Adaptation 5

Question 1

What are the 5 classical plant hormones, their functions, and some general properties of plant hormones

Answer 1

Plant hormones

• not produced in glands
• transported around plant
• exert action both locally and at a distance
• active at low concs.
• often not specific in their action (can elicit multiple responses)

Auxins (IAA) - cell expansion, lateral root initiation, apical dominance, fruit growth

Cytokinins (CK) - cell division, shoot organogenesis, leaf senescence

Abscisic Acid (ABA) - Seed/embryo dormancy, stomatal opening/closure

Gibberellins (GA) cell/stem elongation, flowering, seed germination

Ethylene (C2H4) - fruit ripening, flower senescence, leaf abscission

Question 2

Describe mechanisms of auxin and gravitropism in roots when verticle and horizontal

Answer 2

Roots:

Verticle

• when roots are vertical, statoliths (gravity sensing starch grains) settle onto the bottom ends of statocytes in the root cap.
• Auxin moves upward equally on all sides. Cells elongate equally on all sides
• > root grows downwards

Horizontal

• when roots are verticle, statoliths settle to the sides of statocytes that now face downward
• causes auxin to be transported to the lower side of the root, inhibiting cell elongation
• cells on the upper side continue to elongate
• > root bends downwards

Question 3

Describe the mechanism involved with auxin and apical dominance

Answer 3

• Auxin in Primary shoot apex suppresses growth from axillary buds
• prevents branching
• central stem is dominant over side stems
• removing the bud allows dormant axillary buds to flourish into branches, making plants ‘bushier’

Question 4

Commercial application of synthetic auxins?

Answer 4

Rooting powders -> promote root growth

Herbicides

Question 5

Gibberellin functions,

• its role in a-amylase production in seed germination
• commercial uses

Answer 5

Produced in apical buds, roots, young leaves and seed embryos

Stimulates both cell division and cell elongation
-> promotes stem elongation, flowering and seed germination

GA breaks dormancy of seeds

• > mobilises energy reserves by inducing amylase production in aleurone cells
• > amylase is secreted into endosperm and hydrolyses starch to produce sugars

Question 6

Function of abscisic acid

Answer 6

Regulates guard cell turgor -> induces stomatal closure by increasing turgor (guard cells swell up and create gap)

Inhibits seed germination

Question 7

Function of cytokinins

Answer 7

Synthesised in actively growing tissues

Promote cell division in shoots and roots
- affect apical dominance, axillary bud growth and leaf senescence

ratio of auxin:cytokinin important for plant growth, disruption can cause dense outgrowth of shoots from one point

Question 8

Ethylene production and function

- effect on fruit shelf life

Answer 8

• important in developmental and stress res[pmses
• produced during seedling growth, flower development, fruit ripening

important roles in leaf and petal aging + abscission
- defense against osmotic stress and pathogen attack

influences cell expansion, often with auxin
- cells expand in all direction rather than elongation

Important in fruit ripening

• production of ethylene
• increase in respiration
• wall softening
• pigmentation/aromas develop

it is thought that ethylene induces transcription factors which cause these effects
- genes could potentially be targeted/inhibited to increase fruit shelf life