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Mol. Cells 2012; 33(5): 431-438

Published online March 26, 2012

https://doi.org/10.1007/s10059-012-0071-9

© The Korean Society for Molecular and Cellular Biology

The Mechanism of Phloem Loading in Rice (Oryza sativa)

Joon-Seob Eom, Sang-Bong Choi1, John M. Ward2, and Jong-Seong Jeon*

Graduate School of Biotechnology and Crop Biotech Institute, Kyung Hee University, Yongin 446-701, Korea, 1Division of Bioscience and Bioinformatics, Myongji University, Yongin 449-728, Korea, 2Plant Biology Department, University of Minnesota, St. Paul, MN 55108, USA

Correspondence to : *Correspondence: jjeon@khu.ac.kr

Received: March 5, 2012; Accepted: March 9, 2012

Abstract

Carbohydrates, mainly sucrose, that are synthesized in source organs are transported to sink organs to support growth and development. Phloem loading of sucrose is a crucial step that drives long-distance transport by eleva-ting hydrostatic pressure in the phloem. Three phloem loading strategies have been identified, two active mechanisms, apoplastic loading via sucrose transporters and symplastic polymer trapping, and one passive mechanism. The first two active loading mechanisms require metabolic energy, carbohydrate is loaded into the phloem against a concentration gradient. The passive process, diffusion, involves equilibration of sucrose and other metabolites between cells through plasmodesmata. Many higher plant species including Arabidopsis utilize the active loading mechanisms to increase carbohydrate in the phloem to higher concentrations than that in mesophyll cells. In contrast, recent data revealed that a large number of plants, especially woody species, load sucrose passively by maintaining a high concentration in mesophyll cells. However, it still remains to be determined how the worldwide important cereal crop, rice, loads sucrose into the phloem in source organs. Based on the literature and our results, we propose a potential strategy of phloem loading in rice. Elucidation of the phloem loading mechanism should improve our understanding of rice development and facilitate its manipulation towards the increase of crop productivity.

Keywords diffusion, phloem loading, rice, sucrose, sucrose transporter

Article

Minireview

Mol. Cells 2012; 33(5): 431-438

Published online May 31, 2012 https://doi.org/10.1007/s10059-012-0071-9

Copyright © The Korean Society for Molecular and Cellular Biology.

The Mechanism of Phloem Loading in Rice (Oryza sativa)

Joon-Seob Eom, Sang-Bong Choi1, John M. Ward2, and Jong-Seong Jeon*

Graduate School of Biotechnology and Crop Biotech Institute, Kyung Hee University, Yongin 446-701, Korea, 1Division of Bioscience and Bioinformatics, Myongji University, Yongin 449-728, Korea, 2Plant Biology Department, University of Minnesota, St. Paul, MN 55108, USA

Correspondence to:*Correspondence: jjeon@khu.ac.kr

Received: March 5, 2012; Accepted: March 9, 2012

Abstract

Carbohydrates, mainly sucrose, that are synthesized in source organs are transported to sink organs to support growth and development. Phloem loading of sucrose is a crucial step that drives long-distance transport by eleva-ting hydrostatic pressure in the phloem. Three phloem loading strategies have been identified, two active mechanisms, apoplastic loading via sucrose transporters and symplastic polymer trapping, and one passive mechanism. The first two active loading mechanisms require metabolic energy, carbohydrate is loaded into the phloem against a concentration gradient. The passive process, diffusion, involves equilibration of sucrose and other metabolites between cells through plasmodesmata. Many higher plant species including Arabidopsis utilize the active loading mechanisms to increase carbohydrate in the phloem to higher concentrations than that in mesophyll cells. In contrast, recent data revealed that a large number of plants, especially woody species, load sucrose passively by maintaining a high concentration in mesophyll cells. However, it still remains to be determined how the worldwide important cereal crop, rice, loads sucrose into the phloem in source organs. Based on the literature and our results, we propose a potential strategy of phloem loading in rice. Elucidation of the phloem loading mechanism should improve our understanding of rice development and facilitate its manipulation towards the increase of crop productivity.

Keywords: diffusion, phloem loading, rice, sucrose, sucrose transporter

Mol. Cells
Jan 31, 2023 Vol.46 No.1, pp. 1~67
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RNAs form diverse shapes and play multiple functions as central molecules of gene expression. In this special issue on RNA, seven minireviews illustrate how basic concepts and recent RNA biology findings are transformed into new and exciting RNA therapeutics.

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