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Why do intact chloroplasts fluoresce?

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Why do intact chloroplasts fluoresce?

Postby aidane » Sun Mar 07, 2010 5:21 am

Hi all,

I understand why isolated chlorophyll fluoresces--an electron that has been excited to a higher energy orbital drops back down to the ground-state orbital, releasing energy as heat and light/fluorescence. In an intact chloroplast, the photoexcited electron is captured by a primary electron acceptor and not allowed to fall immediately back to the ground state. So why is it that intact chloroplasts fluoresce (as in http://www.photosynthesisresearch.org/images/Sorghum%20MSBS.jpg)?

Thanks in advance for your help!

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Re: Why do intact chloroplasts fluoresce?

Postby JackBean » Mon Mar 08, 2010 6:45 am

aidane wrote:I understand why isolated chlorophyll fluoresces

aidane wrote:So why is it that intact chloroplasts fluoresce?


So, do you understand or not? :roll:
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Re: Why do intact chloroplasts fluoresce?

Postby aidane » Mon Mar 08, 2010 5:13 pm

JackBean wrote:
aidane wrote:I understand why isolated chlorophyll fluoresces

aidane wrote:So why is it that intact chloroplasts fluoresce?


So, do you understand or not? :roll:


I understand why isolated chlorophyll (the pigment) fluoresces. I don't understand why intact chloroplasts (the organelles) fluoresce. Anyone?

Thanks!
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Postby JackBean » Mon Mar 08, 2010 5:40 pm

ah, chlorophyll vs. chloroplast. I didn't notice that :)

That's simple, chloroplasts contain chlorophyll, that's why they autofluorescence
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Re: Why do intact chloroplasts fluoresce?

Postby aidane » Mon Mar 08, 2010 6:00 pm

Hmm...But I thought that the reason why chlorophyll fluoresces is because the photoexcited electrons spontaneously drop back down to the ground state. This drop doesn't happen in an intact chloroplast, because the excited electron is captured by a primary electron acceptor. So at what point is energy released as light?

Thanks for your reply.
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Postby JackBean » Mon Mar 08, 2010 6:12 pm

No,no. That actually happens only in minor cases. In most cases is the energy released as heat or fluorescence
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Re: Why do intact chloroplasts fluoresce?

Postby aidane » Mon Mar 08, 2010 6:19 pm

I'm sorry, I'm still confused. :? So photons absorbed by chlorophyll in chloroplasts are rarely used for photosynthetic purposes? What determines whether a chlorophyll electron is captured by a primary electron acceptor or not?
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Re: Why do intact chloroplasts fluoresce?

Postby mamoru » Tue Mar 09, 2010 12:32 am

aidane wrote:Hmm...But I thought that the reason why chlorophyll fluoresces is because the photoexcited electrons spontaneously drop back down to the ground state. This drop doesn't happen in an intact chloroplast, because the excited electron is captured by a primary electron acceptor. So at what point is energy released as light?

Thanks for your reply.

Don't they drop back down to near the ground state when going from Photosystem II to Photosystem I? Would that cause the fluorescence in intact photosystems?
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Postby JackBean » Tue Mar 09, 2010 6:27 am

when going from PSII to PSI through b6/f, the energy is slowly released, so there shouldn't be so much fluorescence, but could be a little
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Postby mamoru » Tue Mar 09, 2010 8:04 am

Durrrr... I think I get it now. The main reason for fluorescence even in intact photosystems is because an electron may be excited and return to the ground state several times before actually being picked up by the electron transport chain. Is that about right?
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Postby MrMistery » Sat Apr 03, 2010 9:01 pm

yeah mamoru you have it right! to put it simply, the electron capturing system that exists there isn't 100% efficient, not even close. Most of the time actually the energy just gets emitted as fluorescence. It's a good point - nothing in biology is ever 100% efficient, things are usually much below that line
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