Variation in Quantum Yield for CO₂ Uptake among C₃ and C₄ Plants

The quantum yield for CO(2) uptake was measured on a number of C(3) and C(4) monocot and dicot species. Under normal atmospheric conditions (330 microliters per liter CO(2), 21% O(2)) and a leaf temperature of 30 degrees C, the average quantum yields (moles CO(2) per einstein) were as follows: 0.052 for C(3) dicots, 0.053 for C(3) grasses, 0.053 for NAD-malic enzyme type C(4) dicots, 0.060 for NAD-malic enzyme type C(4) grasses, 0.064 for phosphoenolpyruvate carboxykinase type C(4) grasses, 0.061 for NADP-malic enzyme C(4) dicots, and 0.065 for NADP-malic enzyme type C(4) grasses. The quantum yield under normal atmospheric conditions was temperature dependent in C(3) species, but apparently not in C(4) species. Light and temperature conditions during growth appeared not to influence quantum yield. The significance of variation in the quantum yields of C(4) plants was discussed in terms of CO(2) leakage from the bundle sheath cells and suberization of apoplastic regions of the bundle sheath cells.