Antioxidant Protection By Melatonin On The Regulation Of GSH Synthesis And Metabolism Of Chlamydomonas Reinhardtii Under Cadmium Stress

Heavy metal pollution is one of the most threatening challenges to the natural environment and human health.The accelerated industrialization of world production has led to its widespread presence in the soil and water environment,directly impacting natural organisms.However,several techniques have been developed for the removal of heavy metal ions from environmental media,which not only require significant costs but also have a high-risk rating.Green algae such as Chlamydomonas reinhardtii offer a safer,less costly,and more effective ecological approach to the treatment of heavy metal ions in wastewater because of their adsorption properties.However,the adsorption of heavy metal ions by C.reinhardtii can be affected by their toxic effects,resulting in the growth,reproduction,and physiological and biochemical functions of the algal cells.Melatonin has the property of helping the plant body mitigate damage from adversity stress when the plant is under biotic/abiotic stress.So,can melatonin help C.reinhardtii to mitigate the stressful effects of the heavy metal cadmium on its growth?In this study,we investigated the effects of the heavy metal cadmium on C.reinhardtii and the effect of melatonin on the growth of C.reinhardtii in a cadmium-contaminated environment.These include algal cell morphology,chlorophyll content,chlorophyll fluorescence parameters,changes in enzyme activity and gene expression of the antioxidant system,and changes in the content and gene expression of various substances in the As A-GSH cycle.In this way,a strong case can be made for the functional application of melatonin and the mechanism of heavy metal detoxification in C.reinhardtii.The main conclusions drawn from the above study are as follows.A.With the external application of melatonin,the cadmium-stressed algal sap gradually regained its green color,the cell morphology became intact and the growth and cell morphological damage caused by cadmium ions was alleviated.B.The chlorophyll content,photosynthetic efficiency,and photosynthesis-related genes of C.reinhardtii cells were significantly increased by external application of melatonin during Cd stress.These levels were significantly reduced in the melatonin-silenced strains.This indicates that the presence of melatonin can effectively enhance the photosynthetic capacity of C.reinhardtii and alleviate the damage caused by cadmium toxicity.C.The use of exogenous melatonin or the expression of endogenous melatonin genes can p-regulate the expression of antioxidant enzymes such as SOD1,CAT1,and FSD1 inC.reinhardtii cells under cadmium stress.This will increase the activity of antioxidant nzymes such as CAT,POD,and SOD in the cells and reduce the accumulation of non-enzymatic substances such as MDA,O₂^-.and H₂O₂ in the algae,thus alleviating the damage caused by Cd to the cells.D.Under cadmium stress,external application of melatonin up-regulated the expression of various genes in the GSH metabolic pathway GSH1,GPX5 and GSHR1,enhanced the enzymatic activities of APX and GR,and significantly increased the contents of GSH,As A,and DHA in the As A-GSH cycle pathway.This reduces the accumulation of ROS levels and accelerates the clearance and translocation of intracellular cadmium ions by C.reinhardtii cells.