Growth And Development Phytochrome

Question 1

What is the difference between growth and development?

Answer 1

Growth vs. Development
• Growth is the irreversible increase in size due to increase in cell number, cell size or both.
• Development is the transition to a specific form or function

Question 2

What does differentiation in plants mean?

Answer 2

• Differentiation is the process by which cells become specialized with different structures and functions
In roots cells in the region of elongation increase in length, therefore they grow
Cells in the region of maturation develop into vascular tissue or epidermis


Question 3

Why does Development require Differentiation?

Answer 3

Development requires Differentiation
• Differentiation is a process which cells specialize to take on distinctive functions
• Taking on a role within a plant – Cells divide
– They growth
– Then they differentiate
• What they mature into is determined mainly by where they mature.

Question 4

What is an example of differentiation?

Answer 4

An example of differentiation: Xylem vs. Phloem

Both are side by side in a vascular bundle

Question 5

What does Xylem differentiate to Phloem?

Answer 5

Xylem - 
Rigid secondary wall forms
Cell dies leaving hollow cell wall structure
Functional Xylem vessel
Vessel elements joined end to end

Question 6

How does Phloem differentiate to Xylem?

Answer 6

Phloem - starts out as a product of a meristem
Cell elongate
Cell wall forms
Sieve plates develop in ends Interactions develop with neighbouring cells to form a companion cell association FULL FUNCTIONING PHLOEM
Sieve tube elements and companion cells ( living)

Question 7

What triggers differentiation?

Answer 7

What triggers
differentiation?
• Location, location and location
• Cells experience different environments depending upon their location within the plant
– Light & dark
– Chemicals from surrounding cells e.g. hormones

Question 8

Ultimate Control

Answer 8

Ultimate Control
• Genes and gene regulation
• Every cell in a plant has a full set of DNA (identical copy)
• Where cells are located in the plant and what its function in the system determines which genes are turned on or off.
• No sense in producing chlorophyll in roots or root hairs on flowers.

Question 9

What is Totipotency?

Answer 9

Totipotency
• An ability of differentiated cells to dedifferentiate then to re-differentiate into a different cell-type to take on a new role.
• Plants and some animals can do this
• Key controversy involving stem cell research in humans
• It is what allows stem cuttings to form roots (called adventitious roots) in vegetative propagation
• Chemical signals must be produced to allow this transition (Plant hormones)

Question 10

What are the key steps in plant cuttings?

Answer 10

Key steps in plant cuttings
• Key (essential) part of the plant is removed (e.g. root system)
• Cells of the remaining plant tissue must
de-differentiate
• De-differentiated cells then re-differentiate
into the new organ
• Shoot tissue is replaced by roots and the plant functions normally

Question 11

What is intermediate growth?

Answer 11

Indeterminate growth
• Nosettimelimitto“the game”
• Growthcontinues without restriction from the genes
• External influences control rate and duration of development
• Example: perennials

Question 12

What is Photoperiodism?

Answer 12

Photoperiodism
Plants ability to tell the time of the year
• Short-day plant
(lengthening night)
respond in autumn
• Long-day plant (shortening night) respond in spring
• Day neutral plant (not under light control)

Question 13

What 3 major types of pigments are in light sensitive plants?

Answer 13

Light-sensitive pigments in plants
There are three major light-sensitive plant pigment types that function to signal varies light-mediated developmental process in plants
1.
2. 3.
Phytochromes(sensitivetoredandfar-redlight)regulatethetimeof flowering ( photoperiodism), other include -seedling germination, size, shape and number of leaves
Cryptochromes(sensitivetoblueandUltravioletlightandalso associated with responses to magnetism in animals!)
Phototropins: mediate phototropisms – growth in response to
We will only examine Phytochrome here.


Question 14

What are phytochromes?

Answer 14

Phytochromes
• Phytochromes are a family of blue-green pigments found in all green plants.
• They sense the ratio of red (660 nm) and far-red (730 nm) light.
• Phytochrome is involved in many responses to light.
– shading response
• Involved in germination
• Involved in etiolation
– photoperiod (measurement of night length)

Question 15

What is meant by Measuring day length in plants?

Answer 15

Measuring Day length?
• Photoperiod how long a plant is exposed to light in the daytime.
• Yet another time when we named it wrong
– Long Day = phytochrome ‘measures’ the Short Night – Short Day = phytochrome ‘measures’ the Long Night



Question 16

Why do plants need to be able to do this?

Answer 16

Why do plants need to be able to do this?
– Temperature fluctuation is not a great way of deciding
when to flower (too variable)
– Photoperiod is as consistent as the seasons
• Days always get longer in the spring • Days always get shorter in the fall

Question 17

What are the relationships?

Answer 17

These are the relationships:
• Absorption of red light by P(red) converts it into P(far-red)
• Absorption of far red light by P(far-red) converts it into P(red).
• Inthedark,P(far- red) spontaneously converts back to P(red).

Question 18

What are Short Day plants?

Answer 18

Short Day (Long Night) Plants
• Should be called Lengthening Night Plants
• Only flower when the nights reach a long enough critical length
• This critical length is different for different species and cultivars.

Question 19

What are Long Day plants?

Answer 19

Long Day plants
• Should be called Shortening Night Plants
• Only flower when the nights reach a short
enough critical length
• This critical length is different for different species and cultivars.

Question 20

What are Long Day(Short Night)Plants?

Answer 20

• Should be called Shortening Night Plants
• Only flower when the nights reach a short enough critical length
• This critical length is different for different species and cultivars

Question 21

What is the key concept?

Answer 21

Key Concept
• The absolute length of night required to promote flowering is different for different species.
• Some Short-day plants (need lengthening night) will flower when the night is between 10 and 24 hours long, but they will not flower when there is less than 10 hours of night.
• Some Long-day plants (need shortening night) will flower when the night is between 0 and 10 hours long, but they will not flower when there is more than 10 hours of night.

Question 22

Short Day / Long Night Plants

Answer 22

Short Day / Long Night Plants
• At sundown, all the phytochrome is P(far-red).
• During the night, the P(far-red) converts back to P(red).
• The P(red) form is needed for the release of the flowering signal.
• If this process is interrupted by a flash of 660-nm light, the P(red) is immediately reconverted to P(far- red) and the night’s work is undone
• A subsequent exposure to far-red (730 nm) light converts the pigment back to P(red) and the steps leading to the release of florigen can be completed

Question 23

Phytochrome and Night Length?

Answer 23

Phytochrome and Night Length
• P(far-red) is at max at dusk
• Conversion to P(red) measures length of dark period
• Circadian clock times “reading” of the size of the P(far-red) pool at dawn
• Long-night (SD) plants flower when P(far- red) pool is below critical value (at dawn)
• Short-night (LD) plants flower when P(far- red) pool does not fall below critical value