Physilogical Damage And DNA Mismatch Damage Repair System Of Soybean Seedling Root Under Cd Stress

Soybean(Glycine Max(L.)Merr.)is the main edible oil,edible protein and feed crop in the world.With the rapid development of modern industrial and agricultural activities,a large number of heavy metals are released into the ecosystem through human activities,causing serious damage to the global ecological environment.Cadmium(Cd)is one of the most common and toxic heavy metal pollutants in ecosystems,which adversely affects plant growth and food production.Cadmium is readily absorbed by plant roots,transported and accumulated in other organs such as stems,leaves and seeds,causing toxic reactions to animals and humans through biological accumulation and bioremediation in the food chain.Cadmium can produce extensive cytotoxicity and genetic toxicity to plants and seriously affect the growth and development of plants.This research adopts the susceptibility to cadmium differences of two soybean varieties liao dou10(LD10,cadmium sensitive)and shennong20(SN20,cadmium insensitive)hydroponic experiment was carried out,the seedlings of two soybean varieties of different concentrations of cadmium(0.25-0.5mg·L-1Cd Cl2)processing,to study the growth inhibition of different concentrations of soybean seedlings under cadmium stress,physiological metabolism,the effect of DNA damage,cell cycle regulation,probes into the plant under cadmium stress response and resistance mechanism,to cultivate soybean varieties with low resistance to cadmium,cadmium accumulation theory basis.The main research results are as follows:1.Cadmium stress affects the growth of soybean seedlingsCompared with the control group,0.25mg·L-1 Cd treatment significantly inhibited the root length of LD10 seedlings with an inhibition rate of 29.84%,but had no significant effect on root growth of SN20 seedlings.When the Cd concentration exceeded 0.5 mg·L-1,the root growth of both LD10 and SN20 seedlings was significantly inhibited.2.Cd stress caused oxidative damage to soybean seedlingsCompared with the control group,0.5mg·L-1 Cd treatment for 4 days can induce the accumulation of excessive reactive oxygen species in soybean seedlings of LD10 and SN20.Under Cd stress,compared with SN20,the contents of O2-,H2O2 and MDA and the degree of damage of root cell membrane in the seedlings of LD10 were higher.Compared with the control group,Cd treatment changed the activity of antioxidant enzymes(SOD,POD,CAT and APX)in the seedlings of these two soybean varieties.Under Cd stress,the activity of antioxidant enzyme in SN20 seedlings was higher than that of LD10.3.The sugar metabolism of soybean seedlings were regulated by Cd stressCompared with the control group,0.5mg·L-1Cd treatment for 4 days significantly increased the starch content in the cotyledons of LD10 and SN20,but decreased the starch content in the roots.At the same time,Cd stress increased the content of soluble sugar in cotyledon and root of LD10 and SN20.4.Cd stress caused DNA damage to root tips of soybean seedlingsCd stress significantly increased the frequency of RAPD polymorphism,and significantly decreased the stability of the genomic template of LD10 and SN20.Compared with LD10,the RAPD polymorphism in root tips of SN20 was higher and the genomic template stability was less under 0.25-2.5mg·L-1 Cd treatment.Compared with the control group,there was significantly up-regulated the expression levels of DNA double-stranded damage repair genes HR(RAD51 and BRCA1)and NHEJ(MRE11 and KU70)in the roots of LD10 and SN20 seedlings under 0.25mg·L-1Cd treatment.5.Cd stress causes cell cycle arrest in soybean seedlingsThe results of FCM analysis showed that Cd stress induced G1/S phase arrest and G2/M phase arrest in root tips of LD10 and SN20 seedlings.Cd stress regulated the expression of cell cycle related genes and DNA damage response genes in root tips of seedlings.6.Effect of soybean MMR gene under Cd stressUnder the Cd stress,MLH1,MSH2 and MSH6 were involved in the identification and repair of DNA damage in the roots of soybean seedlings.MLH1 of MMR system participated in cd-induced G1/S phase arrest in the root tips of LD10,while MSH2 and MSH6 participated in cds-induced G2/M phase arrest in root tips of SN20.7.Cd tolerance mechanism of different soybean varietiesUnder the Cd stress,the expression levels of MSH2 and MSH6 genes in SN20 were higher,and MSH2 and MSH6 initiated the Mut S/ATR/ATRIP signaling pathway,resulting in G2/M cell cycle arrest.However,the repair mechanism of cell volume enlargement,proliferation and replication after G2/M cell cycle arrest could still be carried out slowly,so that SN20 showed higher Cd stress resistance.Due to the low expression of MSH2 and MSH6 in LD10,after the cells sensed DNA damage,they initiated the MLH1-mediated MRN complex mediated ATM signaling pathway,resulting in G1/S cell cycle arrest,inhibition of DNA replication and cell volume expansion,thus resulting in lower Cd stress resistance of LD10.