Effects Of Tea Pruning And Polyphenols On Organic Acids Secretion From Roots And Mineral Contents In Camellia Sinensis

Tea plants (Camellia sinensis L.), which have been widely reported to accumulate aluminum (Al) and lead (Pb), grow well in highly acid soils (optimal pH is 4 to 5) containing high levels of these two metals. Pb induced toxic effects on different systems and apparatuses, and Al was a neurotoxin whose toxic effects were particularly in patients with chronic renal failure. The ability of tea to accumulate Al and Pb would affect consumer trust. Therefore, an understanding of the physiological mechanism of Al and Pb tolerance and hyperaccumulation is crucial for improving tea production and quality.Tea pruning contain various mineral nutrients and special biochemical (tea polyphenols), and the amount of branches and leaves returning to the soil is considerable. It is essential to study the effects of tea pruning and ployphenols on plant growth and development under different conditions. Here, the responses of tea plants under Al and Pb stresses for 15,35,55,75 and 95 d were analyzed to investigate the effects of Pb and Al on the secretion of low molecular mass organic acids from roots and mineral uptake. Then, we studied the effects of tea pruning and ployphenols on root exudates, mineral uptake and hyperaccumulation of Al and Pb under different conditions. Our test data supports the following conclusions.Tea polyphenols added in nutrient solution inhibited the uptake of Ca, Mg, Fe, Mn, Zn and growth rate and induced citric and succinic acids efflux from roots. However, the aqueous solution of tea pruning added in nutrient solution promoted the uptake of K, Ca, Mg, Fe, Mn, Zn, Al and growth rate and at the meantime induced oxalic, malic, citric and succinic acids efflux from roots. Besides, the aqueous solution of tea pruning also lowered pH of collection solution, which was closely linked with organic acids secretion changes, indicating tea pruning may result in soil acidification. Therefore, it is not advised to return tea branch and leaves back to the soil.Mechanisms of Al and Pb tolerance with regard to the aspect of roots exudates and mineral uptake affected by Al and Pb stresses were described. The results indicated that more oxalic, citric and malic acids from root exudates were promoted by Al stress, and more citric, tartaric and succinic acids were released to alleviate Pb toxicity, and malic acid was also related to Pb stress. Al and Pb uptake by tea plants both restrained mineral uptake and the mechanisms were also discussed. The restrain caused growth inhibition under Al and Pb stresses. Translocation of Pb and Al from roots to shoots could be one of the limiting factors for bioconcentration of these two metals in shoots, while the pattern of Al accumulation and distribution differed from that of Pb.The later article planed to investigate the effects of tea pruning and ployphenols on accumulation of Pb and Al under Pb and Al stress. The results showed that the addition of high amount of tea ployphenols alleviated Pb toxicity by decreasing Pb uptake, while low levels of tea ployphenols promoted Pb absorption and improved the mobilization and phytoavailability of Pb. Although tea polyphenols inhibited the absorption of mineral nutrition, a synthesis analysis indicates addition of high amount of aqueous solution of tea pruning or ployphenols accelerate growth and reduce the absorption of Pb. Under Al stress, low amount of tea polyphenols had no obvious influence on Al accumulation, while the high amount of tea polyphenols reduced Al uptake, considering inhibitory effect of tea polyphenols on mineral uptake, addition of tea polyphenols or the aqueous solution of tea pruning is not the appropriate choice to alleviate Pb toxicity.