Phenmedipham-Ozone Pollution Interactions in Sugarbeet (Beta vulgarisL. cv. Saxon): A Physiological Study

Abstract

Actively growing sugarbeet is treated with the post-emergent herbicide phenmedipham at times when ozone pollution episodes are likely to occur. There is a possibility of an interaction occurring between ozone and phenmedipham as both treatments produce similar effects in susceptible plants, such as a reduction in growth and photosynthesis and an increase in the activities of endogenous antioxidant enzymes. To investigate this likelihood, laboratory experiments were conducted in which two-to three-leaf sugarbeet plants (Beta vulgaris L. cv. Saxon) were exposed to a simulated two-day ozone episode (100 nl litre-'. 7 h day-I ) followed three days later by treatment with field rate phenmedipham (1.14 kg A1 ha-'). Growth analysis indicated that an interaction was occurring in which plants treated with ozone and phenmedipham had less reduction in shoot fresh weight than expected. Exposure to phenmedipham alone or ozone followed by phenmedipham reduced net photosynthesis by over 50% and transpiration rate by 30%. The activities of antioxidant enzymes such as catalase, guaiacol peroxidase and superoxide dismutase were stimulated by both treatments individually, but to a greater extent when ozone and phenmedipham were combined. For example, three days after herbicide treatment, the activity of superoxide dismutase increased by 20% in plants treated with ozone alone, 20% in plants treated with phenmedipham alone and 85% in plants that were treated with ozone followed by phenmedipham. We conclude that ozone pollution may predispose sugarbeet to tolerate the herbicide phenmedipham by enhancing the activity of the endogenous antioxidant detoxification enzyme system.

The Ozone Component of Global Change: Potential Effects on Agricultural and Horticultural Plant Yield, Product Quality and Interactions with Invasive Species

“…Antioxidant metabolism is considered to be a critical component in plant responses to O 3 stress. Activities of antioxidant enzymes such as peroxidase and glutathione reductase are often increased by O 3 (Dixon et al 1996; Burkey et al 2000; Chen and Gallie 2005; Cheng et al 2006; US EPA 2006). In addition, the antioxidant compound most studied in this regard is ascorbic acid (vitamin C).…”

“…Previous studies have suggested that O 3 can influence the efficacy of some agricultural chemicals, depending on exposure protocols, plant sensitivity to the herbicide and O 3 , O 3 concentrations and other environmental factors such as light intensity (Dixon et al 1996). Herbicides that induce the formation of toxic levels of ROS in plants may be less effective in situations where O 3 has stimulated antioxidant metabolism, which increases their resistance to the herbicide effect (Dixon et al 1996).…”

“…Previous studies have suggested that O 3 can influence the efficacy of some agricultural chemicals, depending on exposure protocols, plant sensitivity to the herbicide and O 3 , O 3 concentrations and other environmental factors such as light intensity (Dixon et al 1996). Herbicides that induce the formation of toxic levels of ROS in plants may be less effective in situations where O 3 has stimulated antioxidant metabolism, which increases their resistance to the herbicide effect (Dixon et al 1996). For example, in young sugar beet plants exposed to 100 nL/L O 3 7 h/d for 2 d in growth cabinets, followed 3 d later by treatment with phenmedipham at prescribed rates, suppression of shoot fresh mass and chlorophyll concentration in the combined O 3 plus herbicide treatment was less than would be expected if the negative effects of the two treatments were additive (Dixon et al 1996).…”

“…Herbicides that induce the formation of toxic levels of ROS in plants may be less effective in situations where O 3 has stimulated antioxidant metabolism, which increases their resistance to the herbicide effect (Dixon et al 1996). For example, in young sugar beet plants exposed to 100 nL/L O 3 7 h/d for 2 d in growth cabinets, followed 3 d later by treatment with phenmedipham at prescribed rates, suppression of shoot fresh mass and chlorophyll concentration in the combined O 3 plus herbicide treatment was less than would be expected if the negative effects of the two treatments were additive (Dixon et al 1996). Activities of several important antioxidant enzymes were stimulated by both treatments, suggesting that upregulation of antioxidant metabolism by O 3 resulted in plants better adapted to resisting increased ROS stress from certain herbicides.…”

Effect of Decreasing Oxygen Concentration on Plant Metabolism in Response to Different Environmental Stresses.

“…Fungicides stress:-A number of agricultural chemicals such as fungicides (91) and herbicides (92) have been shown to possess antiozonant properties. However, most of these investigations have concentrated on the effectiveness of agrochemicals in preventing plants from ozone injury, and relatively little work has focused on the physiological and biochemical modes of action.…”