Starch Pictures

1
Starch Pictures
These are pictures created in starch (within
chloroplasts) in a leaf rather than in particles
of silver in a conventional black and
white photographic negative. If you have access
to one or two reagents and a slide projector you
can make one for yourself.
This is how to smuggle the plans out of the
country as an image, created in starch within a
leaf, now dried and slipped innocuously between
the pages of a book, waiting to be mounted and
stained with iodine.
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When it all started
In 1863 and 1864 I convinced myself that the
starch contained in the chlorophyll-corpuscles
of normally developed leaves may disappear again
in long-continued darkness and that it is
possible to bring about the renewed formation of
starch by a second illumination
Julius Von Sachs (1832-1897)
It suffices to fasten a broad band of tinfoil in
summer on plants with conveniently large leaves
without depriving the plants of light. After a
few days, the leaves so treated are cut off, and
thrown for a few minutes into boiling water in
order to kill them, and to cause the starch in
the chlorophyll-corpuscles to swell. They are
then placed for some hours in strong alcohol,
which removes the chlorophyll coloring-matter,
and the now colorless leaves are finally placed
in a vessel containing a weak, pale brown,
alcoholic solution of iodine. After a short
time, the parts of the leaf which were not shaded
from the light appear blue-black, owing to the
formation of iodide of starch the place shaded
by the band of tinfoil, on the other hand,
remains colorless, simply because the
chlorophyll-corpuscles there contain no more
starch.
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Where it all happens
Cross section of a C3 leaf. (After Sachs)
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Hans Molisch (1856-1937)
The starch picture procedure was invented by
Hans Molisch in 1914
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Contemporary starch pictures

• Re-create the original observation by Sachs that
  starch was only found in illuminated chloroplasts
  and that these must therefore be the organelles
  responsible for photosynthesis.
• 2) Provide visual evidence of transduction of
  light energy to chemical energy in the form of
  CH2O.

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Contemporary starch picture of Jan Ingen-Housz by
William Ruf and Howard Gest
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And in colour!
Courtesy of Howard Gest
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How its done
Starch picture of Dr Jan Ingen-Housz on a
geranium leaf by William Rufand Howard Gest. The
image of Ingen-Housz was photographed, and the
negative placed in a slide projector. Light
passing through the negative was focused on a
geranium leaf (depleted of starch by prior
incubation in darkness) for about one hour After
extraction of pigments from the leaf with
boiling 80 alcohol, the blanched leaf was
flooded with I2-KI solution to stain the starch
granules.
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Starch pictures are developed with an
iodine-potassium iodide solution
There are lots of starches just like there are
lots of proteins but, in essence, just as
proteins are made of amino acids, starch is made
of strings of glucosyl units. Iodine combines
with leaf starch grains,in situ, to form a
blue-black complex.
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At a conference in Marburg (Germany) in 1978, the
next slide but one was given a standing ovation.
At Brookhaven (in the United States) in the same
year, it was less well received
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Warning!
If, like those who put their names to the
question posed on the previous slide, you find
nudity in art offensive, or its use irrelevant,
kindly skip the next starch picture.
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Innocence
Originally drawn, in white on black, by
Pierre-Paul Prudhon (1758-1823)
Here, re-created in starch-iodine within a
Pelargonium leaf
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Why did I reproduce Innocencein starch, in a
geranium leaf?
For reasons which will become clear I wished to
reproduce an original drawing with well defined
lines in black and white. If possible, I wanted
something which would also arrest the attention
of an audience. The sketch of 'Innocence', by
Pierre-Paul Prudhon, often on display in Art
galleries the world over, was first created in
black and white. To my mind, it is well-named,
not in any way salacious or offensive, but a
thing of great intrinsic beauty.
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Now that I have your attention!
Lets get back, in the next few slides, to
something equally interesting - in its own way
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Photographien im Laubblatte
Starch picture created in a "geranium" leaf by
illuminating the starch-free leaf through a
photographic negative. The picture contains a
facsimile of the title of the first work by
Molisch on this subject in 1922 and below it, a
contemporary outline diagram of a chloroplast.
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Close-up of previous image
17
Further enlargement of previous image
The arrows point to circles drawn round many of
the barley visible dots on the leaf surface.
These dots are starch grains in stomatal guard
cells. They are circled to give a measure of the
degree of resolution of the picture. They show
that starch is not formed in cells immediately
adjacent to illuminated ones.
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Resolution
The successive enlargements of the starch picture
in the last three slides illustrate the degree of
resolution which can be attained given the
immense number of chloroplasts in a leaf. At the
highest magnification, the outlines of stomatal
apertures (through which CO2 enters the leaf) can
just be detected,as dots, because starch in
stomatal guard cells, unlike that in the
mesophyll and palisade tissues, is not
mobilised in darkness and is therefore stained by
iodine regardless of prior illumination, or the
lack of it.
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What is the significance of the high resolution?
The very high degree of resolution in starch
pictures shows that while starch is made in
illuminated cells it is not in an adjoining
cells. What is surprising about this is that
chloroplasts in leaves do not need light to make
starch.Float discs from a 'Geranium' leaf on a
solution of sucrose (or indeed many other
sugars) and they will happily do it in the dark.
Why then is the image in these pictures not
blurred? Why does internally generated sucrose
not lead to starch synthesis in darkened parts
of the leaf when externally supplied sucrose
does so very readily? We know that sucrose is
made in the cytosol and that it is the main
carbohydrate transport molecule in leaves. Why is
sucrose, newly synthesised in an illuminated cell
seemingly unable to enter an adjacent but
darkened cell and give rise to starch there?
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An Explanationkindly offered (in March 05) by
Jerry Servaities and Don Geiger
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Brought to you by Oxygraphics
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