| Pakchoi(Brassica campestris L.)is a type of leafy vegetable widely cultivated in China.In recent years,with the discharge of industrial sewage,the heavy metal pollution of farmland soil is more serious.Studies have reported that the content of cadmium(Cd)in pakchoi in some areas has far exceeded the safety standards of vegetable consumption in China,which poses a great threat to the health of consumers.Therefore,in this study,pakchoi was used to investigate whether glutathione(GSH)can reduce the accumulation of Cd in the edible parts and alleviate Cd stress in pakchoi,and the related mechanism was explored.The main results are shown below.1.Cd stress caused yellowing symptoms in leaves,photosynthesis and root morphogenesis were significantly inhibited in pakchoi,which resulted in slow growth for pakchoi.In addition,Cd promoted the accumulation of reactive oxygen species(ROS),lipid peroxidation,imbalance of antioxidative system,and ion flocculation in pakchoi.Application of 100 μM GSH significantly attenuated the toxic symptoms of Cd on pakchoi including promoting root elongation and improving biomasses.The content of Cd in roots and shoots of pakchoi was determined.The results showed that exogenous GSH significantly decreased the content of Cd in shoots,but the content of Cd in roots increased significantly,and the translocation rate significant decrease.Root morphology-related indicators including total root length,root surface area,average root diameter,and root tip number and photosynthesis related indicators including photosynthetic pigment content,net photosynthetic rate,intercellular CO2 concentration,stomatal conductance,and transpiration rate were significantly improved.The activities of antioxidant enzymes including SOD,POD,APX,and CAT and the ratios of GSH/GSSG and AsA/DHA were improved significantly,and ion disorder was alleviated by exogenous GSH in pakchoi exposed to Cd toxicity.The above results indicated that exogenous GSH alleviated a series of toxic symptoms caused by Cd on the growth by reducing the accumulation of Cd in shoots of pakchoi.2.In this part,the effects of GSH and BSO on Cd translocation factor were investigated.Pakchoi was pretreated by GSH/BSO revealed that GSH significantly reduced the transport of Cd from roots to shoots,while BSO significantly increased the translocation factor of Cd from roots to shoots.By analyzing the chemical form of Cd in pakchoi,it was found that exogenous GSH could significantly increase the ratio of Cd extracted by sodium chloride solution,while the ratio of Cd dissolved in water and extracted from ethanol significantly decreased,which indicated that exogenous GSH could promote the transformation of Cd form with strong mobility into Cd form with weak mobility in pakchoi.Compared with sole Cd treatment,exogenous GSH significantly increased the transcriptional level of phytochelatin synthase(PCS)gene in pakchoi under Cd stress.At the same time,the contents of PCs including PC2,PC3,and PC4 in roots of pakchoi under different treatment conditions were determined.The results showed that exogenous GSH could promote the synthesis of PCs in the roots of pakchoi under Cd stress.The subcellular components of Cd in pakchoi showed that exogenous GSH could significantly increase the proportion of Cd in soluble components,which indicated that exogenous GSH could enhance the vacuoles Cd sequestration.Subsequently,the transcriptional levels of ABCC1 and ABCC2 transporters located on the vacuolar membrane were detected by qRT-PCR,and the results shown that exogenous GSH could further induce the expression of ABCC1 and ABCC2 compared with sole Cd treatment in pakchoi.In summary,exogenous GSH could enhance the chelation of Cd by promoting the synthesis of PCs in roots of pakchoi,and induce the expression of ABCC1 and ABCC2 to promote the compartmentalization of Cd-PCs complex in root cell vacuoles,Reducd the transport of Cd from roots to shoot,which leading to decreased Cd content in shoots. |
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