Commercial Use of Plant Hormones, Apical Dominance & Gibberellins

Question 1

What are the commerical uses of ethene?

Answer 1

• Speeds up food ripening
• Promotes fruit drop (abscission)
• Promotes growth of lateral branches
  
  • (not commercial)

Question 2

What is the role of hormone rooting powder?

Answer 2

Promotoes micropropagation: stimulation of plant growth from cuttings

• The application of auxin to cut shoots stimulates the production of roots
  
  • Advantage as you can propagate plants from cuttings

Question 3

How do hormone weed killers work?

Answer 3

• If the balance of hormones is lost to grow plants, they can die. We want this for weeds
• Weeds interfere with commercial food crop by competing for space, light, water and minerals
• Synthetic auxins act as weedkillers
  
  • Most weeds are dicot (most crops are monocot).
    
    • Synthetic auxins are applied to broad leaved dicots affect metabolism, growth rate becomes unsustainable

Question 4

What are the roles of cytokinins?

Answer 4

• Delay leaf senescence (ageing) - increases shelf life
• Promotes bud/shoot growth in tissue culture
• Promotes growth of lateral buds

Question 5

What are the roles of auxins (commercially)?

Answer 5

• Promote root growth in cuttings
• Produces seedless fruit
• Selective weedkiller

Question 6

What are the roles of gibberellins? (commercially)

Answer 6

• Delays fruit senescence and drop to increase harvesting efficiency
• Improves shape of fruit and size
• Speeds up seed production, germination
• Activates enzymes in stored barley to produce malt for brewing

Question 7

What is apical dominance?

Answer 7

Apical Dominance: The inhibition of the growth of lateral buds (side branches further down the plant)

• Auxins produced in the active apical bud indirectly inhibit lateral bud growth
  
  • The produced auxins produce ABA - which inhibits bud growth
  • Produced auxins also lower the levels of cytokinins (which promote bud growth)

Question 8

What experimental evidence is there for the role of auxins in apical dominance?

Answer 8

• If you remove the apical bud the lateral buds grow
• If you apply synthetic auxins to where the tip has been cut, the lateral buds are inhibited

Question 9

What experimental evidence is there for the roles of gibberellins?

Answer 9

Stem Elongation

• Gibberellins affect the length of internodes (regions of stem between leaves)
• A fungus that produces gibberellins (Gibberella) can grow tall and thin, this same process occurs in plants
• If you apply gibberellins from Gibberella stem elongation occurs

Seed Germination

• If gibberellin biosynthesis inhibitors are prresent, seeds do not germinate
  
  • When the inhibitors are removed the seed germinates
• If gibberellins are applied to mutant variants of seeds that lack the gibberellin synthesis gene, the seed germinates