JXB Advance Access originally published online on January 30, 2009
Journal of Experimental Botany 2009 60(3):881-892; doi:10.1093/jxb/ern335
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Sucrose transporter1 functions in phloem loading in maize leaves
1Department of Biology, Pennsylvania State University, 208 Mueller Lab, University Park, PA 16802, USA
2Pioneer Hi-Bred International, Incorporated, Johnston, IA 50131 USA
* To whom correspondence should be addressed: E-mail: dbraun{at}psu.edu
In most plants, sucrose is exported from source leaves to carbon-importing sink tissues to sustain their growth and metabolism. Apoplastic phloem-loading species require sucrose transporters (SUTs) to transport sucrose into the phloem. In many dicot plants, genetic and biochemical evidence has established that SUT1-type proteins function in phloem loading. However, the role of SUT1 in phloem loading in monocot plants is not clear since the rice (Oryza sativa) and sugarcane (Saccharum hybrid) SUT1 orthologues do not appear to function in phloem loading of sucrose. A SUT1 gene was previously cloned from maize (Zea mays) and shown to have expression and biochemical activity consistent with a hypothesized role in phloem loading. To determine the biological function of SUT1 in maize, a sut1 mutant was isolated and characterized. sut1 mutant plants hyperaccumulate carbohydrates in mature leaves and display leaf chlorosis with premature senescence. In addition, sut1 mutants have greatly reduced stature, altered biomass partitioning, delayed flowering, and stunted tassel development. Cold-girdling wild-type leaves to block phloem transport phenocopied the sut1 mutants, supporting a role for maize SUT1 in sucrose export. Furthermore, application of 14C-sucrose to abraded sut1 mutant and wild-type leaves showed that sucrose export was greatly diminished in sut1 mutants compared with wild type. Collectively, these data demonstrate that SUT1 is crucial for efficient phloem loading of sucrose in maize leaves.
Key words: Carbohydrate accumulation, cold-girdling, maize, phloem, sucrose transporter1, sut1
Received 3 November 2008; Revised 26 November 2008 Accepted 27 November 2008
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