Triazine absorption by excised corn root tissue and isolated corn root protoplasts

Abstract

Absorption of four triazine herbicide analogs [ametryn (2-(ethylamino)-4-(isopropylamino)-6-(methylthio)- s-triazine), atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)- s-triazine), atratone (2-methoxy-4-(ethylamino)-6-(isopropylamino)- s-triazine), and hydroxyatrazine (2-hydroxy-4-(ethylamino)-6-(isopropylamino)- s-triazine)] was compared using excised corn ( Zea mays L.) root segments and isolated corn root protoplasts. The tissue absorbed ametryn, atrazine, and atratone for only 20 min. Ametryn and atrazine permeated tissue to passive equilibrium with the ambient solution in 10 min. Atratone permeated to 65 and 82% of passive equilibrium in 10 and 30 min, respectively. In contrast, hydroxyatrazine concentration in tissue was only 15 and 70% of the ambient concentration at 30 min and 24 hr, respectively. However, hydroxyatrazine permeated frozen/thawed tissue to 90% of passive equilibrium in 10 min. Protoplast absorption of ametryn and atratone was complete in 10 sec; hydroxyatrazine absorption by protoplasts did not reach a plateau until 5 min. Protoplasts absorbed the triazines to greater than passive equilibrium. Three kinetically homogeneous pools were detected for ametryn, atrazine, and atratone, whereas elution of hydroxyatrazine produced four pools. The three pools for atrazine were confounded by metabolism of atrazine to hydroxyatrazine. Pools for the triazines could not be identified as the free space, cytoplasm, and vacuole as proposed previously for mineral ions. Although the plasma membrane impeded diffusion of hydroxyatrazine, all analogs penetrated into the symplast.