9.1 5 Phytochrome and flowering Flashcards
Why is light vital for plants
no chlorophyll is formed
no photosynthesis
the plant will die
Day length
determines bud development,flowering ,fruit ripening and leaf fall
Photomorphogenesis
the process by which the form and development of a plant is controlled by the levels and type of light
red light
stimulates germination - produces biologically active Pfr
far red light
inhibits germination (has a larger wave length than red light)
if seeds exposed to a flash of red light
will germinate
flash of red light then far red
will not germinate
what determine if a seed will germinate or not
the final flash
Phytochrome
a plant pigment that reacts with different types of light and in turn affects the responses of the plant
different types of phytochrome
Pfr absorbs far red light
Pr absorbs red light
when one form of the pigment absorbs light
it is reversibly converted into the other form
as seedling breaks through soil
when germinating produces Pr
when exposed begins to convert
in dark
Pfr converted to Pr very slowly but no Pr converted back.–Pr more stable but Pfr more biologoically active
Balance between the two pigments
affected by varying periods of light and dark affects plant metabolism
in daylight hours
sunlight contains more red light than far red light so most is a Pfr
24 hour period
photoperiod
short-day plants
plants that flower when the day is short and the night is long e.g. strawberries and tobacco plant
temperate regions flower in spring and autumn when canopy that blocks light has not developed or has fallen off
long-day plants
plants that flower in relatively long days and short nights
e.g.cabbages
in temperate regions in summer or futher from equator where there may be very long days
day-neutral plants
flowering unaffected by length of day e.g.cucumbers -evolved in tropical regions where day length the same all year round -will have different cues such as available water
environmental cue
is length of darkness -if night interrupted by flashes of light will not flower
in short day plants
Pfr inhibits flowering and lack of Pfr allows to occur -in darkness converted to Pr so flowering occurs
in long day plants
high levels of Pfr stimulate flowering
in day neutral plants
levels of Pr and Pfr are similar so flowering not triggered by this factor
Florigen
hypothetical plant horomone which is involved in the photoperiodic response
- thought to produced due to changing levels of phytochromes and transported to flowering buds
- look at experiment
- thought to be a form of mRNA called FTmRNA shown to be able to travel through the plasmodesmata
- goes to leaves then apex of shoot where other genes associated with flowering are activated
