Growth of Zea mays L. cv Potro roots was inhibited by the herbicide metsulfuron methyl (MSM) at the lowest concentration tested: 5 nanomoles per liter. Pretreatment of corn seeds with commercial 1,8-naphthalic anhydride (NA) at 1% (w/w) partially reversed MSM-induced root growth inhibition. MSM at a concentration of 52 nanomoles per liter was taken up rapidly by roots and accumulated in the corn tissue to concentrations three times those in the extemal medium; the safener NA increased MSM uptake up to 48 hours. The protective effect of NA was related to the ability of the safener to increase the metabolism of MSM; tenfold increases in the metabolic rates of MSM were observed in NA-pretreated corn seedlings grown for 48 hours on 52 nanomolar[14C]MSM solution. DNA synthesis determined by measurement of [3H]thymidine incorporation into DNA was inhibited by root MSM applications; after a 6-hour application period, 13 nanomolar MSM solution reduced DNA synthesis by 64%, and the same reduction was also observed with NA-pretreated seedlings. Pretreatment of corn seeds with safener NA did not increase the acetolactate synthase activity in the roots and did not change, up to 13 micromoles per liter, the in vitro sensitivity of roots to MSM.MSM' is the active ingredient in Du Pont "Ally"' weed killer. This new sulfonylurea herbicide is active on most vascular plants and is used for weed control in small grains. An important feature of this compound is its high herbicidal activity at extremely low application rates; recommended amounts for weed control in wheat are between 6 and 8 g ai/ha. 'Abbreviations: MSM, metsulfuron methyl (methyl 2-[(I[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino] carbonyl} amino) sulfonyl] benzoate); ai, active ingredient; ALS, acetolactate synthase, used in the more general sense of acetohydroxyacid synthase;
Zea mays L., cv. Potro, shoots had a higher level of resistance to imazaquin (IQ) and metsulfuron methyl (MSM) than roots. Shoot lengths were increased by pretreating the seeds with commercial 1,8-naphthalic anhydride (NA) at 1% (w/w) or oxabetrinil at 0.2% (w/w). The growth of shoots of safened seeds was unaffected by 400 nᴍ IQ and by 40 nᴍ MSM.The in vivo activity of acetolactate synthase (ALS) extracted from corn shoots and roots was not affected by treatments with IQ or MSM , but pretreatment of seeds with NA or oxabetrinil, prior to germination, caused an increase in the level of extractable ALS from shoots. ALS activity from roots and shoots of NA-pretreated seedlings was increased to a large degree (> 40 %) when the seedlings were germinated on 40 nᴍ MSM , whereas ALS activities from oxabetrinil-pretreated seedlings were enhanced to a lesser degree (≈20%). ALS from unsafened seedlings was inhibited 21% by 400 nᴍ IQ and 70% by 40 nᴍ MSM in vitro, but ALS from roots of seedlings germinated on 400 nᴍ IQ was not inhibited by 400 nᴍ IQ in vitro.
The influence of the experimental herbicide safener BAS-145–138 on the toxicity of imazaquin and metsulfuron-methyl was investigated in two corn varieties in growth chamber bioassays. BAS-145–138 alone slightly decreased root and shoot growth but this decrease was not dependent on the safener concentration. The imbibition of seeds of both corn varieties with low levels of safener caused substantially less damage in the roots and shoots especially with the highest metsulfuron-methyl doses used in the study. In one variety, the safener significantly increased corn root tolerance to imazaquin and to metsulfuron-methyl 1.5- and 2.3-fold, respectively; the concentrations of both herbicides producing 50% inhibition were higher for safened seedlings. In the other variety, a high antidotal influence of BAS-145–138 imbibition on metsulfuron-methyl was observed in shoot growth.
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