Movement of paraquat in resistant and susceptible biotypes of Erigeron philadelphicus and E. canadensis

Abstract

H. 1986. Movement of paraquat in resistant and susceptible biotypes of Erigeron philadelphicus and E. canadensis. -Physiol. Plant. 66: 605-608.Paraquat (l,r-dimethyl-4,4'-bipyridinium) resistant biotypes of Erigeron philadelphicus and E. canadensis, from fields where paraquat had been used for weed control, showed more than 100 times higher resistance than the susceptible biotype of both plants. Excised leaves of the susceptible biotypes wilted when supplied with more than 5 \iM paraquatat at the cut ends, but those from the resistant biotypes did not wilt even at 500 | xiW. Autoradiographs indicated that ("CH,)-paraquat taken up through the cut ends was rapidly distributed through the vascalar system in leaves of the susceptible biotype, but was barely translocated in leaves of the resistant biotype. The amount of paraquat taken up during 48 h in the resistant biotype was 0.5% of that in the susceptible biotype in Ught. This difference in paraquat movement may be correlated with paraquat resistance in Erigeron.

Kinetic Analysis of Resistance to Paraquat in Conyza

“…These experiments clearly demonstrate that (a) paraquat can and does affect the chloroplasts of the resistant plant, and (b) the resistant plants recover from the effect(s) of paraquat. This effect of paraquat on the chloroplasts is in contrast to the predictions of the sequestration hypotheses, if sequestration was the primary mechanism of resistance (1,6,18,19). Primary sequestration should have blocked paraquat or a detoxification product of paraquat, from inhibiting 14C02 fixation (Fig.…”

“…The data on ethane evolution clearly suggest that the superoxide detoxification pathway that is at constitutively higher levels in the resistant biotype chloroplasts (14), can prevent damage by superoxide, or by the hydroxyl radicals generated from it by reaction with superoxide dismutase greatly enhance the effect of paraquat (15), supporting the importance of this pathway. The kinetic data in Figure 1 and the data on ethane evolution together with the autoradiographic evidence (1,6,18), indicate that: (a) paraquat sequestration or detoxification can only come about after paraquat temporarily inhibits chloroplast activity, and (b) that the high constitutive levels of chloroplast enzymes (14) protect the plant from paraquat damage, while paraquat is being detoxified. Thus, the internal chloroplast protection reactions have temporal primacy over sequestration.…”

“…1). An integration of the data on sequestration 4 h after treatment (1,6,18,19), and our data ( Fig. 1) suggests that paraquat can be sequestered in the leaves of only those resistant plants that managed to stay alive, despite the transient paraquat effect at the chloroplasts.…”

“…Based on two types of observation with paraquat resistant biotypes of Conyza bonariensis (6,19), C. canadensis and C. philadelphicus (18) and Hordeum glaucum (1) it was suggested that the primary mode of resistance is a sequestration of paraquat that occurs before it reaches the chloroplasts. The evidence supporting sequestration is as follows: (a) PSI activity in the isolated thylakoids of the resistant biotypes is as sensitive to paraquat as the wild type; (b) radioactivity measured 4 h after application of paraquat to cut-petioles is localized near the vascular bundles (1,6) or the leaf base (18) in the resistant biotypes, and throughout the leaf in the sensitive biotypes. These findings were interpreted as a sequestration of paraquat which prevents its transport to the chloroplast.…”

The biology of Canadian weeds. 115. Conyza canadensis

“…Paraquat-resistant populations have been identified in several orchards in Essex County, Ontario (Smisek et al 1998), as well as in Hungary, Japan and Mississippi, USA (Yamasue et al 1992;Tanaka et al 1986;and Pölös et al 1988;Heap 2001). Atrazine or simazine resistant populations occur in the United Kingdom, France, Belgium, Switzerland, Poland, Czechoslovakia, and Spain (Heap 2001).…”