PRINCIPLES OF HORTICULTURE/INTRODUCTION TO HORTICULTURE

(NRM103/ HORT103)

OBJECTIVE OF THE MODULE

COURSE OUTLINE

1.0 DEFINITION OF HORTICULTURE

1.1 Divisions of Horticulture

1.2 Characteristics of horticultural crops

1.3 Classification criteria

1.4 Classification of horticultural crops

2.0 TAXONOMY OF PLANTS

2.1 Hierarchy

2.2 Classification process

2.3 Natural and artificial classification

3.0 LIGHT AND PLANT FLOWERING

3.1 Photoperiodism

3.2 Mechanism of photoperiodism

4.0 PLANT GROWTH REGULATORS (PGRs)

4.1 Auxins

4.2 Gibberellins

4.3 Cytokinins

4.4 Abscisins

4.5 Ethylene

4.6 Hormonal control of the whole plant

4.7 Use of PRGs in horticulture

5.0 VEGETATIVE PROPAGATION

5.1 Cloning in horticulture

5.2 Propagation by layering

5.3 Propagation by Grafting and Budding

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5.3 Graft incompatibility

5.4 Propagation from cuttings

5.5 External and internal factors affecting rooting of cuttings

6.0 TISSUE CULTURE

6.1 Micropropagation (Its applications, advantages and disadvantages)

6.2 Embryo culture

6.3 Somatic embryogenesis

6.4 Meristem tip culture

6.5 Anther culture

6.6 Protoplast culture

6.7 Somaclonal variation

6.8 Invitro selection

7.0 PROPAGATION STRUCTURES

7.1 Greenhouses

7.2 Lathhouses

7.3 Hotbeds

7.4 Cold beds

8.0 IRRIGATION AND NUTRITION MANAGEMENT IN HORTICULTURE

8.1 Soil Moisture and its measurement

8.2 Irrigation methods

8.3 Essential element for plant growth

9.0 POSTHARVEST TECHNOLOGY

9.1 Deterioration of produce

9.2 Ethylene production

9.3 Compositional changes

9.4 Physiological breakdown

9.5 Effects of temperature, RH, atmospheric gases, ethylene and light

9.6 Harvesting

9.7 Storage

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Reference texts

Hartman, H. T., Kester, D. E., Davies, F. T. and Geneve, R. L. (2002) Plant

propagation principles and practices(6th Edition) Eastern Economic Edition

Janick, J. (1986) Horticultural Science (4th Edition) Freeman and Company

Jeffrey, C. (1982) An introduction to plant taxonomy (2nd Ed) Cambridge University

Press

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1.0 ORIGINS OF HORTICULTURE The concept of horticulture is part of agriculture.

The word agriculture (agri- field; culture- tillage) means tillage of the soil leading to

the production of crops.

Agriculture can be traced back to the Neolithic Age (9 000-7000BC), when man

changed from being a hunter and a gatherer to managing or manipulating individual

species of plant and animal.

Horticulture is a concept that later started in the 17th Century. In literature, the term

first appeared in 1631 by Peter Lauremberg as ‘horticultura’.

In English, horticulture was first mentioned in “The New World of English Words”

by Phillips E. in 1678.

The word is derived from the Latin names ‘hortus’, which means garden; and ‘colere’

meaning to cultivate.

Horticulture is part of agriculture concerned with garden crops, as contrasted with

agronomy (field crops, mainly grains and forages) and forestry (forest trees and

products)

Garden is derived from Anglo-Saxon term ‘gyrdan’ which means to enclose.

Garden crops traditionally include fruits, vegetables, and all plants grown for

ornamental purposes, as well as spices and medicinal plants.

Horticulture deals with intensively cultivated crops, which are of high value to

warrant high input of labour and capital.

Crops have also been separated using custom e.g. tobacco and potatoes may be

classified as agronomic crops despite their characteristics.

DEFINITION OF HORTICULTURE The division of agriculture which relates to the culture of those plants commonly

known as fruits, vegetables and ornamental plants [Schilleter and Ritchley,

(1940)Textbook of general horticulture. McGraw-Hill Book Company, New York

and London]

The intensive cultivation of plants [Halfacre R. G. and Barden, J. A. (1979),

Horticulture. McGraw-Hill, USA]

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The branch of agriculture concerned with intensively cultivated plants, directly used

by people for food, for medicinal purposes, or for aesthetic gratification [Janick, J.

(1986) Horticultural Science (4th Ed.). W. H. Freeman and Company, USA]

It is part of plant agriculture that is concerned with so-called garden crops [Hartman

H. T., Kester, D. E. and Davies, F. T. (1990)]

RELATIONSHIPS OF HORTICULTURE TO AGRICULTURAL BRANCHES

AGRICULTURE

PLANTS ANIMALS

AGRONOMY AGROFORESTRY FORESTRY HORTICULTURE

FLORICULTURE OLERICULTURE POMOLOGY LANDSCAPE NURSERY

BRANCHES OF HORTICULTUREFloriculture: It is the division of horticulture concerned with the science and art of

growing flowers and foliage plants

Olericulture: It is the division of horticulture concerned with the science and art of

vegetable production

Pomology: It is the division of horticulture concerned with the science of fruit

production.

Nursery culture: It is the branch of horticulture that is concerned with production of

young fruit trees, ornamentals and vegetable seedlings

Landscape design: It is the branch of horticulture that deals with the planning and

planting of outdoor environment to produce the most desirable relationships between

landforms, buildings and plants to best meet people’s objectives for function and beauty.

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IMPORTANCE OF HORTICULTURESOURCE OF FOOD

Society depends on horticulture for a substantial amount of its food. This is

sourced from vegetables, fruits and nuts.

They supply carbohydrates, vitamins and minerals

ORNAMENTALS

Landscaping has become an important component of construction. Plants in

landscape include shrubs, trees, bedding plants and grasses.

Public malls, playgrounds and cemeteries are places where plants are displayed

for specific purposes.

Flowers are important on special occasions such as roses for Valentines Day,

Mothers Day, Graduations, Reconciliation; poinsentias for Christmas and lilies

for Easter.

JOBS

Directly provides jobs to the society. These include nurserymen, florists,

greenhouse managers, extension officers, sales or marketing officers, teachers,

lecturers, farm managers

Indirectly provides jobs in the following areas

Research, Chemical industry (extraction of pigments e.g. oleoresin), Machinery

(engineers and designers of tools for planting, weeding, harvesting). Distribution

(freight forwarders, transporters, drivers)

EXPORT MARKETS

Horticulture provides foreign currency through exports. Floriculture exports of

1985 totalled Z$3.1 million and continued to grow rapidly to $500 million for

1995/96 season.

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CHARACTERISTICS OF HORTICULTURAL CROPS Many have high water content, hence they are utilised mostly in their living state

Highly perishable

Constituent water is essential to their quality

Generally grown more intensively and returns per unit area are normally higher

than with agronomic or forestry crops

Mainly consumed for the supply of micronutrients and vitamins and for their

contribution to flavour (spices) and interest of food (garnishing)

They are generally not staple crops

Consumption levels depend on the selling price and the buyer’s income

Crops are normally traded in relatively small quantities, in free marketing systems

where both supply and demand determine the price.

CLASSIFICATION OF HORTICULTURAL CROPSWhy classifying horticultural plants?

There are many horticultural plants in the world. A lot of knowledge has been

gathered on the plants. Classification makes summarisation of information on the

plants possible hence serves time in information sharing.

It is a means of identification and communication on horticultural plants

It facilitates prediction

TYPES OF CLASSIFICATION There are two types of classification, which are natural and artificial.

Scientific plant classification falls under natural classification

Natural Classification Classifies objects together on the basis of the sum total of all their characters

(features which exist in the group of objects in two or more distinguishable

different states e.g. hair colour, eye colour in human)

It puts together those that are more alike in most respects

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Artificial Classification Classifies objects together on the basis of only one or a very few specially

selected characters and ignores all the characters that the objects might have.

It does not take into account the natural relations of plants.

However, it is useful in horticulture. Plants can be classified on the basis of their

ability to withstand drought e.g. drought tolerant, drought prone etc., which is

useful information for crop husbandry.

COMPARISON OF ARTIFICIAL AND NATURAL CLASSIFICATION

NATURAL ARTIFICIAL

Basis of classification Basis of classification

It utilises the sum-total of all the characters

of its members

It utilises one or very few characters of its

members that are especially selected

Advantages Disadvantages

Groups together plants most alike in their

hereditary constitution

May not group plants that are most closely

related phylogenetically

Generally groups together plants most

closely related phylogenetically

May fail to group plants that are closely

related phylogenetically

Contains a lot of information about

members of the group

Contains limited information about its

members

Additional information of its members can

easily be incorporated

More information about its members

cannot be easily incorporated

Has a high predictive value Low predictive value

Disadvantages Advantages

Identification of members may be difficult Identification of members is made easy

Placing of poorly known plants may be

uncertain or impossible

Poorly known members may be definitely

placed

It is liable to change as more information is

gathered on the plants

Does not change with increase in our

knowledge

Adapted from Jeffrey (1982)

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SCIENTIFIC AND BOTANICAL (NATURAL) CLASSIFICATION SYSTEMS HORTICULTURAL CROPS Scientific systems of classification go beyond the superficial or natural system by

employing a number of criteria that include morphological, anatomical, ultrastructural

physiological, phytochemical, cytological and evolutionary (phylogenetical) criteria.

Individual members are assigned to a descending series of related plants based on

their known common characteristics.

The binomial nomenclature was introduced by Carolus Linnaeus, which used 2

Latin names for naming a plant, which are the genus and the specific epiphet.

Taxonomic hierarchy:

1. KINGDOM2. DIVISION/PHYLUM

3. CLASS4. ORDER

5. FAMILY6. GENUS

7. SPECIES8. FORM/VARIETY

9. CULTIVARCommon terms

1. KINGDOM –It is the highest taxonomic category2. DIVISION3. CLASS –4. ORDER – a category of taxonomic classification ranking above the family and below

the class5. FAMILY – a group of related plants or animals forming a category ranking above a

genus and below an order and usually comprising several to many genera6. GENUS- a class , kind, or group marked by common characteristics or by one

common characteristic7. GENUS – a kind, class or group marked by common characteristics or by one common characteristic8.SPECIES –a category of individuals ranking immediately below the genus or subgenus.

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TAXON EXAMPLE COMMON NAMEKINGDOM Plantae PlantPHYLUM Magnoliophyta Flowering plantCLASS Liliopsida MonocotORDER Liliales Lily orderFAMILY Liliaceae Lily familyGENUS AlliumSPECIES Allium cepa onion

Rules of classification1. The binary name should be underlined or written in italics (to indicate that they

are non-English names)2. Genus starts with a capital letter and the species is written in lowercase

throughout. The term species is both singular and plural. It can be shortened as spp. for plural “species”.

OPERATIONAL (ARTIFICIAL) CLASSIFICATION SYSTEMS

1. CLASSIFICATION BASED ON SEASONAL GROWTH CYCLE

Plants can be classified into three general groups based on growth cycle. These

are: annuals, biennials, perennials (evergreen, deciduous) and mononcarp.

SEED

DEATH VEGETATIVEGROWTH

REPRODUCTIVE

ANNUAL: The plant lives through only one growing season, completing its life cycle

(seed, flowering, fruiting and death). Examples are tomato (Lycopersicon esculentum)

sugarbeans (Phaseolus vulgaris).

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ANNUAL

SEED

DEATH VEGETATIVEGROWTH

DORMANCY

REPRODUCTIVE GROWTH

PERENNIAL: These are herbaceous or woody plants that persist year-round through

unfavourable conditions (winter or drought) and then flower and fruit after a variable

number of years of vegetative growth. Perennials survive harsh conditions as dormant

underground organs. Examples are irises (Iris spp.) & fruit trees.

SEED

DEATH VEGETATIVEGROWTH 1

DORMANCY

VEGETATIVE GROWTH 2

REPRODUCTIVE

BIENNIAL: These are plants that complete a life cycle in two growing seasons. The

first season is for vegetative growth and the second season the plant produces a stem

and flowers. Examples are onions (Allium cepa).

SEED

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PERENNIAL

BIENNIAL

DEATH VEGETATIVEGROWTH

REPRODUCTIVE DORMANCY

Monocarp: These are characterised by

2. CLASSIFICATION BASED ON THE KINDS OF STEMS

Herbs: plants with soft non-woody stems. They have primary vegetative

parts. Examples include Zea mays

Shrubs: A shrub has no main trunk. It is woody and has secondary tissue.

Shrubs are perennial and usually smaller than the trees. Examples are azalea

(Rhododendron spp.), Bougainvillea

Trees: Trees are large plants characterised by one main trunk. They branch

on the upper part of the plant are woody and have secondary tissue.

3. CLASSIFICATION BASED ON COMMON STEM GROWTH FORMS

Erect: A stem is erect if it can stand upright (at an angle 900 to ground level)

without artificial support.

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MONOCARP

Decumbent: The stems of decumbent plants are extremely inclined with the

tips raised. A good example is Arachis hypogea(groundnuts).

Declined/Climbing: These are vines that without additional support, will

creep on the ground. There are three general modes of climbing. Thesea are

1. Twiners – they simply wrap their stringy stems around the support e.g.

sweet potatoes

2. Tendrils – these coil around support on physical contact. An example is

Pisum sativum

3. Climbimg by adventitious roots:

4. CLASSIFICATION BASED ON FRUITS

5. CLASSIFICATION BASED ON OTHER OPERATIONAL ATRIBUTES

OVERALL CLASSIFICATION OF HORTICULTURAL PLANTS

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EDIBLES1. VEGETABLES

1.1 Plants Grown for aerial portions

1) Cole Crops (broccoli, cabbage, cauliflower)

2) Legumes or pulse crops (bean, pea)

3) Solonaceous fruit crops (Capsicum pepper, eggplant, tomato)

4) Vine crops or curcubits (cucumber, melon, squash and pumpkin)

5) Pot Herbs or Greens (chard, dandelion, spinach)

6) Mushrooms (Agaricus, Oyster, Lentinus)

7) Other vegetables (asparagus, okra, sweet corn)

1.2 Plants grown for underground portions

1) Root crops

Temperate (beet, carrot, radish and turnip)

Tropical (cassava, sweetpotato, taro and yam)

2) Tuber crops (Jerusalem artichoke, potato)

3) Bulb and corm crops (garlic, onion, shallot)

2.0 FRUITS

2.1 Temperate (Deciduous)

1) Small fruits

Berries (blueberry, cranberry, strawberry)

Brambles (blackberry, raspberry)

Vines (grape, kiwifruit)

2) Tree fruits

Pome fruits (apple, pear, quince)

Stone fruits (apricot, cherry, peach and plum)

2.2 Subtropical and tropical (Evergreen)

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1) Herbaceous and vine fruits (banana, papaya, passion fruit, pineapple)

2) Tree fruits

Citrus (grapefruit, orange, lime, lemon, naartjies, mandarin)

Non citrus (avocado, date, fig, mango, mangosteen)

3.0 NUTS

1) Temperate (almond, chestnut, filbert, pecan, pistachio)

2) Tropical (Brazil nut, cashew, macadamia)

4.0 BEVERAGE CROPS

1) Seed (cacao, coffee)

2) Leaf (maté, tea)

5.0 HERBS AND SPICES

1) Culinary herbs (dill, rosemary, sage)

2) Flavourings (peppermint, spearmint)

3) Tropical spices (cinnamon, clove, nutmeg and pepper)

ORNAMENTALS1.0 FLOWERS , BEDDING AND FOLIAGE PLANTS

1) Annuals (marigold, petunia, zinnia)

2) Biennials (English daisy, foxglove)

3) Perennials (daylily, rose, delphinium, iris, peony)

Bulbs and corms (crocus, gladiolus, narcissus, tulip)

2.0 LANDSCAPE (NURSERY)

1) Lawn and turf (bermudagrass, bluegrass, fescue, perennial ryegrass)

2) Ground covers and vines (English ivy, Japanese spurge, myrtle)

3) Evergreen shrubs and trees

Broadleaf (holly, rhododendron)

Narrowleaf (fir, juniper and yew)

4) Deciduous shrubs (dogwood, forsythia, lilac, viburnum)

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5) Deciduous trees (ash, crabapple, magnolia, sugar marple)

3.0 INDUSTRIAL

1) Drugs and medicinals (digitalis, quinine)

2) Oil seeds (jojoba, oilpalm, tung)

3) Extractives and resins (Scotch pine, Pará rubber tree)

2.0 TAXONOMY OF PLANTS

2.1 Hierarchy

2.2 Classification process

2.3 Natural and artificial classification

3.0 LIGHT AND PLANT FLOWERING

3.1 Photoperiodism

3.2 Mechanism of photoperiodism

4.0 PLANT GROWTH REGULATORS (PGRs)

4.1 Auxins

4.2 Gibberellins

4.3 Cytokinins

4.4 Abscisins

4.5 Ethylene

4.6 Hormonal control of the whole plant

4.7 Use of PRGs in horticulture

5.0 VEGETATIVE PROPAGATION

5.1 Cloning in horticulture

5.2 Propagation by layering

5.3 Propagation by Grafting and Budding

5.3 Graft incompatibility

5.4 Propagation from cuttings

5.5 External and internal factors affecting rooting of cuttings

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6.0 TISSUE CULTURE

6.1 Micropropagation (Its applications, advantages and disadvantages)

6.2 Embryo culture

6.3 Somatic embryogenesis

6.4 Meristem tip culture

6.5 Anther culture

6.6 Protoplast culture

6.7 Somaclonal variation

6.8 Invitro selection

7.0 PROPAGATION STRUCTURES

7.1 Greenhouses

7.2 Lathhouses

7.3 Hotbeds

7.4 Cold beds

8.0 IRRIGATION AND NUTRITION MANAGEMENT IN HORTICULTURE

8.1 Soil Moisture and its measurement

8.2 Irrigation methods

8.3 Essential element for plant growth

9.0 POSTHARVEST TECHNOLOGY

9.1 Deterioration of produce

9.2 Ethylene production

9.3 Compositional changes

9.4 Physiological breakdown

9.5 Effects of temperature, RH, atmospheric gases, ethylene and light

9.6 Harvesting

9.7 Storage

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CHAPTER 2.0 TAXONOMY OF PLANTS

SCIENTIFIC CLASSIFICATION OF PLANTS

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1) PRACTICAL 1: IDENTIFICATION OF COMMON HORTICULTURAL

CROPS

Full Name : …………………………………………………

Registration Number :…………………………………………………...

SAMPLE

CODE

NAME OF CROP FAMILY OF CROP

A

B

C

D

E

F

G

H

I

J

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Assignment

1. Advise smallholder farmers of the challenges or hardships they are likely to face

in commercial horticultural production [10]

2. Write a short essay on the importance of classifying horticultural crops [10]

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CHAPTER 4.0 Plant Hormones (Plant Growth Regulators)

Introduction

As a plant grows its physical traits, or phenotype, are the outcome of a complex

interaction between its genetic instructions, or genotype, and the external environment.

The growth and differentiation of cells in different parts of the plant are coordinated in

response to these inputs.

There has to be communication between these levels. How does the plant receive and

respond to environmental inputs or "signals"? What communication is inside the plant to

adjust growth and development in response to the environment? The answer lies in an

understanding of plant hormones.

Definition:

Plant hormones are small organic compounds that influence physiological responses to

environmental stimuli at very low concentrations (generally less that 10-7 M). Hormones

are not directly involved in metabolic or developmental processes but they act at low

concentrations to modify those processes.

Plant hormones are used extensively in agriculture, horticulture, and biotechnology to

modify plant growth and development.

Hormones regulate or influence a range of cellular and physiological processes, including

o Cell Division

o Cell Enlargement

o Cell Differentiation

o Flowering

o Fruit Ripening

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o Movement (tropisms)

o Seed Dormancy

o Seed Germination

o Senescence

o Leaf Abscission

o Stomatal Conductance

Not all researchers agree that the term "hormone" should be applied to plants. Plants do

not have a circulatory system and therefore hormone action in plants is fundamentally

different from hormone action in animals. Many plant biologists use the term "plant

growth regulator" instead of "hormone" to indicate this fact. The table below summarizes

some of the differences between plant and animal hormones.

Plant Hormones Animal Hormones

1. Small molecules only

2. Produced throughout the plant

3. Mainly local targets (nearby cells and

tissues)

4. Effects vary depending on interaction

with other hormones

5. "Decentralized" regulation

1. Peptides/proteins and/or small

molecules

2. Produced in specialized "glands"

3. Distant targets ("action at a

distance")

4. Specific effects

5. Regulation by central nervous

system

Broadly speaking, the mechanism by which hormones act at the cellular level is similar in

plants and animals. In both cases, the hormone must first bind to a protein receptor,

either on the cell surface or inside the cell. This activates a signal transduction

pathway, which amplifies the signal and leads to changes in enzyme activities, ion

gradients, gene expression, and other physiological responses.

Five classes of plant hormones are recognized.

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1. Auxins

2. Cytokinins

3. Gibberellins

4. Abscisic Acid

5. Ethylene

Other "hormone-like" substances produced by plants include

o Polyamines

o Jasmonates

o Salicylic acid

o Brassinosteroids

o Florigens

o Phytochrome (photoreceptor)

o Nitric oxide?

Auxins

Name from the Greek work auxein which means to "increase" or "augment"

First plant hormone discovered

1. Phototropism experiments of Charles and Francis Darwin using oat

coleoptiles

2. Auxin eventually isolated by Frits Went

Auxins are produced primarily in shoot tips (shoot apical meristem) and growing

leaves and fruits.

Auxins regulate two important processes in plant growth: phototropism

(response to light) and gravitropism (response to gravity)

Auxins promote stem growth by stimulating cell elongation

Auxins control vascular differentiation of xylem and phloem

Auxins stimulate lateral root growth and root initiation on stem cuttings

Auxins move through the plant by "polar transport"

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- Unidirectional movement down the stem through parenchyma cells

- Auxin apparently does not travel through the vascular tissue

Auxins inhibit lateral bud sprouting. This is called apical dominance

Indole-3-acetic acid (IAA) is the natural auxin

IAA is derived from the amino acid tryptophan

Several synthetic auxins have related structures

1. napthalene acetic acid (NAA) (controls fruit set and sucker growth)

2. indole butyric acid (Rootone)

3. 2,4-D (herbicide, causes uncoordinated growth in broad-leaved weeds)

Cytokinins

Produced mainly in roots; travels through the xylem

Derived from the nucleotide adenine

1. Synthetic cytokinins include benzyladenine and kinetin

2. These growth stimulators are used extensively in plant tissue culture and

are therefore important in biotechnology applications

Promote cell division ("cytokinesis")

Stimulate lateral bud growth

- determined by relative concentrations of auxin and cytokinin

Gibberellins

Largest group of hormones, over 70 known gibberellins

First isolated from a fungus (Gibberella fujikori)

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- cause of "foolish seedling"

Derived from the terpenoid pathway

Produced in embryonic tissues (meristems)

Promotes stem elongation

o Many "dwarf" plants are genetic mutants deficient in gibberellin synthesis

Enhances the effects of auxin

Stimulates germination in buds and seeds

Used commercially to break dormancy

Example: Germination in wheat seeds

1. Seed takes up water

2. Embryo produces GA

3. GA diffuses to aleurone layer (surrounding endosperm)

4. Aleurone produces amylase

5. Amylase diffuses to endosperm and breaks down starch to glucose

6. Glucose feeds growing embyro

Abscisic Acid

Synthesized in plastids from carotenoids

- Derived from terpenoid pathway

Produced in leaves, stems, and green fruits

Causes stomatal closure during water stress

Promotes dormancy in seeds and buds

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Ethylene

Gaseous Hormone

Formed from the amino acid methione

- reaction involves cyclized intermediate 1-aminocyclopropane-1-

carboxylic acid (ACC)

Promotes leaf abscission

Promotes fruit ripening

Used commercially for fruit ripening

Ethephon is a commercial fruit ripener that breaks down to ethylene inside plant tissues

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