Hormones

Question 1

What are hormones?

Answer 1

Organic compounds (not nutrients) produced by plants to regulate physiological processes.
They move within the plant from the site of production to the site of action.

Question 2

Who first postulated the idea of hormones? When?

Answer 2

Darwin, 1880.

Question 3

Name 5 key hormones.

Answer 3

Auxin,
Gibberellin,
Cytokyinin,
Ethylene,
Abscisic acid.

Question 4

What is the principle auxin?

Answer 4

Idole-3-Acetic Acid (IAA).

Question 5

Where is IAA synthesised?

Answer 5

Meristems, leaf primordia, young leaves, developing seeds.

Question 6

How is IAA transported?

Answer 6

Cell to cell via the cambium and procambial strands.

To the roots via the phloem.

Question 7

What are 9 key effects of IAA?

Answer 7

Stimulation or inhibition of shoot growth.
Stimulates cell enlargement and stem growth.
Stimulates cell division in the cambium layer and strands.
Inhibits growth in lateral buds.
In combination with cytokinin stimulates root initiation on stem cuttings and the development of branch roots and the differentiation of roots in tissue culture.
Mediates the tropistic response of shoots and roots to gravity and light (phototropisim).
Delays leaf senescence.
Promotes apical dominance.
Promotes formation of advantageous roots.

Question 8

Name 3 synthetic products the use auxin.

Answer 8

PGR’s,
Weed killers,
Rooting Hormones.

Question 9

Where is cytokinin synthesised?

Answer 9

Root tips,

Developing seeds.

Question 10

How is cytokinin transported?

Answer 10

Via the xylem to roots and shoots.

Question 11

What are 4 key effects of cytokinin?

Answer 11

Induce cell division in tissue culture in the presence of auxin,
Promotes shoot initiation,
Promotes growth of lateral buds,
Delay leaf senescence.

Question 12

What relationship is there between IAA and cytokinin?

Answer 12

Both need to be balanced in order to maintain healthy root/ shoot ratios.

Question 13

Where is gibberellin synthesised?

Answer 13

Tissues of young shoots and developing seeds.

Question 14

How is gibberellin transported?

Answer 14

Through the xylem and phloem.

Question 15

What nation discovered gibberellin? when?

Answer 15

Japan, 1920’s.

Question 16

What are 5 key effects of gibberellin?

Answer 16

Cause hyperelongation of stems by stimulating both cell division and cell elongation producing tall plants.

Bolting in long day plants in response to long days.

Can cause seed germination in some seeds that normally require cold (stratification) or light to induce germination.

Promote flowering, which can result in more financially profitable flowers to sell due to the increased speed of flower growth. More attractive flowers and larger specimens are also produced.

Fruit setting and growth can be induced by exogenous applications in some fruit.

Question 17

Gibberellin was used in the green revolution to engineer new varieties of what crop?

Answer 17

Wheat. Dwarf varieties that yielded 100% more wheat were created.

Question 18

In what form is ethylene synthesised? In response to what?

Answer 18

Gas, in response to stress.

Question 19

How does ethylene move through a plant?

Answer 19

Diffusion

Question 20

Where is ethylene synthesised?

Answer 20

Ripening or senescing tissue. It is not essential for mature vegetative growth.

Question 21

What are 12 key effects of ethylene?

Answer 21

Downward curvature of petioles.
The fruit becomes soft as pectic substances in cell walls break down and starch converted to sugar.
Increase in fruit respiration.
Release from dormancy.
Shoot and root growth and differentiation.
Adventitious root formation.
Leaf and fruit abscission.
Flower opening.
Flower and leaf senescence.
Fruit ripening.
Post-harvest biology- Controlled ripening during storage and transport or when the fruit is displayed in shops, in sealed packages.
Example:
Bananas are picked when they are green and unripe.
Exposed to ethylene gas in storage to speed up ripening.
‘Fruit bowl effect’

Question 22

Where is abscisic acid synthesised? In response to what?

Answer 22

In roots and mature leaves,
Particularly in response to water stress,
Seeds are rich in ABA which may be imported from the leaves or synthesized in situ.

Question 23

How is ABA transported?

Answer 23

ABA is exported from roots in the xylem and from leaves in the phloem.
Some evidence that ABA may circulate to the roots in the phloem and then return to the shoots in the xylem.

Question 24

What are 4 key effects of ABA?

Answer 24

Water shortage induces an increase in ABA which leads to stomatal closure.
ABA induces storage protein synthesis in seeds.
Affects the induction and maintenance of dormancy in seeds.
Exogenous applications can inhibit growth in the plant.