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Lab 2. Plant Cells, Propagation and Mitosis
In today’s lab we will begin by studying the basic unit of a plant body – the cell.
You should observe as many specimens as possible and get an idea of the diversity of cell
shape and function throughout the plant body. One remarkable property of plants is their
ability to regenerate new organs from cuttings (roots and shoots). Plants are commonly
propagated by inducing root or shoot cuttings to grow into new whole plants. You will
take advantage of this property in plants and propagate several species of plants from
cuttings and monitor their growth in the greenhouse throughout the term.
We will also investigate cell division in plants – the process that ultimately results
in plant growth and the differentiation of different plant organs such as flowers, stems
and roots. Cell division resulting in new plant tissues is the product of two processes:
first, the duplication of the nuclear material in the nucleus occurs via a process called
mitosis and second, the rest of the cell body divides resulting in two genetically identical
cells (the latter process is called cytokinesis). In today’s lab you will be introduced to
mitosis by looking at cells in the process of cell division. These cells will come from the
actively growing tips of young onion roots.
1. Components of the Plant Cell
The shape and composition of plant cells is very much related to their function.
In this exercise you will prepare slides to learn about the diversity of cell types in a plant
body. Fill in the table below by looking at slides of plant material available today in lab .
Cell Type or
component
Cork cells
• prepared
slide
Elodea
•
•
chloroplasts
cytoplasmic
Streaming
Onion Epidermis
•
•
epidermal cells
• Nucleus
plasmodesmata
Location in
Plant
Function
Sketch
Diffenbachia leaves
•
Location
Function
Sketch
raphides
crystals
Pepper epidermis
or
Flower Petals
• chromoplasts
Potato tissue
•
leucoplasts
Radish roots
•
root hair
Other plant cells
2. Planting Seed
Most flowering plant species reproduce by seeds. Factors influencing seed
germination for individual plants can vary tremendously. Temperature, moisture, light
and mechanical scarification can all affect germination. Many species will require a cold
period (stratification) before germinating; others will only germinate shortly after the
seed has fallen from the mother plant. When starting plants from seed an important
factor influencing germination success is the preparation of the seed bed. This will
require using the proper soils and planting at the right depth. A rule of thumb for
planting seed is to plant approximately 2-3 times as deep as the smallest diameter of the
seed. Larger seed should be planted deeper than smaller seed. In this exercise you will
test this rule of thumb by setting up a simple experiment in which you will plant seeds
of different sizes at different depths. You will then monitor the germination success
and quality of the resultant seedling.
Seed Depth experiment
1. Work in groups of 2-4
2. obtain lettuce, wheat, and bean seed
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3. in three separate 3 inch deep pots plant 3 or 4 seeds each
a. at bottom (i.e 3 inches deep)
b. at 3 times their diameter
c. on the surface (“watered in”)
4. Monitor every week; use the table below to record your results
5. Record when seedling is visible, measure height and count leaves each week,
record general condition of seedling (i.e spindly, strong, yellowish, etc.)
Bean dia=
Planting depth
Week 1
Week 2
Week 3
Week 4
surface
2 X diameter
3 inches
Wheat dia=
Planting depth
surface
2 X diameter
3 inches
Lettuce dia=
Planting depth
surface
2 X diameter
3 inches
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3. Vegetative propagation
Many plant species can be grown vegetatively from root, shoot and leaf cuttings.
Ornamental and exotic plants are often propagated this way to ensure a consistent quality
of plant (vegetative propagation results in clones). However, many native plants are also
easy to propagate vegetatively using simple but effective techniques. In today’s lab you
will make vegetative clones from a variety of plant materials.
Vegetative Propagation procedure:
•
•
•
•
•
•
obtain cuttings, roots or bulbs to propagate
fill zip-lock plastic bags 1/3 full with pre-moisten soil mixture. Remember to
label the bag with your name and lab section
for stem cuttings: take 3 -4 inch stems sections and remove lower leaves (keep top
2 leaves). Dip lower stem in rooting hormone and push stem into soil in plastic
bag leaving top leaves exposed. Seal bag and place in indirect light.
for leaf cuttings: remove leaf with petiole (if present) attached. Dip lower 1/3 leaf
into rooting hormone and carefully push into soil in bag. Seal bag and place in
indirect light.
for bulbs and roots: cover with soil in plastic bag and seal. Place bag in indirect
light.
look for root development in bag each week. Transplant root cuttings or bulbs
into pots when roots form and place in greenhouse.
4. Grafting
In many cases, plants with
desirable rooting characteristics (e.g.
disease resistance) are matched with
plants that have desirable shoot
characteristics (e.g. attractive flowers
or marketable fruit). For example, it is
common to have roses, fruit trees and
grape vines grafted onto disease
resistant root stock. This form of
propagation (grafting) combines the
best qualities from different plants to
obtain a composite plant, which
performs the best both below and
above the ground. Look at the
examples of grafted plants on display
in lab today. Can you find the graft?
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5. Mitosis
When new growth occurs
during seed germination, vegetative
propagation and graft formation it
does so through the process of
mitosis and cytokinesis. With the
exception of cells used in sexual
reproduction, all new cells are
produced this way in the plant body.
Mitosis occurs in a regular series of
controlled steps that results in the
production of genetically identical
daughter cells. Once new cells are
formed, plant hormones, positional
factors and other forces act on the
cells to affect differentiation into
specific cell types. In today’s lab
you will study actively dividing
cells in the root tip of an onion to
identify the different stages of
mitosis and cytokinesis
Interphase
Prophase
chromatin condenses into chromosomes
nuclear envelope disappears
Metaphase
chromosomes align at the
equatorial plane
spindle becomes evident
Anaphase
chromatids separated and pulled
to opposite poles by spindle fibers
Telophase and Cytokinesis
chromosomes begin to unwind
nuclear envelopes form
cell plate forms from phragmoplast
Mitosis in Onion Root Tip
Procedure:
Interphase
two identical daughter cells
1. Obtain onion germinated in
tube of water
2. Remove the end 2 mm of
root tip with a razor blade
3. Place on glass slide and add 3 drops of 1N hydrochloric acid, heat on alcohol
lamp until a puff of smoke appears (do not let dry out, do not let boil)
4. Blot acid with
paper towel and
Draw the different stages of mitosis observed in onion root tips
add two drops
Interphase
Prophase
Metaphase
of toulodine
blue stain,
warm slide for
60 secs – do not
boil
Anaphase
Telophase
Cytokinesis
5. Blot away stain
with paper
towel and add
one drop of
fresh stain
6. squash under a
cover slip and
observe under compound scope
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