Effect of quinclorac on auxin-induced growth, transmembrane proton gradient and ethylene biosynthesis in Echinochloa spp.

The mechanism of action of quinclorac and its selectivity between rice and resistant (R), intermediately tolerant (I) and susceptible (S) Echinochloa spp. were investigated. The effect on the cell membrane potential (E-m), stimulation of cell elongation growth, ACC production and ethylene formation were examined to verify the auxin characteristics of quinciorac and the possible mechanism of selectivity. Quinclorac did not induce cell elongation growth, neither did it cause hyperpolarization of E-m due to the stimulation of H+-ATPase activity. Quinclorac increased ethylene biosynthesis by increasing the ACC content in susceptible plants, possibly by affecting the autonomous auxin-regulated ACC synthase gene. Increased ethylene biosynthesis was correlated with the phytotoxicity of quinclorac. Ethylene biosynthesis due to quinclorac treatment in I and S biotypes increased 3 and 7 times, respectively, but quinclorac treatment had no effect on ethylene biosynthesis in R Echinochloa spp. and rice at the applied dosages. Quinclorac caused an increase of ACC concentration in the S biotype that was 2.5-fold more than the control. The addition of an ethylene biosynthesis inhibitor decreased the phytotoxicity of quinclorac. The mechanism of selectivity between susceptible and tolerant species/biotypes may be related to the formation of HCN as a coproduct during the stimulation of the ethylene biosynthesis caused by the herbicide only in susceptible grasses.