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
2

Reference texts
Hartman, H. T., Kester, D. E., Davies, F. T. and Geneve, R. L. (2002) Plant propagation principles and practices(6 th
Edition) Eastern Economic Edition
Janick, J. (1986) Horticultural Science (4 th Edition) Freeman and Company
Jeffrey, C. (1982) An introduction to plant taxonomy (2 nd 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 17 th
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 (4 th
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 HORTICULTURE
Floriculture : 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 HORTICULTURE
SOURCE 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 CROPS
Why 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
Basis of classification
ARTIFICIAL
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
Groups together plants most alike in their hereditary constitution
Generally groups together plants most closely related phylogenetically
Disadvantages
May not group plants that are most closely related phylogenetically
May fail to group plants that are closely related phylogenetically
Contains a lot of information about members of the group
Additional information of its members can easily be incorporated
Has a high predictive value
Contains limited information about its members
More information about its members cannot be easily incorporated
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. KINGDOM
2. DIVISION/PHYLUM
3. CLASS
4. ORDER
5. FAMILY
6. GENUS
7. SPECIES
8. FORM/VARIETY
9. CULTIVAR
Common terms
1.
KINGDOM –It is the highest taxonomic category
2.
DIVISION
3.
CLASS –
4.
ORDER – a category of taxonomic classification ranking above the family and below the class
5.
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 genera
6.
GENUS- a class , kind, or group marked by common characteristics or by one common characteristic
7. GENUS – a kind, class or group marked by common characteristics or by one common characteristic
8.SPECIES –a category of individuals ranking immediately below the genus or subgenus.
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TAXON
KINGDOM
PHYLUM
CLASS
ORDER
FAMILY
GENUS
SPECIES
EXAMPLE
Plantae
Magnoliophyta
Liliopsida
Liliales
Liliaceae
Allium
Allium cepa
COMMON NAME
Plant
Flowering plant
Monocot
Lily order
Lily family onion
Rules of classification
1.
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
ANNUAL
DEATH VEGETATIVE
GROWTH
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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SEED
PERENNIAL
AL
DEATH
DORMANCY
VEGETATIVE
GROWTH
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
BIENNIAL
VEGETATIVE
GROWTH 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 ).
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SEED
MONOCARP
DEATH VEGETATIVE
GROWTH
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 90 0 to ground level) without artificial support.
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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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EDIBLES
1. 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)
ORNAMENTALS
1.0 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
17

CHAPTER 2.0 TAXONOMY OF PLANTS
SCIENTIFIC CLASSIFICATION OF PLANTS
18

A
B
C
D
E
F
G
H
I
J
1) PRACTICAL 1: IDENTIFICATION OF COMMON HORTICULTURAL
CROPS
Full Name
: …………………………………………………
:…………………………………………………...
Registration Number
SAMPLE
CODE
NAME OF CROP FAMILY OF CROP
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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]
20

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
21

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
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
Animal Hormones
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?
 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
23

 Auxins stimulate lateral root growth and root initiation on stem cuttings
 Auxins move through the plant by "polar transport"
- 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)
 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
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 Largest group of hormones, over 70 known gibberellins
 First isolated from a fungus ( Gibberella fujikori )
- 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
 Synthesized in plastids from carotenoids
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- Derived from terpenoid pathway
 Produced in leaves, stems, and green fruits
 Causes stomatal closure during water stress
 Promotes dormancy in seeds and buds
 Gaseous Hormone
 Formed from the amino acid methione
- reaction involves cyclized intermediate 1-aminocyclopropane-1carboxylic 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
26