Materials Included In Kit

Additional Materials Required

Prelab Preparation

Make a 1% tetrazolium solution by dissolving 1 g of triphenyl tetrazolium chloride in 100 mL of distilled water. Make only the amount required by your classes and keep the solution in a dark bottle or in the dark until use. Soak the needed corn seeds in water for 24 hours before use in the laboratory. Simply place the seeds in a container and cover them with tap water.

Safety Precautions

Seeds are routinely treated with mold-inhibiting chemicals to help preserve them. Be sure to wash hands and work surfaces thoroughly upon completion of laboratory work. Handle razor blades with care when cutting seeds. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Triphenyl tetrazolium chloride can be disposed of according to Flinn Suggested Disposal Method #8. Seeds can be disposed of following Flinn Suggested Disposal Method #26a.

Teacher Tips

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. The initial setup of the lab can be completed in one laboratory period. Students will require observation time three days later and can complete the worksheet and discussion during the second laboratory period.

Sample Data

Answers to Questions

1. Explain any differences in the results between boiled and unboiled seeds.
   

   Boiled seeds have zero viability and zero germination rate. Non-boiled seeds, on the other hand, have high rates of both viability and germination. Boiling obviously kills the embryos in seeds and thus destroys their ability to metabolize, germinate or grow.
   

2. Explain any differences between the viability test results and the germination test results for non-boiled seeds.
   

   More seeds test positive for viability than actually germinate. Microconditions in and around a seed might prevent a seed from germinating. Only when conditions are favorable for growth and metabolism will a viable seed germinate.
   

3. What would you say to someone who said, “I can tell if seeds are alive just by looking at them”?
   

   Obviously, the person has not tried to plant many seeds nor conduct experiments like this one. It is impossible to tell if a seed is viable just with human eye inspection.
   

4. How might you use the procedures of this experiment on a large scale, such as on a farm? What should be done before planting?
   

   The tetrazolium test can be performed on small, random samples of a large source of seeds to determine their viability rate before actually planting the seeds. If rates are low, seeds could be planted more densely, and conversely, if the rates are high, they could be planted more dispersed.

Introduction

How long can seeds be stored and still be expected to grow? What percentage of seeds can be expected to sprout when planted? These are critical economic questions for gardeners and agriculturalists.

Concepts

• Tetrazolium test

• Seed viability
• Germination

Background

There have been stories of wheat seeds and other edible plant seeds germinating after lying dormant in Egyptian pyramids or Native American tombs for thousands of years. Most of these reports have not been confirmed and there is evidence in many cases that rodents in more recent times actually carried the seeds into the tombs or caves. There have, however, been a few actual documented cases where seeds as old as 1,200 years have proven to be viable. What is the normal viability of common seeds?

Seeds remain viable (retain their capacity to germinate) for periods that vary greatly, depending upon the species and the conditions of storage. Some seeds such as willow, cottonwood, tea, and orchid are viable for only a few days or weeks regardless of how they are stored. The viability of most seeds is extended, however, by months or years by being stored at low temperatures and dry conditions.

This laboratory activity considers two important concepts—viability and germination. A seed is considered viable if the plant embryo is still alive and, therefore, is capable of germination. Germination of a seed depends on the interplay of a number of factors and a viable seed may not germinate. Whether a seed germinates or not depends on a complex set of variables involving dormancy, after-ripening, temperature hardening, water, oxygen, enzyme activity, anaerobic conditions and light conditions among others.

The test used in this laboratory (Tetrazolium Test) is a standard laboratory test used by seed testing companies. The test is often called the quick germination test. The test utilizes the chemical triphenyl tetrazolium chloride. Upon penetrating living cells, the tetrazolium chloride is reduced by dehydrogenase enzymes present in living tissue to give formazin, which is a reddish, water-insoluble compound. Dead tissues do not stain, remaining their original color because of the lack of respiration and formazin production. The key to the test is to understand seed anatomy so that the seed embryo (the living part of the seed) is examined for the tetrazolium color change.

Materials

Safety Precautions

Seeds are routinely treated with mold-inhibiting chemicals to increase preservation. Wash hands and work surfaces thoroughly with soap and water upon completion of laboratory work. Handle razor blades with care when cutting the seeds. Wear chemical splash goggles and chemical-resistant gloves.

Procedure

1. Place 20 soaked corn seeds in a beaker of water and boil them for 5 minutes. Allow them to cool and label them as boiled seeds.
2. Perform a tetrazolium test for viability on ten soaked, non-boiled seeds and on ten soaked, boiled seeds as follows:

1. Use a razor blade or sharp scalpel to carefully cut each kernel lengthwise down the middle of the seed as shown in Figure 1.
2. Discard one half of each seed and place the other half in a Petri dish (top or bottom), cut surface down. Place the boiled seeds in one labeled Petri dish and the unboiled in another.
3. Cover the seed halves with 10 mL of tetrazolium test solution.
4. After 25 minutes use gloves and forceps to remove each half seed and examine the embryo part of the seed for possible color change. Record the number of seeds (boiled vs. unboiled) that show a color change (and therefore are viable seeds). Do this for the group data on the Seed Viability Worksheet.

3. Perform a germination test on ten soaked, non-boiled seeds and ten soaked, boiled seeds as follows:

1. Place the seeds between wet paper towels inside a covered Petri dish. Use separate labeled dishes for the boiled and non-boiled seeds.
2. Let the dishes stand for three days.
3. After three days, determine which seeds have started to germinate (sprouting any amount) and record the results.

4. Pool data from the entire class. Record the class data on the Seed Viability Worksheet. Complete the Post-Lab Questions.
5. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

10436_Student1.pdf