Abstract: The study of plant gravitropism mechnism relates to growth and development of plant in microgravity enveronment. Gravity responses tests on ground-based gravity field (1 x g) were carried out. The results indicated that gravity caused asymmetrical distribution of peroxidase in both upperside and under side of the root tip of horizontally postioned seedlings; the root tip grew towards the high calcium (Ca2+ ) side of horizontally seedlings in gravity field; when the shoot apex of upsidedown positioned seedlings were illuminated with lamp, their negative geotmpism was lost.