Inhibition of photosynthesis and respiration by substituted 2,6-dinitroaniline herbicides: II. Effects on responses in excised plant tissues and treated seedlings

Effects of 12 substituted 2,6-dinitroaniline herbicides were measured on photosynthesis and respiration in excised tissue, and tissue excised from seedlings treated with α,α,α-trifluoro-2,6-dinitro- N,N-dipropyl- p-toluidine (trifluralin). The compounds partially inhibited photosynthesis (measured as oxygen evolution) of strips cut from spinach ( Spinacia oleracea L.) leaf discs. Only 3,5-dinitro- N 4,N 4 -dipropyl-sulfanilamide (oryzalin) strongly inhibited respiration (measured as oxygen uptake) of excised mung bean ( Phaseolus aureus Roxb.) root tips and hypocotyls after a short treatment time. However, root tips excised from corn ( Zea mays L.) seedlings germinated in contact with one representative 2,6-dinitroaniline (trifluralin) showed suppressed oxygen uptake. In addition, phosphorylation was completely uncoupled from oxidation in mitochondria isolated from primary roots of corn seedlings after germination of the seed in contact with trifluralin for 96 hr. Interference with photosynthesis and respiration both in vivo and in vitro by the 2,6-dinitroanilines has been demonstrated. Deviations in growth and metabolism produced by these herbicides can be explained partially by interference with the oxidative and photoproduction of ATP, if recognition is extended to the role played by ATP energy in maintaining cellular and nuclear activities. However, the importance of interference with ATP production to the phytotoxic action of the 2,6-dinitroanilines remains to be established.