Abstract: In order to investigate the effect of aluminium (Al) on root growth of tea plants [Camellia sinensis(L.) O. Kuntze], Anjibaicha tea plant was selected as study material with different Al concentrations for 28 d. Then, the phenotypic differences and parameters of roots, activities of the Expansins and xyloglucan endotransglucosylase (XET), and the gene expression level of Expansins and XTHs, which were related with root growth and key proteins of cell wall were assayed. The results showed that the Al could promote the root growth of tea plant on phenotypic and parameters. The treatment with 0.4, 1.0 mmol·L^-1 Al showed significant (P<0.05) difference with control, as the root total length was increased by 206% and 209%, respectively, the number of root tips was increased by 175% and 166%, respectively, the root surface area was increased by 227% and 286%, respectively, and the root volume was increased by 246% and 385%, respectively. Correspondingly, the gene expression level of CsEXPB14 and the expansins-like gene CsEXLA8 in the roots treated with 0.4 mol·L^-1 Al were significantly (P<0.05) higher than those without Al or with 4.0 mmol·L^-1 Al. The expansins activity in the roots with 0.4 mmol·L^-1 Al was higher than other treatments and was increased by 84.3% as compared to the control. The expression level of CsXTH14 in the roots with 0.4, 1.0 mmol·L^-1 Al were significantly (P<0.05) higher than the other treatments, and XET activity was increased with the elevated Al concentration, and was significantly (P<0.05) inhibited until the Al concentration reached up to 4.0 mmol·L^-1. The gene expression level of Expansins and XTHs, the activities of XET and Expansins showed a positive correlation with root growth of tea plant, which indicated that Al (≤1 mmol·L^-1) could increase XET and Expansins activity by promoting the gene expression of Expansins and XTHs, hence, promote root growth of tea plants.

Key words: environmental stress, plant nutrition, beverage crop, gene expression, root growth