Document Detail

Phloem loading in the tulip tree. Mechanisms and evolutionary implications.
MedLine Citation:
PMID:  11161046     Owner:  NLM     Status:  MEDLINE    
Minor vein ultrastructure and phloem loading were studied in leaves of the tulip tree (Liriodendron tulipifera; Magnoliaceae). Plasmodesmatal frequencies leading into minor vein companion cells are higher than in species known to load via the apoplast. However, these companion cells are not specialized as "intermediary cells" as they are in species in which the best evidence for symplastic phloem loading has been documented. Mesophyll cells plasmolyzed in 600 mM sorbitol, whereas sieve elements and companion cells did not plasmolyze even in 1.2 M sorbitol, indicating that solute accumulates in the phloem against a steep concentration gradient. Both [(14)C]sucrose and (14)C-labeled photo-assimilate accumulated in the minor vein network, as demonstrated by autoradiography. [(14)C]sucrose accumulation was prevented by p-chloromercuribenzenesulfonic acid, an inhibitor of sucrose-proton cotransport from the apoplast. p-Chloromercuribenzenesulfonic acid largely, but not entirely, inhibited exudation of radiolabeled photoassimilate. The evidence is most consistent with the presence of an apoplastic component to phloem loading in this species, contrary to speculation that the more basal members of the angiosperms load by an entirely symplastic mechanism.
F L Goggin; R Medville; R Turgeon
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Plant physiology     Volume:  125     ISSN:  0032-0889     ISO Abbreviation:  Plant Physiol.     Publication Date:  2001 Feb 
Date Detail:
Created Date:  2001-02-22     Completed Date:  2004-01-05     Revised Date:  2013-04-17    
Medline Journal Info:
Nlm Unique ID:  0401224     Medline TA:  Plant Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  891-9     Citation Subset:  IM    
Department of Plant Biology, Cornell University, Ithaca, New York 14853, USA.
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MeSH Terms
Biological Evolution*
Liriodendron / cytology*,  metabolism,  physiology*
Plant Leaves / metabolism
Sorbitol / metabolism
Sucrose / metabolism*
Reg. No./Substance:
50-70-4/Sorbitol; 57-50-1/Sucrose

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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