Increasing food production is necessary to meet the needs of the world’s population. In this regard, pesticides are an integral part of modern agricultural practices aimed at increasing crop yields. The widespread use of synthetic pesticides in agriculture has been shown to cause serious environmental pollution and human health problems. Pesticides can bioaccumulate on human cell membranes and impair human functions through direct contact or consumption of contaminated food, which is an important cause of health problems.
The cytogenetic parameters used in this study showed a consistent pattern indicating that omethoate exerts genotoxic and cytotoxic effects on onion meristems. Although there is no clear evidence of the genotoxic effects of omethoate on onion in the existing literature, a large number of studies have investigated the genotoxic effects of omethoate on other test organisms. Dolara et al. demonstrated that omethoate induced a dose-dependent increase in the number of sister chromatid exchanges in human lymphocytes in vitro. Similarly, Arteaga-Gómez et al. demonstrated that omethoate reduced cell viability in HaCaT keratinocytes and NL-20 human bronchial cells, and genotoxic damage was assessed using a comet assay. Similarly, Wang et al. observed increased telomere length and increased cancer susceptibility in omethoate-exposed workers. Furthermore, in support of the present study, Ekong et al. demonstrated that omethoate (the oxygen analogue of omethoate) caused a decrease in MI in A. cepa and caused cell lysis, chromosome retention, chromosome fragmentation, nuclear elongation, nuclear erosion, premature chromosome maturation, metaphase clustering, nuclear condensation, anaphase stickiness, and abnormalities of c-metaphase and anaphase bridges. The decrease in MI values after omethoate treatment may be due to the slowdown in cell division or the failure of cells to complete the mitotic cycle. In contrast, the increase in MN and chromosomal abnormalities and DNA fragmentation indicated that the decrease in MI values was directly related to DNA damage. Among the chromosomal abnormalities detected in the present study, sticky chromosomes were the most common. This particular abnormality, which is highly toxic and irreversible, is caused by physical adhesion of chromosomal proteins or disruption of nucleic acid metabolism in the cell. Alternatively, it may be caused by dissolution of proteins encapsulating chromosomal DNA, which may ultimately lead to cell death42. Free chromosomes suggest the possibility of aneuploidy43. In addition, chromosomal bridges are formed by the breakage and fusion of chromosomes and chromatids. The formation of fragments directly leads to the formation of MN, which is consistent with the comet assay results in the present study. The uneven distribution of chromatin is due to the failure of chromatid separation in the late mitotic phase, which leads to the formation of free chromosomes44. The exact mechanism of omethoate genotoxicity is not clear; however, as an organophosphorus pesticide, it may interact with cellular components such as nucleobases or cause DNA damage by generating reactive oxygen species (ROS)45. Thus, organophosphorus pesticides can cause the accumulation of highly reactive free radicals including O2−, H2O2, and OH−, which can react with DNA bases in organisms, thereby causing DNA damage directly or indirectly. These ROS have also been shown to damage enzymes and structures involved in DNA replication and repair. In contrast, it has been suggested that organophosphorus pesticides undergo a complex metabolic process after ingestion by humans, interacting with multiple enzymes. They propose that this interaction results in the involvement of various enzymes and the genes encoding these enzymes in the genotoxic effects of omethoate40. Ding et al.46 reported that omethoate-exposed workers had increased telomere length, which was associated with telomerase activity and genetic polymorphism. However, although the association between omethoate DNA repair enzymes and genetic polymorphism has been elucidated in humans, this question remains unresolved for plants.
Cellular defense mechanisms against reactive oxygen species (ROS) are enhanced not only by enzymatic antioxidant processes but also by non-enzymatic antioxidant processes, of which free proline is an important non-enzymatic antioxidant in plants. Proline levels up to 100 times higher than normal values were observed in stressed plants56. The results of this study are consistent with the results33 that reported elevated proline levels in omethoate-treated wheat seedlings. Similarly, Srivastava and Singh57 also observed that the organophosphate insecticide malathion increased proline levels in onion (A. cepa) and also increased superoxide dismutase (SOD) and catalase (CAT) activities, reducing membrane integrity and causing DNA damage. Proline is a nonessential amino acid that is involved in a variety of physiological mechanisms including protein structure formation, protein function determination, maintenance of cellular redox homeostasis, singlet oxygen and hydroxyl radical scavenging, osmotic balance maintenance, and cell signaling57. In addition, proline protects antioxidant enzymes, thereby maintaining the structural integrity of cell membranes58. The increase in proline levels in onions after omethoate exposure suggests that the body utilizes proline as superoxide dismutase (SOD) and catalase (CAT) to protect against insecticide-induced toxicity. However, similar to the enzymatic antioxidant system, proline has been shown to be insufficient to protect onion root tip cells from insecticide damage.
A literature review showed that there are no studies on the anatomical damage of plant roots caused by omethoate insecticides. However, the results of previous studies on other insecticides are consistent with the results of this study. Çavuşoğlu et al.67 reported that broad-spectrum thiamethoxam insecticides caused anatomical damage in onion roots such as cell necrosis, unclear vascular tissue, cell deformation, unclear epidermal layer, and abnormal shape of meristem nuclei. Tütüncü et al.68 indicated that three different doses of methiocarb insecticides caused necrosis, epidermal cell damage, and cortical cell wall thickening in onion roots. In another study, Kalefetoglu Makar36 found that application of avermectin insecticides at doses of 0.025 ml/L, 0.050 ml/L and 0.100 ml/L caused undefined conductive tissue, epidermal cell deformation and flattened nuclear damage in onion roots. The root is the entry point for harmful chemicals to enter the plant and is also the main site most susceptible to toxic effects. According to the MDA results of our study, oxidative stress can lead to cell membrane damage. On the other hand, it is important to recognize that the root system is also the initial defense mechanism against such hazards69. Studies have shown that the observed damage to root meristem cells may be due to the defense mechanism of these cells preventing pesticide uptake. The increase in epidermal and cortical cells observed in this study is likely a result of the plant reducing chemical uptake. This increase may result in physical compression and deformation of cells and nuclei. In addition,70 it has been suggested that plants may accumulate certain chemicals to limit the penetration of pesticides into cells. This phenomenon may be explained as an adaptive change in cortical and vascular tissue cells, in which cells thicken their cell walls with substances such as cellulose and suberin to prevent omethoate from penetrating into the roots.71 Furthermore, the flattened nuclear damage may be the result of physical compression of cells or oxidative stress affecting the nuclear membrane, or it may be due to damage to the genetic material caused by omethoate application.
Omethoate is a highly effective insecticide that is widely used, especially in developing countries. However, as with many other organophosphate pesticides, concerns remain regarding its impact on the environment and human health. This study aimed to fill this information gap by comprehensively assessing the detrimental effects of omethoate insecticides on a commonly tested plant, A. cepa. In A. cepa, omethoate exposure resulted in growth retardation, genotoxic effects, loss of DNA integrity, oxidative stress, and cell damage in the root meristem. The results highlighted the negative impacts of omethoate insecticides on non-target organisms. The results of this study indicate the need for greater caution in the use of omethoate insecticides, more precise dosing, increased awareness among farmers, and stricter regulations. Furthermore, these results will provide a valuable starting point for research investigating the effects of omethoate insecticides on non-target species.
Experimental studies and field studies of plants and their parts (onion bulbs), including collection of plant material, were carried out in accordance with relevant institutional, national and international norms and regulations.
Post time: Jun-04-2025