African Journal of Agricultural Research Vol. 1 (4), pp. 111-117, November 2006          
ISSN 1991- 637X© 2006 Academic Journals

Full Length Research Paper

Gravitropism of loblolly pine (Pinus taeda ) radicles after chemical sterilization of seeds

Dexian He¹ and David B. South²

¹College of Agriculture, Henan Agricultural University, Zhengzhou, Henan 450002, China;

²School of Forestry and Wildlife Sciences and Alabama Agricultural Experiment Station, Auburn University, AL 36849-5418, U.S.A.

*Corresponding author. E-mail: southdb@auburn.edu.

Accepted 10 November, 2006

Certain types of chemicals can affect the gravitropism of roots. In a laboratory study, intact loblolly pine (Pinus taeda L.) radicles (emerged from H₂O₂-treated seeds) exhibited positive gravitropism 8 h after horizontal placement in sterile conditions. The growth angle decreased from almost horizontal (85°) to 21° within one week after treatment (90° is horizontal and 0° is vertical). When seeds were treated with HgCl₂, radicles under sterile growing conditions expressed gravitropism 6.9 h after horizontal alignment. Growth angle changed from 91° to 64° over a 10-day period. Cubic and quadratic functions were used to model growth angle as a function of time. Under similar experimental conditions, radicles from HgCl₂-treated seeds showed a greater degree of gravitropism than those from H₂O₂-treated seeds (as indicated by the growth angle). These results indicate that the gravitropism can occur in sterile environments and that the type of chemicals used to sterilize seeds might affect the rate of geotropic response.

Key words: Loblolly pine, radicle, geotropic growth, microorganism, H₂O₂, HgCl₂, seed sterilization.