google.com, pub-6546753431946252, DIRECT, f08c47fec0942fa0
top of page
Search

Crop Physiology Lesson: Plant Hormones and Regulators Phytohormone Part 3


Lecture on: 24 November 2025


Notes can be downloaded here:

This video segment of the Crop Physiology (AGR3301) lecture focuses on the crucial group of Growth Inhibitors—Abscisic Acid (ABA) and Ethylene—and their roles in stress signaling, development, and senescence.

ABA is a general plant growth inhibitor and is considered the stress hormone due to its pivotal role in plant defenses.

  • Key Functions in Stress Signalling: ABA rapidly induces the closure of stomata in the epidermis in response to drought. This increases the plant's tolerance to various stresses and enhances drought protection.

  • Key Functions in Development: ABA inhibits seed germination and promotes seed and bud dormancy. It also promotes leaf senescence (aging).


Ethylene is unique as the only gaseous PGR and, while sometimes fitting both promoter and inhibitor groups, is largely recognized as an inhibitor of growth activities.

  • Discovery: Recognized in the 1800s for its effect on plants near gas street lights, it was identified in 1901 by Neljubow and later shown by Gane to be naturally produced by plants.

  • Key Functions in Senescence and Ripening: Ethylene famously promotes fruit ripening (causing changes in colour, flavour, and softening) and accelerates senescence (aging) and abscission (shedding) of leaves and flowers.

  • Triple Response: When germinating in the dark or impeded by an obstacle, seedlings produce ethylene, which triggers a characteristic "triple response": reduced elongation, hypocotyl swelling, and apical hook exaggeration.

  • Adaptation: Ethylene synthesis increases upon hypoxia (e.g., flooding), inducing the formation of aerenchyma (air channels) in roots of plants like deepwater rice, allowing oxygen to move into submerged tissues

  • Synthesis: ABA is synthesized from carotenoids and moves nonpolarly throughout the plant


Keywords: Abscisic Acid, ABA, Ethylene, Stress Hormone, Stomatal Closure, Drought Protection, Seed Dormancy, Fruit Ripening, Abscission, Triple Response, Phytohormones, Growth Inhibitors, AGR3301.


Location:

Faculty of Agriculture, Universiti Putra Malaysia

Fakulti Pertanian, Universiti Putra Malaysia, 43000 Seri Kembangan, Selangor

2.983567621706455, 101.73466120334834

Attribution 4.0 International — CC BY 4.0 - Creative Commons


Comments

bottom of page