Grow plants away from gravity

Science in dialogue

Why does a germ that is underground grow upwards?

The green grows upwards, the roots grow downwards - this is how it is almost everywhere in the plant kingdom. This allows the plants to use their roots to supply themselves with water and minerals from the ground and at the same time stretch their leaves towards the sunlight for photosynthesis. So roots tend to orient themselves downwards and sprouts upwards. But how do the plants know where up and down is?

You know because of gravity. A phenomenon called gravitropism. Small heavy stones, so-called gravire receptors, sit in the root tips of the plants. They ensure that the roots recognize the direction of gravity. How they work can be explained quite well with the following experiment:

Seedlings are rotated horizontally on a centrifuge so that the centrifugal force corresponds to the gravitational pull. Result: They do not grow upwards, but at an angle. This is proof that gravity controls the direction of growth.

Depending on how you stimulate plants, they can respond with changes in the direction of their growth. If, for example, they are brought from their upright position to a horizontal position by means of wind pressure or experimental gravity stimulation, then they usually straighten up again through an adapted growth. Plants also show this reaction in the dark, so it is not dependent on light.

Sprouts, on the other hand, usually grow away from the center of the earth, away from gravity, due to the same phenomenon. Their exact direction of growth is, among other things, also subject to the influence of light, since light is the energy source of plants.

Prof. Dr. J├╝rgen M. Schmitt from the Institute for Plant Physiology at the Free University of Berlin.