Plant Hormones and Their Role in Plant Growth

Plant hormones are organic substances that regulate plant growth and development. In animals, hormone production is limited to specialized glands, but in plants each cell can produce hormones – genius! The way that plant hormones regulate plant growth is fascinating. Science is cool; there will be a test!

The plant hormone most used by plant parents in auxin because it is important for successful vegetative propagation outcomes. Check out this week’s video to learn all about Rooting Hormone!

Plant Hormones used in Plant Growth Regulation	What it does	How plant people use it to manipulate plant growth
Auxin (IAA)	Causes several growth responses in plants such as phototropism (bending towards light) and geotropism (downward root growth in response to gravity) Responsible for apical dominance, the tendency of an apical bud to produce hormones that suppress growth of lower buds Involved in flower formation, fruit set, formation of adventitious roots	Auxin is the active ingredient in most rooting compounds and promotes root initiation and formation Used in grafting to promote callus formation which joins the surface of the graft together Some synthetic auxins are used as herbicides. Seedless cucumbers can be induced to set fruit with an application of auxin
Gibberellins (GA)	Stimulates cell division and elongation Breaks seed dormancy and speeds germination Also produced by fungi. Promotes the transition between vegetative and reproductive growth	Some seeds are difficult to germinate, soaking in a GA solution helps get them started Used to promote fruit set in grape crops. Used to promote cell elongation and stretching in long season crops such as pillar geraniums
Abscisic Acid (ABA)	Induces dormancy Prevents seed germination Causes abscission (detachment) of leaves, flowers, and fruit. Causes stoma to close reducing transpiration Cuticular wax formation. Responsible for osmotic regulation.	Applications of ABA regulate drought stress by mediating stomatal closure Expensive to produce so there are not many commercial applications.
Cytokinins (CKs)	Unlike other plant hormones, cytokinins are found in both plants and animals. Stimulates cell division and shoot formation. Differentiation of shoot and root production. Mediates auxin transport. Delays senescence (aging and death)	An additive to sterile media for growing plants from tissue culture. Used in growth control in fruit.
Ethylene	Found only in a gaseous state Promotes ripening Promotes lateral branching Causes epinasty (leaf drop) Produced in response to stress Increase in ethylene in deciduous plant leaves is responsible for fall leaf drop.	Commercially used to ripen fruit, specifically bananas. Used in horticulture and floriculture production to supersede apical dominance and promote lateral branching. Leaf-drop in ornamentals.

That’s a wrap for now folks. Weekend project – make yourself some flashcards and study up. Understanding your plants on the cellular level = not on the plant parent syllabus, but certainly helpful as you get to know your plants and what they are up to! Who knows, one day you might choose a career in plant science? And who will you have to thank for your rock-star plant knowledge? Tonkadale’s Intro to Plant Biology Class of course!