Abstract
There has been no convincing explanation on a mechanism inducing plagiogravitropism of lateral roots. The present work deals with gravitropic features of Vigna angularis lateral roots during the course of their growth and morphometric analysis of root caps, columella cells and amyloplasts. They modified their gravireactions several times during the course of their development: a first horizontal-growth stage when they grow in the cortex of primary roots (stage I), a sloping-down growth stage from their emergence to a length of about 1 mm (stage II), a second horizontal-growth stage (stage III) from a length of about 1 to that of over 4 mm and a curving-down stage thereafter (stage IV). The columella cells were not fully differentiated in the stage I but the turning point from the stage I to II was associated with the development of amyloplasts which were able to form a sediment. Amyloplasts were significantly small in the lateral roots over 10 mm long compared with those in ones 0 - 10 mm long. This dimensional decrease of amyloplasts may be partially involved in weakening gravisensing in the stage III.
