Basic Plant Phys Question

Bob Wise wise at VAXA.CIS.UWOSH.EDU
Fri Nov 27 10:10:59 EST 1998


>Plant-edders,
>  I have a couple more of those simple questions I get asked that turn out
>to be beyond my experiences.
>
>1)  Does lightning affect photoperiodism?  An obvious question since a
>flash of white light can interrupt the night period.  My guess is that it
>does interrupt that night.  It doesn't end up altering flowering as it
>doesn't happen night after night.  However, I am guessing that some places
>in the tropics where rain and T-storms are like clock-work that it is
>possible that lightning might have influence?
>
>2)  Can plants (are there any that can) use moonlight for photosynthesis?
>I am guessing it is possible as moonlight is reflected white light from
>sun.  Does anyone know of any examples?

Hmmm.  Photosynthesis under really low light?   Perhaps I can add a bit.
The chloroplast ATPase is inactivated by oxidation in the dark and
activated by reduction in the light.  The amount of light needed to
activate the ATPase has been shown to be ~2 umol photons m^2 s^1 in
field-grown sunflower (Kramer, D.M., R.R. Wise, J.R. Frederick, D.M. Alm,
D.R. Ort and A.R. Crofts.  1990.  Regulation of coupling factor in
field-grown sunflower:  A redox model relating coupling factor activity to
the activities of other thioredoxin-dependent chloroplast enzymes.
Photosynthesis Res.  26:213-222).  If moonlight is less than 2 umol m2 s
(and I'm guessing it is) then the ATPase would be turned off and there
would be no photophosphorylation.  In addition, FBPase and SBPase are also
inactivated in the dark, much like the ATPase, so the Calvin Cycle would be
shut down too (although no one has shown this in field-grown plants that I
am aware of).  In short, I would guess that moonlight is too dim  to allow
for activation of the photosynthetic machinery.  But other wierd things are
happening in the dark.  Don Ort has shown that the PQ pool can be
completely re-reduced in the dark.  Where it is getting its electrons in
complete darkenss (certainly not from the WSA via PSII) is anybody's guess.
So the thylakoid membrane is not fully "asleep" at night, but I'd betcha
that the Clavin Cycle is.
	In addition, a lot of plants shut their stomates at night.  Except
for CAM plants, of course, which adds a real interesting wrinkle on the
subject of photosynthesis at night.  CAM plants do half of photosynthesis
at night (initial fixation of carbon) then do the other half the next day
(final fixation of the carbon).

>I have been collecting the questions of this sort that I receive intending
>to use them as projects, etc. for plant phys or botany classes.  Things
>like why do leaves stain sidewalks in the fall, why does 7-up, and such
>make cut flowers last longer, etc. (both questions I previously ran past
>plant-ed and got good answers to).  Does anyone have any other questions pf
>similar nature.  Questions that apply what is learned in a plant biology
>class to everyday questions arising OUTSIDE of the classroom.  Others I use
>are why do we cut flowers twice, how does water go 350 feet up a tree, etc.
>
>Any others?
>
>Dave Starrett
>
>
>*************************************************************
>*                                                           *
>*  Dr. David Starrett                                       *
>*  Biology Department, MS 6200                              *
>*  Southeast Missouri State University                      *
>*  Cape Girardeau, MO 63701                                 *
>*  Ph: (573) 651-2382                                       *
>*  Fax: (573) 986-6433                                      *
>*  email: dstarret at biology.semo.edu                         *
>*  WWW: http://biology.semo.edu/web/starrett/starrhpg.html  *
>*                                                           *
>*************************************************************






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