Resource Acquisition & Transport in Vascular Plants

1. Resource Acquisition & Transport in Vascular Plants Campbell and Reece Chapter 36

2. genus of plants (Lithrops, known as stone plants) found in Kalahari Desert of southern Africa has mostly subterreanean existence • tips of 2 succulent leaves above ground • clear, lens-like cells allow light  cells underground • conserve moisture (~20 cm rain/yr), hide from grazing tortoises, avoid high temperatures (up to 45ºC, 113 ºF,) & high light intensity • overall reduces water loss but inhibits photosynthesis,  grow very slowly Underground Plants

4. nonvascular • earliest land plants • grew photosynthetic, leafless shoots above the shallow water in which they lived • most had waxy cuticles & few stomata Early Land Plants

5. anchoring & absorbing functions done by base of stem or threadlike rhizoids Early Land Plants

6. typical land plant inhabits 2 worlds: • under ground • above ground Adaptations of Vascular Plants

7. as competition for light, water, & nutrients grew: • plants with broader leaves had advantage for light but then lost more water by evaporation as surface area increased • larger shoots required more of an anchor which favored production of multicellular, branching roots • as shoots grew higher, needed long-distance transport of water, minerals, products of photosynthesis Evolution of Plants

8. evolution of vascular tissue meant; • Xylem: tubular dead cells that conduct most of the water & minerals upward from roots  rest of plant • Phloem: vascular plant tissue consisting of living cells arranged into elongated tubes that transport sugar & other organic material thru out plant Xylem & Phloem

9. transpiration creates a force thru leaves that pulls xylem sap upward • water & minerals up as xylem sap • phloem sap flows up & down delivering sugars • water & minerals in soil absorbed by roots

10. Xylem & Phloem

11. function: • gather light • take in CO2 LEAVES

12. arrangement of leaves on a stem called: phyllotaxy LEAVES

13. most angiosperms (flowering plants) have alternate phyllotaxy • each successive leaf emerges 137.5º from site of previous leaf • this angle minimizes shading of lower leaves by upper leaves • plants in intense sun: opposite phylloxy which increase shading & so water loss LEAVES

14. affects amt light capture • leaf area index: ratio of total upper leaf surface of a single plant or entire crop ÷ surface area of land on which it grows • valuesup to 7 possible for mature crops • not much agricultural benefit to having higher values • more leaves increases shading of lower leaves to pt. where respiring > photosynthesizing LEAF NUMBERS or SIZE

16. affects amt light captured LEAF ORIENTATION

17. function: • supporting structures for leaves • conduit for long-distance transport of water & nutrients STEMS

18. generally. Enables plants to more effectively capture sunlight • only finite amt of nrg to give to shoot growth • more nrg to shoot growth the less there is for height which may compromise their chances for capturing sunlight • if lots nrg goes into being tall, plant not optimizing resources above ground • species have variety of branching patterns BRANCHING PATTERNS

19. BRANCHING PATTERNS

20. function: • mine the soil for water & minerals • anchor whole plant • evolution of branching roots enabled plants to be more efficient & more anchored ROOTS

21. tallest plants typically have longest taproot & most branches • fibrous roots don’t anchor as well so those plants generally not as tall • fewer branches as root grows thru soil with fewer nutrient; more branching in nitrogen-rich areas ROOTS

22. ROOT GROWTH

23. mutualistic associations formed between roots & some soil fungi that aid in absorption of minerals & water MYCORRHIZAE

24. important ass’c in evolution of land plants • ~80% land plants • fungi provides increased surface area to root system  more water & mineral absorption • especially phosphates Mycorrhizae

26. both active & passive transport controls movement of substances in/out of cells • plant tissues have 2 major compartments: • Apoplast: everything external to plasma membrane of living cells • cell walls, interior of dead cells, tracheids (long tapered water-conducting cell in xylem in most vascular plants • extracellular spaces • Symplast: all cytosol of all living cells in plant Transport in Plants

28. Apoplastic Route • water & solutes  cell walls & extracellular spaces • Symplastic Route • water & solutes  cytosol  plasma membrane  plasmodesmata  next cell • Transmembrane Route • out of 1 cell  cell wall  neighboring cell 3 Routes for Transport in Plants

31. plant plasma membranes have same types of transmembrane proteins as other cells • some differences: • H+ pumps • (not Na+) play primary role in basic transport processes • maintains membrane potential • H+ often ½ cotransporter (Na+ in animals) • part of absorption of neutral solutes, ions, & sucrose Short-Distance Transport Across Plasma Membranes

33. Solute Transport across Plant Cell Membranes

34. free water (not bound with other particle) moves down its concentration gradient across semipermeable membranes = osmosis • Water Potential: physical property that predicts direction in which water will flow based on water pressure & solute concentration Osmosis & Water Potential

35. free water moves from areas of higher water potential  areas of lower water potential if no barrier to its flow • as water moves it can perform work • “potential” refers to its PE • Ψ (psi) represents water potential • measured in a unit of pressure: megapascalMPa Water Potential

36. the Ψ of pure water in open container under standard conditions (sea level, room temperature) = 0MPa • 1 Mpa ~ 10x atmospheric pressure @ sea level • internal pressure of living plant cell due to osmotic uptake of water is ~ 0.5 MPa Water Potential

37. Water Potential equation: How Solutes & Pressure Affect Water Potential

38. directly proportional to its molarity • aka osmotic potential • solutes affect direction water moves in osmosis • plant solutes • mineral ions • sugars Solute Water Potential

39. in pure water the Ψs = 0 • as add solute they bind with water so there is less free water molecules which decreases water’s capacity to move & do work • reason Ψs always a (-) # • as concentration of solute increases Ψs becomes more (-) How Solutes & Pressure Affect Water Potential

40. Ψp = physical pressure on a solution • can be (+) or (-) relative to atmospheric pressure Pressure Potential

41. force directed against a plant cell wall after the influx of water & swelling of the cell due to osmosis Turgor Pressure

42. critical for plant function: helps maintain stiffness of plant tissues & is driving force for cell elongation Turgor Pressure

43. Wilting in Nonwoody Plant

44. difference in water potential determines direction water will flow • How does water get in/out of plant cells? • some molecules diffuse thru lipid bilayer • does not affect the rate water moves • transport proteins called aquaporins affect the rate water molecules move across the membrane Aquaporins

45. Aquaporins

46. on cellular level diffusion effective but too slow for long-distance transport w/in plant • Long-distance transport occurs thru • bulk flow • movement of liquid in response to a pressure gradient (always high  low) Long-Distance Transport

47. occurs in tracheids & vessel elements of xylem & w/in sieve-tube elements of the phloem • tracheid: long, tapered water-conducting cell found in xylem of nearly all vascular plants; functioning tracheids are no longer living Bulk Flow

49. diffusion, active transport, & bulk flow act together transporting resources thru out whole plant