Photosensing + Plant Growth

Question 1

light

Answer 1

key enviro signals to regulate growth and development.

= photomorphogenesis

Question 2

plant photoreceptors

Answer 2

monitor almost all facets of light with them.

• perceive + interpret light.
• initiate signaling pathwayto regulate developmental processes.
• specific wavelength induces confomational change = initiate signal transduction

Question 3

phytochromes

Answer 3

absorb red and far-red light

- key-regulators of photomorphogenesis

Question 4

three types of photoreceptors for UV-A/blue light

Answer 4

cryptochromes
phototropins ( regulate phototropisms (lateral auxin redistribution), stomatal opening
zetlupe: daylegth perception and circadian rhythyms

Question 5

receptors that mediate response to UVB irradiation

Answer 5

UVR8 - no chromophore. excite protein without it

Question 6

chromoproteins

Answer 6

contain chromophore (light absorbing) attached to an apoprotein. 
- phytochrome, cryptochrome, phototropin, ZTL need one

Question 7

photoresponse + spectral property of light

Answer 7

wavelength specificity of biological response.

germination with red light, far-red inibits it.

Question 8

photoresponses + amount of light

Answer 8

light influence + irradiance govern photoresponse.

- some photoresponses are dose-responsive.

Question 9

define fluence

Answer 9

total number of photons striking unit of surface area.

fr: how fast photons are arriving and how long duration of irradiation

Question 10

phytochrome

Answer 10

primary photoreceptor, R + FR.

two states. Pr (red) and Pfr (far-red) Pr inactive & Pfr active

Question 11

Phytochrome photoreversibility - diff types of light

Answer 11

action spectrum = absorption spectrum.

sunlight: red light over far-red
chlorophyll: under canopy = far-red, poor red ight

Question 12

what is phytochromobillin

Answer 12

chromophore in all plant phytochromes.

- can convert between forms easily.

Question 13

phytochrome gene family

Answer 13

multiple genes encoding.

- individual phytochromes play diff roles in regulating developmental + physiological events

Question 14

few examples of what phytochrome photoreversibility mediates?

Answer 14

germination, leaf primordia, internode elongation, flowering, growth,

Question 15

how do phytochrome responses vary?

Answer 15

lag time: time btw exposure + response.

escape time: time before overall sequence of reaction s become irreversible.

Question 16

3 categories of phytochrome initiated responses

Answer 16

1. Very low fluence responses
2. low fluence response
3. high irradiance response

Question 17

what is fery low fluence response?

Answer 17

0.0001-1umol
sensitive: easily initiated
magnitude exhibits reciprocity: brief duration of bright light = long duration of dim ight
- non-photoreversibl
- phytA
- found in dark-grown seeds/seedlings: seed germination, gravitropic orientation, coleoptile elongation

Question 18

what is low fluence response

Answer 18

1-1000 umol/m2

• initiated by brief pulse
• exhibits reciprocity
• R:FR reversible
• Mostly phytB
• include most phytochrome responses: seed germination, inhibit hypocotyl elongation, leaf movement

Question 19

High irradiance responses

Answer 19

• prolonged or continuous exposure to light of relatively high irradiance
  – no reciprocity. need high intensity for short time
• non-photoreversible
  far-red: PhytA
  red + white: Phyt B

= anthocyanin synthesis, seedling de-etiolation, flowering

Question 20

positively photoblastic seeds

Answer 20

seed germination stimulated by light

- negative photoblastic if germination inhibited by high intensity light.

Question 21

germination light ratio?

Answer 21

high R:FR.

Question 22

phytochrome regulates gene expression via

Answer 22

phytochrome-mediated protein degradation

phytochrome interacting factor

Question 23

what is phytochrome interacting factor? what does it do?

Answer 23

transcription factors.

• regulate various aspects of phytochrome-mediated photomorphogenesis.
• negative regulators of photomorphogenesis in dark.

Question 24

what is seedling de-etiolation

Answer 24

repression of skotomorphogenesis in the light via red light-induced Pfr formation promoting degradation of PIFs repressors of photomorphogenesis

Question 25

shade avoidance

Answer 25

trigger plant growth

• elevate leaves towards unfiltered daylight = plants to oovertop competitors
• response initiated because light environment is far-red enriched

Question 26

phytochromes + shade avoidance

Answer 26

perceive light quality

- absorb red + blue. as shading increases, R:FR decreases.

Question 27

sun plants

Answer 27

adapted to open habitat
- sense low R:FR and elongate stems/petioles, upward orientation of leaves, increased apical dominance

= shade avoidance response are target for crop breeding = high density + yield
= phyt B plays role

Question 28

what is photoperiodism

Answer 28

ability to detect day length -> enable seasonal response.

- switch phase of plant development

Question 29

what is critical day length

Answer 29

minimum length of daily light treatment required to initiate flowering

Question 30

2 requirements of critical day length?

Answer 30

qualitative (obligate) : species require absolute minmax day length to flower
quantitative (facultative): flowering increase w longer day/shorter day

Question 31

short day plants
long day plants
day-neutral plants

Answer 31

SDP: flower when day lengths are less than criitical photoperiod.
LDP: flower when the day length exceeds the critical photoperiod
DNP: independent of day length

Question 32

how is day length measured?

Answer 32

length of night, duration of darkness.

• interruption of dark may restart cycle
• may also depend on final exposure. R interruption ldp flower. fr interruption, sdp flower