Question

If a part of pith from the stem of a plant is used as an explant and cultured on nutrient medium, which of the following processes is responsible for the formation of an undifferentiated mass of cells called callus? (a) Growth (b) Differentiation (c) Dedifferentiation (d) Redifferentiation

Short answer

The process responsible for the formation of an undifferentiated mass of cells called callus from an explant is (c) Dedifferentiation.

Step-by-step solution

Understanding the Question

The question is asking for the process that leads to the formation of a callus, which is an undifferentiated mass of cells, from an explant, a part of plant tissue used in tissue culture. In plant tissue culture, certain processes lead to the formation of callus from mature tissue.

Understanding Plant Tissue Culture Processes

In plant tissue culture, the explant cell reverts from its mature differentiated state to a less specialized state through a process known as dedifferentiation. The dedifferentiated cells can proliferate and form a mass of undifferentiated cells called callus.

Identifying the Correct Process

Since the explant forming callus involves reverting back to an undifferentiated state, the process responsible for this is dedifferentiation, not growth, differentiation, or redifferentiation.

Key concepts

Dedifferentiation

Dedifferentiation is a fascinating process in plant tissue culture, where mature cells lose their specialized functions and revert to a more primitive, stem cell-like state. This biological phenomenon is crucial in the context of plant tissue culture, as it allows cells that were once specialized for particular tasks, say photosynthesis or structural support, to regain the capacity to divide and develop into a variety of cell types.

In the context of the educational exercise provided, dedifferentiation is the correct answer to the question about the formation of callus from a plant's pith tissue. This is because mature, differentiated cells from the plant tissue need to undergo dedifferentiation in order to multiply and form an undifferentiated mass of cells. The ability to dedifferentiate is what sets plant cells apart from animal cells, which are often terminally differentiated and do not revert to a stem cell state.

Callus Formation

Callus formation is a critical phase in plant tissue culture that represents the manifestation of cellular dedifferentiation. A callus is essentially a mass of unspecialized, amorphous plant cells that arise from the plant tissue (explant) when cultured on a nutrient medium. These cells are capable of growing and dividing indefinitely in the proper conditions.

To better understand this key concept, envision a lump of clay. Just as clay can be molded into various shapes, the callus can be induced to differentiate into diverse plant structures, depending on the external cues it receives from the environment, especially the composition of the growth medium. This trait is incredibly useful for propagating plants, as it allows for the growth of multiple copies from a single piece of plant tissue, bypassing the slower and less reliable process of growing from seeds.

Explant Culture

Explant culture involves taking a small piece of plant tissue, known as an 'explant,' and placing it in a controlled, sterilized environment rich with nutrients and hormones to encourage growth and cell division. This method is fundamental to the plant tissue culture process and requires precise manipulation of conditions to succeed.

Explants can be derived from various parts of the plant, such as leaves, stems, roots, or even seeds. The choice of explant often depends on the ultimate goal of the culture—whether to clone the parent plant, produce compounds, or engineer plants for specific traits. Explant culture is well-loved in scientific and commercial fields for its ability to clone plants en masse, rapidly and consistently, which is vital for research, agriculture, and horticulture. In our textbook exercise, a piece of pith from the stem is used as an explant, signifying the first step towards generating a callus, and subsequently, potential new plantlets.