Grape_Physiology_7_horones

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Plant Growth Regulators are substances
synthesized by the plant to act as messengers
 They are produced at one site and generally
transported in the xylem or phloem to another
to induce a physiological reaction (eg growth)

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Very small amounts of hormone are required
to cause an action
 They may act either alone or interact with
other hormones

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They may also cause different effects in
different parts of the grape vine
 These reactions are complex and not always
fully understood

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
There are five main groups of hormones in
plants
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Source of production
 New vegetative growth
 Young leaves
 Seeds
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Actions
 Attracts sugar and nutrients to site of
production
 Stimulates cell growth in young tissue
 Inhibits lateral budburst further down the
shoot ie apical dominance
 Promotes growth towards light
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Source of production
 Young growing shoot and leaves
 Root tips
Actions
 Suppresses flower bud initiation and fruitfulness in cool
weather/poor light
 Promotes growth and cell elongation
Example
 GA-3 is sprayed on seedless grapes to increase grape size
and yield
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Source of production
 Root tips
Actions
 Promotes cell multiplication in differentiating
tissues at apices
 Attracts auxin and gibberellin, sugars, nutrients
 Promotes even budburst
 Promotes lateral branching
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Promotes development of leaves, fruit
structures, fruit set with gibberellins to
balance fruitfulness of lateral buds
 Delays senescence
 Promotes berry as a sink
 Involved in anthocyanin and flavour formation

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Source of production
 Mature leaves
 Seeds, roots
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Action
 Generally counteracts effects of auxin, gibberellin
and cytokinin
 Induces stomatal closure in response to water
stress
 Reduces growth in response to water stress, cold
and short days
 Possibly promotes ripening as auxin production
reduces in seeds
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Source of production
 Mature leaves and other parts of vine
Action
 Affects many types of growth, not all of which are
clearly defined
 Promotes ripening and berry colour
 Promotes abscission zone development
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In general terms, auxins and gibberillins
complement each other, promoting growth
 Cytokinin induces fruit and ripening when
weather conditions and other factors are suitable
for fruit to ripen
 Absissic acid and ethylene promotes ripening and
prepares the vine for dormancy

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
Table 7.2: factors affecting hormone
production
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Auxin is produced in the growing tips and
travels downwards
 To prevent uneven budburst and end point
principle, where the end bud bursts first, canes
are arched during pruning to slow the
movement of auxin along the cane
 Spur pruning is not subject to uneven
budburst
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
Removal of the growing tip will promote
lateral growth, as the site of auxin inhibition of
budburst is removed
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Shaded shoots tend to grow long and spindly
with long internodes until they reach light,
where growth becomes normal
 Buds also tend to be less fruitful in shaded
vines, due to the actions of gibberellin

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
Berry size is related to the number of seeds
(developed embryos) due partly to hormone
production, increasing the berry as a sink
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
Warm, well drained soils during budbreak
improve the evenness of budburst due in part
to cytokinins produced from increased root
growth promoted due to the warmer
conditions
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Fruitfulness
 The number of clusters is increased with
warmer temperatures due to cytokinin
production
 Whereas in shaded or cool situations
gibberellins tends to promote tendril
formation

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As vegetative growth slows close to ripening,
less auxin and gibberellins are produced
 Less auxin is produced as the seed ripens in
stage 2

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
Abscissic acid increases in proportion
inducing véraison and the berry becomes a
major sink
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Cytokinin also increases, attracting sugar to
the berry, abscissic acid and perhaps having an
effect on berry colour and flavour
 Continuing ripening during cool climates may
depend partially on warmer soil temperatures
favouring cytokinin production

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Ethylene is used as a growth regulator
 Ethephon liberates ethylene
 Depending on timing of application it may:

›
›
›
›
Increase berry colour and enhance maturation
Slow vegetative growth
Enhance budbreak
Cause cluster abscission
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Researchers have found that irrigating one side
of a plant can produce the same crop with half
the water
 It can also increase colour and flavour
production by up to 30%

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As one half of the vine's root system is watered,
the other half begins to dry out
 This stimulates the production of abscissic acid
 This causes the leaves to partly close their
stomata and the shoot growth to uniformly slow
down, thereby conserving water

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If this situation is maintained, shoot function
will eventually recover
 However, at about the time that recovery
starts the other side of the root system is
watered
 This leaves the first side to dry out which
ensures one side is constantly in a 'dry phase'

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Hormones are synthesized within the vine control
the initiation and development of inflorescence
primordia within the bud
 They do not act in isolation
 Relative proportions of determine what is formed

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
The number size of inflorescences is the first
indication of yield
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Yield
Yield
per vine
Vines
per hectare
Bunches
per vine
Inflorescences
per shoot
Bunch
weight
Shoots
per vine
Nodes
per vine
Berry
number
Percent
bud break
Florets per
inflorescence
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Percentage
fruit set
Berry
size
Berry
abscision

Fecundity
› the potential reproductive capacity of an organism or
population

Fruitfulness
› The presence of inflorescence primordia in latent buds
› Mean bunch number per shoot
› Three step process:
 Formation of an uncommitted primordium
 Development into inflorescence primordium
 Formation of flowers
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The grapevine buds develop in the axil of the
leaf and the shoot, that is, at the node.
 There are various types of grapevine buds:
 Prompt bud
 Compound bud
 Latent bud

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The lateral shoot arises from the lateral or
prompt bud
 It is formed between the primary or new
season’s shoot and the leaf arising from it, that
is, in the leaf axil
 It may be also referred to as the true axillary
bud

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The prompt bud can burst in the current
season to produce short shoot known as the
lateral
 However, lateral shoots will form only under
certain conditions
 Vigorous vines or if topping occurs early in the
season

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Lateral shoots are generally unfruitful but
bunches may grow on the lateral shoot
 If they do they are usually small and ripen
after those carried on the primary shoot
 These bunches are referred to as 'second set'

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The compound bud is formed after the prompt
bud and develops more slowly
 These buds also develop in the leaf axil at the
node.
 It consists of three true buds

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The compound bud does not burst until the
season after its development
 Generally only the middle, or primary, bud
bursts to develop the primary (main) shoot
 If this is damaged (wind, frost, etc) then the
secondary or tertiary buds may burst
 However, these buds are generally less fruitful,
that is they have fewer bunches per shoot

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The number of potential bunches per bud
develops in the previous season before bud
burst
 Those at the base of the shoot will be more
developed than those close to the apical tip.

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Environmental factors during bud
development influence the potential crop in 18
months time
 A major influence is light interception at the
bud and the temperature; increased light and
temperature has been shown to result in
greater fruitfulness.

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These are buds that may be any type of bud
that do not burst in the season that they are
formed
 Instead they remain dormant and viable and at
some later stage may burst. Latent buds may
take several seasons to burst, often as a result
of vine damage or heavy pruning

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Buds undergo differentiation
 That is, primordial structures within the bud
change depending on plant growth regulators
that these structures receive
 The level of plant growth regulators that the bud
receives is dependant on climatic conditions
during differentiation

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Differentiation coincides with flowering
 And the slowing down of vegetative growth
 Very sensitive to water stress

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Anlagen is a primordia that can become
 Inflorescences

› Repeated branching

Tendrils
› Few branches
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Enhance initiation of anlagen
 Encourage tendril formation as opposed to
inflorescence formation

Recall…
 Promote cell elongation so
 Possibly a mechanism to promote vegetative
growth over reproductive?

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Enhance initiation of anlagen
 Encourage inflorescence formation as opposed
to tendril formation

Recall…
 Promote cell division
 Produced in warm conditions
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
Discourage the initiation of anlagen
Recall…
 Produced by the roots in response to water
stress
 The process is very sensitive to water stress

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