1. Water Regulation and Nutrient Absorption © 2011 Pearson Education, Inc.

2. Adaptations for acquiring resources were key steps in the evolution of vascular plants The algal ancestors of land plants absorbed water, minerals, and CO 2 directly from the surrounding water Early nonvascular land plants lived in shallow water and had aerial shoots Natural selection favored taller plants with flat appendages, multicellular branching roots, and efficient transport © 2011 Pearson Education, Inc.

3. The evolution of xylem and phloem in land plants made possible the long-distance transport of water, minerals, and products of photosynthesis Xylem transports water and minerals from roots to shoots Phloem transports photosynthetic products from sources to sinks © 2011 Pearson Education, Inc.

4. Figure 36.2-3 H 2 O and minerals O2O2 CO 2 O2O2 H2OH2O Light Sugar

5. Shoot Architecture and Light Capture Stems serve as conduits for water and nutrients and as supporting structures for leaves There is generally a positive correlation between water availability and leaf size © 2011 Pearson Education, Inc.

6. Root Architecture and Acquisition of Water and Minerals Soil is a resource mined by the root system Taproot systems anchor plants and are characteristic of gymnosperms and eudicots Root growth can adjust to local conditions –For example, roots branch more in a pocket of high nitrate than low nitrate Roots are less competitive with other roots from the same plant than with roots from different plants © 2011 Pearson Education, Inc.

7. Roots and the hyphae of soil fungi form mutualistic associations called mycorrhizae Mutualisms with fungi helped plants colonize land Mycorrhizal fungi increase the surface area for absorbing water and minerals, especially phosphate © 2011 Pearson Education, Inc.

8. Roots Fungus Figure 36.5

9. The Apoplast and Symplast: Transport Continuums The apoplast consists of everything external to the plasma membrane It includes cell walls, extracellular spaces, and the interior of vessel elements and tracheids The symplast consists of the cytosol of the living cells in a plant, as well as the plasmodesmata © 2011 Pearson Education, Inc.

10. Figure 36.6 Cell wall Cytosol Plasmodesma Plasma membrane Apoplastic route Symplastic route Transmembrane route Key Apoplast Symplast

11. Short-Distance Transport of Water Across Plasma Membranes To survive, plants must balance water uptake and loss Osmosis determines the net uptake or water loss by a cell and is affected by solute concentration and pressure © 2011 Pearson Education, Inc.

12. Water potential is a measurement that combines the effects of solute concentration and pressure Water potential determines the direction of movement of water Water flows from regions of higher water potential to regions of lower water potential Potential refers to water’s capacity to perform work © 2011 Pearson Education, Inc.

13. Figure 36.8 Solutes have a negative effect on  by binding water molecules. Pure water at equilibrium H2OH2O Adding solutes to the right arm makes  lower there, resulting in net movement of water to the right arm: H2OH2O Pure water Membrane Solutes Positive pressure has a positive effect on  by pushing water. Pure water at equilibrium H2OH2O H2OH2O Positive pressure Applying positive pressure to the right arm makes  higher there, resulting in net movement of water to the left arm: Solutes and positive pressure have opposing effects on water movement. Pure water at equilibrium H2OH2O H2OH2O Positive pressure Solutes In this example, the effect of adding solutes is offset by positive pressure, resulting in no net movement of water: Negative pressure (tension) has a negative effect on  by pulling water. Pure water at equilibrium H2OH2O H2OH2O Negative pressure Applying negative pressure to the right arm makes  lower there, resulting in net movement of water to the right arm:

14. Water potential affects uptake and loss of water by plant cells If a flaccid cell is placed in an environment with a higher solute concentration, the cell will lose water and undergo plasmolysis Plasmolysis occurs when the protoplast shrinks and pulls away from the cell wall Video: Plasmolysis © 2011 Pearson Education, Inc. Water Movement Across Plant Cell Membranes

15. Figure 36.9 Plasmolyzed cell at osmotic equilibrium with its surroundings 0.4 M sucrose solution: Initial flaccid cell: Pure water: Turgid cell at osmotic equilibrium with its surroundings (a) Initial conditions: cellular   environmental  (b) Initial conditions: cellular   environmental  PP  0 PP  0 SS  PP  0 SS  PP  0.7 SS  0.9   0.9 MPa  SS   0.9  0.9 MPa      0.7 MPa SS  0.7  PP 0  0 0 MPa    0.7 0 MPa 

16. Absorption of Water and Minerals by Root Cells Most water and mineral absorption occurs near root tips, where root hairs are located and the epidermis is permeable to water Root hairs account for much of the surface area of roots After soil solution enters the roots, the extensive surface area of cortical cell membranes enhances uptake of water and selected minerals © 2011 Pearson Education, Inc. Animation: Transport in Roots

17. Pathway along apoplast Casparian strip Endodermal cell Pathway through symplast Plasma membrane Casparian strip Apoplastic route Symplastic route Root hair Epidermis Endodermis Vessels (xylem) Vascular cylinder (stele) Cortex Figure 36.10

18. Bulk Flow Transport via the Xylem Xylem sap, water and dissolved minerals, is transported from roots to leaves by bulk flow The transport of xylem sap involves transpiration, the evaporation of water from a plant’s surface Transpired water is replaced as water travels up from the roots Is sap pushed up from the roots, or pulled up by the leaves? © 2011 Pearson Education, Inc.

19. Pulling Xylem Sap: The Cohesion-Tension Hypothesis According to the cohesion-tension hypothesis, transpiration and water cohesion pull water from shoots to roots Xylem sap is normally under negative pressure, or tension © 2011 Pearson Education, Inc.

20. Outside air    100.0 MPa   7.0 MPa   1.0 MPa   0.8 MPa   0.6 MPa   0.3 MPa Leaf  (air spaces) Leaf  (cell walls) Trunk xylem  Soil  Water potential gradient Xylem sap Mesophyll cells Stoma Water molecule Atmosphere Transpiration Xylem cells Adhesion by hydrogen bonding Cell wall Cohesion and adhesion in the xylem Cohesion by hydrogen bonding Water molecule Root hair Soil particle Water Water uptake from soil Figure 36.13

21. Concept 36.4: The rate of transpiration is regulated by stomata Leaves generally have broad surface areas and high surface-to-volume ratios These characteristics increase photosynthesis and increase water loss through stomata Guard cells help balance water conservation with gas exchange for photosynthesis © 2011 Pearson Education, Inc.

22. Figure 36.14

23. Stomata: Major Pathways for Water Loss About 95% of the water a plant loses escapes through stomata Each stoma is flanked by a pair of guard cells, which control the diameter of the stoma by changing shape Stomatal density is under genetic and environmental control © 2011 Pearson Education, Inc.

24. Mechanisms of Stomatal Opening and Closing Changes in turgor pressure open and close stomata –When turgid, guard cells bow outward and the pore between them opens –When flaccid, guard cells become less bowed and the pore closes © 2011 Pearson Education, Inc.

25. Figure 36.15 Radially oriented cellulose microfibrils Guard cells turgid/ Stoma open Guard cells flaccid/ Stoma closed Cell wall Vacuole Guard cell (a) Changes in guard cell shape and stomatal opening and closing (surface view) (b) Role of potassium in stomatal opening and closing KK H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O

26. Movement from Sugar Sources to Sugar Sinks In angiosperms, sieve-tube elements are the conduits for translocation Phloem sap is an aqueous solution that is high in sucrose It travels from a sugar source to a sugar sink A sugar source is an organ that is a net producer of sugar, such as mature leaves A sugar sink is an organ that is a net consumer or storer of sugar, such as a tuber or bulb © 2011 Pearson Education, Inc.

27. A storage organ can be both a sugar sink in summer and sugar source in winter Sugar must be loaded into sieve-tube elements before being exposed to sinks Depending on the species, sugar may move by symplastic or both symplastic and apoplastic pathways Companion cells enhance solute movement between the apoplast and symplast © 2011 Pearson Education, Inc.

28. Figure 36.17 Mesophyll cell Key Apoplast Symplast Cell walls (apoplast) Plasma membrane Plasmodesmata Mesophyll cell Bundle- sheath cell Phloem parenchyma cell Companion (transfer) cell Sieve-tube element High H  concentration Cotransporter Proton pump Sucrose Low H  concentration HH HH HH S S ATP (a) (b)

29. Bulk Flow by Positive Pressure: The Mechanism of Translocation in Angiosperms Phloem sap moves through a sieve tube by bulk flow driven by positive pressure called pressure flow © 2011 Pearson Education, Inc. Animation: Translocation of Phloem Sap in Spring Animation: Translocation of Phloem Sap in Summer

30. Figure 36.18 Loading of sugar Uptake of water Unloading of sugar Water recycled Source cell (leaf) Vessel (xylem) Sieve tube (phloem) Sucrose H2OH2O H2OH2O H2OH2O Sink cell (storage root) Bulk flow by negative pressure Bulk flow by positive pressure 2 134 21 3 4

31. The pressure flow hypothesis explains why phloem sap always flows from source to sink Experiments have built a strong case for pressure flow as the mechanism of translocation in angiosperms Self-thinning is the dropping of sugar sinks such as flowers, seeds, or fruits © 2011 Pearson Education, Inc.

32. Concept 37.3: Plant nutrition often involves relationships with other organisms Plants and soil microbes have a mutualistic relationship – Dead plants provide energy needed by soil- dwelling microorganisms – Secretions from living roots support a wide variety of microbes in the near-root environment © 2011 Pearson Education, Inc.

33. Soil Bacteria and Plant Nutrition The layer of soil bound to the plant’s roots is the rhizosphere The rhizosphere contains bacteria that act as decomposers and nitrogen-fixers © 2011 Pearson Education, Inc.

34. Rhizobacteria Free-living rhizobacteria thrive in the rhizosphere, and some can enter roots The rhizosphere has high microbial activity because of sugars, amino acids, and organic acids secreted by roots © 2011 Pearson Education, Inc.

35. Rhizobacteria can play several roles – Produce hormones that stimulate plant growth – Produce antibiotics that protect roots from disease – Absorb toxic metals or make nutrients more available to roots © 2011 Pearson Education, Inc.

36. Bacteria in the Nitrogen Cycle Nitrogen can be an important limiting nutrient for plant growth The nitrogen cycle transforms nitrogen and nitrogen-containing compounds Plants can absorb nitrogen as either NO 3 – or NH 4  Most soil nitrogen comes from actions of soil bacteria © 2011 Pearson Education, Inc.

37. Figure 37.10 ATMOSPHERE SOIL N2N2 N2N2 N2N2 Nitrogen-fixing bacteria Denitrifying bacteria H  (from soil) Ammonifying bacteria Organic material (humus) Nitrate and nitrogenous organic compounds exported in xylem to shoot system Root NH 3 (ammonia) NH 4  (ammonium) Nitrifying bacteria NO 3  (nitrate) NH 4 

38. Along a legume’s roots are swellings called nodules, composed of plant cells “infected” by nitrogen-fixing Rhizobium bacteria © 2011 Pearson Education, Inc.

39. Figure 37.11 (a) Soybean root (b) Bacteroids in a soybean root nodule Nodules Roots 5  m Bacteroids within vesicle

40. Figure 37.12 Infection thread Rhizobium bacteria Dividing cells in root cortex Chemical signals attract bacteria and an infection thread forms. Infected root hair Nodule vascular tissue Bacteroids Sclerenchyma cells Bacteroid The mature nodule grows to be many times the diameter of the root. Nodule vascular tissue Bacteroids form. Bacteroid Dividing cells in pericycle Bacteroid Root hair sloughed off Developing root nodule Growth continues and a root nodule forms. The nodule develops vascular tissue. 23451

41. Fungi and Plant Nutrition Mycorrhizae are mutualistic associations of fungi and roots The fungus benefits from a steady supply of sugar from the host plant The host plant benefits because the fungus increases the surface area for water uptake and mineral absorption Mycorrhizal fungi also secrete growth factors that stimulate root growth and branching © 2011 Pearson Education, Inc.

42. Mycorrhizae and Plant Evolution Mycorrhizal fungi date to 460 million years ago and might have helped plants colonize land © 2011 Pearson Education, Inc.

43. The Two Main Types of Mycorrhizae Mycorrhizal associations consist of two major types –Ectomycorrhizae –Arbuscular mycorrhizae © 2011 Pearson Education, Inc.

44. Figure 37.13 Epidermis Cortex Mantle (fungal sheath) Epidermal cell Endodermis Fungal hyphae between cortical cells (Colorized SEM) 1.5 mm (LM) 50  m 10  m Mantle (fungal sheath) (a) Ectomycorrhizae Epidermis Cortex Endodermis Cortical cell Fungal vesicle Casparian strip Arbuscules Plasma membrane (LM) Fungal hyphae Root hair (b) Arbuscular mycorrhizae (endomycorrhizae)

45. In ectomycorrhizae, the mycelium of the fungus forms a dense sheath over the surface of the root These hyphae form a network in the apoplast, but do not penetrate the root cells Ectomycorrhizae occur in about 10% of plant families including pine, spruce, oak, walnut, birch, willow, and eucalyptus © 2011 Pearson Education, Inc.

46. Figure 37.13aa Epidermis Cortex Mantle (fungal sheath) Epidermal cell Endodermis Fungal hyphae between cortical cells (Colorized SEM) 1.5 mm (LM) 50  m Mantle (fungal sheath) (a) Ectomycorrhizae

47. In arbuscular mycorrhizae, microscopic fungal hyphae extend into the root These mycorrhizae penetrate the cell wall but not the plasma membrane to form branched arbuscules within root cells Hyphae can form arbuscules within cells; these are important sites of nutrient transfer Arbuscular mycorrhizae occur in about 85% of plant species, including grains and legumes © 2011 Pearson Education, Inc.

48. Figure 37.13ba 10  m Epidermis Cortex Endodermis Cortical cell Fungal vesicle Casparian strip Arbuscules Plasma membrane (LM) Fungal hyphae Root hair (b) Arbuscular mycorrhizae (endomycorrhizae)