Plant Hormones and Responses in Ecology

Class Announcements

  • Good morning everyone; hope you're having a great week.
  • Upcoming assessments:
    • Entrance quiz on population ecology will be available online in a couple of hours.
    • Exit quiz on plant development scheduled for Friday.
  • Office hours today after class until 3 PM for any discussions or inquiries about midterm, final, or class subjects. Special event: making animal balloons during this session.
  • Additional office hours on Thursday from 1 PM to 2:30 PM via Zoom, but cannot make balloons online.
  • Contact via email: bi111wu.ca

Overview of Today's Class

  • Focus on plant hormones and their role in physiological differences and environmental responses in plants.
  • Discussion about the transformation of wild cabbage (Brassica oleracea) into various cultivars and their significance in our diets.
  • Explore how plants respond to gravity and light through hormonic changes.

Plant Hormones

Overview

  • Plant hormones are crucial for regulating growth and development.
  • Importance of understanding the balance and antagonistic interactions between different hormones for specific growth patterns.

Major Classes of Hormones

  1. Gibberellin

    • Location of Production: Produced in both shoot and root tips
    • Primary Functions:
      • Increases cell division and elongation
      • Plays a crucial role in bolting and breaking winter dormancy in buds and embryos.
    • Influence on Cultivars:
      • Cultivars such as cabbage exhibit shorter internodes due to reduced gibberellin, resulting in less bulging compared to wild types.

  2. Auxin

    • Location of Production: Primarily produced in shoot tips.
    • Primary Functions:
      • Key regulator of plant structure and growth; promotes cell elongation.
      • Establishes apical dominance by inhibiting side branching, leading to more vertical growth.
    • Functions Related to Light and Gravity:
      • Auxin accumulates on the shaded side of a stem, promoting differential elongation and causing the stem to bend towards light (phototropism).
      • Plays a role in gravitropism, allowing plants to grow upward even when knocked over by external forces, through differential cell elongation inspired by gravity.

  3. Gravitropism

    • Mechanism: Involves specialized cells (statocytes) containing heavy starch-filled plastids (statoliths) that settle in response to gravity, influencing auxin distribution and subsequent growth responses.
    • Response Time: Adjustments can occur within a few hours post disturbance.

  4. Abscisic Acid (ABA)

    • Role: Produced in response to stress (e.g., drought, salinity), triggers dormancy, and prepares plants for difficult conditions such as winter dormancy.
    • Auxin's Inhibition: In roots, ABA inhibits elongation, contributing to downward growth in the presence of gravity.

  5. Ethylene

    • Nature: Gaseous hormone produced by maturing plants.
    • Key Functions:
      • Regulates fruit ripening, senescence, and abscission.
      • Ethylene plays an important role in lethal abscission, leading to leaf and fruit drop.
    • Antagonistic Relationship with Auxin:
      • Auxin prevents aging and maintains tissue vitality, while ethylene promotes aging and decay.

Inter-relationships of Plant Hormones

  • Opposing Functions:
    • Auxin stimulates growth while ABA and ethylene tend to inhibit growth or promote senescence.
    • Understanding the balance of these hormones is crucial for cultivating various plant forms, including those used in food production.

Case Studies in Cultivar Development

Examples with Brassica Oleracea (Cabbage)

  • Brussels Sprouts:
    • Lateral growth increase due to reduced auxin, resulting in shorter internodes.
    • Artificial selection leads to desired morphological changes.
  • Kale:
    • Selection for larger leaves that remain attached longer results in reduced levels of ethylene and ABA, enabling growth even in colder conditions.

Conclusion

  • Summary of key points:
    • Understanding how auxin, gibberellins, ABA, and ethylene interact shapes plant growth, development, and responses.
    • Practical implications for agriculture and plant breeding can be drawn from these dynamics.

Closing Remarks

  • Reminder about office hours and student engagement throughout the week.
  • Next class will cover additional plant hormones and respond to changes in environmental stimuli.