Lesson 6

Propagating Plants by Tissue Culture

Next Generation Science/Common Core Standards Addressed!

HS‐LS1‐1. Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins which carry out the essential functions of life through systems of specialized cells. [Assessment Boundary: Assessment does not include identification of specific cell or tissue types, whole body systems, specific protein structures and functions, or the biochemistry of protein synthesis.]

HS‐LS2‐5. Develop a model to illustrate the role of photosynthesis and cellular respiration in the cycling of carbon among the biosphere, atmosphere, hydrosphere, and geosphere. [Clarification Statement: Examples of models could include simulations and mathematical models.]

[Assessment Boundary: Assessment does not include the specific chemical steps of photosynthesis and respiration.]

WHST.9‐12.7 Conduct short as well as more sustained research projects to answer a question (including a self generated question) or solve a problem; narrow or broaden the inquiry when appropriate; synthesize multiple sources on the subject, demonstrating understanding of the subject under investigation. (HS‐LS1‐3)

Bell Work!

1. Discuss the importance of tissue culture2. Discuss a tissue culture method of

propagation used in the greenhouse industry3. Where can tissue culture be applied in the

commercial field of agriculture?4. Discuss what type of plants are best suited

for tissue culture propagation

TermsCultivar

Resistance

Explants

Auxins

Callus

Cytokinins

Explants

Plantlet

Sterile agar medium

Sterile technique

Tissue culture

Interest Approach

We’ve talked about how you can produce African violets through leaf cuttings.

But, what if you had to produce 1,000 of them that are identical to each other in a short period of time?

What problems/challenges would this produce for the grower?

How can tissue culture help solve this problem?

What Is Tissue Culture and Why Is It Important?

Tissue culture is the practice of growing plant cells on artificial media

It involves the culture or growing of small pieces of plant tissue

It is performed on artificial medium under sterile conditions

Foliage plants, pot plants and cut flowers are propagated by this method

Advantages of Tissue Culture

1. Large numbers of plants can be produced from a single plant in relatively small space in a short period of time This reduces growing

space, labor and plant maintenance requirements

Advantages Continued

2. Viruses and other systemic diseases are eliminated by propagating the quickly dividing cells of the shoot tip

3. The grower is able to produce plants with identical flowers

4. Horticultural cultivars can be improved by selecting plants, which vary slightly from the mother plant Examples are leaf shape, disease resistance, growth

habit and flower color5. The growth of identically engineered plant cells

What Process Is Used For Tissue Culture Propagation?

The tissue culture propagation process can be defined in four main stages:

A. First stage - small pieces of plant material, called explants, are carefully removed form the parent plant Explants are obtained from the actively

growing part (shoot tips, sections of leaves, stems and roots, embryos, etc) of a desired plant

The explants are cleaned and placed on sterile agar medium in glass bottles or test tubes

The sterile agar medium is a gel that contains water, sugars, nutrients, and plant hormones to support and promote plant growth

Tiny leaves, stems and roots make tissue culture possible

Removing explants

B. Stage two - the cells of the explants multiply in one of two ways: 1. The cells may form a callus, which is a

group of cells with no particular functionSupplied with the correct hormones in the

medium, these callus cells can develop into a normal plant

2. The explant may produce many new explants if cytokinins, hormones responsible for cell division and differentiation, are placed in the medium

Stage Two: Explant Multiplication

Cytokinins encourage the increase in the number of buds on the explants to six or more per shootEach bud is capable of becoming a plant and

producing more buds

Branching occurs as these buds develop into plant shoots, or plantletsThese plantlets are divided and transferred to new

containers

In this way, a single explant can produce millions of plantlets in a year

D. Stage four - the plantlets are removed form the glass container

C. Stage three - the plantlets have developed and are ready for root formation Shoots are transplanted to

another medium containing auxins, a hormone that induces the growth of roots

The plantlets are also given higher light intensity in preparation for stage four

They are divided, planted in a sterile medium, and placed in a greenhouse

Care must be taken during this transition to acclimatize the plant to their new environment

Tissue Culture Process Continued

One of the most important aspects of tissue culture is sterile technique

Sterile technique is the maintenance of an environment that is free of bacteria, fungi and viruses Sterilization of the agar media is essential In addition, the slightest air movement can stir

spores of bacteria and fungi

Special sterile work stations, called laminar hoods, are used when possible

Cleaning of the plant before removal of the explant is usually accomplished by a brief soaking in a bleach solution, followed by a rinse in sterile water

The tissue culture agar medium and other materials used to prepare and place the explant must be sterilized This is usually done by an autoclave

The autoclave uses pressurized steam to sterilize medium, glassware, and instruments

Cultures are transferred from one container to another at various stages in their development This transfer must occur under sterile

conditions to prevent contamination by microorganisms

Sterilized equipment must be used for each transfer

Summary

Why is tissue culture important in the horticulture industry?

What parts of a plant can be used in tissue culture?

Define explant.Give two advantages for using tissue culture.What is a sterile agar medium?What is the first stage in the tissue culture

propagation method?

Summary Continued

What is a callus?What must be added to a callus in order for

it to continue to develop?What is a plantlet?How do auxins help an explant?What are some practices of sterile

technique?

The End!