phytochrome Flashcards
(15 cards)
what is the flowering of plants stimulated by
the stimulus of the night length
some plants flower when the nights are short
some plants flower when the nights are long
nights are shorter in the spring and summer and longer in the winter and autumn
stimulus causes genes that promote flowering to be switched on or off
nights at different lengths are different stimuli
what does this lead to
the activation or inhibition of flowering
how does the activation or inhibition of flowering work
-genes that’re switched on are expressed, leading to the production of polypeptides for which they code
-genes thatre switched off arent expressed, so the polypeptides for which they code aren’t produced
how can the length of the night be detected by the plant
the length of night determines the quantities of different forms of pigment called phytochrome in the leaf
what are the 2 forms of phytochrome?
Pr (INactive form)
Pfr (active form)
which part of the spectrum and which wavelength does Pr absorb light from?
red part of the spectrum
660nm
remember Pr=active
what part of the spectrum and at what wavelength does Pfr absorb light from?
the far red part of the spectrum
730nm
Pfr=inactive
absorption of different wavelengths of light cause a REVERSIBLE CONVERSION between the Pr and Pfr forms of phytochrome
what happens when Pr absorbs red light?
when Pr absorbs red light (660nm) it’s converted into Pfr
what happens when Pfr absorbs FAR red light (730nm)
it’s converted back into Pr
what happens in the absence of red light?
the unstable Pfr gradually converts back into Pr
which phytochrome is stable?
Pr is inactive and stable
Pfr is active and unstable
which phytochrome levels rise during the day?
-sunlight contains more 660 wavelength than 730 during the day
-so the conversion of Pr to Pfr occurs more rapidly than conversion of Pfr to Pr
conversion of Pfr to Pr still occurs though- yes slowly
pr-pfr occurs RAPIDLY
when do long day plants flower?
when nights are short
how does flowering occur in long day plants
high levels of active form of phytochrome, pfr, activate flowering
-days are long so pr is converted to pfr at a greater rate than pfr is converted to pr
-so the active form of phytochrome (pfr) is present at high levels
-high levels of pfr stimulate flowering
how does Pfr stimulate flowering?
-stimulus=red light
-Pfr activates expression of genes that stimulate flowering
-the active gene is transcribed and translated
-the resulting protein causes flowers to be produced rather than leaves and stems
