Effects Of Tea Polyphenols And Calcium Ions On Physiological Response,Element Absorption And Lead Subcellular Distribution Of Tea Leaves Under Lead Stress

China is a big country in tea production and trade.Tea industry has always played an important role in national economy and international trade.In recent years,lead pollution is still one of the bottlenecks in the development of tea industry in China,but its quality and safety have been paid much attention to.Tea polyphenol is the general name of polyphenol compounds in tea plant.As a natural antioxidant,it can complex with a variety of metal ions.As an important nutrient element for plant growth,calcium can antagonize with excessive mineral elements to reduce toxicity,reduce the degree of membrane lipid peroxidation and improve the activity of antioxidant enzymes in plants,and alleviate the toxicity of plants by reducing the absorption of heavy metals.Therefore,the related effects of tea polyphenols and calcium on alleviating heavy metal lead stress in tea plants are worthy of in-depth study.In this experiment,"Shuchazao" was selected as the test material,and the hydroponic experiment was used to study the effects of the addition of tea polyphenols and calcium ions on the physiological indexes,element absorption and lead subcellular distribution of tea leaves under lead stress.The test results show that:(1)Under the condition of hydroponic culture,the addition of lead in the nutrient solution will increase the activities of SOD,pod,cat and other enzymes in the mature leaves of tea plant,and increase the contents of soluble sugar,soluble protein,proline,chlorophyll and MDA.The addition of tea polyphenols or calcium ions will reduce the activities of SOD,pod,cat and other enzymes in tea leaves,reduce the content of soluble sugar and MDA,and have no effect on the content of soluble protein,proline and chlorophyll in tea leaves.(2)Under lead stress,the absorption of aluminum,iron,calcium,nickel,copper,manganese,magnesium,zinc and other elements in tea buds decreased compared with the blank control,and the absorption of calcium,nickel,copper,manganese,magnesium,zinc and other elements decreased significantly;The absorption of potassium,molybdenum,sodium and lead was higher than that of the blank control,and the absorption of potassium,sodium and lead was significantly higher;The addition of tea polyphenols significantly reduced the absorption of iron,calcium and lead,and significantly increased the absorption of manganese;The addition of calcium ion significantly reduced the absorption of iron and aluminum,and significantly improved the absorption of copper and calcium.Under Pb treatment,the absorption of calcium,copper,iron,potassium,magnesium,molybdenum,sodium,zinc and other elements in mature tea leaves decreased compared with the blank control,in which the absorption of calcium,molybdenum,iron and copper decreased significantly,and the absorption of aluminum,manganese,nickel and lead increased compared with the blank control,in which the absorption of manganese,aluminum and lead increased significantly;The addition of tea polyphenols significantly reduced the absorption of molybdenum and lead,and significantly increased the absorption of calcium,iron and aluminum;The addition of calcium ion significantly reduced the absorption of manganese,nickel,molybdenum and aluminum in mature tea leaves,and significantly improved the absorption of calcium and lead.(3)Different components of mature tea leaf cells were separated by differential centrifugation.It was found that under lead stress,the cell wall component of tea leaf cells had the highest lead content,accounting for 50.91%,the soluble component lead content accounted for 22.05%,the nuclear and chloroplast component lead content accounted for16.17%,and the mitochondrial component accounted for 10.87%.After adding tea polyphenols,the accumulation of lead in tea leaf cells decreased,and lead was more accumulated in cell wall components,and the content of lead in other components decreased significantly.The addition of calcium ion had no significant effect on the accumulation of lead in tea leaves,but the accumulation of lead in cell wall increased significantly,and the deposition in cytoplasm and vacuole decreased significantly.(4)Scanning and transmission electron microscopy showed that compared with the blank control,the folds on the surface and around the stomata of mature tea leaves under lead stress increased,the cell wall morphology of leaf cells changed significantly,there were more lead deposits in the vacuoles,and the intracellular organelles were seriously damaged;After adding tea polyphenols,the folds on the surface of tea leaves and around stomata were reduced,the lead deposition in cells and vacuoles was reduced,and the atrophy of organelles was less than that of lead treatment;After adding calcium ions,the surface of tea leaves was smooth,the folds around stomata were shallow,and the morphology of leaves was similar to that of blank control.There was no obvious atrophy of organelles in cells.There was a small amount of lead deposition in vacuoles,and the cell wall was thicker than the other three treatments.There was obvious lead deposition in cell wall and organelle edge,and the color of cytoplasm and nucleus was darker.The overall morphology of cells was similar to that of blank control.