Phytochrome and Photomorphogenesis Flashcards
is as protein pigment that absorbs red and far-red light most strongly, and also blue light
phytochrome
each subunit of phytochrome consists of a light absorbing pigment molecule called
chromophore
each subunit of phytochrome consists of a polypeptide chain
apoprotein
T/F: Phytochrome is a soluble, light-regulated protein kinase, which first auto phosphorylates and then activates other proteins
true
In dark-grown or – plants, phytochrome is present in a red light-absorbing form Pr
etiolated
Pr is converted by – to a far-red light absorbing form, Pfr
red light
switching of forms between Pr and Pfr
photoreversibility
Pr = red light
650-680 nm
Pfr = far red light
710-740 nm
Which form is physiologically active?
Pfr
– red:far red ratio → germination. Lets wild seeds respond when they arrive in a forest gap or clearing
high
Low red:far red ratio → – in sun plants
elongation
“Etiolation” response involves allocating strongly to –, to escape the shade
long, thin stems
– plants show etiolation response more strongly
Sun-adapted
phytochrome regulates - leaf movements (open day, close night)
nyctinastic
in legumes nyctinastic movements are caused by rhythmic – changes in flexor and extensor motor cells int eh pulvinus at the base of the petiole
turgor
because red:far red ratio is low under canopies, plants can sense –
green shade
domestic plants lose etiolation response so they can be grown in – without etiolating
high densities
floral meristems distinguished from vegetative meristems by their
larger size
transition from vegetative to reproductive dev is marked by an increase in – in central zone of shoot apical meristem
frequency of cell divisions
when reproductive dev is initiated, vegetative meristem is transformed into the – which bears cauline leaves and flowers
primary inflorescence meristem
axillary buds of cauline leaves dev into –
secondary inflorescence meristem
inflorescence meristem has – growth
indeterminate
flowers have – growth
determinate
floral meristems initiate four organ types in concentric rings called
whorls
initiation of – consumes all of the meristematic cells in the apical dome
carpels
specifies sepals
A
specifies petals
A + B
specifies stamens
B + C
specifies carpels
C
loss of A
carpels replace sepals, stamen replace petals
loss of B
sepals replace petals, carpels replace stamen
loss of C
petals replace stamen, new flower replace carpel
– may flower within a few weeks after germinating
annual plants
perennial plants (forest trees) take up to – to flower
20+ years
– and – is an internal factor controlling the switch to reproductive dev
size or age
internal cues
autonomous regulation
environmental cues
obligate response
promoted by environment but flower w/o
facultative response
in many populations of a given species, flowering is – favoring cross-breeding and allowing seeds to be produced in favorable environments
synchronized
gradual change from juvenile to adult accompanied by changes in – like leaf morphology and phyllotaxy, thorniness
vegetative characteristics
shoot dev can be described as a series of independently regulated, overlapping programs which modulate the expression of a common set of processes
combinatorial model
dev phase change tends to occur first at the – of the shoot
base
in rapidly flowering herbaceous species juvenile phase is very short
few days
once meristem has switched to the adult phase, only adult vegetative structures are produced, culminating in –
floral evocation
reversion of adult shoots to juvenile phase
rejuvenation
– cause phase change
gibberellins
once adult phase has been attained it is relatively stable and tends to be maintained during vegetative propagation or –
grafting
two stages of floral evocation
competence and determination
a but is competent if it is able to – when given the appropriate signal which leads to determination
flower
vegetative shoot that is not determined is grafted onto a flowering stock it will
continue in vegetative phase until it achieves determination
vegetative shoot that is determined is grafted onto a flowering stock
flower immediately
organisms can sense and respond to tome of day by showing – attuned to light/dark cycles
circadian rhythms
internal pacemaker exists such that the cycles can continue in the absence of external cues, in continuous light or darkness
endogenous oscillator
three parameters of circadian rhythms
period, phase, amplitude
recognizable features, peaks, troughs
phase
time between comparable points in cycle, peaks
period
in constant light or dark rhythms become
free-running
