| In China,a large number of agrochemicals are put into agriculture production every year,but often accompanied by certain adverse effects on non-target organisms due to unreasonable agrochemicals application.For example,excessive spraying of herbicides may cause phytotoxicity on non-target plants while controlling weeds,and may even pose a risk to human health via the food cycle.In addition,up to 30% of the herbicides currently in use are characterized by chirality,and this proportion is expected to increase.The differences between enantiomers of chiral herbicides have received increasing attention in recent decades,since most of them show different or even opposite herbicidal activity and biological toxicity.The fatty acids in plants play an indispensable role in their growth and metabolism.Firstly,with plant fatty acids as the research entry point,and by using the model plant Arabidopsis thaliana,we revealed the disturbances of fatty acids and related phytotoxicity mechanisms of herbicide dichlorprop in the non-target plant and clarified the differences between the two enantiomers.Secondly,disturbance of lipid metabolism is a signal in the process of Ferroptosis.Considering the similarities between the phytotoxicity of the(R)-enantiomer of dichlorprop((R)-dichlorprop)and Ferroptosis,we explored the associations between the two from the perspective of this new form of cell death,providing a new aspect and idea for revealing the phytotoxicity mechanism of dichlorprop.The main conclusions are as follows.(1)Fatty acids in A.thaliana exposed to herbicide dichlorprop were measured and analyzed from the perspective of the two enantiomers.According to results of GC-MS,three kinds of the most abundant fatty acids in A.thaliana were selected for analysis,namely hexadecanoic acid(C16:0),octadecadienoic acid(C18:2)as well as octadecatrienoic acid(C18:3).The quantitative analysis of plant fatty acids showed that both enantiomers of dichlorprop resulted in significant reductions in fatty acid content.However,(R)-dichlorprop has a much greater influence on fatty acid content than(S)-dichlorprop,reflecting significant difference between the two enantiomers.Moreover,the contents of the two polyunsaturated fatty acids,C18:2 and C18:3,were more severely reduced.In addition,the unsaturation of fatty acids was also significantly decreased under the exposure of dichlorprop.(2)The causes of plant fatty acid disturbances induced by dichlorprop,as well as the enantioselectivity of this chiral herbicide were further analyzed.On the one hand,(R)-dichlorprop caused a significant reduction in the activity of acetyl-Co A carboxylase(ACCase).It indicated that(R)-dichlorprop can affect the key process of de novo fatty acid synthesis by inhibiting the activity of the significant enzyme,thereby resulting in a reduction in fatty acid content.However,such inhibitory effects did not show on ACCase in A.thaliana exposed to(S)-dichlorprop.Moreover,activity of fatty acid synthase(FAS)was not influenced by dichlorprop.On the other hand,plant fatty acids underwent lipid peroxidation and generated a large number of toxic products such as MDA induced by(R)-dichlorprop,leading to an increase in lipid peroxidation level and a decrease in fatty acid unsaturation.Meanwhile,no significant effect on lipid peroxidation level was observed when treated with(S)-dichlorprop.At the same time,dynamic monitoring of lipid peroxidation products and plant morphological changes indicated that the seedlings of A.thaliana experiencing early growth(about three weeks)were more sensitive and vulnerable to the toxicity of dichlorprop.Additionally,the lipid disturbances caused by(R)-dichlorprop further affected the plant cell membrane permeability,doing damage to membrane structure and functions,while(S)-dichlorprop did not cause such damage.Furthermore,both the activities of glutathione peroxidase(GPX)and cytochrome P450 enzyme(CYP450)of A.thaliana exposed to(R)-dichlorprop were significantly increased,but(S)-dichlorprop did not stimulate the stress response of the two enzymes.(3)Focused on the biochemical and morphological characteristics,the relationship between the phytotoxic effects of the(R)-enantiomer of dichlorprop on A.thaliana and the new form of cell death named Ferroptosis were investigated.Firstly,as the exposure concentration of(R)-dichlorprop gradually increased,the oxidative damage and lipid peroxidation level in A.thaliana became more and more serious,and lipid peroxidation products were continuously accumulated.However,the addition of ferrostatin-1(Fer-1),a Ferroptosis inhibitor,alleviated the damages mentioned above.Secondly,with the increase of(R)-dichlorprop exposure dose,the activity of GPX increased first and then decreased.Low-dose exposure activated the GPX activity,while high-dose exposure of the herbicide gradually acting as an inhibitor,and Fer-1 made the activity of GPX go up again.Thirdly,the distribution of iron(Fe)in A.thaliana was abnormally aggregated disturbed by(R)-dichlorprop,but the addition of Fer-1 normalized the Fe distribution.Moreover,the morphological pathological changes of mitochondria in A.thaliana cells treated with(R)-dichlorprop were similar to cells undergoing Ferroptosis,which was alleviated with Fer-1 added.The above research results indicate that the toxicity mechanism of(R)-dichlorprop on non-target plant A.thaliana is closely related to Ferroptosis,providing new ideas and directions for the studies involved in the phytotoxicity of dichlorprop and Ferroptosis. |
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