THE ROLE OF STARCH IN THE GRAVITROPIC RESPONSE OF THE LENTIL ROOT

It is well accepted that the amyloplasts of the cap are responsible fo r gravisensing in primary roots. However, roots with starch-depleted p lastids are able to respond to gravistimulus, but their curvature is s lower than that of roots containing amyloplasts. The goal of our exper iment was to analyse the effects of natural variations of statolith st arch in the gravitropic response of lentil roots to a stimulation in t he horizontal position. In lentil seedlings grown in the vertical posi tion for 26 h, the volume of the amyloplasts in the statocytes differe d between individual roots. The amount of starch in the cap was determ ined parallel to the rate of gravitropic curvature. There was no stati stical correlation between the intensity of the gravitropic response a nd the starch content in the statocytes. Lentil roots were treated wit h gibberellic acid (GA(3)) at 32 degrees C in order to reduce the volu me of starch in the statoliths. There was 53% less starch in the cap o f GA(3) treated roots as compared to the cap of control roots. But the re was no relationship between starch content in the cap and the respo nsiveness of the root to a gravistimulus, except when the amount of st arch was small.