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Photosynthesis down-regulation precedes carbohydrate accumulation under sink limitation in Citrus.
MedLine Citation:
PMID:  21367744     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Photosynthesis down-regulation due to an imbalance between sources and sinks in Citrus leaves could be mediated by excessive accumulation of carbohydrates. However, there is limited understanding of the physiological role of soluble and insoluble carbohydrates in photosynthesis regulation and the elements triggering the down-regulation process. In this work, the role of non-structural carbohydrates in the regulation of photosynthesis under a broad spectrum of source-sink relationships has been investigated in the Salustiana sweet orange. Soluble sugar and starch accumulation in leaves, induced by girdling experiments, did not induce down-regulation of the photosynthetic rate in the presence of sinks (fruits). The leaf-to-fruit ratio did not modulate photosynthesis but allocation of photoassimilates to the fruits. The lack of strong sink activity led to a decrease in the photosynthetic rate and starch accumulation in leaves. However, photosynthesis down-regulation due to an excess of total soluble sugars or starch was discarded because photosynthesis and stomatal conductance reduction occurred prior to any significant accumulation of these carbohydrates. Gas exchange and fluorescence parameters suggested biochemical limitations to photosynthesis. In addition, the expression of carbon metabolism-related genes was altered within 24 h when strong sinks were removed. Sucrose synthesis and export genes were inhibited, whereas the expression of ADP-glucose pyrophosphorylase was increased to cope with the excess of assimilates. In conclusion, changes in starch and soluble sugar turnover, but not sugar content per se, could provide the signal for photosynthesis regulation. In these conditions, non-stomatal limitations strongly inhibited the photosynthetic rate prior to any significant increase in carbohydrate levels.
Authors:
Sergio G Nebauer; Begoña Renau-Morata; José Luis Guardiola; Rosa-Victoria Molina
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-3-1
Journal Detail:
Title:  Tree physiology     Volume:  -     ISSN:  0829-318X     ISO Abbreviation:  -     Publication Date:  2011 Mar 
Date Detail:
Created Date:  2011-3-3     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100955338     Medline TA:  Tree Physiol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
Departamento de Producción Vegetal, Universitat Politècnica de València, Camino de Vera sn, 46022 Valencia, Spain.
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