Basic Plant Phys questions

Janice M. Glime jmglime at MTU.EDU
Wed Nov 25 11:23:01 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?

My first impulse was to say no, but then I remembered an article I read a
long time ago.  Someone used a strobe light for a short period (2 minutes,
I think) at the beginning and end of the day (using a long-day
photoperiod) and caused plants in the greenhouse to have as much
photosynthesis as if they had had the intense light all day.  This
suggests that the brief lightning is probably long enough to stimulate
some pigment, but the miss record would probably be far greater than the
hit record. The next question is whether lightning has the right spectrum. 
Anyone know the right physics to answer that? 

A follow-up question is the role of cryptochromes in this.  They have been
implicated in tropisms, coupled with phytochrome in some way, but are they
also involved in photoperiodism?

> 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?

This suggests another question to me.  Humans are supposed to see black
and white in moonlight.  Photographs depict it as bluish.  We see black
and white because our cones do not receive enough light to be active and
only our rods are active.  Rods respond only to black and white.  But, my
question to add to Dave's list and to ponder on this list is whether this
is an on-off response or is it a quantitative response.  Since the change
to rod activity involves the joining of retinal and rod opsin in the dark
to form rhodopsin, it suggests to me that the response may be quantitative
and that some cones may be active in the low light of the moon.  OOPS!
This is a plant list.  
  So, my next question is whether there is a threshhold for light level to
activate a chlorophyll molecule, or if it is quantitative, resulting in
few molecules being activated in the low light of the moon and more energy
lost to respiration than gained in photosynthesis.  And is
photorespiration totally inactive in moonlight?  What is the determining
factor for it, light quality or quantity?

 Janice M. Glime, Professor  
 Department of Biological Sciences
 Michigan Technological University
 Houghton, MI 49931-1295
 jmglime at
 FAX 906-487-3167 

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