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Aspects of Plant Biology

Aspects of Plant Biology. What Makes Plants Tick?. Plant Water Relations (from CH 36). Plants need water for Nutrient transport Metabolic solvent Turgor pressure Cooling. Plant Water Relations. Plants obtain water passively Plants transport water without a systemic pump

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Aspects of Plant Biology

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  1. Aspects of Plant Biology What Makes Plants Tick?

  2. Plant Water Relations (from CH 36) • Plants need water for • Nutrient transport • Metabolic solvent • Turgor pressure • Cooling

  3. Plant Water Relations • Plants obtain water passively • Plants transport water without a systemic pump • Plants transport water through two different, but interconnected, systems

  4. Transport in Plants • water travels down a gradient of water potential • water potential = osmotic potential + pressure potential y = ys + yp

  5. Transport in Plants • water moves through membranes by osmosis in response to water potential differences • water moves through xylem or phloem by bulk flow • diffusion vs. unidirectional flow

  6. Transport in Plants • Bulk flow in xylem and phloem is driven by different forces • phloem transport is under positive pressure • xylem transport is under tension (negative pressure)

  7. Transport in Plants • phloem transport • at the source • sugar is pumped into sieve tube by active transport (phloem loading) • as sieve tube ys decreases, sieve tube y decreases • extracellular water moves into sieve tube by osmosis • sieve tube yp (and y) increases

  8. Transport in Plants • phloem transport • at the sink • sugar is pumped out of sieve tube (phloem unloading) • ys (and y) in sieve tube increases • water moves out of sieve tube by osmosis • yp in sieve tube decreases

  9. Phloem transportFigure 36.14

  10. Transport in Plants • phloem transport • phloem sap flows from source to sink down a gradient of ydominated by the difference in yp • flow can be from any source to any sink THE PRESSURE-FLOW MODEL

  11. Transport in Plants • xylem transport • yis lower high in the transpiration stream • water is under increasing tension (negative pressure) up the stem • water is pulled up the transpiration stream • evapotranspiration through the stomata drives the transpiration stream

  12. transpiration streamFigure 36.8

  13. pressure bombFigure 36.9

  14. evapotranspiration of water from a leafFigures 35.23, 36.1

  15. ygradient increases with temperature vpd = ygradient

  16. RH drops as temperature rises Leaf & air temperature (˚C) 10 20 30 RH of air (%) 80 43 25 Vapor Pressure in leaf 1.227 2.337 4.243 Vapor Pressure in air 0.981 1.015 1.050 Vapor Pressure Gradient0.246 1.322 3.193

  17. airflow increases transpiration Tb/Ta: wind/still air Ta = transpiration rate of plant in still air Tb= transpiration rate of plant in wind

  18. leaf surface stoma steep gradient shallow gradient Gentle Breeze steep gradient

  19. Transport in Plants • xylem transport • tension can drive the transpiration stream because • water is cohesive • water is adhesive to xylem cell walls THE COHESION-ADHESION TENSION THEORY

  20. Table 36.1

  21. Figure 35.2

  22. Developmental Regulation • Like animals • Environmental signals provide cues • Receptors receive and transduce signals • Hormones integrate responses • Unlike animals • Growth is indeterminate • Organs are modular • Most tissues contain totipotent cells

  23. Plant Responses to Challenges (from CH 40) • Challenge: Pathogenesis • Response(s): • cell wall and cuticle repel most pathogens • reinforcement of the cell wall prevents pathogen from spreading • lignin precursors are toxic • toxic phytoalexins are produced rapidly by infected cells and their neighbors • PR proteins mediate a variety of defenses

  24. Hypersensitive responseFigure 40.2

  25. Salicylic acidPage 767 Magnesium salicylate R-COO-2·Mg2+

  26. Gene-for-gene resistanceFigure 40.3

  27. composite of cellular responsesFigure 40.1

  28. Plant Responses to Challenges (from CH 40) • Challenge: Pathogenesis • Response(s): • resistant plants employ the hypersensitive response to limit the spread of pathogens • systemic acquired resistance is non-specific immunity mediated by salicylic acid • gene-for-gene resistance triggers defensive mechanisms to specific pathogen strains • siRNAs block viral infection

  29. interference RNA (RNAi)Figure 16.11

  30. Plant Responses to Challenges • Challenge: herbivory

  31. Response to herbivoryFigure 40.4

  32. toxic amino acid analogpage 770

  33. Plant Responses to Challenges • Challenge: herbivory • Response(s): • Modular development - replace lost parts • Chemical defenses - toxic or repellent • secondary metabolites

  34. Table 40.1 > 10,000 characterized compounds in these and other classes

  35. Leaf positioning in a eucalypt

  36. stomatal cryptsin Nerium oleanderFigure 40.8

  37. Plant Responses to Challenges • Challenge: Water problems • Response(s): anatomical • Leaf position • Surface hairs • Stomatal position & condition • Leaf abscission - seasonal or more often

  38. preparation for seasonal leaf drop

  39. opportunistic leaf production in ocotillo Figure 40.9

  40. Sequestering salt in the extracellular compartmentFigure 40.13

  41. Plant Responses to Challenges • Challenge: Water problems • Response(s): metabolic • Fermentation • Salt sequestration • Heavy metal detoxification

  42. Grasses resistant to heavy metal wasteFigure 40.15

  43. Plant Responses to Challenges • Challenge: temperature • Response(s): • Heat shock protein synthesis • Cold hardening • Antifreeze protein synthesis

  44. Information Processing in Plants step plants animals response less elaborate elaborate stereotyped selected asymmetric rapid morphogenic complex advantages energy savings motility

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