Photoperiod

Question 1

What is phototropism?

Answer 1

This is where plants bend in the direction of light

Question 2

What are the stages of phototropism?

Answer 2

Light perception, asymmetrical auxin distribution, cell elongation and growth, curvature, and continued growth and photoreceptor regulation.

Question 3

What initaties phototropism?

Answer 3

Blue Light (450-470nm) perception by phototropins (photoreceptor proteins)

Question 4

Where are phototropins located?

Answer 4

Found in plant cell plasma membranes, in various growing regions like shoot tips.

Question 5

How is phototropism activated?

Answer 5

Blue light absorption by phototropins induces CC, leading to downstream signalling cascade initiation.

Question 6

What does downstream signalling following phototropin activation lead to?

Answer 6

Redistribution of Auxin, like indole-3-acetic acid, with phosphorylation of downstream proteins, resulting in

Question 7

Where does Auxin accumulate?

Answer 7

On shaded size of plant, resulting in enhanced elongation on shaded sides, which causes curvature of the leaf.

Question 8

How was evidence of auxins role provided?

Answer 8

F.W. Went (1926) - using oat coleoptiles, placed them horizontally in agar petri dish, exposing coleoptiles to unilateral light source(blue light), induced bending, hypothesised if a chemical substance was responsible for this, it should be able to diffuse from illumintaed side to shaded side, so he cut thin agar block soaked in nutrient solution containing auxin, placed it on shaded side, observing bending towards side containing auxin after a few hours, due to auxin diffusion.

Question 9

What processes are photoropin dependent?

Answer 9

Phototrpism, chloroplast movement, stomatal opening, seedling responses, gravitropism…

Question 10

How do phototropin-dependent processes optimise plant performance?

Answer 10

Optimisation of light capture, photosynthetic efficiency, and allocation of resource.

Question 11

What are the stages of seasonal flowering?

Answer 11

Photoperiod perception, signal transduction pathways, gene expression regulation, environmental/hormonal signals, floral meristem identity initiation, floral organogenesis, then flower maturation/reproduction.

Question 12

How is photoperiod perceived?

Answer 12

By photoreceptors like phytochromes and cryptochromes

Question 13

What is the molecular basis of perception?

Answer 13

Conversion from Pr to Pfr

Question 14

How do phytochromes interact with CR?

Answer 14

Interact with Tf involved in flowering time, like CONSTANS.

Question 15

What does CONSTANS do?

Answer 15

This promotes flowering under long-day conditions.

Question 16

How do phyochromes facilitate CO expression?

Answer 16

Bind promoter regions or modulate TF activity.

Question 17

What does CO do following expression by phytochromes?

Answer 17

Triggers transition to reproductive growth.

Question 18

How does CO integrate with CR?

Answer 18

Ensures induction occurs at appropriate time of day, coinciding with peak Pfr accumulation, for maximising reproductive success.

Question 19

What is the biochemical basis of CO activation of seasonal flowering?

Answer 19

CO activation of FLOWERING LOCUS T expression (upregulated with CO accumulation), promoting floral transition and inflorescence development

Question 20

What does FT interact with following CO-induced expression?

Answer 20

Moves from leaves to the Shoot Apical Meristem, interacting with other proteins to initatie gene transcription for floral organogenesis

Question 21

Why is transition to reproduction phases important?

Answer 21

Reproductive success to maximise production of seeds and offspring survival.

Question 22

What are the consequences of flowering early?

Answer 22

Not enough energy stored for seed development.

Question 23

What are the consequences of flowering late?

Answer 23

Potential of seed maturation taking place in adverse weather conditiosn.

Question 24

What are the two phototropins?

Answer 24

Phot1 and Phot2

Question 25

What do phototropins do?

Answer 25

Absorb UV-A/blue light for photo-induced movement responses.

Question 26

How do shoots/roots relate to phototropism?

Answer 26

The former how positive, moving towards the light, whilst shoots show negative.

Question 27

What physiological responses does blue-light drive?

Answer 27

Opening of stomatal pores in leaves and stems to regulate CO2 uptake for PS, as well as movement of chloroplasts in response to different light intensities.

Question 28

What is the process of flowering initiation?

Answer 28

Regulated by an antagonistic relationship between CCA1 and CONSTANS expression. Phototropin upregulates CO expression with blue light. CO is responsible for flowering initiation. However, to maximise fitness, flowering should only occur during long-days, where light is most abundant. Thus the circadian rhythm tracks day length through an internal oscillating clock. CCA1 is a part of this, and is kept at low concentrations during day periods. With long-days, CCA1 declines eariler, allowing increased CO expression, and thus floral induction.

Question 29

How does CO interact with CR?

Answer 29

Circadian clock oscillator components like CCA1 and LHY downregulate CO promoter expression

Question 30

How does CCA1 relate to photoperiod?

Answer 30

CCA1 follows diurnal rhthms, peaking during night, low at day.

Question 31

How does CR interact with phototrpism?

Answer 31

Control of the light sensitivty of photoreceptor to light, and regulates auxin asymmetric distribution through gene expression of auxin transporter control.

Question 32

How does light get to auxin in phototropism?

Answer 32

Light perception by phototrpins in PM by CC from unilateral blue light, autophosphorylation triggers signalling cascades activating non-phototrpic hypoctoyl 3 and root phototropism 2, transmitting light to cytoplasm, phototropins redistribute to shaded side of cells, guiding plant response to light direction, ion channels lead to Ca ion influx activating proton pups transporting protons from cytoplasm to cell wall, acidifying cell wall on shaded side, activationg expansin enzymes loosening cell wall components, with auxin redistribution then occuring.

Question 33

What study talks about the process of phototropism?

Answer 33

Liscum and Stowe-Evans, 2000)