TRANSPORT in PLANTS. What must be transported in plants? H 2 O & minerals Sugars Gas Exchange.

TRANSPORT in PLANTS

What must be transported in plants?

H2O & minerals

Sugars

Gas Exchange

Transport of Water & Minerals

Occurs in the xylem H2O is moved from

root to leaves Transpiration loss

of H2O from leaves (thru stomata) Processes

Evaporation Cohesion Adhesion Negative Pressure

Transport of Sugar

Occurs in the phloem Bulk Flow

Calvin Cycle (Dark Rxns) in leaves loads sugar into the phloem

Positive Pressure Movement

Source (where sugar is made) to Sink (where sugar is stored/consumed)

Gas Exchange Photosynthesis

CO2 in O2 out Transport occurs through

stomata Surrounded by guard cells

Control opening & closing of stomata

Respiration O2 in CO2 out Roots exchange gases w/

air spaces in the soil

Why can over-watering kill a plant?

Transport in Plants

Three main physical forces that fuel transport in plants: Cellular

Gases from the environment into plant cells H2O & minerals into root hairs

Short-Distance Transport Cell to cell Moving sugar from leaves into phloem

Long-Distance Transport Moving substances through the xylem &

phloem of a whole plant

Cellular Transport Passive

Diffusion down a concentration gradient Occurs faster w/ proteins

Carrier Proteins (facilitated diffusion) Active

Requires energy Proton Pump

Pumps H+ out of a cell Creates a proton gradient (stored energy) Generates a membrane potential

Used to transport many solutes

Cellular Transport –Active Transport

Cellular Transport -Water Potential

Combined effects of solute concentration & physical pressure

Moves from high H2O potential to a low H2O potential Inversely proportional to solute concentration

Adding solutes – Lowers water potential Directly proportional to pressure

Raising pressure- Raises water potential Negative pressure (tension) decreases water

potential

Cellular Transport-Water Potential

H2O potential =

pressure potential + solute potential

A) adding solutes reduces H2O potential

B & C) adding pressure, increases H2O

potential D) negative pressure

decreases H2O potential

Short-Distance Transport Movement from cell to

cell by… Transmembrane

Crosses membranes & cell walls

Slow, but controlled Called the apoplastic

route Cytosol (cytoplasm)

Plasmodesmata junctions connect the cytosol of neighboring cells

Called the symplast route

Long-Distance Transport

Bulk Flow Movement of a fluid driven by pressure Xylem: tracheids & vessel elements

Negative pressure Transpiration creates negative pressure by

pulling xylem up from the roots Phloem: Sieve tubes

Positive pressure Loading of sugar at the leaves generates a

high positive pressure, which pushes phloem sap thru the sieve tubes

Four Basic Transport Functions

1) Water & Mineral Absorption of Roots

2) Transport of Xylem Sap3) Control of Transpiration 4) Translocation of Phloem Sap

Water & Mineral Absorption

Root Hairs Increase surface area

Mineral Uptake by Root Hairs Dilute solution in the soil Active Transport Pumps

May concentrate solutes up to 100X in the root cells

Water Uptake by Root Hairs From high H2O potential to low H2O potential Creates root pressure

Water and Mineral Absorption – Root Structure

DICOT ROOTMONOCOT ROOT

Water and Mineral Absorption –Water Transport in Roots

Apoplastic or symplastic Until the endodermis Is reached!!

Water and Mineral Absorption –Control of Water & Minerals in the Root

Endodermis Surrounds the stele Selective passage of

minerals Freely enters via the

symplastic route Dead end via the

apoplastic route Casparian Strip

Waxy material Allows for the

preferential transport of certain minerals into the xylem

Water & Mineral Absorption & Mycorrhizae

Symbiotic relationship b/w fungi & plant Symbiotic fungi

increase surface area for absorption of water & minerals

Increases volume of soil reached by the plant

Increases transport of water & minerals to host plant

Transport of Xylem Sap: Pulling

TRANSPIRATION-COHESION-TENSION MECHANISM Transpirational Pull

Drying air makes H2O evaporate from the stomata of the leaves

Cohesion b/w H2O molecules causes H2O to form a continuous column

Adhesion H2O molecules adhere to the side of the xylem

Tension As H2O evaporates from the leaves, it moves into

roots by osmosis

Transport of Xylem Sap: Pushing

Root Pressure – pushes H2O up xylem Due to the flow of H2O

from soil to root cells at night when transpiration is low

Positive pressure pushes xylem sap into the shoot system

More H2O enters leaves than exits (is transpired) at night

Guttation - H2O on morning leaves

Transport of Xylem Sap-Ascent of H2O in Xylem: Bulk Flow

Due to three main mechanisms: Transpirational Pull

Adhesion & cohesion Water potential

High in soil low in leaves

Root pressure Upward push of

xylem sap Due to flow of H2 O

from soil to root cells

Control of Transpiration: Gas Exchange Stomate Function

Compromise b/w photosynthesis & transpiration

Amount of transpiration (H2O loss) must be balanced with the plant’s need for photosynthesis

Leaf may transpire more than its weight in water every day!

OPENSTOMATA

CLOSEDSTOMATA

Control of Transpiration-Leaf Structure

Control of Transpiration - Photosynthesis vs. Transpiration

Open stomata allow for CO2 needed for photosynthesis to enter

There is a trade-off….. Plant is losing water at a rapid rate

Regulation of the stomata allow a plant to balance CO2 uptake with H2O loss

What types of environmentalconditions will increase transpiration?

Control of Transpiration –Stomatal Regulation

Microfibril Mechanism Guard cells attached at tips Microfibrils elongate & cause cells to arch open Microfibrils shorten & cause cells to close

Ion Mechanism Uptake of K+ by guard cells during the day

H2O potential becomes more negative H2O enters the guard cells by osmosis Guard cells become turgid & buckle open

Loss of K+ by guard cells H2O potential becomes more positive H2O leaves the guard cells by osmosis Guard cells become flaccid & close the stomata

Control of Transpiration-Stomatal Regulation

Control of Transpiration –Stomatal Regulation

Three cues that open stomata at sunrise: Light Trigger

Blue-light receptor in plasma membrane Turns on proton pumps & takes up K+

Depletion of CO2 in air spaces CO2 used up at night by the Calvin Cycle

Internal Clock (Circadian Rhythm) Automatic 24-hour cycle

Control of Transpiration-Adaptations that Reduce Transpiration

Small, thick leaves Reduces surface area-to-

volume ratio Thick cuticle Stomata on lower leaf

side with depressions Depressions shelter the

stomata from wind May shed leaves during

dry months Fleshy stems for water

storage CAM metabolism

Takes in CO2 at night & can close stomata during the day

Translocation of Phloem Sap

Phloem Sap Water & sugar (mostly

sucrose) Moved through sieve tube

members Porous cross walls that allow

sap to move through Travels in many directions

From source to sink (where sugar is consumed/stored)

Source: leaf Sink: roots, shoots, stems,&

fruits

Translocation of Phloem Sap-Loading of Sugars

Flow through the symplast or apoplast in mesophyll cells into sieve-tube members

Active co-transport of sucrose with H+

Proton pump

Translocation of Phloem Sap-Pressure Flow

Bulk Flow Movement Sugar loaded at the source

Reduces water potential Causes H2O to move into sieve-tube

members Creates a hydrostatic pressure that

pushes sap through the tube Sucrose is unloaded at the sink Water moves into xylem & is carried

back up the plant

Phloem Transport

Pressure Flow and Translocation of Sugars