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  s +  p

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  s decreases, sieve tube  decreases extracellular water moves into sieve tube by osmosis sieve tube  p (and  ) increases

8. Transport in Plants phloem transport –at the sink sugar is pumped out of sieve tube (phloem unloading)  s (and  ) in sieve tube increases water moves out of sieve tube by osmosis  p in sieve tube decreases

9. Phloem transport Figure 36.14

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

11. Transport in Plants xylem transport –  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 stream Figure 36.8

13. pressure bomb Figure 36.9

14. evapotranspiration of water from a leaf Figures 35.23, 36.1

15.  gradient increases with temperature vpd =  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 0.9811.015 1.050 Vapor Pressure Gradient 0.2461.322 3.193

17. airflow increases transpiration T a = transpiration rate of plant in still air T b = transpiration rate of plant in wind T b /T a : wind/still air

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

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 response Figure 40.2

25. Magnesium salicylate R-COO - 2 ·Mg 2+ Salicylic acid Page 767

26. Gene-for-gene resistance Figure 40.3

27. composite of cellular responses Figure 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 herbivory Figure 40.4

32. toxic amino acid analog page 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 crypts in Nerium oleander Figure 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 compartment Figure 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 waste Figure 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 stepplantsanimals responseless elaborateelaborate stereotypedselected asymmetricrapid morphogeniccomplex advantagesenergy savingsmotility