EFFECTS OF GRAVITROPIC STRESS ON THE DEVELOPMENT OF THE PRIMARY ROOT OF LENTIL SEEDLINGS GROWN IN-SPACE

Root growth and cell differentiation were analysed in lentil seedlings grown (1) in microgravity (F mu g), (2) on the 1 x g centrifuge (F1 x g), (3) in microgravity and placed on the 1 x g centrifuge for 4 h [F (mu g + 1 x g)], (4) on the 1 x g centrifuge and placed in microgravit y for 4h [F(1 x g + mu g)]. In microgravity, there were strong oscilla tions of the root tip, even when the seedlings were grown first on the 1 x g centrifuge [F(1 x g + mu g)]. In the [F(mu g + 1 x g)] sample, the roots grown in microgravity were oblique with respect to the 1 x g acceleration when the seedlings were placed on the centrifuge. They w ere therefore gravistimulated. However, root length was similar in the 4 samples after 29 h of growth and growth rate of the root was the sa me between 25 h and 29 h although it appeared to be slightly greater i n the [F(mu g + 1 x g)] sample. Cell elongation was analysed as a func tion of the distance from the root cap junction. Cell length was simil ar in the seedlings grown in microgravity or on the 1 x g centrifuge. The transfer from the 1 x g centrifuge to microgravity [F(1 x g + mu g )] did not modify cell elongation in the roots. Cell length in the roo ts which were grown in microgravity and gravistimulated [F(mu g + 1 x g)] was different from that observed in microgravity but this was only due to gravistimulation. Thus, gravity does not have an effect on cel l elongation when the roots are strictly oriented in the vertical posi tion but it does as soon as the root tip deviates from this orientatio n.