Growth in Dicot Stem Using Developmental Terms
The cloned sheep called Dolly often made headlines....we even heard when she died. This clone facilitated the interest in stem cells. The term stem cells  does not mean that they are derived from plant stems. Rather this use of the term describes early cell development potential. Animal researchers describe various types of stem cells based on their developmental potential. These terms can also be used to describe the developmental potential of plant cells. 

Humans have been cloning plants for generations. My grandmother cloned by taking "slips" of existing plants. Have you heard anyone in your family use this term. 

It is important to understand these terms because of the controversy that is growing with the techniques called therapeutic cloning. 

 

 Cells Regions Description Primary Meristem or Tissues Development
Totipotent  Meristematic These cells continually to divide by the mitosis cell cycle. They have the potency to develop into any plant cell or tissue. This means that all genes can be turned on and transcribed. 
Pluripotent 

Region of Elongation

 The totipotent cells are becoming committed meaning they can only develop into cells with a particular type of function, such as in plumbing, a covering, or metabolism.  These newly formed committed cells are called pluripotent. This means that certain genes are turned on and transcribed to make the molecular machines {enzymes} necessary to cause these three primary meristems to develop. Other genes in these pluripotent cells are permanently turned off and can never again be transcribed. Protoderm(1) Can only develop into epidermal cells
Ground Meristem Can only develop into the pith and pith ray cells
Procambium Can only develop into the vascular tissue
 Multipotent  Region of Maturation These pluripotent cells produce cells that have additional genes turned on and other additional genes permanently turned off. This type of cell is called multipotent. Multipotent cells are  committed into making particular cells....the cells found in adult plant tissues such a chlorenchyma, collenchyma, etc.  Epidermis(2) Mature Tissue
Cortex Mature Tissue
Pith Mature Tissue
Pith Ray Mature Tissue
Vascular Bundles Mature Tissue
(1) The protoderm, procambium, and ground meristem are grouped into a category called primary meristems.
(2) Epidermis, Cortex, Pith, Pith Ray, and Vascular Bundles are adult plant tissues or often considered regions in stems or roots.

         

Instant Replay of  Primary Development
It works by... going from little specialization to more specialization and still more specialization.
Specialization is caused by turning on and off genes.
  • Maintain cells that contain genes available for producing all plant structures and cells.
    •  Totopotent cells reproduce themselves using the mitosis cell cycle. Each cell has the same genes that can be used  produce all the different cell types of the plant they are growing in. These cells are only using the genes to make this very general uninteresting meristematic cell. The genes to make the "interesting" different useful cells.....like plumbing....are just sitting there, waiting to be turned on and transcribed.
  • Make  specialized groups of cells that will provide the main plant structures or functions.
    • Pluripotent cells are produced from these totipotent cells by
      • turning on particular genes by causing them to be transcribed. The code in these genes are used to make the enzymes to make cells that will be used for a general functional need as:
        • plumbing.....the procambium
        • covering......the protoderm
        • metabolism and storage....ground meristem
      • The protoderm, procambium, and ground meristem are lumped into the Primary Meristems.
      • permanently turning of other particular genes because they will no longer be used
  • Make certain of these specialized groups of cells even more specialized that will only produce one or two cell types.
    • Multipotent cells. are produced from pluripotent cells by
      • turning on more genes by causing them to be transcribed. The code in these genes are used to make the enzymes to make cells that will be used for a specific functions such as
        • plumbing.....the xylem and phloem
        • covering......the epidermal and guard cells
        • metabolism and storage....chlorenchyma and parenchyma