Studies on the Selective Mechanism of Pretilachlor

I. Relation of Glutathione Content and Glutathione S-Transferase Activity to Pretilachlor Selectivity in Several Plant Species

Abstract

The relation of pretilachlor (2-chloro-2′, 6′-diethyl-N-[2-propoxyethyl]-acetanilide) tolerance to glutathione content, investigated in 4 gramineous species and 3 perennial weeds of paddy fields. The effects of light, exogenous glutathione (the reduced from: GSH), and safener CGA-123407 on pretilachlor resistance were also examined.
Corn and rice were tolerant, while barnyardgrass and finger millet showed a sensitivity to pretilachlor. Of the perennials, Sagittaria pygmaea MIQ. and Eleocharis kuroguwai OHWI were highly resistant and Cyperus serotinus ROTTB. comparatively sensitive (Table 1). Glutathione content was the highest in corn plants and the lowest in barnyardgrass plants; it was also lower in mature seedlings than in young seedlings. An extremely low content of glutathione was determined in the above 3 perennials than in the gramineous species (Table 2). GST activity was higher in the tolerant than in the susceptible gramineous species, regardless of the substrate used. The relationship of pretilachlor selectivity to the glutathione content of the these plant species was not obtained, although it had high correlation to the GST activity. The enzyme activity of the above perennials was much lower than that of the gramineous plants but it also had no relation to pretilachlor tolerance (Fig. 1). GST was induced by pretilachlor treatment and the inducibility was higher in the tolerant than in the susceptible gramineous plants (Tables 3, 4).
Light illumination increased the glutathione content of rice; however, it did not reduce the pretilachlor phytotoxicity to rice (Table 5). The exogenous GSH was easily absorbed, while the pretilachlor phytotoxicity in rice and finger millet plants was little changed even by increased glutathione content (Tables 6, 7). The growth inhibition of rice by pretilachlor treatment was selectively recovered by CGA-123407 treatment (Fig. 2). Glutathione content also was raised by CGA-123407 treatment in both plants, while GST activity was activated selectively only in the rice plants (Tables 8, 9). The increment of GST activity, therefore, coincided with the reduction effect of pretilachlor phytotoxicity.