Question

In the shoots of plants, do auxins cause curvature and elongation of the cells or allow them to grow faster? Or is it both?

In "bitesize" they say that cells in the shoots of plants grow more when there is a higher concentration of auxins....

Yet my textbook says that auxins only cause curvature....

So what does "bitesize" mean when they say that more cells grow when there's more auxins?

I'm terribly confused.... And any help would be greatly appreciated,
All the best!

Answer 1

Auxins affect growth of shoots by promoting cell elongation and control phototropic response due to differential cell elongation.

Explanation:

Auxins enhance shoot growth by causing cell elongation and not by causing increase in number of cells. Thus auxins do not promote growth by addition of more cells by enhancing meristematic activity.

Phtotropic response of shoots is also caused by differential cell elongation in shoot on the side towards light and away from light.

Auxins are metabolized in shoot apex and move down wards in the shoot.

The rate of cell elongation increases with an increase in concentration of auxins.

The auxins are sensitive to light, The auxins are either oxidized on the side exposed to light or move towards the other side. The concentration of auxins becomes higher on the side away from light as compared to the side towards light.

The cells on the side away from light elongate more than those on side exposed to light. The shoot thus grows toward light (positive phototropic response).

Similarly geotropic responses in root are also due to differential cell elongation caused by differential concentration of auxins on the side away from gravity or towards gravity. The rate of cell elongation decreases with an increase in concentration of auxins ( response to auxins just the reverse to that in shoot).