Plant Growth Regulators (PGRs)

Plant Growth Regulators

Quiz PGRs

Precursors of Plant Growth Regulators (PGRs)

• 🌱 Auxin - Tryptophan (Zn)
• 🌱 Gibberellin - Ent-Kaurene (Acetyl Co-enzyme)
• 🌱 Cytokinin - Adenine (Adenosine Monophosphate - AMP)
• 🌱 Ethylene - Methionine (Aminocyclopropane-1-carboxylic acid - ACC)
• 🌱 Abscisic Acid (ABA) - Violaxanthin

Auxin

• 📍 Inhibit root elongation and promote cell division in tissue culture
• 📍 Cell enlargement
• 📍 Prevention of lodging
• 📍 Induce Parthenocarpy
• 📍 Delay abscission
• 📍 Promote root initiation
• 📍 Increase female flower

IAA: Prevents premature fruit drop

IBA: Root formation

NAA: Fruit thinner, prevents fruit drop

2,4-D: Fruit setting hormone, also used as a herbicide

Cytokinin

• 📍 Richmond-Lang effect
• 📍 Dormancy breaker, stimulate cell division, induce flowering
• 📍 Delay senescence, increase female flower

Gibberellins (kaurene & Acetyl Co-enzyme)

• 📍 Cell elongation
• 📍 Increase fruit size
• 📍 Increase germination
• 📍 Internodal elongation
• 📍 Induce parthenocarpy
• 📍 Delay ripening
• 📍 Increase male flower, dormancy breaking

Abscisic Acid (ABA)

• 📌 Dormancy induced stomata closure, anti-gibberellin

Ethylene

• 📍 Ripening of fruits
• 📍 Isodiametric growth of stem and roots
• 📍 Available in two forms: Ethrel, Ethephon
• 📍 Dormancy breaking, increase female flower

Other Important Chemicals

Chlormequat

• 📌 Lodging preventer, also known as Cycocel
• 📌 Dwarfing effect

Malic Hydrazide

• 📍 Growth retardant
• 📍 Prevent onion sprouting in storage
• 📍 Sold under trade name Sproutstop

Ethephon

• 📌 Trade name: Cepa (liquid form)
• 📌 Used as a fruit ripener and for degreening in citrus

Paclobutrazol

• 📌 Plant growth retardant, decreases shoot growth, increases root growth
• 📌 Antagonist effect to GA3, inhibits GA3 biosynthesis
• 📌 Avoids alternate bearing in mango
• 📌 Also reduces frost sensitivity in plants