Graduate Thesis Or Dissertation
 

Mechanisms of uptake and some factors influencing the toxicity of 2-chloro-2', 6'-diethyl-N-(methoxymethyl) acetanilide (alachlor) for selected plant species

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  • A number of studies with ¹⁴C-labeled 2-chloro-2', 6'-diethyl- N-(methoxymethyl) acetanilide (alachlor) were conducted to obtain information about the mechanisms of uptake of this herbicide. In other studies, technical alachlor as well as the emulsifiable concentrate formulation of the chemical were used to investigate the effect of several factors on the toxicity of the herbicide. Corn and oats absorbed alachor primarily in a passive way. The uptake of the herbicide in both species was slightly reduced in the presence of metabolic inhibitors. The reduction was somewhat stronger in corn than in oats. A raise in temperature increased the uptake of alachlor only slightly. Q₁₀ values of about 1.2 were found. The part of the total uptake affected by metabolic inhibitors followed Michaelis-Menten kinetics over the alachlor concentration range of 0.1 mM to 0.5 mM. Uptake of alachlor was measured in the presence of an analog, propachlor. Propachlor reduced the uptake of alachlor at a concentra- tion of 0.3 mM for both chemicals. At a concentration of 0.03 mM for each herbicide alachlor uptake was less reduced. Total uptake by corn and oats was nearly identical up to a concentration of 0.1 mM. At higher concentrations alachlor absorption by oats was about twice as high as by corn. This would suggest that selective uptake by the two species could at least partly account for the difference in tolerance towards alachlor. A study was conducted to determine if P, K and Ca levels in oat plants were affected by alachlor treatment. P and Ca content was not affected by the presence of alachlor, but a gradual decrease in K level with increasing herbicide concentrations was observed. Uptake of alachlor through the shoot region exceeded absorption by the roots in the two monocotyledonous species, corn and oats. Two dictos, soybean and cucumber, absorbed higher amounts of the herbicide through the roots. Shoot exposure of corn and cucumber was most damaging to the plant, while root exposure was more damaging to oats and soybean. The effect of alachlor on the growth of oats and cucumber at various levels of sub-irrigation and carrier volume could be explained on the basis of differences in effective absorption regions in the plants. Photoperiod had, in contrast with light intensity, no effect on the activity of the herbicide to corn, cucumber and oats. An increase in light intensity up to 1600 ft-c increased the toxicity of alachlor in corn and cucumber, but not in oats. The activity at 2000 ft-c was only slightly higher than at 60 ft-c, and less than at 660 ft-c. In the case of cucumber, an increase in alachlor concentration had very little effect at 2000 ft-c, in contrast with the other light intensities.
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