 QUIESCENT CENTER  STRUCTURE OF ROOT  ROOT CAP  Function  EPIDERMIS  CORTEX  EXODERMIS  ENDODERMIS

1. The discovery by Clowes (1954,1956) of a
quiescent center in the root apex brought about
a fundamental change of view about the
behavior of root meristems.

2. QUIESCENT CENTER:
Clowes(1958)studied the root tips of Zea mays
and observed an inactive center in between root
cap and active meristematic region.
 fewer mitochondria ,
 ER ,
 very small nuclei ,
 low rate of DNA
synthesis and protein
synthesis.

3. QUIESCENT CENTER
 SPECIES Q.C cells
 Zea mays 174 500-600
 Vicia faba 292 1100
 Sinapis alba 520 600

4.  A quiescent center arises twice in primary roots:
1.Embryogeny 2.stages of seed germination
 The quiescent center is variable in volume:
Thin roots- smaller or entirely absent
long roots- distinctive centers
short roots- no Q.c
seedless vascular plants- it lacks qc

5. The relatively inactive state of the quiescent center cells
does not mean that they have become permanently non
functional.
Quiescent center cells do divide occasionally and serve to
renew the more actively dividing regions around them, the
cells of which are unstable and displaced from time to time.
In roots injured experimentally by radiation or surgical
treatments the quiescent center is able to repopulate the
meristem

6. STRUCTURE OF ROOT
Arrangement of primary tissue in root:
• Root cap
• Epidermis
• Root cortex
• Vascular or central cell

7. ROOT CAP:
• Site of geoperception.
• Situated at the tip.
• Made up of living parenchymatous cell.
• Cells contain starch grains.
• May be arranged in radiating rows or no special
arrangement.
• Statoliths: starch containing
plastids.

8. Function:
• Protection
• Penetration
• Geotropism, (it controls the geotropic growth of root).
• Root cap cells secrete a polysaccharide slime.
(the process of secretion is accompanied by:
Hypertrophy of dictyosome cisternae form large vesicles
vesicle content released. )
,this secretion moves outwards through the wall.
•Root develops continuously.
•Root caps are absent in parasites and mycorrhizal roots.
•Root caps develop in true water plants but they degenerate early.
eg. Eichornia

9. EPIDERMIS:
CORTEX:
 Outermost cell layer
 Root epidermis – epiblemma or
rhizodermis
 Made up of parenchymatous cells
 May be cutinized
 Uniciliate or multiciliate
 Char. Feature: production of root
hair.
 Absorb water and minerals
 It is found below the epidermis
 In dicots,gymnosperm- paren. cells
 In monocots- paren. + scleren. cells
 Major role – storage
 Innermost layer – endodermis
 Outermost layer – exodermis
 Chloroplast absent

10. EXODERMIS
-Walls of the cells of outer subepidermal layer of cortex
become suberized ,this layer known as exodermis.
• Protective tissue
• Lignin present
• Casparian strips may also present
• Cells of the exodermis contain viable protoplasts .
• In pteridophytes, no exodermis
• Variation in thickness of the
exodermis:
• In Phoenix , exodermis is fibrous.

11. ENDODERMIS
• Inner boundary of the root cortex.
• Consists of a uniseriate cylinder
of cells.
• Casparian strips appear in the
radial and crosswalls of the
endodermal cells.
• Band plasmolysis is found in
endodermis.
• Plasmodesmata is found.
• Help in primary growth of roots.
• In the formation of lateral roots.

12. THANKYOU…