Is Cell Division Required for Xylem Differentiation? | Plant Tissue Culture

Get the answer of: Is cell division required for xylem differentiation?

Whether cell division is a prerequisite for xylem differentiation or not is a subject of de­bate.

Studies have shown that tracheary element differentiation may be related to cell cycling ac­tivity, although some cells differentiate directly without any expression of mitotic division.

Evidences in Support of Cell Cycle Activity Required for Xylem Differentiation:

1. BUdR is an inhibitor of DNA synthesis. It has been observed that xylem differentia­tion is completely suppressed in 10^-5M BUdR treated Coleus stem explants, pea root explant, Jerusalem artichoke tuber ex- plant and lettuce pith tissue. Therefore, DNA synthesis is a critical factor in differ­entiation phenomenon.

2. High doses of gamma-irradiation also pre­vents both DNA synthesis and mitosis. So, gamma irradiated cells do not take part in xylem differentiation.

3. Malawer and Phillips (1979) also added some evidences to support the concept that xylem differentiation is preceded by mitotic division. They used ³H thymidine in the culture medium and observed the uptake of ³H thymidine by the cell up to xylem dif­ferentiation. From their experiment, they noted that xylem cell in culture had under­gone three rounds of DNA synthesis.

Evidences in Support of Cell Division not Required for Xylem Differentiation:

In some cases, cell division is not a prereq­uisite for xylem differentiation.

This concept is supported by the following observations:

1. Inhibitor studies with caffeine and colchi­cine have provided evidence that wound xylem formation in Pisum roots is a direct differentiation process.

2. In cell culture of Centanurea cyanus some of the single parenchymatous cell differenti­ates directly into tracheary elements with­out cell division. But the opponents ar­gued that the cells directly forming xylem elements could have been derived from a recent cell division because the cells were taken from fast-growing suspension culture.

Evidences in Support of Both Concept:

1. In case of Zinnia elegans, mesophyll system consists of two different cell populations; some of mechanically isolated cells after a period of extension growth directly differ­entiate into xylem elements without a cell division, whereas others require cell cycle activity for differentiation.

2. In Helianthus tuberoses, direct differentia­tion of xylem without DNA replication and mitotic division occurs only when the ex- plants are taken from immature tubers. But in mature tuber, xylem differentiation takes place only after cell division. Therefore, the question of cell division prior to xylem differentiation remains unresolved. To answer the question, the more critical studies on diverse plant systems are required.