terminology used in biotechnology, differentiation, de-differentiation, re-differentiation, growth etc.

1. TERMINOLOGY
LECTURE #7

2. • Explant
• A plant organ (or) an excised part used to initiate Tissue culture
• Growth:-
• An increase in size (vol/wt/length) due to cell division and
subsequent enlargement
• Differentiation:
• The development of cells / tissues with the specific function
and / or the regeneration of organs / organ like structures /
pro-embryos
• The phenomenon of mature cells reverting to a meristematic
state and forming undifferentiated callus tissue is termed as
‘De-differentiation’

3. • The ability of component cells of the callus to differentiate into a
whole plant or a plant organ is termed as Re-differentiation
• Callus may be defined as an unorganized mass of loosely arranged
parenchymatous tissue which develop from parent cells due to
proliferation of cells
• Cellular Totipotency
• The capacity of a plant cell to give rise to a whole plant is known as
cellular Totipotency
• Generally a callus phase is involved before the cells can undergo
re-differentiation leading to regeneration of a whole plant. The
dedifferentiation cells can rarely give rise to whole plant directly
without an intermediate callus phase (Direct regeneration)

4. • Growth and differentiation although proceed together they
are independent
• Differentiation may be categorized into 2 groups
• 1) Structural 2) physiological
• 1) Structural differentiation
• It is further distinguish into external and Internal
differentiation.
• a) External
• Most common example is root and shoot differentiation
another familiar example of is vegetative and reproductive
phases of life cycle Further differentiation in reproductive

5. • b) Internal
• This includes differentiation of various types of cells and tissues.
Differentiated cells mostly occur into groups forming different type of tissues
• Eg:- Vascular tissues.
• c) Physiological
• The variations in the structure between root and shoot are the expressions of
fundamental physiological differences
• Cyto-differentiation
• In both plants and animals specialized cells perform different functions. This
specialization is known as cytodifferentiation.
• The cells in a callus are parenchymatous in nature. The differentiation of
these cells into a variety of cells is required during re-differentiation of the
cells into whole plants. This re-differentiation of cells is known as Cyto-
differentiation.
• Eg:- Vascular tissue differentiation (Xylem and phloem)

6. • Organogenic differentiation
• For the regeneration of whole plant from cell (or) callus tissue
cyto differentiation is not enough and there should be
differentiation leading to shoot bud and embryo formation.
• This may occur either through organogenesis (or) somatic
embryogenesis. Organogenesis refers to the process by which
the explants, tissues (or) cells can be induced to form root and
the (or) shoot and even whole plants. In other words formation
of organs is called organogenesis this may be categorized into
2 groups.
• Rhizogenesis: The process of root formation
• Caulogenesis: The process of shoot initiation

7. • Somatic embryogenesis.
• Development of embryos from somatic cells in culture whose
structure is similar to zygotic embryos found in seeds and with
analogous embryonic organs such as cotyledons (or) cotyledony
leaves.