plant evolution

seager at ias.edu seager at ias.edu
Thu Jul 25 14:24:21 EST 2002


Hello,

I am an astrophysicist with a few plant related questions.
I hope someone will be able to answer these and to provide
references, or to point me in the right direction.
These questions are about the red edge reflectance
signature of chlorophyll producing plants--the order of magnitude
increase in reflectance just redward of about 700nm. I have
read that the high reflectance redward of 700m is from light scattering
in the air gaps between plant cells, a function that has evolved as a
cooling mechanism to prevent degradation of chlorophyll. This
red-edge signature has become
something of interest to astrophysicists as an indicator
of life--a civilization 100s of light years away from us with a large
space telescope would be able to detect the red-edge signature
on the spatially unresolved Earth.

1) Would evolution of a light-harvesting organism
always lead to a reflectance signature (at a different wavelength
regime than the harvested one)?
Or could it also be likely that another method of energy
dissipation could evolve?

2) Do photosynthetic plants absorb at optical wavelengths
because of the required energy for molecular electronic
transitions?

I'm hoping that there are specific examples from light-harvesting
organism evolution or existing photosynthetic organisms
(e.g., bacteria that absorbs light in the infrared) that will
shed light on these questions, if not an answer to them.

Please email any responses directly to me at
seager at dtm.ciw.edu

Sincerely,
Dr. Sara Seager
Faculty, Carnegie Institution of Washington
Washington, D.C.


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