Unit
Plant Science
Problem Area
Initiating Plant Growth
Lesson
Conducting the Warm
Germination Test and TZ
Test for Seed Viability
Student Learning Objectives
1. Identify the parts of the seed and their
role in germination.
 2. Describe the stages of seed
germination.
 3. Understand that moisture, temperature,
oxygen, and light affect germination.
 4. Explain how and why germination tests
are conducted.

Terms







cold germination test
cotyledon
embryo
endosperm
epicotyl
hypocotyl
imbibition






micropyle
radicle
seed coat
seed viability
TZ (tetrazolium
chloride) test
warm germination
test
What are the parts of the seed and their role
in germination?
Seeds consist of three primary parts: the
seed coat, embryo and food reserves.
 A. The seed coat is responsible for
protecting the seed embryo and allowing
or inhibiting the exchange of gas and
water. The micropyle is an opening in the
seed coat where the sperm entered the
ovule prior to fertilization.


B. The embryo is an immature plant in an arrested state
of development. When conditions for germination are
correct the development of the embryo resumes. The
epicotyl is the portion of the embryo above the
cotyledon(s), or seed leaves. The epicotyl develops into
the seedling shoot. Below the cotyledon(s) is the
hypocotyl. From the hypocotyl the radicle develops
which is the primary root.

C. The seed needs food to remain viable during storage.
Food is also needed for germination and the
development of the embryo into a plant prior to
photosynthesis. In grass seeds this food is stored in the
endosperm. In legumes and other dicotyledonous plants
the food is stored in the cotyledons.
What are the steps in the seed germination
process?

There are three steps in the germination process
that take place simultaneously.

A. Imbibition is the intake of water. It is the first
step in the germination process. When the seed
takes up water through the seed coat, cells
begin to divide. Water content rises from 5–10%
to 30–40% as mitosis begins. The intake of
water is also associated with an increase in
respiration.

B. Increased metabolic rate is the second process in
germination. This increase in metabolic activity
requires that the large starch and protein molecules
stored in the endosperm or cotyledons must be
broken down for use by the embryo. An enzyme,
amylase, converts starch to sugar.

C. The enlargement of the embryo is the third
process. Once the starch and protein molecules are
broken down they are then used to accelerate the
development of the embryo. As this occurs the
embryo increases in size causing the seed coat to
rupture. The radicle emerges from the seed followed
by the emergence of the shoot.
How do environmental factors affect
germination?

A. Moisture is necessary for the germination of
seeds. Moisture is responsible for the mobilization of
food reserves and for the increase in respiration in
the embryo.

B. Correct temperature is needed for optimum
germination. As with many biological processes the
rate of germination is affected by temperature. It is
important to understand that soil temperature, not
air temperature, is the key for optimum germination.

C. Oxygen is needed for seeds to respire.
Respiration is the process of oxygen combining
with glucose to provide energy. Without energy
the development of the embryo will not occur.

D. The presence or absence of light affects
germination. Some plants require light to
germinate, while others need darkness.
Why are germination tests conducted?


A. Seed viability, the presence of a live embryo, is
tested under ideal germination conditions using a
warm germination test. For most crop species the
warm test usually lasts 7 days with the seeds being
held at 77 º F with 100% humidity.
Seeds are usually tested on a paper towel-like
material. If the seed is considered viable it should
germinate at a rate of at least 90%. The warm test is
limited in that typical planting conditions do not
include 77 º F soil temperatures, or 100% humidity.

B. Cold germination tests predict how seed will perform
when planted under normal planting conditions. The cold
germination test involves holding the seeds at 50 º F for
seven days followed by 77 º F for three days. Soil from
the field that contains natural microorganisms is used and
only seeds that emerge are counted. This test indicates
the seed lot’s vigor or ability to withstand less than
desirable conditions.

C. The TZ(tetrazolium chloride) test identifies seeds
that are viable. The seeds are first soaked in water to
initiate germination. They are then split in half and put into
a 1% TZ solution. The TZ is changed to a red or deep
pink chemical called formazan when it comes into contact
with enzymes found only in live seeds. The degree of
redness is indicative on the viability of the seed.
Review/Summary
What are the parts of the seed and their
role in germination?
 What are the steps in the seed
germination process?
 How do environmental factors affect
germination?
 Why are germination tests conducted?
