R_L in Col-0 and hpr1 mutants. R_L was measured as the flux of ¹²CO₂ occurring when a leaf was fed 99% (mol/mol) ¹³CO₂. The LI-COR LI-800 gas analyzer is only 2.4% as sensitive for ¹³CO₂ as for ¹²CO₂, and it was assumed that the ¹³CO₂ concentration in the air stream was the same as the ¹²CO₂ had been before beginning the labeling. Differences between the wild type and treatments were tested by one-way ANOVA followed by Tukey’s test. The box encompasses the middle two quartiles, the mean is shown as an open square inside the box, the median is shown as a line inside the box, and the whiskers show the sd of the data. Statistical differences are indicated as follows: ⁺, α = 0.1 and *, α = 0.05. n = 3.