Have plants already discovered "anti-gravity" ?

Question

Hi Folks,

A thought occured when planting some vegetable seeds.

OK, seeding compost, warmth, water etc, but how, buried in darkness do they always know how to grow upwards towards the necessary sunbeams?

Have such things as simple vegetables discovered a way of knowing which way is "up" ?

Bob

Answer 1

They follow the source of vitamin D supplied by our Sun baking the Earth in which they are buried.

Answer 2

It's called geotropism or gravitropism, and it's related to plant hormones, in particular one called auxin.  Auxin is a major player in plant growth.  Its effect on plant cells depends on its concentration and where the target cells are located.

The details surrounding geotropism aren't fully worked out, but one hypothesis says that cells near the growing parts of plants (i.e. shoot and root tips) contain special plastid organelles called statoliths.  These statoliths are denser than the rest of the cell, so they settle to the lower portion of the cell, drawn by gravity.  Apparently, auxin is attracted to these statoliths, and so it accumulates in the lower portion of the cells as well.

In stems, cell walls elongate in response to auxin; as a result, the accumulation of auxin the in the bottom portion of the cells causes them to grow faster than the top parts.  In effect, the cells become "bent" upward.

In roots, cell walls have the opposite response to auxin; it actually inhibits their elongation.  Therefore, the bottom portions of the root cells elongate MORE SLOWLY than the top portions, and the roots curve downward.

This is one hypothesis; geotropism isn't fully understood at the moment.  But I hope it helps anyway, and good luck!

Answer 3

Check-out "geotropism" on Google/wikipedia

Plant shoots demonstrate positive geotropism

Plant roots - negative geotropism

Roots also sensitive to water so exhibit positive hydrotropism

Shoots are also sensitive to light - positive phototropism.

Answer 4

the ground must get harder going down so maybe this is how they know?