Transcript Mechanism of water uptake by roots - Dr.PDKV, Akola

Welcome
WEL-COME
Mechanism of water uptake by roots ,transport in
roots,aquaporins ,movement of water in plants,
mycorrhizal
association on water uptake.
Department of Agricultural Botany
Post Graduate Institute, Dr. PDKV, Akola.
MECHANISUM OF WATER UPTAKE BY ROOTS
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Plants absorb water from the soil by their roots .
Roots play the principle role in absorption of water .
ROOT :
Root consist of five regions
1)Root cap region
2)Meristematic region
3)Region of elongation
4)Region of root hair
5)Mature region
Regions Plant Root
Roots absorb water mainly from the apical region.
Apical organization of root shows three clear
Demarcation.
The zone of meristematic cells ,the zone of elongation
and the zone of absorption or differentiation .
The important one are described here
Root hair :
It consist of epidermis cells for the absorption of water.
The wall of root hair consist of cellulose and pectic
substances both are highly hdrophilic in nature.These
substances have great capacity of water absorption .
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Mechanism of water absorption
Water absorption have been explained by two different approaches.
1) Active absorption
2) Passive absorption
Active absorption:
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When root are involved actively in water absorption and water
absorbing forces in plant are developed primary in roots .
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It is found in those plant where transpiration is less and water
present in sufficient amount.
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Active absorption requires ATP released during respiration.
Two theories of active absorption
1) Osmotic Theories (At kins 1961 & priestley 1992)
2) Non -Osmotic Theories (Thimann 1951 & Kramer 1959)
Pathway of water in Root
Root hair Epidermal cellVarious successive cortex cells
Endodermal cells (passage cells)Cell of pericycle  Xylem
cells  Xylem ductUpward movement of water .
Passive absorption:
Absorption of water into the roots are governed by other cells.The
governing force originate in the cells of transpiring shoots and other than in roots its
self . This force develop due to transpiration .
Thus passive absorption take place due to activity of upper part of plant such as
shoot and leaves .
ACTIVE ABSORPTION
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Active absorption of water take
place due to the activity of root
and root hair.
Absorption occurs by osmotic
and non osmotic pressure .
The root hairs have high DPP as
compare to soil solution and
there for water is taken.
In the movement of water living
part of protoplast is involved.
In non osmotic type of
absorption respiratory type of
energy is utilized.
PASSIVE ABSORPTION
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It taks place due to activiy of
upper part of plant,such as
shoot and leaves .
Water is absorbed due to active
transpiration .
The absorption occurs due to
tension created in xylem sap by
transpiration pull thus water is
sucked in by tension .
The movement of water is
through free spaces or apoplast
of root.
energy is never required.
FACTORS AFFECTING WATER ABSORPTION RATE
External environmental factors
a) Available soil water
b) Concentration of soil solution
c) Soil temperature
d) Soil aeration
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FACTORS AFFECTING WATER ABSORPTION RATE
Internal environmental factors
a) Transpiration
b) Absorption of root system
c) metabolism
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AQUAPORINS
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Aquaporins : some integral membrane protein
which form water selective channels in cell
membranes and facilitate faster movement of
water across the membranes into the plant cell
this channel have been called as Aquaporins.
The direction of water transport across the
membrane however is not affected by Aquaporins
Movement of water in plants
The water has to move upward through the stem . this upward
movement of water is called as ascent of sap .
Mechanism of ascent of sap : no of theories have been put
forward .
a) Vital theories
b) Root pressure theories
c) Physical force theories
d) Transpiration pull and cohesion of water theory.
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Transpiration pull and cohesion of water theory
Proposed by dixon and jolly (1894) it based on following feature
1. Cohesive and adhesive
2. Transpiration pull
Mycorrhizal association on water uptake
The association of a fungus whith root of plant is called as Mycorrhizae .
The relationship of mycorrhizae is symbiotic or mutual in which both parteners are
benefitted .
The fungus absorb water and mineral salt from the soil and release them into cells of
host root .The host root supply carbohydrate to fungus .
The mycorrhizae fungi grouped into two categoris
a) Ectotrophic micorrhizae
b) Vesicular arbuscular micorrhizae (VAM)
Ectotrophic micorrhizal fungi infect exclusively gymnosperm and woody
angiosperms
VAM fungi infect roots of most spp.of herbaceus angiosperms.