Role of Epidermis Tissue in Paraquat Resistance of Erigeron philadelphicus L.

Abstract

The relation between the epidermis tissue of E. philadelphicus and paraquat resistance was examined.
Results obtained are as follows:
1. Excised leaves of E. philadelphicus were treated as shown in Fig. 1 and paraquat penetration through them was examined. When a disk of the susceptible biotype was put on an excised leaf of the resistant biotype, it was not destroyed by paraquat applied at a concentration of 4×10^-5M or lower. However, when paraquat was used at a concentration of 2×10^-4M or higher, the disk of the susceptible biotype placed on an excised leaf was destroyed. Thus, it was concluded that paraquat penetrated through the excised leaf of E. philadelphicus (Fig. 2, 3).
2. The lower epidermis tissue of excised leaves of 10 lines of paraquat-resistant E. philadelphicus was peeled off and the disappearance of the resistance was examined. At a concentration of paraquat 2×10^-4M or lower the resistance was occasionally observed whereas at a dose of 4×10^-4M or higher, all the leaves of the lines was destroyed. Such observations suggest that the epidermis tissue contributes to the paraquat resistance of E. philadelphicus (Fig. 4, 5).
3. The influence of paraquat on protoplasts in E. philadelphicus was examined. Protoplasts showed abnormalities (deformation) 8 to 15 minutes after the application of paraquat in the resistant biotype. After 16 to 31 minutes the chloroplasts coagulated in the wall of the cell membrane and some of them collapsed. In the susceptible biotype, 8 to 14 minutes after paraquat application, the protoplasts showed abnormalities, and the cell membrane became uneven. After 9 to 21 minutes, the chloroplasts gathered on the wall of the cell membrane and some of them were broken. As described above, there was differences in the reaction of the protoplasts of both biotypes to paraquat (Table 1, Fig. 6).