Document Detail

Evidence for recycling of inorganic phosphate by wheat chloroplasts during photosynthesis at air levels of CO2 and O2.
MedLine Citation:
PMID:  14658388     Owner:  NLM     Status:  MEDLINE    
Phosphate recycling under photorespiratory conditions was investigated using intact wheat chloroplasts from Triticum aestivum (cv. Maris dove). A decline in the optimal Pi level needed to support steady-state photosynthesis was observed (a) as the bicarbonate supply became limiting, or (b) as oxygen concentrations were increased. Further, at subsaturating CO2 and elevated O2 (52%), photosynthetic induction periods were shortest in the absence of exogenous Pi, and severely extended by its addition. Thus, photosynthesis under low CO2 levels which favor ribulose 1,5 bisphosphate (RuBP) oxygenase activity and glycolate synthesis by chloroplasts decreases their dependency on exogenous Pi from the initial illumination of chloroplasts through to the attainment of steady state rates of O2 evolution. Uptake of phosphate (Pi) was directly measured at ambient O2 concentrations and showed the stoichiometry of O2 evolved to Pi consumed at 10 mmol/L bicarbonate (saturating) had a mean value of 3.0, and was increased to 5.4 at 2.5 mmol/L bicarbonate and to > 8.0 at 1.0 mmol/L bicarbonate. The observation is consistent with enhanced stromal recycling of Pi released during hydrolysis of phosphoglycolate produced in greater quantities as the ratio of RuBP carboxylase relative to oxygenase activities (vc/vo) declines. The theoretical relationship between vc/vo and O2/Pi stoichiometries was derived and compared favorably to experimental data obtained.
Gabriel P Holbrook; Alfred J Keys
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Journal of plant physiology     Volume:  160     ISSN:  0176-1617     ISO Abbreviation:  J. Plant Physiol.     Publication Date:  2003 Nov 
Date Detail:
Created Date:  2003-12-08     Completed Date:  2004-03-22     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9882059     Medline TA:  J Plant Physiol     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  1351-60     Citation Subset:  IM    
Plant Molecular Biology Center, Northern Illinois University, DeKalb, IL 60115, USA.
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MeSH Terms
Carbon Dioxide / pharmacology*
Chloroplasts / drug effects,  metabolism*
Glycolates / metabolism
Oxygen / pharmacology*
Phosphates / metabolism*,  pharmacology
Photosynthesis / drug effects,  physiology*,  radiation effects
Ribulose-Bisphosphate Carboxylase / metabolism
Triticum / drug effects,  metabolism*
Reg. No./Substance:
0/Glycolates; 0/Phosphates; 124-38-9/Carbon Dioxide; 7782-44-7/Oxygen; 79-14-1/glycolic acid; EC Carboxylase

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

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