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 Respiration 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 Active 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 Water & Mineral Absorption of Roots Transport of Xylem Sap Control of Transpiration 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 MONOCOT ROOT DICOT 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! OPEN STOMATA CLOSED STOMATA

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 environmental conditions 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 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