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• Workbook from last week – 86-94 – questions?

• This weeks homework – Any workbook pages between 40 and 94 that you haven’t done (we have done most of these).

• Holidays – Plant responses pg’s 99-110 – Facebook me if you get stuck – highlight any you want to ask about next term.

Plant responses

Tropisms• Direction of plant growth

in response to a stimuli

• Compared with Taxis and Kinesis (movement of animals)

Phototropismsplants grow in response to light

Positive phototropism: growth towards light (stems)

Negative phototropism: growth away from light (roots)

gravitropism

thigmotropism

chemotropism

hydrotropism

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https://www.pathwayz.org/Tree/Plain/PHOTOTROPISM+-MECHANISM

Do plants grow towards or away from light?

Why?

How?

• A hormone called auxin (eg indole acetic acid or IAA) is made by the growing tips, or meristem, of shoots and roots.

• How can we prove that auxin is made in the meristem?

• This means there is more auxin on the shaded side just below the tip.

• Auxins change the flexibility of cell walls and this allows for more rapid growth of the cells.

• The net result is that the shoot tip grows towards the light (remember photosynthesis requires light).

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What do these experiment suggest? What does this experiment suggest?

• The auxin is water soluble and diffuses from the tip

• Therefore removing the tip and placing it on Agar - will not stop it diffusing

What does this experiment suggest?

• The auxin is water soluble and diffuses from the tip

• Therefore removing the tip and placing it on A sheet of mica or foil - will stop the diffusion

In a bioassay, concentration is expressed in terms of biological effect rather than quantitatively. Went (1926)

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• Stem growth is faster with HIGHER auxin concentrations.

• But root tip growth is faster with LOWER auxinconcentrations

• In shoots, auxin stimulates growth.

• In roots, auxin inhibits growth.

Conclusions?

• When a shoot tip is exposed to light the auxins move to the shaded side of the tip.

• How can we prove this?

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https://www.youtube.com/watch?v=H9MV5CgPgIQ

• Always – link to survival• This weeks homework – Any workbook pages between 40 and

94 that you haven’t done (we have done most of these).

• Holidays – Plant responses pg’s 99-110 – Facebook me if you get stuck – highlight any you want to ask about next term.

Plant Hormones

Plant Hormones1. State the effect of auxin on roots, shoots and lateral

buds.2. Describe and explain apical dominance.3. Describe the origin and effects of

- gibberellins.- cytokinins.- ethene (ethylene) gas.- abscisic acid.

4. What are some applications of each of these plant hormones in industry?

Apical dominance

• Apical dominance is where the central stem of the plant is dominant over (i.e., grows more strongly than) other side stems.

• Apical dominance is caused by auxin produced in the growing tips

Apical dominance and auxins

• auxins from the apical meristem inhibit the

lateral buds

• If the apical meristem is lost, then the lateral buds start growth due to the lower auxinlevels.

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1. Low [auxin] stimulates root and lateral bud growth. High [auxin] inhibits.

High [auxin] stimulates shoot growth.

2. Apical buds inhibit lateral bud growth. Remove the apical bud and lateral buds grow as [auxin] drops.

The effect of Gibberellic acid

Overcomes seed dormancy Increases height of plants

• Gibberellins play an important role in germination, initiating the mobilisation of nutrients stored within the seed.

• Absorption of water by the seed causes production of GA (gibberellic acid) .

• They also promote the elongation of stems, flowering and cell division (growth).

The effect of Abscisic acid

• Causes leaf fall

• Controls stomatal opening

Abscisic acid (ABA)

• In general, abscisic acid inhibits growth / germination.

• Abscisic acid induces bud and seed dormancy, preventing germination during winter.

• Abscisic acid also preventing seeds from germinating within the fruit

• It slows growth in more "mature" parts of the plant and closes stomata (tiny pores on the undersides of the leaves) in response to a lack of water.

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The effect of ethylene

ripens

Ethylene

• A gas that promotes fruit ripening and abscission (drop) of leaves and fruit.

• Ethylene production increases when the seeds are mature, ensuring the fruit is released when only when the seeds are capable of germination.

• Fruit often releases ethylene gas as it ripens (this is why storing unripened fruit with a ripening apple will accelerate the ripening process).

• Many plants have their time of flowering delayed unless they have undergone a preceding period of wintertime cold.

• The change brought about by this prolonged exposure to the cold is called vernalisation.

• Plants respond to their environment by growing – a response called a __1___.

• They can do this because of hormones called ___2____ which are made in the ____3____ . Growth can be towards a stimulus eg ___4_____ or away from it.

• Early experiments were done with sheaths covering grass shoots called ___5____ Expts showed that the sensitive part is the ___6___ and it causes its affects by _ _7_

Recap

• Lots of hormone in stem cells cause _8_ _ whereas in root cells it causes _ _9_ _ .

• Non directional responses to a stimulus eg a flower closing at night are called __10___ responses.

• Being positively thigmotropic is of adaptive value because _ _ _11_ _ _

Root tip

light

12. Draw the resulting

root tip showing WHY

this is what happened

RecapSummary of Functions of Major Plant Hormones

Hormone Function Location

Auxins (IAA)*

stem elongation apical dominance root formation

produced in shoot apical meristem

Cytokininscell division differentiation

produced in roots

Gibberellins(GA)*

stem & intemode

elongation

seed germination

produced in apical portion of root & shoot

Ethene/ethylene*abscission fruit ripening

produced in leaves, stems & young fruits

Abscisic Acid

supression of bud growth stomatal opening leaf senescence

mature leaves, fruits & root caps

*most horticultural/ agricultural applications

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3.Giberellins produced in young leaves, buds and roots. Stimulate internode growth, flowering and germination. Breaks dormancy.

Cytokinins produced in roots. They promote cell division and slow the aging process.

Ethene gas produced by all parts of plant. It causes fruit to ripen and leaves to age.

Abscisic acid produced in stalks. Inhibits bud development, seed germination and causes leaf and fruit abscission.

4. Giberellins used to increase height of plants, induce flowering, induce germination of grain in brewing process.

Cytokinins extend shelf-life of plants by preventing abscission.

Ethene gas used to ripen fruit and cause fruit abscission on demand.

IS

• Complete worksheet and practice questions

• To discuss on Thursday

• This weeks homework – Any workbook pages between 40 and 94 that you haven’t done (we have done most of these).

Summary of Functions of Major Plant Hormones

Hormone Function Location

Auxins (IAA)*stem elongation apical dominance root formation

produced in shoot apical meristem

Cytokininscell division differentiation

produced in roots

Gibberellins(GA)*

stem & intemode elongation seed germination

produced in apical portion of root & shoot

Ethene/ethylene*

abscission fruit ripening

produced in leaves, stems & young fruits

Abscisic Acidsupression of bud growth stomatal opening leaf senescence

mature leaves, fruits & root caps

*most horticultural/ agricultural applications

Today

• Describe Nastic responses

• Explain the adaptive advantage of nastic responses

Remember Kinesis ???

• A kinesis is non-directed orientation – moves, but not towards or away from a stimulus.

• The amount of movement is related to the extent of the stimulus

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Nastic Responses in Plants

•Plant reacts to strength of stimulus •eg light, touch, temperature but not to the direction of the stimulus

Nastic responses:

• https://www.youtube.com/watch?v=bczox-dDKP0

• https://www.youtube.com/watch?v=L9cxT0Uv9n4

• https://www.youtube.com/watch?v=n859bkmNXsU

• What would happen with photonasty?

• flower opens/closes in response to light

• What is the adaptive advantage?

• What would happen with thigmonasty?

• Leaves move to touch

• What is the adaptive advantage?

Etiolation

• Stimulus is…

lack of light

What is the adaptive advantage?

Do Workbook pages

• 107-109 – Nastic responses.

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Recap.

• Niche, Biotic, Abiotic

• Gause's Principle, Liebig's law of the minimum

• Taxes, chemotaxes, phototaxes, thigmotaxes, hydrotaxes, klinotaxes and tropotaxes.

• kinesis, orthokinesis, klinokinesis

• Endogenous, Exogenous, diurnal, nocturnal, crepuscular, arrhythmic, circalunar, circatidal, circannual, biological clock.

• Free running, zietgeber, phase shift, actogram, entrainment

• Migration, Navigation, Homing

• Interspecific, predator, prey, cryptic, aposematic, coevolution

• Batesian mimicry, Mullarian mimicry

• Predator- prey relationships, Herbivory, Pollination

• Mutualism, Symbiosis, commensalism, antibiosis, allelopathy

• Parasites, ectoparasites, endo–parasites, parasatoids, social parasites, plant parasites, facultative and obligatory parasitic relationships.

• Zonation, Stratification, Succession

• Territory, Hierarchy, Aggressive, Dominant, Submissive, Pecking order, Alpha, Beta, Kin alliance

• Tropism, Phototropism, thigmotropism, hydrotropism, gravitropism, geotropism, positive and negative responses.

• giberellin, cytokinin, abscisic acid, ethelene, inhibit, stimulate

• Nastic response, Etiolation

Homework this week:

• Workbook pages – 95-98

• Create a set of notes about photoperiodism (what's your strategy? write/ highlight workbook etc…)

• Update your glossary.

Photoperiodismregulation of activity by the photoperiod

Remember – photo = light

The phenomenon is called photoperiodism.

Plants use photoperiod to measure the seasons and to coordinate seasonal events.

• Why is this useful?

• What sorts of things are coordinated seasonally?

Plant responses to photoperiod

• autumn leaf drop

• formation of winter dormant buds (short days)

• development of frost hardiness

• formation of roots on cuttings

• formation of many underground storage organs such as bulbs and tubers

Flowering

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Many plants flower at about the same time every year.

Their flowering is a response to the changing length of day and night as the season progresses.

It helps promote cross pollination as plants all flower around the same time.

(cross pollination contributes to diversity)

Some flower only when exposed to short periods of light

• They are called short-day plants.

• Tobacco

• chrysanthemums

• poinsettias

• the cocklebur

Short-day plants (SDP)

…need a sufficiently long night.

They have a critical day length (CDL) that

MUST NOT be exceeded.

Long-day plants (LDP)

• Some plants such as

• spinach

• Arabidopsis

• sugar beets and the

• radish

flower only after

exposure to long days

so are called

long day plants.

Long-day plants

… need a short night.

They have a critical day length (CDL) that

MUST be exceeded.

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Still other plants, e.g. the tomato, dandelion and

rose are day neutral; flowering is not regulated by photoperiod.

Photoperiodism also explains why some plant species can be grown only in a certain latitude.

Spinach, a long-day plant, cannot flower in the tropics because the days never get long enough (14 hours)

Note: It is the length of the night that is most important!!

? ? ?

? ? ?

Flowers when nights are long so is a short day plant

Short day plant or long day plant?

To flower, night must be 12 hours OR MORE so is a short-day plant

Shor

t day p

lant

or

long

day p

lant

?

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SDP or LDP?

Needs 8 or more hours of dark to initiate flowering so is a short day plant

To flower, nights must be 12 hours OR LESS, so it is a long-day plant

Shor

t day p

lant

or

long

day p

lant

?

Florigen

Photoperiod is detected in the leaves.

Even if only a part of one leaf is exposed to the correct

photoperiod, the entire plant will bloom (middle figure).

Florigen

It is thought that the leaves produce a chemical

signal — called florigen — that is transmitted

to the apical meristems to start the development of

flower buds

Why are plants and animals more likely to respond to photoperiod than temperature?

• day length provides an extremely accurate means of determining the season at a given latitude.

• other environmental factors eg light levels and temperature also vary with the seasons but vary from year to year.

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Animal responses to photoperiod

• control of several stages in the life cycle of insects

• moulting, development of gonads, deposition of body fat, and migratory behaviour in birds

• controls reproduction in sheep, goat and snowshoe hare

• fur colour in certain species (snowshoe hare)

• growth of antlers in American elk and deer

Remember! Homework this week:

• Workbook pages – 95-98

• Create a set of notes about photoperiodism (what's your strategy? write/ highlight workbook etc…)

• Update your glossary.

Remember! Homework this week:

• Workbook pages – 95-98

• Create a set of notes about photoperiodism (what's your strategy? write/ highlight workbook etc…)

• Update your glossary. Photoperiodism&

Phytochrome

Cocklebur

flower only if they have been kept in the dark for a

certain no. of hours - the critical period.

SDP or LDP? SDP

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• Interruption of an otherwise long night by red (660 nm) light prevents flowering.

It will flower if this flash of red light is followed by irradiation with far red (730 nm) light

Red

Far red

Humans can see from about 390nm to 700nm – this is the visible spectrum, ROY G BIV

An intense exposure to far red light at the start of the night reduces the dark requirement by 2 hours

These responses are due to phytochromes.

To flower, or not to flower . . . .

Phytochromes

Phytochromes are proteins that exist in two interconvertible forms

• Pr because it absorbs red (r; 660 nm) light

• Pfr because it absorbs far red (fr; 730 nm) light

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• Absorption of red light by Pr converts it into Pfr

Absorption of far red light by Pfrconverts it into Pr. In the dark, Pfr spontaneously converts

back to Pr.

Sunlight is richer in red (660 nm) than far

red (730 nm) light so at sundown, all the

phytochrome is Pfr.

More red light in DAY

Means more Pfr by evening

The longer the day, the more Pfr is formed

• During the night, the Pfr converts back to Pr

the longer the night, the more Pr by morning.

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The behaviour of phytochromeexplains the experimental results with the short day cocklebur.

• During the night, the Pfr converts back to Pr –the longer the night, the more Pr (and the lessPfr.)

• A low amount of Pfr is needed for the release of the flowering signal in short day plants. The cocklebur needs 8.5 hours of darkness in which

to • convert all the Pfr present at sundown into Pr • carry out the reactions leading to the release of the

flowering signal ("florigen")

If this process is interrupted

by a flash of red (660nm)light, the Pr is immediately reconverted to Pfr and thenight’s work is undone

More red in DAY

More far red at NIGHT

Low levels of Pfr is needed for the release of the flowering signal.

Exposure to far red (730 nm)

light again converts the

pigment back to Pr and

the steps leading to the

release of florigen can

be completed

More in DAY

More at NIGHT

Low levels of Pfr is needed for the release of the flowering signal.

Exposure to intense far red light at the beginning of the night sets the clock ahead about 2 hours or so by eliminating the need for the spontaneous conversion of Pfr to Pr

More in DAY

More at NIGHT

Low levels of Pfr is needed for the release of the flowering signal. Long Day Plants

Lots of the Pfr form is needed for the release of the flowering signal

.

More in DAY

More at NIGHT

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Long Day Plants

So long days (or short nights) are needed to get enough Pfr

.

More in DAY

More at NIGHT

Long Day Plants(Lots of Pfr is needed for the release of the flowering signal)

will bloom successfully on a short-day schedule if the night periods are interrupted by a brief

exposure to light.

So these plants are really short-night plants. They can bloom only if the nights are not too long (so not too much Pfr is lost to Pr)

Plants that need a critical night length

or LESS are called long-day plants

Need enough daylight to make enough Pfr

Seasons affect daylength

It is the presence or absence of Pfr that is important rather than the amount of Pr

Pfr inhibits flowering in short day plants and induces it in long day plants

1

9

8

7

3

4

5

6

2

12

11

10

• It seems that Phytochrome Pfr goes into the nucleus and combines with transcription factors.

• This enables promotor genes to be turned on

• this allows the transcription of the genes that are expressed when a plant is exposed to light (eg make chlorophyll, florigen)

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But…it’s not always about the photoperiod….

Vernalisation-promotion of flowering by chilling

• Seed germination or flowering needs a period of cold first

• Growth has been continual but the type of growth changes.

Advantages…

• Favourable conditions will follow.

• First year of biennials is vegetative – to create energy reserves.

Dormancy – seeds and buds

• Period of low metabolism to ensure they survive till conditions are suitable.

Buds produced in summer, then sit dormant until after period of cold.

Kept dormant by which hormone?

Abscisic acid

•Vernalisation causes a change in the location of growth whilst dormancy causes a change in the rate of growth.

Advantages of Abscission – leaf fall

•Caused by which hormone?•Abscisic acid•Reduces water loss, or survive icy soil when water cannot be replaced.

•Gets rid of waste substances in the leaves.

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Create a summary of the followingNiche, Biotic, AbioticGause's Principle,Liebig's law of the minimum

Chemo,Photo,Thigmo,GravoHydro,Klino,

TaxesKinesisTropismNastic response

Endogenous, Exogenous, biological clock.Free running,zietgeber, phase shift, actogram, entrainment

diurnal, nocturnal, crepuscular, arrhythmic, circalunar, circatidal, circannual,

cryptic, aposematic, Batesian mimicry, Mullarian mimicry

Predator- prey Herbivory, PollinationMutualism, commensalism, antibiosis, Allelopathy

Coevolution

Symbiosis

Migration, Navigation, Homing

Parasites, ectoparasites, endo–parasites, parasatoidsocial parasites, plant parasites, facultative and obligatory parasitic relationships

Zonation, Stratification, Succession

Territory, Hierarchy, Aggressive, Dominant, Submissive, Pecking order, Alpha, Beta, Kin alliance

giberellin, cytokinin, abscisic acid, ethelene, inhibit, stimulateNastic response, Etiolation

FloriginPhytochromes

IS:

Bring your questions to the library

Finish workbook pages 112-116

Finish your summary page