Enantioselective Effect Of Three Chiral Herbicides On The Behavior Of Trace Elements And Photosynthesis In Arabidopsis Thaliana

There are a large number of pesticides used in agricultural production each year in China, which is a big threat to environmental health. Nowadays, more than a quarter of the pesticides are chiral, and this ratio is increasing because of the compounds with more complex structures are introduced into use. Enantiomers may behave differently in vivo as their different interactions with biomacromolecules like enzymes and DNA. So enantiomers of pesticides may show opposite herbicidal or insecticidal activity though they share the same physical and chemical properties.It is a hard but important work for us to separate the chiral pesticides with a more simple and economical method, and find out the more active enantiomers for the use of agricultural production. The main conclusions of our research are as followed.(1) Numerous studies have shown that it is necessary for plant development to keep the relative balance of trace elements. In this work, we used IM as a representative chiral herbicide to evaluate its enantioselective effect on the behavior of trace metal elements in Arabidopsis thaliana. We analyzed the content of trace metal elements (Mn, Zn, Cu, Fe) in the shoot and the expression patterns of genes related to the transporter of these four trace metal elements. Six ZIP genes (IRT1, IRT2, ZIP2, ZIP4, ZIP5, ZIP9), three NRAMP genes (NRAMP1, NRAMP3, NRAMP4), two FRO genes (FRO2, FRO3), two COPT genes (COPT1, COPT2), MTP11 and ECA3 coding for metal transporters in leaves and roots of Arabidopsis thaliana were analyzed in our work. The results showed that (R)-IM led to the decreasing amount of Na, P, K, Ca, Mg, Mn, Cu but increasing amount of Fe in the shoot compared to the control and (S)-IM. (R)-IM inhibited the shoot absorption and transporter of trace metal elements compared to the control and (S)-IM. In leaves, (R)-IM induced the up-regulation of FRO3, ZIP2, ZIP4, NRAMP1, NRAMP3, and NRAMP4 compared to the control and (S)-IM, while FRO2, IRT2, ZIP9, COPT1, COPT2 and MTP11 were significantly down-regulated. IRT1, ZIP5 and ECA3 showed no significant difference among all the treated groups. In the root, (R)-IM induced the up-regulation of FRO2, FRO3, IRT1, ZIP4, ZIP9, NRAMP1, NRAMP3, NRAMP4 and ECA3 compared to the control and (S)-IM, while ZIP2, ZIP5 and COPT2 were significantly down-regulated. IRT2, COPT1 and MTP11 showed no significant difference among all the treated groups. Our results indicated that (R)-IM greatly changed the expression patterns of genes coding for the transporters of Mn, Zn, Cu, Fe in leaves and roots of Arabidopsis thaliana compared to the control and (S)-IM. We also found that (R)-IM led to the decrease of chlorophyll a, chlorophyll b and chl a/chl b compared to the control and (S)-IM. (R)-IM induced more production of ROS in leaves and roots than the control and (S)-IM.(2) Other studies have shown that Dichlorprop (DCPP), which acts as plant hormones, showed different herbicidal activity between enantiomers. In our work, we used DCPP as another representative chiral herbicide to evaluate its enantioselective effect on the behavior of trace metal elements in Arabidopsis thaliana. The strategies of this research were the same as previous study on IM. The results showed that (R)-DCPP led to the decreasing amount of P, K, Mg, Mn, Zn, Fe but Na, Ca, Cu showed no significant change compared to the control and (S)-DCPP in the shoots of Arabidopsis thaliana. (R)-DCPP inhibited the shoot absorption of trace elements compared to the control and (S)-DCPP. In leaves, (R)-DCPP induced the up-regulation of FRO2, FR03, ZIP2, ZIP4, NRAMP4 and COPT2 compared to the control and (S)-DCPP, while IRT1, IRT2, ZIP5, ZIP9, NRAMP1, NRAMP3 and ECA3 were significantly down-regulated. COPT1 and MTP11 did not show significant difference among all the treated groups. In the root, (R)-DCPP induced the down-regulation of ZIP2, ZIP4, ZIP9, NRAMP1, NRAMP3 and COPT2 compared to the control and (S)-DCPP. FRO2, FRO3, IRT1, IRT2, ZIP5, NRAMP4, COPT1, ECA3 and MTP11 did not show significant difference among all the treated groups. Compared to the control and (S)-DCPP, (R)-DCPP greatly changed the expression patterns of genes coding for metal transporter in leaves and roots, and led to the decrease of chlorophyll a, chlorophyll b and chl a/chl b, as well as induced more production of ROS in leaves and roots.(3) The effect of bromacil on photosynthesis showed significant difference between enantiomers in Arabidopsis thaliana. Bromacil inhibited the synthesis of photosynthetic pigments, destroyed the self-defense mechanism of photosystem II, and caused irreversible damage to PSII. Bromacil inhibited the expression of genes involved in electron transport and oxygen evolution, and the genes regulating the synthesis of light-harvesting proteins. Based on these reasons, bromacil inhibited the photosynthesis of Arabidopsis thaliana and showed significant enantioselectivity.