Abstract
We reported that Al inhibited the Mn toxicity of tea (Camellia sinensis L. ) plants in culture solution. In this report, the relationships between the Mn toxicity inhibition mechanisms by Al and the uptake and distribution of Al, Mn, K in tea plants, and polyphenol, were examined. In the absence of Al, Mn accumulated mainly in the epidermis and cortical layers of absorbing roots (root tip 2 cm) at 100, 300 mg L^<-1> of Mn. Mn and K also accumulated in the upper epidermis and lower epidermis of tea leaves. In the presence of Al (21.6 mg L^<-1>), the competition for the uptake and translocation of Al and Mn existed in tea roots at 100, 300 mg L^<-1> of Mn. The Mn accumulation in tea shoots treated with Al was lower than that in nontreated shoots, and the accumulation of K in epidermis of tea leaves was inhibited by the Al supply. The polyphenol concentration in tea leaves increased at 21.6 mg L^<-1> of Al and 300 mg L^<-1> of Mn. From the above results, the following suggestions have been summarized to explain the mechanisms responsible for the inhibition of Mn toxicity by Al : (1) The translocation of Mn from roots to shoots in tea plants was inhibited because roots give priority to Al uptake. (2) In the presence of Al, cells of tea plants produce large amounts of polyphenol to mask Mn which is absorbed in order to maintain normal growth. This masking effect results in the decrease of the efflux of K from cells and reduces accumulation of Mn and K in the epidermis of tea leaves.
