Estimates of in vivo and in vitro Rubisco activity versus Rubisco content in flag leaves of different ages measured between 22 d before anthesis and 18 d after anthesis in experiment 3. Plants were grown at 36 (open symbols) and 100 (closed symbols) Pa CO_{2} partial pressure. Top, *V*_{cmax} required to maintain observed *A* at a PPFD of 1500 μmol quanta m^{−2} s^{−1} and the growth CO_{2} partial pressure estimated from the *A* − *p*_{i} response using Equation . Bottom, Initial, total, and maximal in vitro activities determined at 25°C of Rubisco isolated from leaves freeze-clamped under a PPFD of 1500 μmol quanta m^{−2} s^{−1} and the growth atmospheric CO_{2} partial pressure. Lines are regressions forced through the origin. Separate regressions were used for the two treatments where this improved the r^{2} value (dashed lines); otherwise a single regression was used (solid line). Second-order linear regressions were used where this improved the r^{2} value (gas-exchange, elevated-CO_{2} treatment, and initial and total, both treatments); otherwise, first-order regression was used.

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