Abstract: Treated with 0.1 to 1.0 mg/L La(NO3)3 in Hoagland solution, root-pruning masson pine ( Pinus massoniana Lamb. ) seedlings developed the lateral roots 1.75 to 3.75 times more in number than the control. The fresh and dry weight of roots were increased by 33.7 % and 46.4 %. The root length was only in the range of 0.05 to 0.5 mg/L La(NO3)3, had slightly pmmotive effect but when the concentration of La(NO3)3 exceeded more than 1.0 mg/L, the root length of root-pruning masson pine seedling was decreased to 53.3% of the control. The free-lAA content of the lateral root was raised with the increase of La(NO3)3 concentration in cultural solution, while the activity of IAA oxidase was decreased. On the other hand, La (NO3)3 was exerted less pmmotive effect on shoots than on roots.

Key words: La(NO3)3, Masson pine, Root growth, IAA, IAA oxidase