DIFFERENTIAL EFFECTS OF PHENOXY HERBICIDES ON LIGHT-DEPENDENT CO2-(C-14) FIXATION IN ISOLATED CELLS OF C3-PLANT AND C4-PLANT

Cells were isolated from the developing leaves of Ipomoea aquatica and Digitaria sanguinalis. The effects of phenoxy alkanoic acid herbicides on light-dependent 14CO2 fixation and oxygen evolution in these leaf cells were studied. (2,4-Dichlorophenoxy)acetic acid and (2,4,5-trichlorophenoxy) acetic acid (2,4,5-T and 2,4-D) caused a 20% stimulation of 14CO2 fixation at 0.8 × 10-5M and an inhibition at 1 × 10-4M in I. aquatica leaf cells. Temperature seemed to have a marked influence on such action. No effect or very little effect was observed in the leaf cells of D. sanguinalis. The nonactive (2,4,6-Trichlorophenoxy)acetic acid (2,4,6-T) caused a similar stimulation of CO2 fixation as 2,4-D and 2,4,5-T at low concentrations in I. aquatica leaf cells, but no inhibition was observed at high concentration. Increase of hight intensity increased the rate of CO2 fixation in both control and 2,4,6-T-treated cells; however, the percentage of stimulation remained the same. At stimulatory concentration, all three compounds did not cause any stimulation in either photosystem I and II or photosystem II-mediated oxygen evolution. At higher concentrations, the differential effects of 2,4-D and 2,4,5-T on the light-induced CO2 fixation and photosystem II-mediated oxygen evolution in the I. aquatica leaf cells and D. sanguinalis mesophyll (ms) cells may be attributed in part to their selective action against dicotyledonous plants. © 1979.