Abstract

Dexian He and David B. South

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.