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The regulation of gelation of Phloem exudate from cucurbita fruit by dilution, glutathione, and glutathione reductase.
MedLine Citation:
PMID:  16666036     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Abstract/OtherAbstract:
The average glutathione equivalent concentration in phloem exudate collected from squash fruit (Cucurbita moschata [Duchesne] Poir. var Butternut) and pumpkin fruit (Cucurbita pepo [L.] var Jack-o-lattern) was 1.02 and 0.60 millimolar, respectively. Glutathione reductase (EC 1.6.4.2) activity in phloem exudate from squash and pumpkin fruit averaged 0.48 and 1.74 micromole NADPH oxidized per minute per milliliter, respectively. Protein concentrations in fruit phloem exudates averaged 67 milligrams per milliliter for squash and 57 milligrams per milliliter for pumpkin. The phloem-specific P-proteins account for most of the protein content of exudate. Pure exudate from fruit does not gel for hours or days, but when diluted with neutral or alkaline aqueous solutions, exudate gels rapidly. Exudate solutions undergo biphasic pH changes with dilution. We suggest that P-protein undergoes conformational change upon dilution, exposing titratable groups and sulfhydryl residues. Oxidation of the latter forms the intermolecular disulfide bridges of the gel. The gelation of diluted exudate is regulated by factors (oxygen, pH, glutathione, NADPH) which affect the maintenance of reduced sulfhydryl residues and the activity of glutathione reductase. While these factors may also act in vivo to regulate redox conditions in phloem, their relationship to hypothetical sol/gel transitions or motile and nonmotile phases in the transport conduit is unknown.
Authors:
M C Alosi; D L Melroy; R B Park
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Plant physiology     Volume:  86     ISSN:  0032-0889     ISO Abbreviation:  Plant Physiol.     Publication Date:  1988 Apr 
Date Detail:
Created Date:  2010-06-29     Completed Date:  2010-07-02     Revised Date:  2010-09-14    
Medline Journal Info:
Nlm Unique ID:  0401224     Medline TA:  Plant Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1089-94     Citation Subset:  -    
Affiliation:
Department of Botany, University of California, Berkeley, California 94720.
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