is an important nutrient needed for plant growth. In animals Ca2+
is found in bones and helps to maintain shape and structure. In plants
too, Ca2+ is important for cell shape and plant form. High
levels of free Ca2+ in the cell can be very toxic, and therefore
cells have many ways to control and maintain a low level of free Ca2+.
One way is to bind Ca2+ in plant cell walls and store Ca2+
inside the cell in internal compartments (called "organelles").
If the free Ca2+ increases in the cell, energy or ATP
is needed to carry or transport the excess Ca2+ into the stores
or out of the cell. The free Ca2+ in the cell is about 1000 times
lower than in the cell wall or organelles.
A plant needs to be able to sense changes in its environment and adjust
its growth accordingly or respond. As mentioned before, in many instances
the change in environment or signal is detected in one part of the plant,
but the growth response may occur in another part of the plant. The message
therefore has to travel within cells and tissues rather like the way information
from various parts of our bodies is carried to our brain.
This brings us to another very important role of Ca2+ in living
cells. Because the plant controls where and how much Ca2+ is
present, even very small changes in the amount of Ca2+ can be
detected by the cell. Changes in the environment or signals (such as an
increase or decrease in temperature) cause changes in the amount of free
Ca2+ in the cell. Ca2+ acts as a second messenger
so the cell can sense the signal and respond to it.
This particular experiment must be studied at school because it requires
the use of chemical solutions.
- Is Ca2+ required for the shoot gravitropic response?
- What effect do Ca2+ chelators ( chemicals that bind up
all the Ca in a solution) have on the gravitropic response?
- Does pretreatment with Ca2+ or the chelator affect the
will need the following materials:
3-4 week old Sunflower plants
Foam or sponge plugs
Styrofoam holder or a stand to hold the plugs so the plants are kept
Dark box, humid chamber or a cupboard- If you use a box be sure that
the you place a pan of water inside or damp paper towels so that the
plants do not dry out.
Ca2+ solutions (50 mM - 0.735g CaCl.2H2o to 100ml H2O)
Ca2+ chelator (10 mM EDTA = Disosium Ethylene Diamine Tetra
Procedure (what to do)
- Sunflower seeds may be planted in potting soil in small pots. Fill
the pots with soil and wet thoroughly. Plant the seeds at a depth of
about 1/2 inch and cover with soil. Water plants regularly. Keep plants
in a greenhouse or on a sunny window sill.
- Each treatment will need a control (this is a plant that is handled
the same except it is not treated with Ca or EDTA. Pure water is a good
- Choose plants of the same size and shape for experiments and controls.
- Cut Sunflower stems at the soil level and immediately immerse the
cut end in water and cut the stem again at a slight angle under water.
(This will prevent the stem from drying out).
- Soak the foam plugs in the solutions and set them in the holder.
- Make a small opening in each plug to insert a plant.
- Using a ruler and a marker pen, mark the stem of the plant in inches
or cm so that you will be able to clearly see the region of the stem
that will elongate or bend.
- Set the holder with the plants in the dark, humid chamber so that
the plant are vertical, to give the plants time to absorb the chemicals.
- One hour later, turn the plants on their side, so that they are vertical
- Cover the chamber with a black cloth to prevent any light getting
in to the plants.
- Check the growth and bending every hour for about 2-3 hours.
- Q: Of the three solutions used, is there a solution that inhibits
growth or bending?
- Q: Is there a solution that accelerates growth or bending?
- Q: What do you think that this might suggest?
Observations:Calcium is important for plant growth and raises interesting
questions for the part played by calcium in gravitropism.
| Tropisms | Phototropism
| Gravitropism | Calcium