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Vegetative Propagation Name___________________________

In this exercise you will learn about propagating plants asexually (from cuttings, etc.). It is expected that you have read the appropriate sections in the textbook prior to coming to class.

Leaf and Stem Propagation

Observation. All vegetative cells contain two sets of chromosomes. Each set contains genes sufficient for a complete organism. Each cell uses only a small portion of the two genomes present in its nucleus.

Question. Is it possible to make cells already specialized (for example as a leaf petiole parenchyma cell) change their developmental pathway toward something else (for example a root meristem)?

Hypothesis. An optimal concentration of rooting hormone (auxin, IAA) can cause roots to form from petiole cells of a leaf cutting.

Prediction. If the hypothesis is true, then leaf petiole cells will form the most roots, when the optimum one of three concentrations of rooting hormone is supplied.

Experiment. You have already made leaf petiole cuttings of Peperomia obtusifolia, Kalanchoe blossfeldiana, and stem cuttings of either Plectranthus australis (Swedish Ivy) or Plectranthus amboinicus (Cuban oregano), and placed them in the greenhouse. Retrieve the pots now.

The side of the pot should be labeled as to the location of the cuttings of various treatments. The cuttings were: untreated, treated with Hormodin #1, Hormodin #2 or Hormodin #3. Carefully and gently uproot the cuttings so as not to damage any young roots, and observe the number of roots which have formed at the base of the petiole. Then gently replant the cuttings. You will observe the cuttings again later in the semester to determine the number of roots which may have formed later. Do not use the ∞ symbol!

 PeperomiaKalanchoe 
Treatment___ weeks___ weeks___ weeks___ weeks___ weeks___ weeks
Untreated      
Hormodin #1      
Hormodin #2      
Hormodin #3      

Analysis. Compare the numbers you have obtained above. Considering that Hormodin #1 has the least auxin, #2 is intermediate, and #3 has the most auxin, at what auxin concentration do the cuttings root best?

Peperomia   none     low     medium     high  

Kalanchoe   none     low     medium     high  

_______________   none     low     medium     high  

Why did you have an untreated cutting? 

Decision.The hypothesis: "An optimal concentration of rooting hormone can cause roots to form from petiole cells of a leaf cutting"

is:   rejected       not rejected  

-   /17

Stem Cuttings

Observation. As in previous project. In addition, stem cells contain parenchyma in the pith, cortex, and phloem.

Question. Could an optimal concentration of rooting hormone cause roots to form from simple stem parenchyma?

Hypothesis. At an optimal concentration, auxin causes roots to form from stem parenchyma.

Prediction. If the hypothesis is true, then the greatest amount of root formation will occur, when the optimum of three concentrations of rooting hormone is supplied.

Experiment. Mung bean stems about 10 days old were cut 2 cm below the cotyledonary node with a razor blade. Ten cuttings were placed immediately in separate cups containing 20 mL of a test solution of Indole Butyric Acid (IBA) as in the chart below. After one or two days, the cuttings used up the test solution and distilled water was added up to the cotyledonary node. After one week, the 10 stems were observed at each concentration for small bumps (root primordia) or small roots. The number of roots on each type of cutting were counted and other necessary observations were made. Do not use the ∞ symbol!

0 M IBA 10-7 M IBA 10-5 M IBA 10-3 M IBA
# Roots            
           
           
           
           
Average #        
Observations  
 
 
 
 
 
 
 
 
 
 
 

Analysis. Compare the results above. Also make a graph of the results on the next page.

Which concentration was optimum?  0     10-7     10-5     10-3  M  

Do a t-test comparing 0 M with the trial having maximum effect:

t-statistic: ________ degrees of freedom: ______ t-value: ________ decision: _______________

What is the name of the kind of roots formed from stem tissue?_________________________________
spelling counts!

Decision. The hypothesis: "At an optimal concentration, auxin causes roots to form from stem parenchyma"

is:   rejected       not rejected  

 

-   /20

Make a line graph using your Mung Bean data--accuracy and neatness count!

-   /6

QUESTIONS:

Five plants are propagated from the seeds from a single fruit on a plant. Five plants are propagated from leaf cuttings of the same plant. Compare the degree of genetic congruence between:

Mother and Seedlings:   virtually identical       some similarities       completely different  

Seedling Siblings:   virtually identical       some similarities       completely different  

"Mother" and Cuttings:   virtually identical       some similarities       completely different  

"Sister" Cuttings:   virtually identical       some similarities       completely different  

When roots form along the mung bean stem, are the cells of the stem:

___ being genetically re-programmed into a new pathway of development, or

___ continuing in their original genetic pathway?

When shoots form from callus at the base of the Peperomia leaf cutting, are the cells of the callus:

___ being genetically re-programmed into a new pathway of development, or

___ continuing in their original genetic pathway?

If a plant was very bushy (had many stem tips) and continues to branch as it grows, how many individual plants could be cloned from it by stem cuttings?

  none       a few       as many as there are stem tips       indefinitely many  

When cloning we hope to produce identical plants, but is it possible to obtain at least a few individuals which are different from the original plant?

  yes       no   if so, by what biological process?____________________________

 

 

 

 

 

 

-   /9

 

This page © Ross E. Koning 1994.

 

 

Go to the Course Schedule Page.

 

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Send comments and bug reports to Ross Koning at koningre∂gmail⋅com.