cell signalling in plants

Question 1

factors that plants sense and respond to

Answer 1

• light
• heat or cold
• internal chemical signals/hormones
• touch
• drought or flooding
• time
• gravity
• wounding
• infection

Question 2

de-etiolation

Answer 2

• growing in absence of light

Question 3

de-etiolation - reception stage

Answer 3

• light signal is detected by phytochrome receptor
• activates at least two signal transduction pathways

Question 4

de-etiolation - transduction stage

Answer 4

a) pathway uses cAMP as second messenger to activate a protein kinase
b) another pathway increases cytosolic level of Ca2+, activates a different protein kinase

Question 5

de-etiolation

Answer 5

• both pathways lead to expression of genes for proteins that function in de-etiolation response

Question 6

1) synthesis of plant hormone

Answer 6

• many tightly regulated biochemical pathways contribute
• conjugation can temporarily store a hormone in inert form, lead to catabolic breakdown or be means for producing active hormone

Question 7

2) transport and perception of plant hormones

Answer 7

hormones can move:
- through xylem or phloem
- across cellular membranes
- through regulated transport proteins

Question 8

3) signal transduction of plant hormones

Answer 8

• hormonal signals are transducer in diverse ways
• common methods = reversible protein phosphorylation & targeted proteolysis

Question 9

4) responses of plant hormones

Answer 9

• downstream effects can involve changes in transcription & changes in other cellular activities, e.g. ion transport

Question 10

phototropism

Answer 10

• growth towards light

Question 11

thigmotropism

Answer 11

• growth in response to touch stimulus
• can be growing around or away from object

Question 13

hydrotropism

Answer 13

• growth towards water

Question 14

coleoptiles

Answer 14

• tissues that protect monocot leaves during germination

Question 15

cutting/covering coleoptile…

Answer 15

• interferes w/ response
• unaffected coleoptile bends towards light
• shielded/removed coleoptiles do not bend
• light signal is perceived at tip, though bending occurs at base

Question 17

what did Paal show?

Answer 17

• removing the tip and replacing it on one side of the base is sufficient to cause bending

Question 18

auxins roles in cell elongation and plant development

Answer 18

• stimulate elongation of cells within young, developing shoots
• rapidly alters gene expression
• stimulates sustained growth responses

Question 19

practical uses for auxins

Answer 19

• vegetative propagation of plants by cutting
• herbicides
• assisting fruit development

Question 20

cytokinins functions

Answer 20

• cell division and differentiation
• apical dominance
• ‘anti-aging’

Question 21

gibberellins

Answer 21

• discovered from gibberella fungus infection
• stem elongation
• fruit growth
• germination

Question 22

abscisic acid

Answer 22

• often antagonises the actions of growth hormones
• seed dormancy
• drought intolerance

Question 23

ethylene

Answer 23

• the triple response to mechanical stress
• leaf abscission
• fruit ripening

Question 24

triple response to mechanical stress

Answer 24

• slowing of stem elongation
• stem thickening
• horizontal stem growth

Question 25

abscission

Answer 25

- controlled by change in the ratio of ethylene to auxin - after leaf falls, a protective layer of cork becomes the leaf scar that helps prevent pathogens from invading the plant