Phytochrome as the photoreceptor

What acts as the photoreceptor?

Phytochrome pigments

What is Phytochrome sensitive to and whats the suitability for this role linked to?

• sensitive to light

• its ability to exist in 2 inconvertible forms

What are the 2 inter convertible forms?

• P660 (Pr) absorbs red light with an absp peak of 660nm

• P730 (Pfr) absorbs far red light with an absp peak of 730nm

Why are they know as 2 diff things?

Due to the differences in absp peaks

When are they rapidly converted to their diff forms?

• P660 is rapidly converted to P730 if subjected to red light

• P730 is rapidly converted to P660 if subjected to far red light

  (In darkness P730 will slowly convert to the P660 form, as P730 is much less stable than P660).

what happens because daylight contains more far red light and why?

• P660 is converted to P730 during the day.

What happens when the day length gets longer?

• As the day gets longer in spring/summer the proportion of phytochrome that exists in the P730 form increases.

What initiates flowering in LDPs

• as the day length increases, the amount of P730 eventually reaches a critical level that initiates flowering

• the intensity of light is also important, as the conversion is quicker in high light intensities

What is the physiologically active form?

• The P730 form

• whether its that sufficent P730 has accumulated to promote flowering in LDPs or that there is too much P730 to allow flowering to occur in SDPs.

Why must the inhibitory effect of high levels of P730 be removed?

so flowering can take place