Photosynthetic 14C fixation in leaves and isolated chloroplasts of some scrub species under the influence of paraquat and 2,4,5-T

The diurnal course of carbon dioxide uptake in the leaves of six nonsucculent semiarid scrub species was investigated. Five nonsucculent scrub species, Carissa spinarum, Maba buxifolia, Flacourtia sepiaria, Gymnosporia emerginata and Dodonaea viscosa exhibited nocturnal carbon assimilation while day time CO2 uptake was predominant in Chomelia asiatica. Foliar application of paraquat (100 mg 1sup(-1)) or 2,4,5-T (2000 mg 1sup(-1)) caused a marked inhibition in the dark uptake of CO2. On the other hand, carbon uptake during day was slightly reduced. Studies on the carbon assimilation of isolated chloroplasts under the influence of paraquat or 2,4,5-T revealed that paraquat is more effective than 2,4,5-T in the suppression of carbon assimilation of in vivo and in vitro chloroplasts. The data suggested that the process of nocturnal carbon assimilation is far more sensitive to paraquat than the light dependent carbon fixation during day. (author)