Gavitropism of Pine Radicles in the Dark

Although gravitropism of maize (Zea mays L.) roots is dependent on light, it is not known if light affects the gravitropism of pine radicles. Therefore, seeds of slash pine (Pinus elliottii Englm.) and loblolly pine (Pinus taeda L.) were germinated under constant light or constant darkness. A gravitropic set-point angle (GSA) of 90° indicates the radicle is pointed horizontally while a GSA of 0° indicates the radicle is growing toward the center of the earth. After 20 days from sowing, the GSA was less than 10° in both light and darkness. Therefore, gravitropism of both pine species occurred in the dark. The presence of light initially stimulated gravitropism but this effect was ephemeral. After 25 days from sowing, there was no significant difference in radicle growth among light treatments, suggesting that darkness did not affect pine radicle gravitropism. However, light did increase germination of both species. Radicle length was slightly increased when seeds germinated in the dark.