Figure 1.

Measured and predicted response of Pn to leaf temperature in cotton leaves at different internal partial pressures of CO₂ (Ci) and O₂ concentrations. Pn was determined at 210 (●) or 10 mbar O₂ (□) at 280 (A), 550 (B), 750 (C), and 1,200 (D) μbar Ci. For each leaf, steady-state Pn was attained at 28°C, 280 μbar Ci, and either 210 or 10 mbar O₂, after which the Ci was increased incrementally to 550, 750, and 1,200 μbar. After readjusting the Ci to 280 μbar, leaf temperature was increased and the process was repeated. The response of Pn predicted from the kinetic properties of fully activated Rubisco at 210 (solid line) and 10 mbar O₂ (dashed line) were determined as described in Materials and Methods.