light as a developmental cue

Question 1

name the 4 things involved in light as a ligand in the signal transduction pathway

Answer 1

phytochrome
phototropism
photomorphogenesis
circadian rhythms

Question 2

does light directly activate promoter elements?

Answer 2

no, instead light is perceived, then a signaling pathway is activated where TFs bind to light responsive elements

Question 3

studies of seed germination led to discovery of ___

Answer 3

phytochrome (plant photoreceptors)

Question 4

phytochrome structure consists of two ____ joined to form ____

each of these proteins has 2 domains:

Answer 4

identical proteins joined to form one functional dimer molecule

photoreceptor activity & kinase activity

Question 5

phytochrome is a ____, it exists in two different protein form that are reversible by ___

Answer 5

photoreceptor
light wavelengths (interconversion triggers diff responses)

Question 6

phytochrome alternates between 2 forms:

Answer 6

Pr absorbs red light (660 nm) and is converted to Pfr

Pfr absorbs far-red light (730 nm) and is converted to Pr

Question 7

phytochrome: red light stimulates ___ and far-red light inhibits ____

Answer 7

seed germination
seed germination

Question 8

how does light effect phytochrome?

Answer 8

light activation of phytochrome to the Pfr (active) form allows it to rapidly accumulate in the nucleus and activate gene expression

Question 9

light signaling in the eye:
cone cells are sensitive to ___
rod cells are sensitive to ___

Answer 9

colors
light, not colors

Question 10

photoreceptors in the retina: light induces…

Answer 10

dissociation of retinal from opsin
- in the dark, enzymes convert retinal back to its cis-configuration (going from bright environment to a dark one: not enough cis-retinal available, blinding effect

Question 11

light signal transduction in animals involves ____, followed by ___ and ____

Answer 11

a light induced isoform change
G-protein signal pathway
ion channal activation

Question 12

name the 4 classes of plant photoreceptors

Answer 12

1- phytochromes
2- cryptochrome
3- phototropins
4- UVR8

Question 13

cryptochrome is ___ light

Answer 13

blue

Question 14

phototropins are ___ light

Answer 14

blue

Question 15

UVR8 is ___ light

Answer 15

UV-B

Question 16

what is phototropism?

Answer 16

growth response to light

Question 17

shoot exhibit ___ phototropism
roots exhibit ___ phototropism

Answer 17

positive (grows toward light)
negative (grows away from light)

Question 18

tropism = any ___ response that results in the ___ of plant parts toward or away from a stimulus

what does it result from?

Answer 18

growth
curvature

results from differential cell growth on opposite sides of stem or root

Question 19

phototropism involving auxin:

asymmetrical distribution of auxin moving down from the shoot top causes cells on the ___ side to…

Answer 19

darker side to elongate faster than cells on brighter side

Question 20

photomorphogenesis means…

Answer 20

light affecting development

Question 21

cyclical responses to environmental stimuli are ___

approximately ___ long

Answer 21

circadian rhythms
24 hrs

Question 22

480 of 8,000 tested genes are under ___ control

Answer 22

circadian

Question 23

many plants follow a circadian rhythm of ___ their leaves

Answer 23

raising-lowering (light regulated)

Question 24

in plants - what is referred to as light quality or the ___ can determine the effect of light on the biological clock

perception of this ratio/amount is done by ___

Answer 24

ratio of red to far red light
phytochrome

this then provides the organisms’ biological clock with environmental cues

Question 25

photoperiod is the ____

Answer 25

relative lengths of night and day, is the environmental stimulus plants use most often to detect the time of year

Question 26

____ is a physiological response to photoperiod

Answer 26

photoperiodism

Question 27

photoperiodism (flowering time) name 3 plants

Answer 27

short-day plants - requires light period short than a critical length to flower

long-day plants- required longer

day-neutral plants- unaffected by photoperiod