Unraveling the Toxicity Mechanisms of the Herbicide Diclofop-Methyl in Rice: Modulation of the Activity of Key Enzymes Involved in Citrate Metabolism and Induction of Cell Membrane Anion Channels

Abstract

Residual soil concentrations of the herbicide diclofop-methyl (DM) can be toxic to other nontarget plant species, but the toxicity mechanisms at play are not fully understood. In the present study, we analyzed the toxic effect of DM on root growth and metabolism in the rice species Oryza sativa. The results show that a 48-h exposure to a trace level (5 μg/L) of DM inhibits rice root growth by almost 70%. A 48-h exposure to 5 μg/L DM also leads to an ≈2.5-fold increase in citrate synthase (CS) activity (and CS gene transcription) and an ≈2-fold decrease in the citrate lyase gene transcripts, which lead to an increase in the intracellular concentration of citrate and in citrate exudation rate. Addition of a specific inhibitor of cell membrane anion channel, anthracene-9-carboxylic acid, decreased citrate release in the culture, suggesting that DM-induced citrate loss from the cells is mediated by a specific membrane-bound channel protein. This study brings new insights into the key biochemical mechanisms leading to DM toxicity in rice.

Herbicide-related signaling in plants reveals novel insights for herbicide use strategies, environmental risk assessment and global change assessment challenges

“…Pre-treatment with the auxin-like herbicide 2,4-D induces protection against diclofop in the major global weed Lolium rigidum (Gaines et al, 2014). Such interactions between herbicides, herbicide residues and other pesticides and the impact of pesticide carryover levels on plants (Cui et al, 2010;Ding et al, 2014;Rong Tan et al, 2015) suggest that soil residual pesticides could be additional risk factors for crop injury or for weed control failure. Thus, in the long term and at least in certain agricultural contexts, background contaminating organic pollutants could be monitored for potential interactions with further herbicide treatments and the choice of herbicide treatment could take into account this information.…”

“…These effects can occur on plant species of outstanding ecosystemic importance, such as perennial ryegrass (Serra et al, 2015a), a major component of grazed pastures and grasslands that cover over 40% of Earth's land surface area (Barbehenn et al, 2004), or rice (Zhou et al, 2015), with a global harvested area of 14% of Earth's arable land (Philippot and Hallin, 2011). The effects of residual levels of herbicides and herbicide derivatives on soluble sugars, starch, carbon metabolism and root functioning (Ding et al, 2014;Serra et al, 2013Serra et al, , 2015a suggest potential perturbations of carbon allocation in the plant, and could lead, at the global scale of grasslands, to potential perturbations of carbon sequestration and of plant-rhizosphere relationships. Effects on the balance between soluble sugars and N-rich (asparagine) or S-rich (methionine) amino acids (Serra et al, , 2015a could have cascading effects leading to enhanced plant-associated production of CH 4 and N 2 O greenhouse gases and hamper processes of climate change mitigation (Lenhart et al, 2015;Philippot and Hallin, 2011).…”

Metabolomic and Transcriptomic Investigation of Metabolic Perturbations in Oryza sativa L. Triggered by Three Pesticides

“…The other gigantic portion persists in soils because of off-target deposition or accumulates in crops via foliar absorption and soil-root migration. , China is the largest pesticide user worldwide, with the average annual amount being approximately 1.5- to 4-fold higher than the global average . This high level of application inevitably causes pesticide residue accumulation in crops, thereby affecting food safety and quality. , Although pesticide application is based on the evaluation of its visible phytotoxicity to nontarget crops, there are likely to be many nonvisible and subtle effects on crops at the physiological, biochemical, and molecular level. − …”

“…Generally, the metabolic response of plants to pesticide stress is a highly complex process involving transcriptional regulation of multiple genes. These genes have been reported to perform fundamental structural and physiological functions, including transcription, translation, cellular communication and signaling, central metabolism, energy metabolism, and stress responses. − Previous research has elucidated that the herbicide diclofop-methyl can induce citrate loss in the citric acid cycle (TCA cycle) in rice plant cells, by enhancing the activity and gene transcription of citrate synthase and reducing gene transcripts of citrate lyase . Moreover, studies have shown a similar inhibition of acetylcholinesterase (AChE) in rice and animals, following exposure to the insecticide diazinon, with the subsequent accumulation of AChE mainly affecting the metabolism of osmolytes and TCA intermediates .…”

Diclofop-methyl: A phenoxy propionate herbicide with multiple toxic effects in mouse embyro fibroblast (NIH/3T3) cell line

“…Diclofob-methyl is used to control a wide range of grasses due to its high target selectivity and low nontarget toxicity [1,5,6]. Total annual usage of diclofop-methyl in United States is approximately 750.000 pounds of active ingredient, 1.5-fold more in China [1,7]. Diclofop-methyl is a possible endocrine disrupter and a carcinogen [8].…”