Effects Of Glyphosate And Cadmium Combined Stress On Maize Seedlings

Nowadays,thepesticideresidueandthepollutionof heavy metal have been aroused widespread public concern.In order to investigate the underlying mechanisms of effects on maize seedlings under the combined stress of glyphosate?PMG?and cadmium?Cd?,the pot experiments were carried out,including a single treatment with one of the PMG concentration sets(0,1.25,2.5,5,10 and 20 mg·kg^-1)and a combined treatment together with one of the concentration sets of PMG(the concentration of 0,1.25,2.5,5,10,20 mg·kg^-1,respectively)and 5 mg·kg^-1of Cd²⁺.The maize seedlings antioxidant enzymes?peroxidase POD,catalase CAT and superoxide dismutase SOD?,malondialdehyde?MDA?content,chlorophyll content,chlorophyll fluorescence dynamic curve and related parameters,and metabolite content?amino acids,carbohydrate,organic acid,resistant substances,etc.?were determined by using spectrophotometry,a continuous excitation fluorometer and GC-MS analysis techniques.The data were processed and analyzed by means of principal component analysis and other relevant statistical analysis methods.The main results are as follows:1.With the increase of PMG concentration,the growth indexes?plant height,root length,plant fresh weight,root fresh weight?and antioxidant enzymes activities?SOD,POD,CAT?of maize seedlings showed a trend of increasing first and then decreasing.Also,the concentration of PMG at 5mg·kg^-1 and 2.5 mg·kg^-1 were the sensitive points of the four kinds of growth indexs and antioxidant enzymes activities under the single stress of PMG and the combined stress of PMG and Cd,respectively.The content of MDA in the maize seedlings was increasing by the two kinds of stress induction.2.With the increase of PMG concentration,two kinds of stress induced the chlorophyll content of maize seedlings with a trend of increasing first and then decreasing.The concentration of PMG at 5 mg·kg^-11 and 2.5 mg·kg^-1were the sensitive points of the chlorophyll in maize seedlings under the single and combined stress,respectively.The effects of PMG and Cd stress on photosynthesis of maize seedlings were evaluated by using fluorescence kinetics and related fluorescence parameters(M_O??_PO??_O??_EO??_DO?ABS/RC?TR_O/RC?ET_O/RC?DI_O/RC?PI_ABS),and the results were basically consistent with the indicators of seedlings growth,antioxidant enzyme activity,and chlorophyll content.3.Forty-one kinds of metabolites on maize seedlings were identified by using GC-MS technology combined with the automatic mass spectral deconvolution and identification system?AMDIS?,including six amino acids,seventeen organic acids,twelve carbohydrates and six resistant substances.?1?The results of principal components analysis showed that the different treatment groups can be clearly distinguished under the two kinds of stress,and the differences among the metabolites were significant.The four repeated scatter in the same treatment are relatively concentrated and the reproducibility was preferable.?2?The results of multivariate analysis of variance showed that the two kinds of stress had significant effects on the rest of the metabolites of maize seedlings,except serine and gulonic acid for the single stress of PMG and methyl phosphate for the combined stress.There is interaction between PMG and Cd,PMG and Cd both affected the changes of the metabolism of maize seedlings.?3?The results of maize seedlings metabolic pathway analysis showed that the content of?-alanine,most carbohydrates,organic acids and resistant substances in maize seedlings were increased under the two kinds of stress.In general,the content of?-alanine,carbohydrates,and organic acids under the combined stress was higher than that of PMG single stress.?4?The metabolic pathway of maize seedlings showed that the two kinds of stress had roughly the same effect on the amino acid,tricarboxylic acid cycle,and resistant substances metabolism of seedlings,but showed significant differences in carbohydrates metabolism.The differences in carbohydrates metabolic pathways between single and combined stress are mainly caused by Cd²⁺.In summary,both the single stress of PMG and the combined stress of PMG and Cd had different degrees of influence on growth physiological indexes,photosynthetic indicators and metabolites of maize seedlings.The concentration of PMG at 5 mg·kg^-1 and 2.5 mg·kg^-11 was the sensitive points of the growth of maize seedlings under the single and combined stress,respectively.Compared the single effect of PMG,Cd²⁺aggravated the damage to the apparent,physiological function and metabolites of maize seedlings.