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Resistances along the CO2 diffusion pathway inside leaves.

Evans, John R. and Kaldenhoff, Ralf and Genty, Bernard and Terashima, Ichiro (2009):
Resistances along the CO2 diffusion pathway inside leaves.
In: Journal of experimental botany, pp. 2235-48, 60, (8), ISSN 1460-2431,
[Article]

Abstract

CO(2) faces a series of resistances while diffusing between the substomatal cavities and the sites of carboxylation within chloroplasts. The absence of techniques to measure the resistance of individual steps makes it difficult to define their relative importance. Resistance to diffusion through intercellular airspace differs between leaves, but is usually of minor importance. Leaves with high photosynthetic capacity per unit leaf area reduce mesophyll resistance by increasing the surface area of chloroplasts exposed to intercellular airspace per unit leaf area, S(c). Cell walls impose a significant resistance. Assuming an effective porosity of the cell wall of 0.1 or 0.05, then cell walls could account for 25% or 50% of the total mesophyll resistance, respectively. Since the fraction of apoplastic water that is unbound and available for unhindered CO(2) diffusion is unknown, it is possible that the effective porosity is <0.05. Effective porosity could also vary in response to changes in pH or cation concentration. Consequently, cell walls could account for >50% of the total resistance and a variable proportion. Most of the remaining resistance is imposed by one or more of the three membranes as mesophyll resistance can be altered by varying the expression of cooporins. The CO(2) permeability of vesicles prepared from chloroplast envelopes has been reduced by RNA interference (RNAi) expression of NtAQP1, but not those prepared from the plasma membrane. Carbonic anhydrase activity also influences mesophyll resistance. Mesophyll resistance is relatively insensitive to the manipulation of any step in the pathway because it represents only part of the total and may also be countered by pleiotropic compensatory changes. The parameters in greatest need of additional measurements are S(c), mesophyll cell wall thickness, and the permeabilities of the plasma membrane and chloroplast envelope.

Item Type: Article
Erschienen: 2009
Creators: Evans, John R. and Kaldenhoff, Ralf and Genty, Bernard and Terashima, Ichiro
Title: Resistances along the CO2 diffusion pathway inside leaves.
Language: English
Abstract:

CO(2) faces a series of resistances while diffusing between the substomatal cavities and the sites of carboxylation within chloroplasts. The absence of techniques to measure the resistance of individual steps makes it difficult to define their relative importance. Resistance to diffusion through intercellular airspace differs between leaves, but is usually of minor importance. Leaves with high photosynthetic capacity per unit leaf area reduce mesophyll resistance by increasing the surface area of chloroplasts exposed to intercellular airspace per unit leaf area, S(c). Cell walls impose a significant resistance. Assuming an effective porosity of the cell wall of 0.1 or 0.05, then cell walls could account for 25% or 50% of the total mesophyll resistance, respectively. Since the fraction of apoplastic water that is unbound and available for unhindered CO(2) diffusion is unknown, it is possible that the effective porosity is <0.05. Effective porosity could also vary in response to changes in pH or cation concentration. Consequently, cell walls could account for >50% of the total resistance and a variable proportion. Most of the remaining resistance is imposed by one or more of the three membranes as mesophyll resistance can be altered by varying the expression of cooporins. The CO(2) permeability of vesicles prepared from chloroplast envelopes has been reduced by RNA interference (RNAi) expression of NtAQP1, but not those prepared from the plasma membrane. Carbonic anhydrase activity also influences mesophyll resistance. Mesophyll resistance is relatively insensitive to the manipulation of any step in the pathway because it represents only part of the total and may also be countered by pleiotropic compensatory changes. The parameters in greatest need of additional measurements are S(c), mesophyll cell wall thickness, and the permeabilities of the plasma membrane and chloroplast envelope.

Journal or Publication Title: Journal of experimental botany
Volume: 60
Number: 8
Divisions: 10 Department of Biology > Applied Plant Sciences
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10 Department of Biology
Date Deposited: 31 Aug 2011 12:02
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