Download The Root: Structure and development

The Root:
Structure and development
Roots
The four major functions of roots are
1) 
2) 
3) 
4) 
Absorption
Conduction
Storage
Anchorage
wheat, Tri$cum, germ Electron microscopy Root systems
• A primary (taproot) root system
consists of:
ü  A primary root and secondary roots.
ü Present mainly in dicots
ü Radicle of seedling gives rise to the
root.
• Fibrous (adventitious) root system:
ü There is not a tap root
ü Present in monocots, ferns and
some dicots.
ü The roots arise from the stem
ü The radicle is short-lived
Root extension
Secale cereale
Root system including root
hairs = 639 m2
occupying only 6 liters of soil
Medicago can extend its roots
10 m or more
stele Root tissues
The three primary meristems
occur near to the apical
meristem
Phloem sieve tubes reach
maturity earlier
Columella Controls gravitropism Contains amyloplasts Mucigel cells Mucigel is a slimy substance
made by dictyosomes.
1.  lubrication
2.  It contains allelopathic
compounds
3.  Water and nutrient
absorption
4.  help establish beneficial
symbioses with soil
microbes.
Casparian strip or Casparian tissue
The endodermal cell walls, contain the casparian strip with suberin, a waxy
water repellant substance.
Secondary growth
Mainly consist in the formation of
secondary vascular tissues and periderm
(cork tissue)
Not capable of extension.
Does not undergo reversible changes in
thickness.
True pits present.
No plasmodesmata present.
Secondary growth
In some cases dead roots are
replaced immediately by young
roots
If the cortex is retained, their
walls will be covered with a
suberin lamella, lignin and
cellulose
Origin of lateral roots Branch roots originate in the pericycle, so they are endogenous.
Never happen in the elongation section of the root
Arabidopsis lateral root development
0
I
II
High auxine concentra9on Credit: Yvon Jaillais (Thierry Gaude lab) III
IV
V
Origin of adven33ous roots, process of rhizogenesis. Primordial cells
differentiated from the
cambium.
Radicles are generated with
a formed apical meristem.
Modifications of the roots
Potamogeton and Myriophyllum have air chambers extending from the shoots and leaves to the roots. Specialized roots
Pneumatophores are
structures with spongy
tissues
Negative geotropism
Aerating roots which are
found in some plants found
growing in water-logged,
badly aerated soils.
Swamp Cypress (Taxodium dis$chium) has characteris9c "knees” Pneumatophores Prop roots are adventitious
roots
Banyan tree with stilt roots.
Aerial roots
Aerial roots
There are many species of epiphytes. (i.e.
plants which grow attached to other plants)
Velamen: multi-layered epidermis on the
outside surfaces of the roots.
Bu<ress roots Common in large tropical trees.
Buttress roots are immense
exaggerated wall-like structures at
the interface between the trunk and
the ground.
Storage roots Tuberous roots are storage organs which act as perennating organs in
environments which have extreme fluctuations of either temperature or
moisture.
Ipomoea sp. (Sweet Potato)
Attendance
Define dictyosome
What are the four main functions of the Mucigel cells?
What is suberin?
What is the velamen?
__________ is the hormone related with the root elongation