[In this exercise, several experiments were performed on different organelles
of various plant species to test hypotheses concerning different aspects of
plant cell physiology (Melanie Shadish)]. A freshly mounted section of
Forsythia stem exhibited xylem that was greenish in color. The wood
cell boundaries treated with the stain, Phloroglucinol HCl, turned purple
probably due to a chemical reaction with the lignin in the wood. [Lignin
is known is known to have a chemical structure that would cause this reaction
(Melanie Shadish)]. [Further testing with a different dye that interacts with
lignin would assist in verifying that lignin is present in the cell wall
(Jeff Holt)]. A Mnium leaf was wet mounted to test whether its cells
were alive, and therefore had a functional cell membrane capable of excluding
sodium and chloride ions but not water. One wet mount was made in distilled
water and another was made in 6% sodium chloride. [Because of the cell wall
resisting turgor pressure in the distilled water, the cells did not enlarge or
burst (Patricia Tellekamp)]. The cytoplasm shrunk and separated from the cell
wall in the presence of sodium chloride. This response is known as plasmolysis,
which ultimately results from a loss of turgor pressure when a cell is in a
severely hyptertonic solution. We concluded that the cells were alive because
the cell membrane was functional; it was able to exclude salt ions, but not water.
Another experiment was designed to determine the function of the chloroplasts
in cells of the Mnium leaf. In the presence of iodine, the chloroplasts
displayed purple/black spots. These spots were starch grains; a storage form
of a photosynthetic product (carbohydrate), indicating that chloroplasts
function in photosynthesis. [We observed the plant-specific organelle,
the vacuole, by observing a wet mount of Rhoeo discolor leaf lower
epidermis which has a large vacuole containing a purple pigment. We hypothesized
that, since mitochondria were not seen at all, plant cells lack mitochondria.
(Melanie Shadish)]. To determine the presence of mitochondria in plant cells,
methylene blue was used [since it is known to change to a dark blue color in
the presence of electrons and hydrogen ions. The respiration pathway includes
enzymes which liberate electrons and hydrogen ions (Amy Lusk)]. Small
structures [presumably mitochondria (Chuck Goddard)] could be seen. [Our
final experiment was to determine if cytoplasmic streaming in plant cells
could operate like the mechanism based on electrical action potential,
calcium ions, and ATP causing the actin and myosin of vertebrate muscle
cells to slide past one another. The hypothesis was tested using the
slime mold, Physarum (Melanie Shadish)]. An action potential
created by brief contact with wires connected to a 1.5 volt battery
was applied to the plasmodium undergoing cyclosis on an agar surface.
[Microscopic observation showed nuclei moving through the cytoplasmic
channels at a slow rate with regular reversals in direction of flow.
When the action potential was applied, cyclosis became more rapid.
When a drop of 10-4 M Ca+2 was applied to the
plasmodium, cyclosis seemed to have ceased. A drop of 10 M
Ca+2 was applied, cyclosis was very slow. However a drop of
EGTA restored the rate of cyclosis.(Melanie Shadish)] [It is important
that cells both produce sufficient ATP and release sufficient Ca+2
to increase cyclosis. Adding excess calcium probably depletes ATP supplies,
slowing cyclosis. The EGTA chelating agent probably sequesters excess
free-calcium thus restoring ATP driven cyclosis (Ross Koning)]. [If calcium
and electricity are applied to the cell for too long or too rapidly, all
of the ATP in the cell is used up quickly and cyclosis stops (Tracy Gervais)].
[This series of experiments served to acclimate students to the use of
microscopes, chemicals, and give experience with dose responses to
visualize processes that are not commonly familiar (Damon Crooks)].
This page © Ross E. Koning 1994. Go to the Course Schedule Page. Go to the Plant Physiology Information Homepage. Send comments and bug reports to Ross Koning at email@example.com.
This page © Ross E. Koning 1994.
Go to the Course Schedule Page.
Go to the Plant Physiology Information Homepage.
Send comments and bug reports to Ross Koning at firstname.lastname@example.org.