The rate-limiting step for CO₂ assimilation at different temperatures is influenced by the leaf nitrogen content in several C₃ crop species
2011
YAMORI, WATARU | Nagai, Takeshi | MAKINO, AMANE
Effects of nitrogen (N) supply on the limiting step of CO₂ assimilation rate (A) at 380 µmol mol⁻¹ CO₂ concentration (A₃₈₀) at several leaf temperatures were studied in several crops, since N nutrition alters N allocation between photosynthetic components. Contents of leaf N, ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) and cytochrome f (cyt f) increased with increasing N supply, but the cyt f/Rubisco ratio decreased. Large leaf N content was linked to a high stomatal (gs) and mesophyll conductance (gm), but resulted in a lower intercellular (Ci) and chloroplast CO₂ concentration (Cc) because the increase in gs and gm was insufficient to compensate for change in A₃₈₀. The A-Cc response was used to estimate the maximum rate of RuBP carboxylation (Vcmax) and chloroplast electron transport (Jmax). The Jmax/Vcmax ratio decreased with reductions in leaf N content, which was consistent with the results of the cyt f/Rubisco ratio. Analysis using the C₃ photosynthesis model indicated that A₃₈₀ tended to be limited by RuBP carboxylation in plants grown at low N concentration, whereas it was limited by RuBP regeneration in plants grown at high N concentration. We conclude that the limiting step of A₃₈₀ depends on leaf N content and is mainly determined by N partitioning between Rubisco and electron transport components.
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