Types of plant geotropisms

Question

Write down the types of plant geotropisms? Why do root and stem present opposite geotropisms?

Answer 1

The types of geotropisms are positive geotropism, that in which the plant grows for the gravitational force, as for instance in roots, and the negative geotropism, which against the gravitational force, for instance, in stem. Stem geotropism and Root geotropism are opposed because of different sensitivities to auxin concentration in these structures. The following experiment can demonstrate phenomenon: Root and Stem are placed in a horizontal position (parallel to ground) and naturally auxins concentrate along with their bottom part.

Under this situation it is observed that the stem grows upwards and root grows downwards. This occurs because in stem the high auxin concentration in bottom creates these sides grow (longitudinally) more and the structures arcs upwards. In root the high auxin concentration in the bottom inhibits growth of this side and upper side grows more making the root to curve downwards.