Abstract:

Objective: This study aims to investigate the biological characteristics of root border cells of Cunninghamia lanceolata and their response to aluminum stress, which could provide important basis for elucidation of response to aluminum stress and selection of aluminum-tolerant germplasms in C. lanceolata. Method: In this study, seeds of C. lanceolata were germinated through aeroponic culture methid. The biological characteristics of root border cells were investigated with the seedlings of C. lanceolata. The response of root border cells to aluminum stress was also surveyed by aluminum ion treatment. Result: It was found that the root tip began to be produced root border cells when the seeds just germinated, and the number of root border cells gradually increased with the elongation of the roots. When the root length was 1.5 cm, the number of root border cells reached the maximum (about 7 497 in average). The cell activity test showed that when the root length was less than 0.5 cm, the activity of root border cells could reach 95%. With the elongation of roots, the activity of root border cells decreased gradually, but basically stabilized around 80%.During the development of root border cells, the activity of pectin methylesterase (PME) in root cap showed its highest level when root length less than 0.5 cm, and then decreased with the root elongation. And, further EGCG treatment indicated that the PME activity was not required for the formation of root border cells but rather related to their spatial separation. The results of aluminum stress showed that Al³⁺ was able to significantly inhibit the root elongation of C. lanceolata seedlings, and this inhibition effect was more obvious after removal of the root border cells. Low concentration of Al³⁺ (100-200 μmol·L^-1) promoted root border cells to secrete more mucilage and form a thicker mucilage layer, which prevented Al³⁺ from adsorbing to the root tips and thus played a protective role for the root tips. Conclusion: The root tips of C. lanceolata seedlings can produce a great number of living root border cells, and the process of their separation into the rhizosphere might be mainly regulated by PME. In response to aluminum stress, these root border cells will secrete more mucilage to reduce aluminum toxicity or protect the root tips of C. lanceolata seedlings from aluminum toxicity.

Key words: Cunninghamia lanceolata, root border cells, pectin methylesterase, aluminum stress