This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Preston, C. Articles by Powles, S. B. Search for Related Content PubMed PubMed Citation Articles by Preston, C. Articles by Powles, S. B. Agricola Articles by Preston, C. Articles by Powles, S. B.

Environmental and Stress Physiology

On the Mechanism of Resistance to Paraquat in Hordeum glaucum and H. leporinum¹

Delayed Inhibition of Photosynthetic O₂ Evolution after Paraquat Application

Department of Crop Protection, Waite Agricultural Research Institute, The University of Adelaide, PMB 1, Glen Osmond S.A. 5064, Australia

The mechanism of resistance to paraquat was investigated in biotypes of Hordeum glaucum Steud. and H. leporinum Link. with high levels of resistance. Inhibition of photosynthetic O₂ evolution after herbicide application was used to monitor the presence of paraquat at the active site. Inhibition of photosynthetic O₂ evolution after paraquat application was delayed in both resistant biotypes compared with the susceptible biotypes; however, this differential was more pronounced in the case of H. glaucum than in H. leporinum. Similar results could be obtained with the related herbicide diquat. Examination of the concentration dependence of paraquat-induced inhibition of O₂ evolution showed that the resistant H. glaucum biotype was less affected by herbicide compared with the susceptible biotype 3 h after treatment at most rates. The resistant H. leporinum biotype, in contrast, was as inhibited as the susceptible biotype except at the higher rates. In all cases photosynthetic O₂ evolution was dramatically inhibited 24 h after treatment. Measurement of the amount of paraquat transported to the young tissue of these plants 24 h after treatment showed 57% and 53% reductions in the amount of herbicide transported in the case of the resistant H. glaucum and H. leporinum biotypes, respectively, compared with the susceptible biotypes. This was associated with 62% and 66% decreases in photosynthetic O₂ evolution of young leaves in the susceptible H. glaucum and H. leporinum biotypes, respectively, a 39% decrease in activity for the resistant H. leporinum biotype, but no change in the resistant H. glaucum biotype. Photosynthetic O₂ evolution of leaf slices from resistant H. glaucum was not as inhibited by paraquat compared with the susceptible biotype; however, those of resistant and susceptible biotypes of H. leporinum were equally inhibited by paraquat. Paraquat resistance in these two biotypes appears to be a consequence of reduced movement of the herbicide in the resistant plants; however, the mechanism involved is not the same in H. glaucum as in H. leporinum.

This article has been cited by other articles:

				D. Abarca, M. Roldan, M. Martin, and B. Sabater Arabidopsis thaliana ecotype Cvi shows an increased tolerance to photo-oxidative stress and contains a new chloroplastic copper/zinc superoxide dismutase isoenzyme J. Exp. Bot., July 1, 2001; 52(360): 1417 - 1425. [Abstract] [Full Text] [PDF]

				G. Váradi, E. Darkó, and E. Lehoczki Changes in the Xanthophyll Cycle and Fluorescence Quenching Indicate Light-Dependent Early Events in the Action of Paraquat and the Mechanism of Resistance to Paraquat in Erigeron canadensis (L.) Cronq Plant Physiology, August 1, 2000; 123(4): 1459 - 1470. [Abstract] [Full Text]