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Naturally low carbonic anhydrase activity in C 4 and C 3 plants limits discrimination against C 18 OO during photosynthesis
Author(s) -
Gillon J. S.,
Yakir D.
Publication year - 2000
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.2000.00597.x
Subject(s) - photosynthesis , carbonic anhydrase , chemistry , carbon dioxide , botany , environmental chemistry , biology , biochemistry , enzyme , organic chemistry
The 18 O content of CO 2 is a powerful tracer of photosynthetic activity at the ecosystem and global scale. Due to oxygen exchange between CO 2 and 18 O‐enriched leaf water and retrodiffusion of most of this CO 2 back to the atmosphere, leaves effectively discriminate against 18 O during photosynthesis. Discrimination against 18 O ( Δ 18 O) is expected to be lower in C 4 plants because of low c i and hence low retrodiffusing CO 2 flux. C 4 plants also generally show lower levels of carbonic anhydrase (CA) activities than C 3 plants. Low CA may limit the extent of 18 O exchange and further reduce Δ 18 O. We investigated CO 2 –H 2 O isotopic equilibrium in plants with naturally low CA activity, including two C 4 ( Zea mays, Sorghum bicolor ) and one C 3 ( Phragmites australis ) species. The results confirmed experimentally the occurrence of low Δ 18 O in C 4 , as well as in some C 3 , plants. Variations in CA activity and in the extent of CO 2 –H 2 O isotopic equilibrium ( θ eq ) estimated from on‐line measurements of Δ 18 O showed large range of 0–100% isotopic equilibrium ( θ eq = 0–1). This was consistent with direct estimates based on assays of CA activity and measurements of CO 2 concentrations and residence times in the leaves. The results demonstrate the potential usefulness of Δ 18 O as indicator of CA activity in vivo . Sensitivity tests indicated also that the impact of θ eq < 1 (incomplete isotopic equilibrium) on 18 O of atmospheric CO 2 can be similar for C 3 and C 4 plants and in both cases it increases with natural enrichment of 18 O in leaf water.