Fig. 4.

Reduced transpiration and maintenance of CO₂ assimilation in RCAR6-3 and RCAR10-4 lines. Whole plant gas exchange analysis at well-watered conditions (A–C) and during drought (D). (A) Transpiration (black bars) and net CO₂ assimilation rates (open bars) of RCAR6 (R6) and RCAR10 (R10) lines in comparison with Col-0 and gas exchange mutants era1-2 and er2 at water potential Ψ > −0.03 bar and external CO₂ concentration C_a of 420 μmol⋅mol⁻¹. (B) Transpiration efficiency, i.e., ratio of rates for net CO₂ assimilation and transpiration (mmol CO₂ mol H₂O⁻¹) and (C) intercellular CO₂ concentration C_i of the same plants as in A. (D) Transpiration efficiency affected by soil water content in RCAR6 (open squares), RCAR10 (open triangles), and wild type (filled circles); single whole plant measurements with 10 technical replicates per data point (D), **P < 0.001 compared with wild type. (E) Analysis of net CO₂ assimilation rates in response to external CO₂ concentrations (C_a, ambient C_a in red) and (F) mesophyll (g_m) and stomatal conductance (g_s) in single leaves at high photosynthetic photon flux density (1,500 μmol⋅m⁻²⋅s⁻¹) and soil Ψ > −0.03 bar. The CO₂ concentration in chloroplasts (C_c; Inset) and conductance rates were analyzed at ambient C_a (400 μmol⋅mol⁻¹). Labeling of plant lines is as in D. (E) n ≥ 5 with six technical replicates. (Inset and F) Data of single measurements.