Slide 1 : Dr Subroto Biswas
How much ? : How much ? Water retaining plants
Adapted to arid climate or soil
Succulents or Fat plants : Succulents or Fat plants They store water in leaves, stems and roots
Slide 4 : Pebble Plant, Lithops julii
Water storage in orchids : Water storage in orchids
Slide 6 : The storage of water often gives succulent plants a more swollen or fleshy appearance than other plants
Slide 7 : Saguaro cactus
Slide 8 :
Slide 9 :
Slide 10 : To prevent water loss, the stomata of these plants are closed by day, to open only at night when temperature decreases and humidity rises.
Since the absorption of CO2 is only possible at night, CO2 storage and changes in metabolism are necessary to carry out photosynthesis by day.
At night CO2 is stored as malate in the large vacuoles, to be released for photosynthesis by day.
This mechanism was discovered first in Crassulacean plants, such as Crassula and therefore is called Crassulacean Acid (acid: malate) or CAM Metabolism.
Jatropha berlandieri : Jatropha berlandieri A large, globose caudex
Caudiciform plants are adapted to prolonged periods of drought
Belongs euphorbia family (Euphorbiaceae)
They can store water and survive many months without rain in hot, arid desert regions.
Most remarkable and truly bizarre plants on earth.
Slide 12 :
The boab tree : The boab tree Adansonia, species
Native to Madagaskar, Africa and Australia ?
Slide 14 : Baobabs are often of enormous girth and store water inside their swollen trunks.
Slide 15 : Baobabs change in size at various times during the season due to the storage of water.
Baobabs store water inside the swollen trunk, up to 120,000 liters (32,000 US gallons)
An adaptation allowing them to endure the harsh drought conditions particular to each region
Rightly called the bottle tree : Rightly called the bottle tree Diameter often of seven meters (23 feet)
Exceptional trees have a diameter over eleven meters (thirty-six feet) tore water
The bottle tree : The bottle tree Unusual swollen shape of its trunk
Acts as a water store.
Traditional hunters in northern Namibia have used its highly toxic sap as an arrow poison.
Slide 18 : Pachypodium lealii Image: Barbara Curtis
Roots primarily absorb water from the soil. The chief source being the rain water. : Roots primarily absorb water from the soil. The chief source being the rain water.
Water Pathways in Roots : Water Pathways in Roots Water is absorbed by the root hair cells.
Then it reaches the leaves, by passing through a number of cells.
Slide 21 : From the root hair,
It moves into the cortical cells.
Crossing the cortical cells, the water reaches the endodermis
Slide 22 :
Slide 23 : The endodermal cells lying opposite to root hairs are specially modified to transport the absorbed water.
These endodermal cells are called passage cells.
Slide 24 : The passage cells are permeable to water because they lack Casparian thickenings in their walls.
Other endodermal cells are provided with Casparian thickening and are impermeable to water.
Slide 25 : The water from the passage cells pass into the pericycle cells and into the xylem cells
From where the water moves up through stem to reach the leaves.
The root hair, passage cells and xylem cells are a line to facilitate easy movement of water.
The water movement from one cell to another is brought about by turgor pressure.
Slide 26 : Thus
The absorbed water passes through a variety of cells such as..
cortical cells,
passage cells (endodermis),
pericycle cells and
xylem tubes to reach the leaves.
Slide 27 : In the soil, water is transported predominantly by bulk flow.
From the epidermis to the endodermis of the root, there are three pathways through which water can flow,
the apoplast,
the transmembrane pathway and
the symplast.
Apoplast (freespace) pathway : Apoplast (freespace) pathway Water movement through the cell wall only
Without crossing any membranes.
Continuous system of cell walls
Transmembrane pathway : Water crosses at least two membranes
The plasma membrane on entering and on exiting.
Transport across the tonoplast Transmembrane pathway
Symplast : Symplast Second component of the cellular pathway
Water moves from one cell to the next via the plasmodesmata.
The symplast consists of the entire network of cell cytoplasm interconnected by plasmodesmata.
Slide 31 : A combination of apoplast, transmembrane and symplast pathways transports water across the root.
P.J. Kramer (1949) proposed that water is absorbed by two important mechanisms, active and passive. : P.J. Kramer (1949) proposed that water is absorbed by two important mechanisms, active and passive. Active absorption
Passive absorption
Active Absorption : Active Absorption By their own efforts
Occurs when transpiration is low
Quantity of water in the soil is high.
Root cells play active role
Metabolic energy of cellular respiration is consumed by roots to absorb water.
Passive absorption : Passive absorption Root hairs remains passive
Transpiration causes absorption
Other absorptive structures : Other absorptive structures Young leaves
Mycorrhizae
Arial roots (velamen)
What is …… Ascent of sap ? : What is …… Ascent of sap ? The upward movement of water from the root system to the aerial parts of the plant through the xylem is called ascent of sap
Takes place through sap wood only.
Upward conduction occurs mainly by xylem vessels.
Ringing experiment : Ringing experiment The ringing experiment shows that break in phloem do not allow translocated materials from leaves to reach the roots.
However, water minerals reach the shoot through xylem elements
Slide 38 :
Can Root Pressure help in absorbtion of water ? : Can Root Pressure help in absorbtion of water ? Yes
Roots accumulation water by absorbtion
The ascent of sap is due to a hydrostatic pressure which develops in the treachery elements of the xylem as a results of the metabolic activities of roots.
A cut stump of a plant demonstrates the root pressure (3 to 5 bars) that causes the mercury to rise in the column : A cut stump of a plant demonstrates the root pressure (3 to 5 bars) that causes the mercury to rise in the column
Can root pressure cause ascent of sap ? : Can root pressure cause ascent of sap ? Pressure or force developed is of little magnitude and fails to explain the transport of water
Root pressure theory does not apply to tall trees.
Maximum root pressure observed is 2 atm.
Do Atmospheric Pressure help in ascent of sap? : Do Atmospheric Pressure help in ascent of sap? Yes
This is not accepted universally because atmospheric pressure cannot act on water present in the xylem of roots.
Atmospheric pressure cannot raise water beyond 34 feet.