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Critical review: incorporating the arrangement of mitochondria and chloroplasts into models of photosynthesis and carbon isotope discrimination.

Authors :
Ubierna N
Cernusak LA
Holloway-Phillips M
Busch FA
Cousins AB
Farquhar GD
Source :
Photosynthesis research [Photosynth Res] 2019 Jul; Vol. 141 (1), pp. 5-31. Date of Electronic Publication: 2019 Apr 06.
Publication Year :
2019

Abstract

The arrangement of mitochondria and chloroplasts, together with the relative resistances of cell wall and chloroplast, determine the path of diffusion out of the leaf for (photo)respired CO <subscript>2</subscript> . Traditional photosynthesis models have assumed a tight arrangement of chloroplasts packed together against the cell wall with mitochondria located behind the chloroplasts, deep inside the cytosol. Accordingly, all (photo)respired CO <subscript>2</subscript> must cross the chloroplast before diffusing out of the leaf. Different arrangements have recently been considered, where all or part of the (photo)respired CO <subscript>2</subscript> diffuses through the cytosol without ever entering the chloroplast. Assumptions about the path for the (photo)respiratory flux are particularly relevant for the calculation of mesophyll conductance (g <subscript>m</subscript> ). If (photo)respired CO <subscript>2</subscript> can diffuse elsewhere besides the chloroplast, apparent g <subscript>m</subscript> is no longer a mere physical resistance but a flux-weighted variable sensitive to the ratio of (photo)respiration to net CO <subscript>2</subscript> assimilation. We discuss existing photosynthesis models in conjunction with their treatment of the (photo)respiratory flux and present new equations applicable to the generalized case where (photo)respired CO <subscript>2</subscript> can diffuse both into the chloroplast and through the cytosol. Additionally, we present a new generalized Δ <superscript>13</superscript> C model that incorporates this dual diffusion pathway. We assess how assumptions about the fate of (photo)respired CO <subscript>2</subscript> affect the interpretation of photosynthetic data and the challenges it poses for the application of different models.

Details

Language :
English
ISSN :
1573-5079
Volume :
141
Issue :
1
Database :
MEDLINE
Journal :
Photosynthesis research
Publication Type :
Academic Journal
Accession number :
30955143
Full Text :
https://doi.org/10.1007/s11120-019-00635-8