Movement of Paraquat in Excised Leaves of Resistant and Susceptible Biotypes of Erigeron philadelphicus L.

Abstract

The distribution of paraquat applied to the cut end of petioles and the foliar surface of leaves excised in E. philadelphicus was examined.
Results obtained are as follows:
1. The time course of ¹⁴C-paraquat absorption was not different between the resistant biotype and the susceptible one until 6 hours after foliar application and 24 hours after petiole application. Thereafter, the resistant biotype absorbed more ¹⁴C-paraquat than the susceptible one when both methods of application were compared (Fig. 1).
2. The patterns of ¹⁴C-paraquat absorption, transfer, and diffusion were significantly different between the resistant biotype and the susceptible one in the case of foliar application. These patterns indicated that ¹⁴C-paraquat in the resistant biotype was mostly bound in the mesophyll tissue while in the susceptible type ¹⁴C-paraquat had mostly been absorbed and transferred to the mesophyll tissue (Fig. 2).
3. Leaf disk application did rot result in any distinct difference in the ¹⁴C-paraquat absorption and transfer between the biotypes (Fig. 3).
4. Distribution of ¹⁴C-paraquat within the leaf tissue was not different between the two biotypes (Table 1).
These results suggest that the resistance to paraquat may not be due to the difference in the amount or the distribution of the absorbed paraquat, since paraquat penetrated through the epidermis tissue of E. philadelphicus to reach the mesophyll tissue after foliar application, although the patterns of paraquat absorption and transfer were somehow different between the biotypes.