Secondary Metabolic Disturbance Induced By Chiral Herbicide Imazethapyr And HO-1 Mediated Mechanism In Wheat Seedlings

As a defense means for plants to cope with external stress,secondary metabolism is sensitive to environmental changes and plays a prominent role in maintaining plant health.Some secondary metabolites are natural nutrients and have edible and medical value.The quantity and quality of crops have been given high expectations due to the rapid increase in global population.In view of the prominent role of weeds on crop loss,the types and expend of chiral herbicides has been predicted to increase in a period of time.Chiral herbicides will unavoidably invade the peripheral soil and groundwater when they are produced and used,causing adverse effects on the ecosystem,and finally condition terrible effects on humans through food delivery.Furthermore,considering the different biological activities of chiral herbicide enantiomers,it is important to evaluate the safety of chiral herbicide use.Therefore,researches on the enantioselective effect of chiral herbicides on non-target plants has significant implications.In this paper,the enantioselective toxicity of chiral herbicide imazethapyr（IM）on secondary metabolism and nutrient levels of wheat seedlings was studied.The effect of heme oxygenase（HO-1）on regulation of iron homeostasis in plants and IM-mediated DIMBOA and iron interactions were studied.The effects of IM on plants were elucidated by biochemical toxicity and possible molecular mechanism.Specific research contents are as follows:（1）The enantioselective toxic effects of IM on wheat seedlings were elucidated from the perspective of secondary metabolism,nutrients and oxidative stress.R-IM could have negative effects on wheat seedlings,which were shown as interference of secondary metabolism,dietary fiber and trace elements.At the third week,the secondary metabolic perturbation was the most significant.The bioactive enantiomer R-IM significantly activated the phenylpropane pathway in secondary metabolism,Phenylalanine aminolyase（PAL）activity and jasmonic acid（JA）content increased by71.17%and 33.01%,respectively.It also promoted the synthesis of phenolic acids,flavonoids,and carotenoids,but inhibited the synthesis of benzoxazines.The DIMBOA content was 55.26%lower than that of the CK group.At the same time,dietary fiber content decreased,and trace elements of Fe,Mn and Zn increased.The antioxidant system also had a strong response to R-IM,and the activities of the three enzymes which have the ability to reduce oxidant damage were significantly induced,the GSH increased first and then decreased.The CYP450 activity of the R-IM group was 23.91%and 86.52%higher than that of the S-IM and CK groups,respectively.（2）The mechanism of HO-1 in the enantioselective toxic effect of IM on wheat seedlings was investigated.In terms of the apparent phenomenon,HO-1 played an important role in the synthesis of plant photosynthetic pigments.The decrease of HO-1 activity would aggravate the etiolation of wheat seedling leaves caused by IM,and the chlorosis of leaves were alleviated after increasing HO-1 activity.In terms of molecular mechanism,HO-1 activity had a significant effect on iron homeostasis.When HO-1 activity increased,heme degradation and free ferrous ion release increased,with ROS and lipid peroxidation product content increasing.HO-1 activity decreased by 15.97%and 23.26%under the inhibitor treatments,while ROS and MDA content decreased by 21.59%and 45.88%under the inhibitor treatments,respectively.HO-1was an important factor of oxidative damage of wheat seedlings induced by IM.（3）The defense mechanism of DIMBOA and the coaction discipline between DIMBOA and Fe by adding IM was explained,which further proved the mechanism of herbicide.DIMBOA content was influenced by Fe content.IM reduces the production of DIMBOA by inhibitingβ-glucosidase,the precursor enzyme of DIMBOA.Meanwhile,HO-1 was activated and the release of Fe²⁺was increased.After the oxidant reaction,the increased Fe³⁺chelates with DIMBOA to form DIMBOA-Fe complex,which further reduces the free DIMBOA content,which suggested IM had a negative effect on unite of DIMBOA and Fe.DIMBOA-Fe has no significant decomposition effect on H₂O₂,which may play a defensive role by chelating free iron ions to reduce the oxidant reaction.Accordingly,deeply explaining the feasible toxic mechanism of IM by the mutual contact in DIMBOA,Fe.