TRANSIT AMPLIFYING CELLS

Transit Amplifying Cells

Transit Amplifying Cells

Introduction

Stem Cells, which have an ability of self—renewal and potency to differentiate multiple types of cells, exist in plants as well as in animals, and play essential roles for the growth and development of both plants and animals. The most characterized stem cells in plants reside in growing tips of shoots (above—ground part of plants) and roots. Stem cells in shoot tips differentiate into the tissues that compose leaves and stems. In some circumstances these cells change their identity to produce flowers.(Brian , 2008) Stem cells in root tips differentiate into various root structures. In woody plants, stem cells named cambial cells produce additional tissue that forms a thick trunk for support of shoot tissues (i.e. secondary growth).

Stem Cell Niche in Shoot Tip

Stem cells reside in a dome—shaped organ known as the shoot apical meristem, which is located at the growing tip of the shoot. Stem cells are maintained by an underlying organizing cell group named the organizing center. Around two—thirds of stem cells are not physically interacted with the organizing center, thus physical interaction with organizing cells is not prerequisite to maintain stem cell identity in plants. Stem cells divide into stem cells themselves and transit—amplifying cells by asymmetric division.(Koster, 2005) Transit—amplifying cells are intermediate cells before cell differentiation, which retain dividing activity. They proliferate themselves in the meristem to accumulate enough cells to develop new organs.

The upper center region of the shoot apical meristem including the stem cell niche is the central zone, which is distinguished from other regions because of its slower rate of cell division. (Jensen , 2006)This slow cell division may reduce the possibility of mutations. Such mutations could be very detrimental as they can affect the large part of the shoot tissues including gametes (pollens and eggs), and can be transmitted into the next generation. In the peripheral zone, which is located around the central zone, cells divide more rapidly and initiate differentiation into several organs. In and below the peripheral zone, cells expand vertically, pushing the stem cell niche upward.(Brian , 2008)

Stem Cell Niche In Root Tip

The structure of stem cell niches in root tips differ from those in shoot tips. A few organizing cells are surrounded by several different types of stem cells. These organizing cells rarely divide, and have thus been called quiescent centers. Stem cells in root tips asymmetrically divide to produce stem cells themselves and differentiated root cells without forming transit—amplifying cells. On the distal (tip) side, stem cells produce a root cap that is continuously sloughed off and that serves to protect the stem cell niche. In the basal direction, stem cells differentiate into cell types that compose a typical root. Differentiated cells expand vertically to push the stem cell niche further in the soil, resulting in the elongation of roots.(Brian , 2008)

Stem Cell Reprogramming Of Differentiated Cells

Certain differentiated cells are reprogrammed into stem cells in plants. In shoots, stem cell niches are formed from differentiated cells ...