BIOL 3002 Midsem Exam With
Correct Solution
What are the phenotypic responses to changes in light exposure? - ANSWER
Photomorphogenesis - Increased stem elongation, suppressed leaf expansion,
suppressed chloroplast development (+SE, -LE, -CD)
Skotomorphogenesis - Increased leaf expansion, increased chloroplast development,
suppressed stem elongation (+LE, +CD, -SE)
What are photoreceptors and differentiate the different types? - ANSWER
Photoreceptors sense and detect light.
Different types of photoreceptors detect different light wavelengths.
Phytochromes detect red and far red light.
Cryptochromes, phototropins and F-box proteins detect blue light.
Understand the general mechanism of detection and response during red light? -
ANSWER Activity of phytochrome dictated by state of covalently attached bilin
chromophore (binds to photosensory module of protein).
To work, complex forms as a homo-dimer
Activation of complex (Pfr) upon exposure to Red light (day).
Complexes aggregate together to form nuclear photobodies due to conformational
change of output module induced by activation.
Deactivation of complex (Pr) upon exposure to Far Red light (night).
This is faster than activation and driven as a shade avoidance response.
Downstream signaling response driven by secondary phytochrome interacting factors
(PIFs)
Involved in seed germination and hypocotyl elongation.
PIF is active in dark, inactivated by phytochrome which is active red light.
Understand the general mechanism of detection and response during bluelight? -
ANSWER Phototropin.
Blue light activates phototropin which acts as a membrane-bound protein kinase.
, Activation of phototropin results in auto-phosphorylation of the kinase domain and the
phosphorylation of another substrate (often an ion channel).
Open the guard cells.
Cryptochrome.
Blue light activates cryptochromes (is a chromophore involved?) which allows for
binding of BIC.
What is the function of florigen? - ANSWER Universal name for flowering signal in plants
How is florigen transported from the leaf to the shoot apex? - ANSWER Through the
phloem
What is the relationship between leaf production and flowering state? - ANSWER Inverse
correlation; early flowering = less leaves
How does florigen accumulation and timing affect the vegetative phase? - ANSWER
Influences the length of the vegetative phase, which affects biomass and seed
production
Give an example of a florigen-inducing gene in Arabidopsis. - ANSWER FT gene
What regulates the FT gene in Arabidopsis? - ANSWER CONSTANS transcription
enhancer proteins, circadian clock, and blue light photoreceptors
What represses the FT gene in Arabidopsis? - ANSWER FLC repressors
How are FLC repressors downregulated in response to cold temperatures? - ANSWER
Through epigenetic modification of the FLC gene
How did florigen contribute to the domestication of Rice? - ANSWER Movement of crops
to different photoperiods accelerates or delays heading time
What is vernalisation? - ANSWER Subjecting certain plants to a period of cold
temperatures to induce flowering or other developmental change
How does vernalisation impact flowering in Arabidopsis? - ANSWER Through
florigen-dependent and florigen-independent pathways
What does FLC repress in the florigen-dependent pathway? - ANSWER FT in the leaf
What does FLC repress in the florigen-independent pathway? - ANSWER SOC1 and FD
in the meristem shoot
What determines the specific temperature-dependent repressor combinations in other
plants? - ANSWER Unknown
What is Frigida? - ANSWER Gene in Arabidopsis thaliana
Correct Solution
What are the phenotypic responses to changes in light exposure? - ANSWER
Photomorphogenesis - Increased stem elongation, suppressed leaf expansion,
suppressed chloroplast development (+SE, -LE, -CD)
Skotomorphogenesis - Increased leaf expansion, increased chloroplast development,
suppressed stem elongation (+LE, +CD, -SE)
What are photoreceptors and differentiate the different types? - ANSWER
Photoreceptors sense and detect light.
Different types of photoreceptors detect different light wavelengths.
Phytochromes detect red and far red light.
Cryptochromes, phototropins and F-box proteins detect blue light.
Understand the general mechanism of detection and response during red light? -
ANSWER Activity of phytochrome dictated by state of covalently attached bilin
chromophore (binds to photosensory module of protein).
To work, complex forms as a homo-dimer
Activation of complex (Pfr) upon exposure to Red light (day).
Complexes aggregate together to form nuclear photobodies due to conformational
change of output module induced by activation.
Deactivation of complex (Pr) upon exposure to Far Red light (night).
This is faster than activation and driven as a shade avoidance response.
Downstream signaling response driven by secondary phytochrome interacting factors
(PIFs)
Involved in seed germination and hypocotyl elongation.
PIF is active in dark, inactivated by phytochrome which is active red light.
Understand the general mechanism of detection and response during bluelight? -
ANSWER Phototropin.
Blue light activates phototropin which acts as a membrane-bound protein kinase.
, Activation of phototropin results in auto-phosphorylation of the kinase domain and the
phosphorylation of another substrate (often an ion channel).
Open the guard cells.
Cryptochrome.
Blue light activates cryptochromes (is a chromophore involved?) which allows for
binding of BIC.
What is the function of florigen? - ANSWER Universal name for flowering signal in plants
How is florigen transported from the leaf to the shoot apex? - ANSWER Through the
phloem
What is the relationship between leaf production and flowering state? - ANSWER Inverse
correlation; early flowering = less leaves
How does florigen accumulation and timing affect the vegetative phase? - ANSWER
Influences the length of the vegetative phase, which affects biomass and seed
production
Give an example of a florigen-inducing gene in Arabidopsis. - ANSWER FT gene
What regulates the FT gene in Arabidopsis? - ANSWER CONSTANS transcription
enhancer proteins, circadian clock, and blue light photoreceptors
What represses the FT gene in Arabidopsis? - ANSWER FLC repressors
How are FLC repressors downregulated in response to cold temperatures? - ANSWER
Through epigenetic modification of the FLC gene
How did florigen contribute to the domestication of Rice? - ANSWER Movement of crops
to different photoperiods accelerates or delays heading time
What is vernalisation? - ANSWER Subjecting certain plants to a period of cold
temperatures to induce flowering or other developmental change
How does vernalisation impact flowering in Arabidopsis? - ANSWER Through
florigen-dependent and florigen-independent pathways
What does FLC repress in the florigen-dependent pathway? - ANSWER FT in the leaf
What does FLC repress in the florigen-independent pathway? - ANSWER SOC1 and FD
in the meristem shoot
What determines the specific temperature-dependent repressor combinations in other
plants? - ANSWER Unknown
What is Frigida? - ANSWER Gene in Arabidopsis thaliana
