The mechanism of resistance to paraquat is strongly temperature dependent in resistant Hordeum leporinum Link and H. glaucum Steud.

Abstract

Abstract. Paraquat-resistant biotypes of the closelyrelated weed species Hordeum leporinum Link and H. 91aucum Steud. are highly resistant to paraquat when grown during the normal winter growing season. However, when grown and treated with paraquat in summer, these biotypes are markedly less resistant to paraquat. This reduced resistance to paraquat in summer is primarily a result of increased temperature following herbicide treatment. The mechanism governing this decrease in resistance at high temperature was examined in H. leporinum. No differences were observed between susceptible and resistant biotypes in the interaction of paraquat with isolated thylakoids when assayed at 15, 25, or 35~ About 98 and 65% of applied paraquat was absorbed through the leaf cuticle of both biotypes at 15 and 30 ~ respectively. Following application to leaves, more herbicide was translocated in a basipetal direction in the susceptible biotype compared to the resistant biotype at 15 ~ However, at 30 ~ more paraquat was translocated in a basipetal direction in the resistant biotype. Photosynthetic activity of young leaf tissue from within the leaf sheath which had not been directly exposed to paraquat was measured 24 h after treatment of plants with paraquat. This activity was inhibited in the susceptible biotype when plants were maintained at either 15 ~ or 30 ~ after treatment. In contrast, photosynthetic activity of such tissue of the resistant biotype was not inhibited when plants were maintained at 15 ~ after treatment, but was inhibited at 30 ~ The mechanism of resistance in this biotype of H. leporinum correlates with decreased translocation of paraquat and decreased penetration to the active site. This mechanism is temperature sensitive and breaks down at higher temperatures.

The Role of GIGANTEA Gene in Mediating the Oxidative Stress Response and in Arabidopsis

“…Enhanced detoxification of oxygen radicals and defects in the uptake of PQ or the sequestration of PQ from its site of action are two possible mechanisms related to the enhanced tolerance of plants to oxidative stress mediated by PQ (Hart and Ditomaso 1994;Purba et al 1995). Several lines of evidence indicated that loss-of-function gi mutations result in the enhanced detoxification of oxygen radicals.…”

Glyphosate, paraquat and ACCase multiple herbicide resistance evolved in a Lolium rigidum biotype

“…Correspondingly, wilting/desiccation of both treated and untreated leaves (including young leaves) were observed in the S but not in the R plants. Reduced paraquat movement in paraquat resistant plants has been demonstrated in Erigeron philadelphicus and E. canadenisis (Tanaka et al 1986), C. bonariensis (Fuerst et al 1985), Hordeum glaucum (Bishop et al 1987;Preston et al 1992;Purba et al 1995), A. calendula (Soar et al 2003) and L. rigidum (Yu et al 2004a). Unlike glyphosate, paraquat is a contact herbicide, moving upwards largely in the apoplast with transpiration.…”

Tracking photosynthetic injury of Paraquat-treated crop using chlorophyll fluorescence from hyperspectral data

“…Paraquat is an active ingredient in several herbicide preparations and is extensively used in agriculture as a non-selective contact herbicide, which is the secondly most widely used herbicide in world, and still widely used in most developing countries. Non-selective herbicides act by siphoning electrons from photosystem I (PSI), and donating them to O2, producing superoxide and other active oxygen species [Purba et al, 1995]. Application in bright sunlight can lead to rapid necrosis of affected leaves without death of the plant [Baldwin, 1963].…”