Tissues in Action · Lesson 10 of 11
From one cell to an organism: Totipotency
“A carrot cell remembers it could become an entire carrot, which is quite ambitious.”
• Describe the sequence of F. C. Steward’s carrot-cell investigation. • Explain dedifferentiation, redifferentiation and totipotency. • Interpret how light, air and nutrient conditions affect cultured cells. • Distinguish observations from conclusions in an investigation. • Connect the study of uncontrolled division with useful plant applications.
A mature cell in a carrot root appears to have settled into a permanent job. Yet under suitable conditions, some such cells can reverse their specialised state, begin dividing again and eventually help produce an entire plant. This ability reveals that specialisation does not always erase the cell’s potential.
Think as a Scientist
In 1958, F. C. Steward and his team cultured cells obtained from the vascular phloem of carrot. Small fragments were placed in a nutrient medium containing simple sugars and hormones under suitable conditions. Stirring released individual cells into the liquid. These cells divided, formed an embryonic plant, developed into a plantlet and eventually produced a complete adult plant.
Dedifferentiation is the process by which specialised cells regain the ability to divide and form an undifferentiated mass of cells.
Redifferentiation is the process by which dividing, unspecialised cells specialise again to form structures such as roots and shoots.
Totipotency is the ability of some plant cells to divide and develop into a complete plant under suitable conditions.
The sequence contains two changes. First, mature phloem cells dedifferentiate and begin dividing. Later, cells in the growing mass redifferentiate to form the different tissues of roots and shoots. A zygote also divides and differentiates into a complete organism, so the comparison helps explain the meaning of developmental potential.
| Light | Air | Medium | Observed change in fresh weight |
|---|---|---|---|
| Present | Absent | Solid medium with nutrients | Reduced |
| Present | Present | Liquid medium with nutrients | Increased by about 20% |
| Absent | Present | Liquid medium with nutrients | Reduced |
The highest increase occurs when light and air are both available and the cells are in a liquid nutrient medium. Removing air or light is associated with reduced fresh weight in the listed conditions. Because more than one condition differs between some treatments, conclusions should be stated carefully. The table supports the importance of suitable surroundings, but a stronger comparison would change one factor at a time while keeping all others constant.
Problem
Separate what was observed from what can be concluded in the treatment with light, air and liquid nutrients.
- 1.Observation: the fresh weight increased by about 20%.
- 2.Conclusion: this combination supported greater growth than the other listed combinations.
- 3.The observation is a recorded result; the conclusion is an interpretation of that result.
- 4.A fairer investigation would keep the medium and other conditions identical while testing one selected factor.
Bridging Science and Society
Crown gall disease produces tumour-like swellings on plant stems because cells divide rapidly and without normal control. The disease is caused by the bacterium Agrobacterium tumefaciens. Scientists studied how this bacterium transfers genetic material into plant cells.
Understanding that natural process allowed the bacterium to be used as a tool for introducing useful genes into plants. The source chapter connects this knowledge with production of useful plant chemicals, improved crops and disease-resistant varieties. The important idea is that studying a harmful biological process can reveal a mechanism that is later used for human benefit.
The investigation demonstrates the potential of certain carrot cells under suitable culture conditions. It should not be turned into the claim that every mature cell of every organism will produce a complete organism in the same way.
Quiz
Which description best matches Dedifferentiation?
Which description best matches Redifferentiation?
Which term matches this description: Dedifferentiation is the process by which specialised cells regain the ability to divide and form an undifferentiated mass of cells.
Which term matches this description: Redifferentiation is the process by which dividing, unspecialised cells specialise again to form structures such as roots and shoots.
Which statement is a key takeaway from this lesson?
Practice Problems
- Arrange these stages in order: adult plant, single cells, root fragments, plantlet and embryonic plant.
- Distinguish dedifferentiation from redifferentiation.
- What does totipotency mean?
- Which listed combination produced the greatest increase in fresh weight?
- Why should only one condition be changed at a time in a controlled comparison?
- How did the study of crown gall disease lead to a useful application?
Key Takeaways
• Some mature plant cells can regain the ability to divide. • Dedifferentiation produces dividing unspecialised cells. • Redifferentiation produces specialised roots, shoots and other structures. • Totipotency allows some plant cells to form a complete plant under suitable conditions. • Reliable conclusions depend on careful interpretation of experimental conditions.