Lab #8 - Plant Hormones & Experimental Analysis

Lab Objectives

• Understand the roles and production sites of the five major plant hormones.
• Focus on Auxin (IAA) and Gibberellin (GA) effects.
• Examine how synthetic hormones impact plant growth.
• Perform statistical analyses: variance, standard deviation, and ANOVA.

The Five Major Plant Hormones

1. Auxin (IAA)

• Role:
  • Cell elongation
  • Inhibits lateral bud growth (apical dominance)
  • Embryo development
  • Fruit maturation
• Produced in:
  • Shoot tips (apical meristems)
  • Young leaves
  • Seed embryos
• Effect:
  • Promotes vertical growth and root production

2. Cytokinin

• Role:
  • Cell division (mitosis)
  • Promotes shoot formation
  • Delays aging
  • Stimulates flowering & fruit development
• Produced in:
  • Root tips
• Effect:
  • Encourages growth of new shoots and seed germination

3. Gibberellin (GA)

• Role:
  • Internode elongation (stem height)
  • Promotes bolting
  • Helps seeds break dormancy
• Produced in:
  • Root and shoot tips
• Effect:
  • Stimulates fast stem and seed growth; flowering

4. Abscisic Acid (ABA)

• Role:
  • Slows growth
  • Promotes dormancy
  • Closes stomata during drought
• Produced in:
  • All major organs (especially chloroplasts)
• Effect:
  • Prepares plant for environmental stress (e.g., winter)
  • Triggers leaf drop

5. Ethylene

• Role:
  • Ripening and senescence (aging)
• Produced in:
  • Ripening fruits
  • Aging flowers
  • Germinating seeds
  • Wounded tissue
• Effect:
  • Promotes fruit ripening, flower and leaf drop, senescence

Hormone Interactions

• Auxin + Cytokinin: Control apical dominance
  • High auxin inhibits lateral buds.
  • Removing apical tip reduces auxin → side buds grow (turning plant bushy).
• GA vs ABA:
  • High GA → triggers spring growth (bolting, flowering).
  • High ABA → maintains dormancy (winter survival).

Activity 1: Auxin & Meristematic Tissue

Experimental Groups:

• Group A: Intact, No IAA
• Group B: Removed, No IAA
• Group C: Intact, Yes (5% IAA)
• Group D: Removed, Yes (5% IAA)

Prediction:

• Tallest: Group C (intact tip + synthetic IAA)
• Shortest: Group B (no tip, no IAA)

Activity 2: Gibberellin, Dwarfism & Bolting

Experimental Groups:

• Group E: Wildtype, No GA
• Group F: Wildtype, Yes (2 mM GA)
• Group G: Dwarf, No GA
• Group H: Dwarf, Yes (2 mM GA)

Prediction:

• Most Growth: Group F (Wildtype + GA)
• GA Effect on Dwarfs: Group H should grow taller than Group G.

Statistical Analysis

Standard Deviation (SD) & Variance Process:

1. Find mean of all values.
2. Subtract mean from each value (calculate deviation).
3. Square deviations.
4. Add squared values together.
5. Divide by total number of values to get Variance.
6. Square root of variance to obtain Standard Deviation.

ANOVA (Analysis of Variance):

• Purpose: Compare means of 3 or more groups.
• Hypotheses:
  • H₀: All means are equal.
  • H₁: At least one mean is different.

ANOVA Terms:

• SSb: Between group variance.
• SSe: Within group variance (error).
• MSb = SSb / dfb
• MSe = SSe / dfe
• F = MSb / MSe.

Decision Criteria:

• If F > critical F, then reject H₀ (indicates significant difference).
• If F < critical F, then accept H₀ (no significant difference).