9.3 Growth in Plants Cheat Sheet by Arsh.b

Meristems are tissues in a plant consisting od undiff­ere­ntiated cells capable of indete­rminate growth.

Occur at the shoot and root tips.
Responsible for primary plant growth
Give rise to new leaves and flowers.

Auxin efflux pumps can set up concen­tration gradients within tissues - changing the distri­bution of auxin within the plant.
These pumps can control the direction of plant growth by determ­ining which regions of plant tissue have high auxin levels.
Auxin efflux pumps can change position within the membrane and be activated by various factors.

Auxin stimulates cell elonga­tion, so high concen­tra­tions of auxin promote growth as cells become larger.

In shoots, auxin increases the flexib­ility of the cell wall to promote plant growth via cell elonga­tion.

Auxin activates a proton pump in the plasma membrane which causes the secretion of H+ ions into the cell wall.

Additi­onally, auxin upregu­lates expression of expansins, which similarly increases the elasticity of the cell wall.

Growth at the tips of roots and shoots is due to a combin­ation of cell enlarg­ement and repeated cell division.

In the stem, growth occurs in sections called nodes, while the remaining meristem tissue forms an inactive axillary bud.

When auxins are produced n the shoot apical meristem, it promotes growth in the shoot apex via cell elongation and devision.

Apical dominance ensures that a plant will use its energy to grow towards the light in order to outcompete other plants.

Tropisms describe the growth or turning movement of an plant in response to a direct­ional external stimulus.

Photot­ropism is the growth movement in response to a unidir­ect­ional light source.

Hydrot­ropism is growth in response to a water gradient.

Both photot­ropism and geotropism are controlled by the distri­bution of auxin within the plant cells.
- in geotro­pism, auxin will accumulate on the lower side of the plant in response to the force of gravity.
- in photot­ropism, light receptors trigger the redist­rib­ution of auxin to the dark side of the plant.

Microp­rop­agation is a technique used to produce large numbers of identical plants from a selected stock plant.

Steps of microp­rop­aga­tion:

1. Specific plant tissue (typically undiff­ere­ntiated shoot apex) is selected from the stock plant and steril­ised.

3. The explant is treated with growth hormones to stimulate shoot and root develo­pment.

5. Once the root and shoot are developed, the cloned plant cane transf­erred to soil.

Desirable stock plants can be cloned via microp­rop­agation to conserve the fidelity of the selected characteristic.
This process is more reliable than selective breeding because new plants are geneti­cally identical to the stock plant.
This technique is also used to rapidly produce large quantities of plants created via genetic modifi­cation.

Microp­rog­agation is commonly used to increase numbers of rare or endangered plant species.
It is also used to increase numbers of species that are difficult to breed sexually.
It may also be used to increase numbers of plant species that are commer­cially in demand.