|Plant Physiology (Biology 327) - Dr. Stephen G. Saupe; College of St. Benedict/ St. John's University; Biology Department; Collegeville, MN 56321; (320) 363 - 2782; (320) 363 - 3202, fax; firstname.lastname@example.org|
Testing for Seed Viability
Objectives: The purpose of this lab
experience is to provide an opportunity to:
Germination percentage is a good measure of seed quality. One disadvantage of conventional germination tests is that they require a waiting period of two weeks or more. The tetrazolium test is a quick chemical test that can be conducted in a short period of time with minimal equipment.
In this test, a seed is incubated in a dilute (0.1%) solution of 2,3,5-triphenyltetrazolium chloride. Initially the tetrazolium solution is water-soluble and colorless. The tetrazolium is reduced by respiratory enzymes (dehydrogenases) to triphenylformazon which is insoluble and red. Thus, if respiratory activity is present, which is presumed to be a sign of metabolism, the seeds will turn red and are considered "viable." The darker the color the greater the respiratory activity in the seed. Light pink color indicates an seed with reduced viability when compared to a seed that stains dark red.
There is some evidence that microwaving a seed will improve its ability to germinate (Coburn & Airhart, 1988). This effect may be the result of increased permeability due to the heating. Microwave frequency is not as important as the final temperature of the seed with 75 C being reported to be optimal. In this experiment we will use the tetrazolium test to monitor the effect of microwaves on maize seed viability.
Exercise 1: Tetrazolium Testing of Maize
Question: What percentage of maize grains will show staining with tetrazolium? Where will the grains stain red?
Hypotheses: Corn grains will show high degrees of tetrazolium staining. The embryos will stain red.
|Fig 1. Sketch of tetrazolium stained seed|
|Table 1: Tetrazolium staining of maize grains|
|Treatment||# grains in treatment||# grains stained||% viability|
Exercise 2: Comparing Tetrazolium Results with Conventional Germination Results
Question: Is tetrazolium viability a good predictor for the germination percentage of maize?
Hypothesis: Based on the tetrazolium results, the germination percentage of corn will be ______________.
|Table 2. Germination of maize grains|
It is likely that we will need to perform a statistical test to determine if our germination rate and tetrazolium viability are significantly different. To do this we will use a Chi square 2 x 2 contingency table test. We will set it up using the model below. The statistical test is available through the Concepts of Biology web site and we will discuss it in class.
Null hypothesis (Ho):
Exercise 3: The Effect of Microwaves on Maize Seed Viability
Question: Will the viability of maize grains increase when treated with short duration of microwaves?
Hypothesis: Unhydrated maize grains that are microwaved for short periods will show greater viability than those not microwaved. Hydrated maize grains will quickly loose their viability when microwaved
|Table 3. Tetrazolium staining of microwaved maize grains|
|Treatment (sec)||# grains in treatment||# grains stained||% viability|
|0 (data from Ex 1)|
01/07/2009 © Copyright by SG