not involve differential Sucrose transporter expression. United States. doi:10.1186/s12870-015-0572-8.
Bihmidine, Saadia, Baker, R. Frank, Hoffner, Cassandra, and Braun, David M. Thu . "Sucrose accumulation in sweet sorghum stems occurs by apoplasmic phloem unloading and does not involve differential Sucrose transporter expression". United States. doi:10.1186/s12870-015-0572-8.
@article{osti_1494218,
title = {Sucrose accumulation in sweet sorghum stems occurs by apoplasmic phloem unloading and does not involve differential Sucrose transporter expression},
author = {Bihmidine, Saadia and Baker, R. Frank and Hoffner, Cassandra and Braun, David M.},
abstractNote = {Background: Sorghum (Sorghum bicolor L. Moench) cultivars store non-structural carbohydrates predominantly as either starch in seeds (grain sorghums) or sugars in stems (sweet sorghums). Previous research determined that sucrose accumulation in sweet sorghum stems was not correlated with the activities of enzymes functioning in sucrose metabolism, and that an apoplasmic transport step may be involved in stem sucrose accumulation. However, the sucrose unloading pathway from stem phloem to storage parenchyma cells remains unelucidated. Sucrose transporters (SUTs) transport sucrose across membranes, and have been proposed to function in sucrose partitioning differences between sweet and grain sorghums. The purpose of this study was to characterize the key differences in carbohydrate accumulation between a sweet and a grain sorghum, to define the path sucrose may follow for accumulation in sorghum stems, and to determine the roles played by sorghum SUTs in stem sucrose accumulation. Results: Dye tracer studies to determine the sucrose transport route revealed that, for both the sweet sorghum cultivar Wray and grain sorghum cultivar Macia, the phloem in the stem veins was symplasmically isolated from surrounding cells, suggesting sucrose was apoplasmically unloaded. Once in the phloem apoplasm, a soluble tracer diffused from the vein to stem parenchyma cell walls, indicating the lignified mestome sheath encompassing the vein did not prevent apoplasmic flux outside of the vein. To characterize carbohydrate partitioning differences between Wray and Macia, we compared the growth, stem juice volume, solute contents, SbSUTs gene expression, and additional traits. Contrary to previous findings, we detected no significant differences in SbSUTs gene expression within stem tissues. Conclusions: Phloem sieve tubes within sweet and grain sorghum stems are symplasmically isolated from surrounding cells; hence, unloading from the phloem likely occurs apoplasmically, thereby defining the location of the previously postulated step for sucrose transport. Additionally, no changes in SbSUTs gene expression were detected in sweet vs. grain sorghum stems, suggesting alterations in SbSUT transcript levels do not account for the carbohydrate partitioning differences between cultivars. A model illustrating sucrose phloem unloading and movement to stem storage parenchyma, and highlighting roles for sucrose transport proteins in sorghum stems is discussed.},
doi = {10.1186/s12870-015-0572-8},
journal = {BMC Plant Biology},
number = 1,
volume = 15,
place = {United States},
year = {2015},
month = {7}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1186/s12870-015-0572-8

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Cited by: 22 works
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Works referenced in this record:

Genetic manipulation of lignin reduces recalcitrance and improves ethanol production from switchgrass
journal, February 2011

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