what in a plant tells it to grow its roots down and grow its stem up?
In: Biology
Most plants have a “hormone” or chemical that was named I believe gravitron or gravitran or whatever. Anyway, this chemical pretty much stops plant growth but the thing is that this chemical
falls with gravity through the plant. The plant will always grow in the opposite direction of this chemical because it can’t grow where the chemical is. That’s why lots of plants have a Christmas tree or pine tree shape. The chemical is produced near the buds and as the tree grows the chemical doesn’t really make it to the bottom of a tall tree and the branches down there can start to grow outwards. If you turn a potted plant over, the chemical will then start draining to the now bottom of the plant and they’ll make it start growing up again. You turn the plant upside down, the gravitron chemical that was on the top (now bottom of the plant) will begin to fade over time as the chemical falls to the new bottom due to gravity and soon the plant will bend back over and grow up.
Stems share half of the roots dna and half of the leaves dna, so id imagine the roots are more attracted to certain materials and don’t contain very much of this chemical or If the roots do use the chemical it may have a different effect on the dna of roots but generally the roots are attracted to certain chemicals and just go through mitosis and grow.
The full picture is still being studied, but auxin (a plant hormone) plays a significant role. Auxin prevents cells from getting longer and the [Cholodny–Went model](https://en.wikipedia.org/wiki/Cholodny%E2%80%93Went_model?wprov=sfla1) says that the auxins move to the shady side of the growth point. The opposite cells then get longer, which bends the tip towards the light.
In the roots the auxin goes to the lower side and the other side gets longer, bending the tip down.
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