Translocação do inseticida tiametoxam no floema de mamoneiras, utilizadas como plantas-modelo

Abstract

The present work aimed to investigate the effi ciency of phloem transport of the insecticide thiamethoxam in castor bean plants, used as model plants, due to the easy collection the elaborated sap. The utilized test plants were three weeks old, kept in nutrient solution, remaining two developed leaves and an apical growing leaf per plant. Using a microsyringe, a small volume of an aqueous solution of thiamethoxam was injected inside the petiole of one or both developed leaves. The collection of phloem exudates was performed on the inferior and superior regions of the stem. The concentration of thiamethoxam in the phloem sap and in the different parts of the plants was determined by high performance liquid chromatography, after extraction and purifi cation of the compound. The translocation of thiamethoxam in the phloem of castor bean plants was confi rmed, and its concentration in the sap collected from the inferior region of the stem was about 30% of its concentration in the developed leaves. The amount of insecticide in the apical leaf, 72 hours after the application, was of about 2% of the total amount applied. In the roots, the thiamethoxam concentration was very low, due to the transfer of the compound back to the leaves and to the nutrient solution. When applied to a simple mature leaf, signifi cant mounts of thiamethoxam were verifi ed in the opposite non-treated leaf, as a result of its redistribution inside of the plant. The concentration of the compound in the phloem exudate collected in the inferior part of the stem was about 20% lower than that in the superior part of the stem, confi rming that, as the thiamethoxam is transported downwards on the plant, through the phloem, the compound escapes from the phloem vessels to the tissues of the stem adjacent to theme. It was concluded that thiamethoxam is transported both in xylem and in the phloem of castor bean plants, reinforcing the hypothesis that polar compounds translocate in the phloem.