Welcome to My Presentation

BY – RAZIA SULTANA JEMIM

Mechanism of plant nutrient absorption by plant root and

plant tissue

Nutrients Absorption

Mechanisms of Nutrient Uptake

Prior to absorption, nutrients reach the root by 3 mechanisms:

Mass flow – movement with the water flow. Most prominent.

Diffusion – movement in response to a concentration gradient. Slow.

Root interception – root extension. Very important to find new nutrient sources.

Absorption through roots

Passive Uptake: Some ions such as nitrate, can move passively through the outer membrane of the root surface along with water in the transpiration stream.

Active Uptake: Not well understood, but many nutrients (e.g., K+ and H2PO4

-) must somehow bond with an ion-specific carrier (see Insight: p.270).

Maintaining an Electrical Balance: As cations are absorbed H+ is excreted or organic anions are produced. As anions are absorbed HCO3

- is excreted or compensating cations are absorbed.

Stomatal Absorption: •Rapid absorption of soluble ions from nutrient enriched water.•Used mostly for the immediate correction of critical nutrient deficiencies. •Most efficient for the micronutrients. Does not build soil fertility. Danger of phytotoxic effects if over applied.

Absorption through leaves

The plasma membranes of root cells control solute uptake A plant can absorb enough water and inorganic ions

through its roots to survive and grow Root hairs greatly expand surface area for absorption

Substances enter roots in solution Water and solutes can move through the root's

epidermis and cortex by two routes Intracellular: via cell interiors, through plasmodesmata Extracellular: via cell walls; stopped by Casparian strip Plants usually use a combination of both

Water and solutes must cross a plasma membrane to enter the xylem for transport upward Controls solutes that enter xylem

LE 32-2b

Dermal tissue systemKey

Ground tissue system

Vascular tissue system

Root hair Epidermis Cortex Phloem

XylemCasparianstrip

Endodermis

Casparian stripExtracellular route,via cell walls;stopped byCasparian strip

Root hair

Xylem

Plasmodesmata

Endodermis

Cortex

Intracellularroute, viacell interiors,throughplasmodesmata Epidermis

Transpiration pulls water up xylem vessels Xylem sap travels from roots to top of plant through

the tracheids and vessel elements in xylem Root pressure can push sap up a few meters Most sap is pulled up by the transpiration-cohesion-

tension mechanism Transpiration

Loss of water from plant's aerial parts Aided by two properties of water: cohesion, adhesion

LE 32-3-3

Water uptake from soil

Root hair

Soil particle

Water

Flow

of

wat

er

Cohesion andadhesion in the xylem

Xylemcells Cohesion,

by hydrogenbonding

Watermolecule

AdhesionCellwall

Transpiration

Xylem sap

Mesophyll cells

Air space within leafStoma

Outside air

Guard cells control transpiration Plants can lose water through transpiration Leaf stomata help plants regulate their water

content Opened and closed by flanking guard cells

Controlled by movement of H2O and K+

Generally stay open during the day, allowing for entry of CO2 for photosynthesis

Stay closed at night, conserving water Respond to cues from sunlight, CO2 level,

biological clock

LE 32-4

Stoma Guard cells

Vacuole

K+

Stoma opening Stoma closing

Root hairs take up certain inorganic particles by cation exchange Hairs are in direct contact with water films on soil

particles Ca2+, Mg2+, K+ adhere tightly to soil particles H+ released into soil solution by root hairs displaces

them Can then be absorbed

Anions less tightly bound to soil particles More readily available, but may leach from soil

LE 32-8bSoil particle surroundedby film of water

Root hair

Water

Air space

LE 32-8c

Clayparticle

Root hair

H+

K+

K+

K+K+

K+

K+

K+

K+

Thank you!