|Lasat Mitch M, - CORNELL UNIVERSITY|
|Ditomaso Joseph, - CORNELL UNIVERSITY|
|Hart Jonathan J, - CORNELL UNIVERSITY|
Submitted to: Weed Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 11, 1995
Publication Date: N/A
Interpretive Summary: The mechanism of action of the widely used herbicide, paraquat, which rapidly kills plants upon contact is well understood. However, until recently, little was known about how paraquat enters plant cells, where it exerts its herbicidal action. We have recently shown that paraquat is transported into and within plants via a transport system normally used for the transport of the polyamine, putrescine. In the current study, we have investigated a novel mechanism of resistance of weeds to paraquat that involves alterations in the transport of the herbicide in the plant. In this study, we measured the uptake and compartmentation of radioactively labeled paraquat in a paraquat-resistant and susceptible line of wall barley. There were no differences found in binding of paraquat within the cell wall or paraquat transport into plant cells, between the resistant and susceptible lines. The results are significant in that they suggest that if altered transport of paraquat is involved in paraquat resistance, it must involve differences in intercellular compartmentation of the herbicide. This was the subject of the research detailed in the accompanying manuscript.
Technical Abstract: Apoplasmic sequestration of paraquat was investigated as a possible mechanism of resistance in two biotypes of wall barley (Hordeum glaucum Steud). No significant differences were measured in [14C]paraquat binding to cell walls and membranes of paraquat-resistant (R) and -susceptible (S) plants. Time-dependent kinetics of paraquat influx across the plasmalemma were similar for the two biotypes. Concentration-dependent uptake kinetics were saturable with similar Vmax values for the two biotypes. Herbicide uptake, however, was influenced by the growth temperature, with Vmax values 88 and 68% higher for 15 deg. C-grown R and S biotypes respectively, compared with plants grown at 25 deg. C. Following an 8 h uptake period, the amount of paraquat accumulated in the cells of S and R plants grown at 15 deg. C was 56% and 51% greater respectively, compared with plants grown at 25 deg. C. Similarly, whole plant sensitivity following foliar application of paraquat differed dramatically in the two biotypes grown at 15 deg. or 30 deg. C. Susceptible plants were 2-fold more sensitive when grown at 15 deg. C. In contrast, R seedlings were 63- to 85-fold more tolerant when grown at the cooler temperature, despite a greater intracellular accumulation of the herbicide. These results suggest that enhanced apoplasmic binding or altered transport across the plasma membrane are not the basis of paraquat resistance.