The document discusses the root apical meristem, highlighting its characteristics, theories of development, and significance in the formation of root tissues. It explains major theories such as the apical cell theory, histogen theory, and korper-kappe theory, each detailing different organizational structures and functions of root cells. Additionally, it describes the quiescent center, a region of inactive cells that can become active under certain conditions, serving as a reservoir for cell replenishment in root growth.

1. Plant Tissue
Lecture-3 Root Apical Meristem
By: Dr. Sunita Sangwan
Assistant Prof.
Deptt. of Botany
MNSGC Bhiwani

2. Root Apical Meristem

3. Root apical meristem
The cells of the apical meristem of primary root have dense
cytoplasm, large nuclei and divide actively.
This meristem differentiates into embryonic radicle.
All the permanent tissues of the root are originated from the
root apical meristem.
The root apical meristem is sub-terminal in position as terminal
position is occupied by a root-cap.
The meristem that develop root cap is termed as calyptrogen.

5. 1. Apical Cell Theory
2. Histogen Theory
3. Korper-Kappe Theory
Theories of Root apical meristem

6. Apical Cell Theory
Nageli proposed this theory in 1958.
This theory state that there is a single
apical tetrahedral cell, which gives rise
to all the tissues of the root.
The base of the apical cell from the root
cap and the upper three sides of apical
cell give rise to other tissues like
epidermis, cortex and vascular cylinder.
This theory is applicable only to the
vascular cryptogams only as a group of
the initial cells has been observed in the
root apical meristem of angiosperms.

7. Histogen Theory
Hanstein postulated this theory in 1868.
He proposed that there are three distinct meristematic zones termed as
histogens.
These three zones are dermatogen, periblem and plerome. Each zone has
its specific function.
Dermatogen form epidermis, periblem give rise to cortex and vascular
cylinder are originated from plerome.
Later on calyptrogen was defined as the fourth histogen that played a role
in formation of root cap.
Haberlandt proposed the name protoderm, ground meristem and
procambium for these three histogens dermatogen, periblem and plerome
respectively.

8. Histogen Theory

9. Histogen Theory
Based on cellular configuration, Schuepp in 1926 divided the root apical meristem into four
types.
Type A: All the permanent tissues of root are originated from a single apical cell. It is found
in all vascular cryptogams.
Type B: There are two separate groups of initials. One give rise to the vascular cylinder and
other tissues like epidermis, cortex and root cap derived from second group. It is most
commonly observed in gymnosperms.
Type C: There are poorly organized initials that develop into root cap, cortex and vascular
cylinder and it is found in dicotyledons.
Type D: There are three separate groups of initials. One group forms root cap; other group
give rise to epidermis and cortex while vascular cylinder derived from separate group. This
type is commonly found in monocotyledons.

10. Histogen Theory

11. Korper-Kappe Theory
Schuepp (1917) advocated this theory.
He described the organization of root
apex based on planes of division. He
proposed that the cells at the root apex
divide in two planes.
First transverse division takes place that
divide the initial cell into two daughter
cells.
One of daughter cell divides by
longitudinal division to form T shaped
structure due to which it is also known
as ‘T’ division.
Based on the divisions root apical
meristem is differentiated in two zones

12. Korper (Cap) and Kappe (body)
In the inner region, inverted T shaped structure is formed
because of the upper daughter second division in cell and it is
known as Korper (cap).
In the outer region, the second division occurs in lower
daughter cell and form straight T shaped structure termed as
Kappe (body).
These Korper and Kappe are clearly differentiated in
monocotyledons.

13. Korper-Kappe Theory
The central region of root cap the cells are arranged in
longitudinal files is called columella and cells of this region
divide rarely.
Like the korper-kappe theory of root apex, tunica-corpus theory
of shoot apical meristem also based on the plane of cell division
so these two theories shows similarity in organization of apical
meristem.

14. Quiescent Centre
A central cup like hemispherical region
is found between the root cap and
active meristematic zone in the root tip
of Zea, Clowes.
Quiescent centre is hemispherical
shaped group of mitotically and
metabolically inactive cells located just
behind the root cap.

15. Characteristics of Quiescent center cells
The amount of DNA, RNA and protein is less in these cells.
These cells also have low mitotic activity.
The cell organelles like mitochondria, endoplasmic reticulum,
dictyosomes are also less in numbers.
Later on, quiescent zone found in the root tips of many plants.

16. Quiescent Centre
When the cells of this region are exposed to X-rays, the
meristematic cells stop dividing and the cells of quiescent centre
become active because the cells of quiescent centre are more
resistant to the radiations than meristematic cells.
Therefore, quiescent centre is considered as central mother cells
that form promeristem of the apex. It act as a reservoir of
diploid cells when the root tip is damaged.

17. Thanks