Problem understanding result of lighting regime-phytochrome

[ADAS137]

I am really confused with a past paper question, on the website http://www.rewardinglearning.org.uk/...&f=0&q=175&d=d , may/june 2011, A21 (physiology and ecosystems( , question 5.

What I don't understand is how lighting regime 3 (given that it is a short day plant) leads to flowering? I thought that even just a flash of daylight leads to the (pretty much total) conversion of P660 to P730, and therefore the inhibition of the growth of the short-day plant.

Surely then, since it's clearly more than just a flash of daylight(several hours), and its' a short day plant in which high levels of P730 inhibit flowering, it shouldn't flower?


I would understand if the short day was followed by a long night; I am not used to seeing the regime 'flipped around'.

Thanks

[ADAS137]

Sorry the link didn't work , here is a picture:http://clip2net.com/s/1oXHb

[JackBean]

I'm sorry, but I do not understand your confusion. The regime 3 has full long night, while regime 4 has flash of light inside the night, thus the plant doesn't flower.

http://en.wikipedia.org/wiki/Photoperio ... day_plants

[ADAS137]

I'm sorry, but I do not understand your confusion. The regime 3 has full long night, while regime 4 has flash of light inside the night, thus the plant doesn't flower.

http://en.wikipedia.org/wiki/Photoperio ... day_plants

I am confused as in regime 3, the long night is followed by a period of daylight. I thought during daylight, P730 accumulates,which inhibits flowering in the short day plant.

[ADAS137]

Basically, i've been taught that ANY period of daylight almost totally converts al p660 into p730. Hence why the flash of light in regime 4 leads to no flowering.

So, if a few minutes of light leads to total conversion, then why doesn't several hours have the same effect?

[JackBean]

start from slide 15 in this presentation
It seems, that the florigen is produced during night in sufficent amount, so that it is not degraded during day.

[JackBean]

but the length of light is not that important, what matters is length of dark

[ADAS137]

but the length of light is not that important, what matters is length of dark

I don't get why people keep saying that!

[ADAS137]

How much faster is the conversion of Pr--->Pfr during the day, than the conversion of Pfr---->Pr during the night?

Could you please explain regime 3 and regime 4, step by step in terms of phytochrome and hence flowering?!

[JackBean]

but the length of light is not that important, what matters is length of dark

I don't get why people keep saying that!

I guess because it's true
I don't think it's about the stability of Pr or Pfr, but rather of the florigen, which is accumulated.

[ADAS137]

Would I be correct in saying that the level of P730 tells the plant 'it's time to grow because we are in a long night, or short night'?

So since during night, P730 converts to P660, this low level of P730 makes the plant 'think' that a short day is in place-therefore it's time to grow.

And a cheeky little flash of light during night time keeps the level of P730 high and therefore 'tricks' the plant into thinking that (because high P730 levels are associated with long days) there are long days and therefore it shouldn't flower?

I've probably dumbed this down; I'm doing A-level Biology (17 years old) so wouldn't be up to degree level

[ADAS137]

I just don't understand regime 3- why doesn't the daylight period following the darkness cause a huge boost in P730 levels, which tell the plant that it shouldn't grow?

My problem is I don't know how fast the accumulation of P730 in daylight is, compared to the accumulation of P600 during night time.