Gerry Deitzer gd3 at UMAIL.UMD.EDU
Mon Oct 20 14:29:52 EST 1997

In response to Ms. Hirte's question about Carotenoids, these are
compounds that are produced in the chloroplasts of plants that are an
integral part of the photosynthetic apparatus.  They are a part of the
Light Harvesting and Core Complexes of both Photosystem I and
Photosystem II.  They are closely associated with both chlorophylls and
proteins in the chloroplast membranes.  They absorb light strongly in
the blue region of the spectrum, which has about twice as much energy as
light in the red end of the spectrum. Chlorophyll absorbs in both

When the light is very low the carotenoids are able to harvest
additional light energy and transfer it to chlorophyll to increase the
level of photosynthesis.  When the light is too high the very energetic
blue light is too much for chlorophyll to dissipate by transferring
electrons out of the reaction centers and through the electron transport
chain. The electrons then pile up in the reaction centers.  These excess
electrons then cause oxidation of membrane components and destruction of
chlorophyll.  Carotenoids help to dissipate this excess energy by
absorbing the blue light and not transferring the electrons.  They
generally fluoresce and dissipate the energy harmlessly as light at
longer wavelengths or as heat.

Hope that this was helpful, understandable and that it answers your
excellent question.

Gerald F. Deitzer
Dept. of Natural Resource Sciences
University of Maryland
College Park, MD 20742-4452


Tia Lynn Ashman wrote:
> Can any one help with this studnet's question?
> Tia-Lynn Ashman
> Assistant Professor
> Department of Biological Sciences
> University of Pittsburgh
> Pittsburgh, PA  15260
> Phone: 412-624-0984
> FAX: 412-624-4759
> Email: tia1+ at
> ---------- Forwarded message ----------
> Date: Thu, 18 Sep 1997 17:45:55 -0400 (EDT)
> From: Dana M Hirte <dmhst38+ at>
> To: "Dr. Ashman" <tia1+ at>
> Subject: question from plant bio
> Dr. Ashman,
> I was reading through ch 7 on photosynthesis, and on pg. 139, I came
> across the description of the function of carotenoids.  Apparently, they
> help to protect the plant from photo-oxidation.  The book explains what
> photo-oxidation is, but not how the carotenoids protect the plant.  I was
> wondering if you knew how that was accomplished.  This is merely to
> satisfy my own curiosity, so it really is not that critical.  But any
> explanation you might have would be appreciated.
> Thank you.
> Sincerely,
> Dana Hirte

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