Document Detail

The efficiency of C4 photosynthesis under low light conditions: assumptions and calculations with CO2 isotope discrimination.
MedLine Citation:
PMID:  21527629     Owner:  NLM     Status:  Publisher    
Leakiness (), the proportion of carbon fixed by phosphoenolpyruvate carboxylation that leaks out of the bundle-sheath cells, determines C(4) photosynthetic efficiency. Large increases in have been described at low irradiance. The underlying mechanisms for this increase remain uncertain, but changes in photorespiration or the energy partitioning between the C(4) and C(3) cycles have been suggested. Additionally, values of at low light could be magnified from assumptions made when comparing measured photosynthetic discrimination against (13)C (Δ) with the theoretical formulation for Δ. For example, several simplifications are often made when modelling Δ to predict including: (i) negligible fractionation during photorespiration and dark respiration; (ii) infinite mesophyll conductance; and (iii) CO(2) inside bundle-sheath cells (C(s)) is much larger than values in mesophyll cells (C(m)). Theoretical models for C(4) photosynthesis and C(4) Δ were combined to evaluate how these simplifications affect calculations of Δ and at different light intensities. It was demonstrated that the effects of photorespiratory fractionations and mesophyll conductance were negligible at low light. Respiratory fractionation was relevant only when the magnitude of the fractionation factor was artificially increased during measurements. The largest error in estimating occurred when assuming C(s) was much larger than C(m) at low light levels, when bundle-sheath conductance was large (g(s)), or at low O(2) concentrations. Under these conditions, the simplified equation for Δ overestimated , and compromised comparisons between species with different g(s), and comparisons across O(2) concentrations.
Nerea Ubierna; Wei Sun; Asaph B Cousins
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-4-28
Journal Detail:
Title:  Journal of experimental botany     Volume:  -     ISSN:  1460-2431     ISO Abbreviation:  -     Publication Date:  2011 Apr 
Date Detail:
Created Date:  2011-4-29     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9882906     Medline TA:  J Exp Bot     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA 99164-4236, USA.
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