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Re: [APD] Re: Closing up for the night - or Nyctinasty

> >. That is called Nyctinasty ( a rythmic diurnal
> > movement).

Terry in Arizona responded: 
> Interesting.  What triggers this cycle if it's not
> light?   I know that in animals various glands or
> parts of the brain control these rhythms.  A couple
> weeks ago, I heard an NPR story that told of recent
> discoveries in animals that in addition to these,
> each organ has its own 'clock', though they didn't
> go into what controls it, or even what that 'clock'
> is.  I assume there must be some biochemical change
> in the plant that causes the leaves to fold up - do
> we even know what triggers it or what the actual
> chemical change is?    

Plants respond largely to light, but there are many
other factors like temperature (and 'accumulated'
temperature exposure like 'degree days'), water
availability, and even simple genetics.  Not all are
understood.  However, 'light' tends to control
diurnal cycles as it's one of the most 'reliable'
system inputs (biologically speaking).

I didn't hear the news on 'each organ has its own
clock', but I'm interested if you find any more info
on that.  As far as *organism* clocks, there's a lot
of work there I know about, where much research is
based on a light-sensitive pigment found in the eye
in 1998, which tends to be present even in blind 


The pigment, called cyryptochrome (CRY) drives
circadian rhythm (24-hour cycle).  I seem to recall
another discovery a year ago that suggested there
are also 'specialized' cones in the back of the eye
that had nothing to do with vision, but *did* heavily
influence the circadian rhythm (and I think it was
for non-mammals too).  The 'surprise' was that it
functions well for blind critters, and seems to serve
this purpose even for species that don't 'see'.

For a quick refresher on eye rods and cones, there's
a nice kids' tutorial at:


As far as the biochemical change in plants driving
nictinasty, yes, several bioactive substances have
been identified that regulate leaf movement, and some
have even been synthesized (much of this work is done
with legumes, which close their leafs every night).
Much plant chemistry is based on ratios of two types
of phytochromes, where one is more sensitive to red
light recieved in the day, and far-red light received
at night.  Then, there are 'secondary' processes that
kick in, as some molecules built during the day take
a *long* time to break down (many hours in the absence
of light), but they build up very quickly (minutes, or
even seconds in the right light spectra).  These
heavily influence seasonal change.  For example, it
takes extraordinary effort to grow poinsettias and get
the top leaves to 'turn red' for sale at Christmas 
time (US).  (Those aren't flowers, but the top
The leaves are actually etiolated, where the plants
turn red in the winter after the green phytochrome
shrinks due to seasonal lack of light in the winter.
Back in horticulture class, we were told that a good
way to 'destroy' an entire crop for the year is to
turn on the lights for only a couple of minutes in the
middle of the night sometime in November.  ;-)


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