Photosynthetic capacity of intact leaves of resistant and susceptible cultivars of Brassica napus L. to atrazine

The rate of photosynthesis in intact leaves attached to plants of an atrazine-resistant cultivar of Brassica napus L. was compared with that in leaves of an atrazine-susceptible, rather isogenic cultivar, in a number of irradiance series. The resistant cultivar had been obtained from the susceptible cultivar by crossing the resistant biotype of Brassica campestris L. with the susceptible cultivar of B. napus, and using the fourth back-cross for comparison. At a natural CO₂ concentration (360 cm³ m^?3) the rate of photosynthesis of leaves of the atrazine-resistant cultivar was significantly (17–21%) less than that of leaves of the susceptible cultivar, over the whole range of irradiances up to 250 W m^?2 At the enriched CO₂ concentration of 1500 cm^?3 m^?3 this reduction in rate amounted to 9–12%.