Transport in Plants

Title :

Transport in  Plants

Author :

Kim Foglia & Kelly Reidell

Number of slides:

17

Source:

Science Slideshow Blog

Slideshow :

Content transcript :

Review:  Transport proteins

* Facilitate diffusion via carrier or selective channel formation

* Carrier proteins 

* Selective to solute molecule 

* Produces conformational change of protein

* Releases molecule to opposite side

* Selective channel 

* Passageways for certain solutes 

* May be gated  -  open/close

Transport in plants

* H2O & minerals

* transport in xylem 

* transpiration

* evaporation, adhesion & cohesion

* negative pressure

* Sugars

* transport in phloem

* bulk flow

* Calvin cycle in leaves loads sucrose into phloem

* positive pressure

* Gas exchange

* photosynthesis 

* CO2 in; O2 out

* stomates

* respiration

* O2 in; CO2 out

* roots exchange gases within air spaces in soil

Ascent of xylem fluid

Water & mineral absorption

* Water absorption from soil

* osmosis 

* aquaporins

* Mineral absorption

* active transport

* proton pumps

* active transport of H+

Mineral absorption

* Proton pumps

* active transport of H+ ions out of cell

* chemiosmosis

* H+ gradient

* creates membrane

potential

* difference in charge

* drives cation uptake

* creates gradient

* cotransport of other

solutes against their

gradient

Water flow through root

* Porous cell wall

* water can flow through cell wall route & not enter cells 

* plant needs to force water into cells

Controlling the route of water in root

* Endodermis

* cell layer surrounding vascular cylinder of root

* lined with impermeable Casparian strip

* forces fluid through selective cell membrane 

* filtered & forced into xylem cells

Mycorrhizae increase absorption

* Symbiotic relationship between fungi & plant

* symbiotic fungi greatly increases surface area for absorption of water & minerals 

* increases volume of soil reached by plant

* increases transport to host plant

Mycorrhizae

Control of Stomates

* Uptake of K+ ions by guard cells

* proton pumps

* water enters by osmosis

* guard cells become turgid

* Loss of K+ ions by guard cells

* water leaves by osmosis

* guard cells become flaccid

Water potential and osmosis

* Osmosis

* Net absorption or loss of water

* Water potential (?)

* Combined effects of solute concentration and pressure

* Determines direction of water movement

* Water moves from areas of high water potential to areas of low water potential

* 0 Mpa = pure water open at sea level & room temp

Water potential (?)

* Solute potential (?s)

* Proportional to number of dissolved solutes

* Osmotic potential

* ?s = 0 in pure water

* ?s = -0.23 in 0.1M solution of sugar

* Addition of solutes lowers the ?

* Pressure Potential (?P)

* Physical pressure on a solution

* Can be + or –

* Water in xylem is often negative

* Water in cell is often positive

* Additional pressure raises the ?

? = ?p + ?s

* ?p  - pressure potential

* ?s - solute potential = osmotic potential

* Flaccid cell (P = 0) placed in hypertonic solution will lose water via osmosis 

* Plasmolysis - protoplast pulls away from cell walls

* Same cell placed within a hypotonic solution will gain water via osmosis = turgid

Transport of sugars in phloem

* Loading of sucrose into phloem

* flow through cells via plasmodesmata

* proton pumps

* cotransport of sucrose into cells down proton gradient

Pressure flow in phloem

* Mass flow hypothesis

* “source to sink” flow

* direction of transport in phloem is dependent on plant’s needs

* phloem loading

* active transport of sucrose 

into phloem

* increased sucrose concentration decreases H2O potential

* water flows in from xylem cells

* increase in pressure due to increase in H2O causes flow

Experimentation

* Testing pressure flow hypothesis

* using aphids to measure sap flow & sugar concentration along plant stem