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Association between Carbonyl Sulfide Uptake and 18 Δ during Gas Exchange in C 3 and C 4 Leaves

2011; Oxford University Press; Volume: 157; Issue: 1 Linguagem: Inglês

10.1104/pp.111.176578

1532-2548

Keren Stimler, Joseph A. Berry, S. A. Montzka, Dan Yakir,

Plant Water Relations and Carbon Dynamics

Carbonyl sulfide (COS) and C18OO exchange by leaves provide potentially powerful tracers of biosphere-atmosphere CO2 exchange, and both are assumed to depend on carbonic anhydrase (CA) activity and conductance along the diffusive pathway in leaves. We investigated these links using C3 and C4 plants, hypothesizing that the rates of COS and C18OO exchange by leaves respond in parallel to environmental and biological drivers. Using CA-deficient antisense lines of C4 and C3 plants, COS uptake was essentially eliminated and discrimination against C18OO exchange (18Ɗ) greatly reduced, demonstrating CA's key role in both processes. 18Ɗ showed a positive linear correlation with leaf relative uptake (LRU; ratio of COS to CO2 assimilation rates, As/Ac, normalized to their respective ambient concentrations), which reflected the effects of stomatal conductance on both COS and C18OO exchange. Unexpectedly, a decoupling between As and 18Ɗ was observed in comparing C4 and C3 plants, with a large decrease in 18Ɗ but no parallel reduction in As in the former. This could be explained by C4 plants having higher COS concentrations at the CA site (maintaining high As with reduced CA) and a high phosphoenolpyruvate carboxylase/CA activity ratio (reducing 18O exchange efficiency between CO2 and water, but not As). Similar As but higher Ac in C4 versus C3 plants resulted in lower LRU values in the former (1.16 ± 0.20 and 1.82 ± 0.18 for C4 and C3, respectively). LRU was, however, relatively constant in both plant types across a wide range of conditions, except low light (<191 μmol photon m−2 s−1).