Effect of diclofop‐methyl and 2,4‐D on transmembrane proton gradient: a mechanism for their antagonistic interaction

Abstract

1989. Effect of diclofop-methyl and 2,4-D on transmembrane proton gradient; a mechanism for their antagonistie interaction. -Physiol. Planl. 77; 107-114.The site of aetion of the postemergence graminieide, dielofop-methyl (DM), in susceptible plants is possibly the plasmaletntna. Indole-acetic aeid (IAA)-and fusicoccin (FC)-induccd net proton exetetion in Avena coleoptiles was inhibited by the free aeid, dielofop. However, net proton excretion recovered within 2 h when 2,4-dichlorophenoxy acid (2,4-D) was added sitnultaneously with diclofop. Dielofop depolarized the metnbrane potential (Em) within 12 min but the Em recovered within 30 min when diclofop was removed and replaeed with either IAA or 2,4-D. The inhibition of lAA-induced eoleoptile growth by DM and the membtane effects of its acid, diclofop, were partially reversed by 2,4-D if it was added shortly after treatment of the tissue. These results are consistent with the reversal of DM injury in whole plants with 2,4-D.

Effect of Diclofop on the Membrane Potentials of Herbicide-Resistant and -Susceptible Annual Ryegrass Root Tips

“…4). A similar response following diclofop depolarization in susceptible oat (Avena sativa) coleoptiles was induced by 2,4-D and IAA (27). The reversal of phytotoxicity in whole plants by 2,4-D and other auxinic compounds is a temporally related interaction (11,16,17,25).…”

“…Em was determined by the microelectrode technique as previously described (27,33). The emerging primary root 2 Mention of trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.…”

“…In field experiments, a simultaneous application of both herbicides or a split application of 2,4-D or an auxinic herbicide made within 8 h following application of DM will reverse its phytotoxicity (16,17). DM acts as an effective auxin antagonist in oat coleoptiles, but antagonism may be overcome by the application of IAA, 2,4-D, or dicamba (23,24,27). However, 2,4-D must be applied within 3 h to oat coleoptiles treated with DM to prevent irreversible growth inhibition (27).…”

“…Biotypes of annual ryegrass (Lolium rigidum) with resistance to DM have appeared in all major cereal cropping areas of Australia (6, 7). The physiological or biochemical mechanism for resistance to DM has not been determined for these ryegrass biotypes.The 13,18,19,27,33) and (b) inhibition of ACCase, a key enzyme in acyl lipid biosynthesis located in the chloroplasts and plastids of nongreen tissues (2,10,20,21,29 The basis for resistance in annual ryegrass biotypes is not due to differential metabolism and detoxification of DM (9,26) or to altered sensitivity of ACCase to inhibition by diclofop (14). The plasma membrane of several DM-resistant and -susceptible biotypes of annual ryegrass was sensitive to membrane depolarization by diclofop (5, 9).…”

“…Another mechanism of selectivity is the differential sensitivity of proposed target sites to DM. Two mechanisms of phytotoxicity with separate target sites have been proposed for DM and other analogs: (a) reduction of the electrogenic component of the Em at the plasmalemma (5,9,13,18,19,27,33) and (b) inhibition of ACCase, a key enzyme in acyl lipid biosynthesis located in the chloroplasts and plastids of nongreen tissues (2,10,20,21,29). The interaction between 2,4-D or IAA and DM on proton transport, coleoptile growth, Em, and morphogenesis in tissue culture has been demonstrated in susceptible tissues (25).…”