**6. Results of differential absorption, translocation, and metabolism of herbicides in resistant and susceptible weeds**

Several researchers have studied herbicides behavior in weeds in order to find resistance mechanics through the differential of 14C-herbicide absorption, translocation, and metabolism, according to **Table 1**. These results suggest that reduced translocation and accelerated metabolism of herbicide plays a major role in herbicide resistance in resistant biotypes of weed. Likewise, differences in absorption may contribute to the differential sensitivity of herbicide resistant and susceptible weed populations.

Overall, herbicide absorption is similarly compared with resistant and susceptible biotypes, but the difference in herbicide translocation is notorious in most studies reported (**Table 1**). Although differential translocation can be observed between resistant and susceptible weeds, it is unclear whether this difference is a cause of herbicide resistance or an effect of some other physiological process [23].

Herbicide metabolism studies are not always researched together with herbicide absorption and translocation studies, because the increased herbicide metabolism in resistant biotypes compared with susceptible transforms this product on metabolites without herbicidal action (**Table 1**). Among herbicides reported, glyphosate is more studied. Studies on glyphosate metabolism, expression, and sensitivity of target enzyme EPSPS synthase


Procedures for Detection of Resistant Weeds Using 14C-Herbicide Absorption, Translocation, and Metabolism http://dx.doi.org/10.5772/68092 169

described for the absorption and translocation study. In case the fresh samples of plants are not adequate for processing after the collection, the ideal is to store them at −20°C to assure the stability of the active substances and metabolites. The techniques employed on studies on the metabolism of herbicides in plants are thin layer chromatography (TLC), high-performance liquid chromatography (HPLC), and gas chromatography (GC), depending on the herbicide

For the extraction, the adequate system of solvents for the studies herbicide must be known. The treated leaf must be rinsed with non-polar solvent (usually ethanol or methanol). Then, the plant must be dried with an absorbing paper, immediately frozen in liquid nitrogen and stored at −80°C up to its use. The plant tissue must be macerated in crucibles that must be

tion of 80% (v v−1). A stainless steel homogenizer may also be used. The solution must be centrifuged; the supernatant decanted; and the residue must go through re-extraction with the chosen cold solvent at 80%, followed by extraction with the same cold solvent at 50% (v v−1). The supernatants must be mixed, and the radioactivity must be determined by LSS, in order to know the mass balance, which is expressed as the rate between the radioactivity applied at the beginning of the experiment and the total radioactivity measured (originated from rinsing all parts of the plant). The mass balance may be also referred to as the radioactivity recovery percentage. Approximately 7 mL of the supernatant must be evaporated, resuspended in 300 mL of the solvent at 50%, and centrifuged. The final sample may be analyzed by any previously

described technique, usually TLC or HPLC, with the respective solvent system [4].

**herbicides in resistant and susceptible weeds**

bicide resistant and susceptible weed populations.

physiological process [23].

**6. Results of differential absorption, translocation, and metabolism of** 

Several researchers have studied herbicides behavior in weeds in order to find resistance mechanics through the differential of 14C-herbicide absorption, translocation, and metabolism, according to **Table 1**. These results suggest that reduced translocation and accelerated metabolism of herbicide plays a major role in herbicide resistance in resistant biotypes of weed. Likewise, differences in absorption may contribute to the differential sensitivity of her-

Overall, herbicide absorption is similarly compared with resistant and susceptible biotypes, but the difference in herbicide translocation is notorious in most studies reported (**Table 1**). Although differential translocation can be observed between resistant and susceptible weeds, it is unclear whether this difference is a cause of herbicide resistance or an effect of some other

Herbicide metabolism studies are not always researched together with herbicide absorption and translocation studies, because the increased herbicide metabolism in resistant biotypes compared with susceptible transforms this product on metabolites without herbicidal action (**Table 1**). Among herbicides reported, glyphosate is more studied. Studies on glyphosate metabolism, expression, and sensitivity of target enzyme EPSPS synthase

, and homogenized with the specific cold solvent at a concentra-

molecule.

previously cooled with N2

168 Herbicide Resistance in Weeds and Crops


**Table1.** Absorption, translocation, and metabolism of 14C-herbicides in resistant and susceptible weeds.

are necessary to elucidate the mechanism of glyphosate resistance in weed population [28]. However, Feng et al. [29] suggested that glyphosate resistance is likely due to altered cellular distribution that impaired phloem loading and plastidic import of glyphosate resulting in reduced overall translocation as well as inhibition of EPSPS. Taken together, these results suggest that metabolic deactivation is not a likely mechanism for glyphosate resistance in weeds.
