Learn how to apply botanical knowledge in horticulture, agriculture and environmental science.
Understanding plant growth allows us to influence how a plant grows.
What causes what to happen
in a plant? What makes growth speed up or slow down, or a certain type
of growth start or stop? Learn about the processes that occur within a
plant to cause flowers to form, leaves to grow and die, roots to form,
etc.
By
the end of the course you will better understand and be able to conceive
how you might affect the way a plant grows, to run a more productive
farm, propagate plants easier, or manage the landscape more
effectively.
Lessons include: Flower physiology; phytoperiodism; control of flower
bud initiation and development; dormancy; effects of plant associations
and competition; respiration and post harvest physiology; post harvest
storage, transport, retailing and shelf life; endogenous and synthetic
growth regulators; risks involved with plant growth manipulation.
ACS Student comment: "I find the course quite interesting! At first glance, the reading material and questions look so simple, but they
actually require quite a bit of thinking and probing. The course is
very well designed!" - Joanne McLeod, Australia - Botany II course.
Lesson Structure
There are 10 lessons in this course:
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Flower physiology
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Introduction
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The flowering response
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Genes control flowering
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Physiological age
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Minimum leaf number
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Photoperiodism
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Terminology
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Phytochrome
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Light sensing systems
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Blue light responses
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Red light responses
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Other light responses
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Phytochrome
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Photoreceptor forms: Pr, Pfr
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How molecules change
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Relevance to commercial horticulture
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Controlling light
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Terminology
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Photoperiodism
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Light
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Measuring light
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What wavelengths do plants need
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Typical photoperiod responses
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Photoperiodic responses in seasonal flowering plants
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Photoperiodic classification of plants: short day plants, long day plants, day neutral plants
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Detection of photoperiod
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Critical photoperiod and flowering
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Research facts
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Other photoperiodic effects
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Terminology
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Control of flower bud initiation and development
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Stages in flower bud growth
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What can affect flower bud initiation
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Differentiation
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Development
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Anthesis
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Effect of temperature on growth and flowering
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Vernalisation
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Thermoperiodism
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Research reports or reviews of specific plants
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Terminology
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Dormancy
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Dormancy in plants
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Abscisic acid and dormancy
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Breaking dormancy
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Dormancy in seeds
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Factors affecting seed dormancy
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Breaking seed dormancy
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Terminology
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Effects of plant associations and competition
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Introduction
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Competition
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Parasitism
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Coevolution
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Mutualism
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Plant herbivore and pathogen interactions
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Crop spacing and crop yields
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Crop canopy and plant density
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Impact of weeds
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Protected environments
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Greenhouses
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Shadehouses
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Respiration and post harvest physiology
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Respiration
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Glycolysis
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Aerobic respiration
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Anaerobic respiration
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Bioluminescence and Fluorescence
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Post harvest respiration
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Terminology
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Post harvest storage, transport, retailing and shelf life
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Effect of growing conditions on post harvest life
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Controlled storage conditions: temperature, atmosphere, humidity
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Normal atmospheric conditions
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Controlled and modified atmospheres
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Effect of oxygen levels Effect of carbon dioxide levels
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Ethylene
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Controlling ethylene levels
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Modified Atmosphere Packaging
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Commodity transport
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Retailing and shelf life
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Endogenous and synthetic growth regulators
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Nature of plant hormones
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Auxins: IAA, IBA, NAA
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Gibberellins: natural and synthetic
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Cytokinins: over 130 different types
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Abscisic acid
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Ethylene
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Other hormones: anti auxins, growth inhibitors, growth retardants, defoliants, growth Stimulators, non standard hormones
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Controlled ripening and degreening
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Waxing
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Risks involved with plant growth manipulation
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Commercial risks
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Human health and safety risks
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Plant pathology risks
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Ecological risks
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Genetic modification
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Benefits
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environmental hazards
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Human hazards
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Terminology
Aims
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Investigate the physiology of growth development and flowering.
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Describe the nature of phytochrome and its effect on flowering in the phytochrome reaction.
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Describe the photoperiodic responses of flowering plants to differing dark and light periods.
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Explain the effect of temperature on the onset of flowering and flower development.
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Describe the causes of dormancy in seeds and plants and describe the methods of breaking dormancy.
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Explain plant associations and competition and their effects on quality and marketable yield.
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Explain the process of respiration in plant cells and its effect on post-harvest storage and transportation of crops.
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Describe physiological processes in post-harvest crops in relation to the storage conditions.
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Investigate the effect on plants of endogenous and synthetic growth regulators.
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Explain risk assessments relevant to plant growth manipulation.
Plant Growth
Plant
growth is the process by which a plant increases in size, creating more
leaves and stems. Plant development is the process by which plants
change from one stage of growth to the next. These stages include
juvenility, maturity, flowering and seeding. Plant development involves
differentiation of the plant into specialised parts. This may include
visible changes such as the structural organisation of the plant and new
patterns of growth as well as less visible changes such as localised
biochemical and metabolic activity.
Growth and development are characteristics not
only of the entire plant, but also of each cell within that plant.
Active cell division occurs in parts of the plant called meristems. Cell
division results in growth in length and diameter of the plant, and in
the differentiation of specialised plant organs. Differentiation results
in the development of individual plant parts such as stems, leaves, new
shoots, flowers, fruits, seed and other structures.
Flowering
For
plants to flower they must first go through a vegetative phase, during
which the main processes are elongation of the stem and roots and
increase in stem girth. The end of the vegetative phase is marked by
flower initiation, whereby the vegetative shoot apex undergoes a
sequence of physiological and structural changes to become a
reproductive apex (reproductive apical meristem – that which develops
into a flower or an inflorescence). The transition from a vegetative to a
floral apex is often preceded by an elongation of the internodes and
the early development of lateral buds below the shoot apex. The apex
undergoes a marked increase in mitotic activity, accompanied by changes
in dimensions and organisation. The development of the flower or
inflorescence terminates the meristematic activity of the vegetative
shoot apex. When these flowers are formed, the plant is prepared for
sexual reproduction.
A Plant's Age can Impact Health, Reproduction and Other Things
The plant’s physiological age may be a determining factor in whether a plant is able to form flowers. Physiological age refers to the plant’s stage of development. The stages are embryonic growth, juvenility, transition stage, maturity, senescence and death:
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Embryonic growth – the growth and development of the seed within the parent plant.
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Juvenility – following germination the plant increases in size as the cells enlarge and differentiate to form stems, leaves and roots. In some woody plants, this stage is characterised by the plant’s inability to form flowers, or the loss or reduction in the ability of cuttings to form adventitious roots.
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Maturity – this phase is marked by the formation and development of the sexual organs (the flower buds, flowers, fruit and seed).
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Senescence – the decline of the plant due to physiological change (due to the decline of cell division and reproduction) or environmental stress or pathogenic attack.
Many perennial species have two phases with distinctive morphological and physiological characteristics. The juvenile phase in such plants has the following characteristics:
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The leaves may be morphologically different to those of the adult or mature phase
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Flowering cannot be induced
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There is an increased ability of stem cuttings to form adventitious roots.
The adult or mature phase has the following characteristics:
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The leaves may be morphologically different to those of the juvenile phase
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Flowering and reproduction can occur
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Rooting ability is diminished or lost.
The juvenile phase may last from one year up to 40 or more years, but commonly in trees lasts for 5 to 10 years.
The English Ivy (Hedera helix) is a well known example of a plant showing distinct juvenile and mature phases. In the juvenile phase it grows as a creeping vine, with palmate, lobed leaves. In the mature phase, ivy becomes shrub-like and forms flowers and berry fruits.
The leaves are entire and ovate. Frequent pruning prevents the formation of flowers and keeps the plant in a prolonged juvenile (vegetative) phase, hence ivy is most commonly seen in gardens as a creeper. (For this reason, propagators frequently prune mother stock plants, keeping them in a juvenile, vegetative stage which ensures high rooting ability in the cuttings taken from those plants).
Juvenility may be induced in mature plants by treating shoots that develop from lateral buds with GA3 (discussed later in the course). A similar condition is known as ‘ripeness to respond’ or ‘ripeness to flower’, whereby some species can only commence flowering in response to their environment (particularly to day length and temperature) when the organs that detect the environmental change (usually leaves and meristems) have reached physiological maturity.
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