Resource Acquisition and Transport CO2 O2 Light H2O Sugar Figure 36.2 An overview of resource acquisition and transport in a vascular plant O2 H2O and minerals CO2

Leaf area index Ground area covered by plant Figure 36.4 Leaf area index Plant A Leaf area = 40% of ground area (leaf area index = 0.4) Plant B Leaf area = 80% of ground area (leaf area index = 0.8)

mycorrhiza, a symbiotic association of fungi and roots 2.5 mm Figure 36.5 A mycorrhiza, a symbiotic association of fungi and roots

Proton pumps provide energy for solute transport CYTOPLASM EXTRACELLULAR FLUID _ + _ + H+ Proton pump generates mem- brane potential and gradient. ATP _ H+ + H+ H+ H+ H+ _ H+ + H+ Figure 36.6 Proton pumps provide energy for solute transport _ H+ +

Solute transport in plant cells _ CYTOPLASM + EXTRACELLULAR FLUID _ + K+ _ K+ + K+ K+ K+ _ K+ K+ + _ Transport protein + (a) Membrane potential and cation uptake _ + H+ H+ NO3− NO3− _ + _ + H+ H+ H+ H+ H+ H+ NO3− NO3− _ + NO3− _ NO3− + H+ H+ _ H+ + H+ (b) Cotransport of an anion with H+ Figure 36.7 Solute transport in plant cells _ + S H+ H+ _ H+ H+ + _ H+ + H+ S H+ H+ H+ H+ S S _ + S H+ _ + H+ _ S H+ + (c) Cotransport of a neutral solute with H+

Cotransport - a transport protein couples the diffusion of one solute to the active transport of another. _ + H+ H+ NO3− _ NO3− + _ + H+ H+ H+ H+ H+ H+ NO3− _ NO3− + NO3− _ NO3− + H+ H+ Figure 36.7b Solute transport in plant cells _ H+ + H+ Cotransport of an anion with H+

Water potential and water movement. (b) (c) (d) Positive pressure Increased positive pressure 0.1 M solution Negative pressure (tension) Pure water H2O H2O H2O H2O ψP = 0 ψS = 0 ψP = 0 ψS = −0.23 ψP = 0 ψS = 0 ψP = 0.23 ψS = −0.23 ψP = 0 ψS = 0 ψP = 0.30 ψS = −0.23 ψP = −0.30 ψS = 0 ψP = 0 ψS = −0.23 Figure 36.8 Water potential and water movement: an artificial model ψ = 0 MPa ψ = −0.23 MPa ψ = 0 MPa ψ = 0 MPa ψ = 0 MPa ψ = 0.07 MPa ψ = −0.30 MPa ψ = −0.23 MPa

Water relations in plant cells Initial flaccid cell: ψP = 0 ψS = −0.7 0.4 M sucrose solution: ψ = −0.7 MPa Pure water: ψP = 0 ψS = −0.9 ψP = 0 ψS = 0 ψ = −0.9 MPa ψ = 0 MPa Plasmolyzed cell Turgid cell ψP = 0 ψS = −0.9 ψP = 0 ψS = −0.7 ψ = −0.9 MPa ψ = 0 MPa Figure 36.9 Water relations in plant cells (a) Initial conditions: cellular ψ > environmental ψ (b) Initial conditions: cellular ψ < environmental ψ

Cells in wilted plant to the left - plasmolysis A wilted Impatiens plant regains its turgor when watered Cells in wilted plant to the left - plasmolysis Cells in plant below - turgor. Figure 36.10 A wilted Impatiens plant regains its turgor when watered

Short Distance Transport Cell wall Cytosol Vacuole Plasmodesma Vacuolar membrane Plasma membrane (a) Cell compartments Key Apoplast Apoplast Transmembrane route Apoplast Symplast Figure 36.11a Cell compartments and routes for short-distance transport Symplast Symplastic route Apoplastic route (b) Transport routes between cells

Transport of water and minerals from root hairs to the xylem Casparian strip Endodermal cell Pathway along apoplast Pathway through symplast Casparian strip Plasma membrane Apoplastic route Figure 36.12 Transport of water and minerals from root hairs to the xylem Vessels (xylem) Symplastic route Root hair Epidermis Endodermis Stele (vascular cylinder) Cortex

Transport of water and minerals from root hairs to the xylem Casparian strip Plasma membrane Apoplastic route Vessels (xylem) Figure 36.12 Transport of water and minerals from root hairs to the xylem Symplastic route Root hair Epidermis Endodermis Stele (vascular cylinder) Cortex

Pathway along apoplast Casparian strip Endodermal cell Pathway along apoplast Pathway through symplast Figure 36.12 Transport of water and minerals from root hairs to the xylem

Guttation Figure 36.13 Guttation

Generation of transpiration pull Cuticle Xylem Upper epidermis Microfibrils in cell wall of mesophyll cell Mesophyll Air space Figure 36.14 Generation of transpirational pull Lower epidermis Cuticle Stoma Microfibril (cross section) Water film Air-water interface

Ascent of xylem sap Figure 36.15 Ascent of xylem sap Xylem sap Outside air ψ = −100.0 Mpa Mesophyll cells Stoma Stoma Leaf ψ (air spaces) = −7.0 Mpa Water molecule Transpiration Leaf ψ (cell walls) = −1.0 Mpa Atmosphere Adhesion by hydrogen bonding Xylem cells Cell wall Water potential gradient Trunk xylem ψ = −0.8 Mpa Cohesion by hydrogen bonding Cohesion and adhesion in the xylem Figure 36.15 Ascent of xylem sap Water molecule Root hair Trunk xylem ψ = −0.6 Mpa Soil particle Soil ψ = −0.3 Mpa Water Water uptake from soil

Water molecule Root hair Water Water uptake from soil Soil particle Figure 36.15 Ascent of xylem sap Water Water uptake from soil

Adhesion by hydrogen bonding Xylem cells Cell wall Figure 36.15 Ascent of xylem sap Cohesion by hydrogen bonding Cohesion and adhesion in the xylem

Xylem sap Mesophyll cells Stoma Water molecule Transpiration Figure 36.15 Ascent of xylem sap Transpiration Atmosphere

An open stoma (left) and closed stoma (right) Figure 36.16 An open stoma (left) and closed stoma (LMs)

Stomatal Openings Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed Radially oriented cellulose microfibrils Cell wall Vacuole Guard cell (a) Changes in guard cell shape and stomatal opening and closing Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed H2O H2O H2O H2O Figure 36.17 Mechanisms of stomatal opening and closing H2O K+ H2O H2O H2O H2O H2O (b) Role of potassium ions in stomatal opening and closing

Xerophytic - Desert Plants Adaptations Ocotillo - leafless Xerophytic - Desert Plants Adaptations Oleander leaf cross section and flowers Cuticle Upper epidermal tissue 100 µm Trichomes (“hairs”) Crypt Stomata recessed Lower epidermal tissue Figure 36.18 Some xerophytic adaptations Ocotillo leaves after a heavy rain Ocotillo after heavy rain Old man cactus

Loading of sucrose into phloem proton pump -- Cotransport of Sucrose High H+ concentration Cotransporter Mesophyll cell Proton pump Cell walls (apoplast) Companion (transfer) cell Sieve-tube element H+ S Plasma membrane Plasmodesmata Key ATP Apoplast Sucrose H+ H+ Bundle- sheath cell Phloem parenchyma cell S Symplast Low H+ concentration Figure 36.19 Loading of sucrose into phloem Mesophyll cell

Loading of sucrose into phloem: Cotransport High H+ concentration Cotransporter Proton pump H+ S Figure 36.19b Loading of sucrose into phloem ATP Sucrose H+ H+ S Low H+ concentration

Bulk flow by positive pressure. Pressure Flow in a sieve tube Source cell (leaf) Vessel (xylem) Sieve tube (phloem) 1 Loading of sugar H2O 1 Sucrose H2O 2 2 Uptake of water Bulk flow by positive pressure Bulk flow by negative pressure 3 Unloading of sugar Figure 36.20 Bulk flow by positive pressure (pressure flow) in a sieve tube Sink cell (storage root) 4 Water recycled 4 3 Sucrose H2O

Does phloem sap contain more sugar near sources than sinks? EXPERIMENT 25 µm Sieve- tube element Figure 36.21 Does phloem sap contain more sugar near sources than sinks? Sap droplet Sap droplet Stylet Aphid feeding Stylet in sieve-tube element Separated stylet exuding sap

Question: Do alterations in symplastic communication affect plant development? EXPERIMENT Results Base of cotyledon Root tip Figure 36.22 Do alterations in symplastic communication affect plant development? 50 µm 50 µm Wild-type embryo Mutant embryo

Wild-type seedling root tip Mutant seedling root tip Question: Do alterations in symplastic communication affect plant development? Experiment RESULTS Figure 36.22 Do alterations in symplastic communication affect plant development? 50 µm 50 µm Wild-type seedling root tip Mutant seedling root tip

Resource Acquisition and Transport H2O CO2 O2 O2 CO2 Minerals H2O

Explain: Root Hairs Short Distance Transport of Water to Stele: Xylem …

You should now be able to: Describe how proton pumps function in transport of materials across membranes. Define the following terms: osmosis, water potential, flaccid, turgor pressure, turgid. Explain how aquaporins affect the rate of water transport across membranes. Describe three routes available for short-distance transport in plants.

Relate structure to function in sieve-tube cells, vessel cells, and tracheid cells. Explain how the endodermis functions as a selective barrier between the root cortex and vascular cylinder. Define and explain guttation. Explain this statement: “The ascent of xylem sap is ultimately solar powered.”

Describe the role of stomata and discuss factors that might affect their density and behavior. Trace the path of phloem sap from sugar source to sugar sink; describe sugar loading and unloading.