Question

Examples of tissues that are formed by redifferentiation are - (a) secondar xylem (b) secondary phloem (c) cork cell (d) all of these.

Short answer

(d) all of these.

Step-by-step solution

Understanding Redifferentiation

Redifferentiation is the process by which cells that have undergone dedifferentiation differentiate once again, often into another type of cell. These cells typically contribute to the formation of secondary structures in plants.

Identifying Redifferentiated Tissues

Examine the options given and determine whether each one is a product of redifferentiation. Secondary xylem and secondary phloem are formed as a plant grows and ages, while cork cells are formed from the cork cambium, all of which are secondary structures that differentiate after the primary structures are in place.

Determining the Correct Answer

Since all the given options are tissues that are formed during the secondary growth of plants, they are all examples of redifferentiated tissues. Consequently, each of them fits the definition provided in the first step.

Key concepts

Secondary Xylem

The secondary xylem is a critical component of a plant's vascular system, serving as the principal conduit for water and mineral transport from the roots to the rest of the plant. It is formed during the secondary growth of the plant from the vascular cambium, a lateral meristem. This formation occurs through the process of redifferentiation, whereby cells that may have previously served a different function or were undifferentiated, acquire the specialized traits typical of xylem cells.

In addition to transport, secondary xylem also contributes significantly to the structural support of the plant, as it becomes a part of the wood. The wood you see in trees is primarily made up of secondary xylem, which also gives rise to annual rings in temperate climates, each representing a year of the tree's life.

Secondary Phloem

Secondary phloem, like secondary xylem, originates from the vascular cambium and is another example of redifferentiation in plants. Its main function is the translocation of sugars and other metabolic products downward from the leaves to other parts of the plant. This tissue is crucial for sustaining the plant's non-photosynthetic parts, such as roots and stems.

The cells of the secondary phloem are more prone to breakdown and do not accumulate to the same extent as xylem, hence they don't contribute as much to the increase in girth of the tree. Unlike the longevity of secondary xylem, secondary phloem is a more transient tissue; older phloem cells are crushed and replaced by new ones over time.

Cork Cells

Cork cells, which originate from the cork cambium or phellogen, are yet another product of redifferentiation. These cells are unique in that once they mature, they undergo a process called suberization, in which they are infused with suberin. Suberin is a waxy substance that renders cork cells impermeable to gases and water. This characteristic makes cork an excellent protective barrier, insulating the plant stem and preventing water loss as well as protecting from pathogens.

As part of the outer bark, and because these cells are dead at maturity, cork significantly contributes to the defense of the plant. The same material is also harvested from certain trees, like the cork oak, to create cork products used by humans.

Plant Secondary Growth

Plant secondary growth refers to the increase in girth or thickness of stems and roots in woody plants, such as trees and shrubs. This growth is perpendicular to the length of the stem and is facilitated by the activity of lateral meristems, including the vascular cambium and cork cambium. Through redifferentiation, these meristems give rise to the secondary xylem and phloem, as well as to cork cells.

Secondary growth is a distinguishing factor between woody and herbaceous plants and is of paramount importance in the life of a perennial plant. It enables plants to grow taller and stronger, offering additional support needed to transport nutrients and water efficiently and survive for many years.