Related Experiment Video
Updated: May 31, 2026

Assessing Structural Traits in Triticum aestivum and Zea mays for C3 and C4 Photosynthetic Differentiation Using Free-hand and Semi-thin Sections
Published on: July 12, 2024
Association between carbonyl sulfide uptake and (18)Δ during gas exchange in C(3) and C(4) leaves
Keren Stimler1, Joseph A Berry, Steve A Montzka
1Environmental Sciences and Energy Research, The Weizmann Institute of Science, Rehovot 76100, Israel.
Abstract:
Carbonyl sulfide (COS) and C(18)OO exchange by leaves provide potentially powerful tracers of biosphere-atmosphere CO(2) 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 C(3) and C(4) plants, hypothesizing that the rates of COS and C(18)OO exchange by leaves respond in parallel to environmental and biological drivers. Using CA-deficient antisense lines of C(4) and C(3) plants, COS uptake was essentially eliminated and discrimination against C(18)OO exchange ((18)Δ) greatly reduced, demonstrating CA's key role in both processes. (18)Δ showed a positive linear correlation with leaf relative uptake (LRU; ratio of COS to CO(2) assimilation rates, A(s)/A(c), normalized to their respective ambient concentrations), which reflected the effects of stomatal conductance on both COS and C(18)OO exchange. Unexpectedly, a decoupling between A(s) and (18)Δ was observed in comparing C(4) and C(3) plants, with a large decrease in (18)Δ but no parallel reduction in A(s) in the former. This could be explained by C(4) plants having higher COS concentrations at the CA site (maintaining high A(s) with reduced CA) and a high phosphoenolpyruvate carboxylase/CA activity ratio (reducing (18)O exchange efficiency between CO(2) and water, but not A(s)). Similar A(s) but higher A(c) in C(4) versus C(3) plants resulted in lower LRU values in the former (1.16 ± 0.20 and 1.82 ± 0.18 for C(4) and C(3), 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)).
Related Concept Videos
The Calvin Benson Cycle
C4 Pathway and CAM
C4 Pathway
The C4 pathway is used by plants such as...
Adaptations that Reduce Water Loss
Sulfur Assimilation
Gas Exchange and Transport
Regulation of Transpiration by Stomata

