Role of Growth Hormones in Plants

Plant hormones are chemicals produced in very small amounts within the plant body.

Most growth hormones are produced at the tip of a shoot and transported downwards to the root.

These include;

1. Auxins (most common auxin is Indole Acetic Acid (IAA))
2. Gibberellins
3. Cytokinins
4. Ethylene
5. Abscisic acid
6. Florigen

Describe the role of growth hormones in plant growth and development

Auxins/Indole Acetic acid

• Promote cell division and cell elongation.
• Influence tropic responses;
• Promote parthenocarpy;
• Cause apical dominance/inhibit growth of lateral branches/buds;
• Promote growth of adventitious roots;
• Promote formation of abscission layers/bring about fruit fall/leaf fall;
• In association with cytokinins, auxins cause formation of callous tissue which cause healing of wounds.

Cytokinins (kinetins)

• Promote growth of roots, leaves and buds;
• Promote formation of the callus tissue in plants.
• Promote flowering in some plant species;
• Breaks seed dormancy in some plant species;
• Promote formation of adventitious roots from stems.
• Stimulate lateral bud development in shoots.
• In low concentration it promotes leaf aging and hence leaf fall;

Gibberellins

• Promote cell division and cell elongation in dwarf plants;
• Promote fruit formation
• Promotes parthenocarpy;
• Promote ripening of fruits after fertilization;
• Initiate formation of side branches and breaks dormancy in buds;
• Inhibit growth of adventitious roots;
• Slow down leaf abscission hence reduce leaf fall;
• Break seed dormancy by activating hydrolytic enzymes during seed germination;

Ethylene/ethyne

• Induces ripening of fruits;
• Induces stem thickening;
• Inhibit stem elongation;
• Break dormancy in certain seeds ;
• Promotes development of abscission layer leading in fruit/leaf fall;
• Promotes flower formation mostly in pineapples.

Abscisic Acid

• Causes seed dormancy and bud dormancy;
• Retards stem elongation;
• Promote leaf and fruit fall;
• In high concentration it leads to closure of stomata;

Florigen

• Promote flowering