Genotvpic Difference Of Tea Plant Resisting Aluminum Toxicity And Its Mechanism

Tea (Camellia sinensis L.) is an Al-tolerant and Al-accumulating plant, and it can accumulate up to30,000mg Al3+kg-1in mature leaves, which demonstrates the ex-traordinary capacity to accumulate and tolerate Al. In recent years, serious soil acidi-fication leaded to more and more aluminum dissolved in tea garden soils which cor-respondingly increased aluminum content in tea leaves. And with the expansion of tea products, the negative effect of such a high concentration of aluminum got people’s attention. Although there had a lot of reports on the mechanism of Al tolerance in tea plants, the difference of accumulation and tolerance among different genotype tea plants was not studied yet. This paper mainly to screening the varieties as aluminum cumulative differences, and studied its mechanism of genotypic difference from the physiological response, aluminum distribution in tea leave under tissue and subcellu-lar levels, and to provide theoretical basis for breeding low Al-accumulation type of tea varieties in future. At the same time it was also discussed the effects of tea poly-phenols on alleviating aluminum in soil activated effect and tea polyphenols on alu-minum toxicity in barley. The main research results are as follows:(1)Two kinds of tea varieties (pingyangtezao and wuniuzao) were selected to in-vestigate the effects of aluminum (Al) on the growth of tea plants in solution culture. The results showed that the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were significantly higher in tea leaves treated with0.4mM Al3+than control(no Al3+), and the content of malondialdehyde (MDA) was reduced under Al treatment However, differences of those indexes were observed in two va-rieties. Therefore, the sensitivity to Al toxicity of these two varieties is different, and it was inferred that there is a genotypic difference for response of tea varieties on Al toxicity.(2) Hematoxylin staining results showed that the absorbed site of aluminum in tea root mainly located in the apical tip. The Al in cell mainly distributed in the cell wall of root tip cells, and accounts for about60～70%of the total Al in cell. With the increased concentration of aluminum in culture medium, pH also decreased. (3)The Al content in the leaves was determined among51tea cultivars and sig-nificant genotypic difference in Al accumulation was observed. The Al content in Zhenghedabaicha was the highest, up to2493.03mg kg-1, four-fold higher than the lowest variety Zhenong25(587.19mg kg-1). All varieties were classified into three groups (high-, medium-and low-Al content group) as its A1content. Aluminum loca-lized in cell walls accounted for about74%of the total A1content for each cultivar, which suggested that cell walls acted as important organism for Al accumulation in tea plant. The highest concentration of Al was found in the residual fraction, which indicated that the toxicity of leaf Al is lower to tea plant. The proportion of Al ex-tracted by0.6M HC1was higher in young leaves than mature leaves, which suggested that Al was mainly bound to oxalate ligands in young leaves and oxalic acid might plays an important role in the resistance of young leaves to A1toxicity. The propor-tion of A1extracted with H2O from mature leaves was higher than that from young leaves. The A1content in extract solution treated with pectin enzyme and cellulose enzyme were increased significantly, and the effect of pectin enzyme is better than that of cellulose enzyme. There are no relationship between A1content in leave and pectin content, and Al content and cellulose content in tea leaves.(4)The addition of tea polyphenols could effectively increase the content of available Al in soil. The contents of exchangeable aluminum and soluble aluminum in soil increased with addition of tea polyphenol in the range of pH3.5-5.5. The activa-tion effect of tea polyphenols on soil aluminum reduced with the culture time, indi-cating that it may be due to tea polyphenol deposition which is caused by oxidation. The results also hinted that tea polyphenols had a potential in phytoremediation of heavy metal contaminated soil as a natural heavy metal chelating agent.(5) The mitigation effects of tea polyphenols on aluminum toxicity in barley was observed by solution-culture experiments. The results showed the barely treated with tea polyphenols and aluminum grown better than those treated with aluminum only, and its height and root length both increased significantly. The activities of SOD and CAT in leaves treated with tea polyphenols were both enhanced compared to the treatments adding Al only.