plant hormones

Question 1

Factors that affect plant growth and development:

Answer 1

Environmental factors (day length and water availability)

Receptors (which allow plants to detect environmental factors)

Genetic makeup of plant
Hormones; chemical messengers (move through phloem or cell to cell)

Question 2

Tropism:

Answer 2

the growth or movement to directional external stimuli (can be positive or negative)

Question 3

Phototropism

Answer 3

responses/growth to light

Question 4

Auxin

Answer 4

Auxin: a plant growth hormone that affects the gene expression in shoots; causes cell elongation and development. Found in the embryo of seeds, meristems of apical buds and young leaves. Only work on plants with auxin receptors.

Question 5

How does auxin work

Answer 5

Affects the patterns of gene expression

Redistribution of available auxin to the side of the stem away from the light source. Plant Auxin is called indoleacetic acid (IAA)

Auxin efflux pumps that move auxin out of cells closer to light (using ATP) to create a high auxin concentration in the space between cells

As a result, auxin moves down the concentration gradient into adjacent cells until (auxin influx) there is a greater conc. Of auxin in darker cells resulting in the elongation of the stem away from the light

Elongation of cells is caused by the expansion of the cell walls

Question 6

Sequence of events in stem causing it to bend towards a light source:

Answer 6

Auxin is produced by all cells in the stem towards the light source
Auxin moves by efflux pump action into the nuclei of cells on the side of the stem opposite to the light
The auxin and a receptor in the nuclei form a complex that activates a proton pump
The proton pump moves protons into the spaces of the cell wall
These protons cause a pH drop, resulting in hydrogen bonds between cellulose fibres of the cell wall breaking
This results in the elongation of the cells away from the light source

Question 7

Auxins are involved in:

Answer 7

Cell division stimulation in most meristematic tissue
Xylem and Phloem differentiation
Lateral Root development in tissue cultures
Lateral bud growth suppression when present in apical bud
Growth of flower parts stimulation
Fruit production without pollination induction

Question 8

propagation

Answer 8

Using knowledge of hormones and meristems to clone plants to produce large numbers of progeny
- a stock plant is used; a meristem is cut off and placed into an agar growth medium with nutrients and hormones to stimulate growth; samples develop into plantlets that grow into a clone of of the cell