1. The Shoot: Primary Structure & Development 1

2. Shoot Above-ground parts Above-ground parts Stem + leaves Stem + leaves Embryonic Embryonic  Plumule – epicotyl,  1 leaves, and SAM  SAM only Support Support Conduction Conduction 2

3. Shoot Complexity More complex than root More complex than root Shoot has nodes (with leaves) and internodes Shoot has nodes (with leaves) and internodes Root apex has no lateral organs Root apex has no lateral organs Gaps in vascular cylinder Gaps in vascular cylinder No root cap No root cap 3

4. Origin & Growth of Primary Tissues SAM -- repetitively produces leaf primordia and bud primordia – phytomeres SAM -- repetitively produces leaf primordia and bud primordia – phytomeres  Leaf primordia – leaves  Bud primordia – lateral shoots 4

5. Shoot Apex Shoot apex is not synonymous with SAM Shoot apex is not synonymous with SAM Shoot apex – SAM and subapical region with leaf primordia Shoot apex – SAM and subapical region with leaf primordia 5

6. Vegetative SAM Tunica-corpus Tunica-corpus  Tunica o One or more peripheral layers o Surface growth – anticlinal divisions  Corpus o Interior layer o Volume growth – both anticlinal and periclinal Separate initials Separate initials 6

7. Tunica-Corpus L1 – generally anticlinal L1 – generally anticlinal  If periclinal – cell becomes part of L2 and behaves accordingly – cell differentiation positional.  Same for L2 and L3 layers 7

8. Tunica-Corpus Central zone (promeristem) – corpus + adjacent tunica cells Central zone (promeristem) – corpus + adjacent tunica cells Peripheral zone/meristem – ring around central zone Peripheral zone/meristem – ring around central zone  Partly from tunica (L1 & L2) and partly from corpus (L3) Pith Meristem Pith Meristem 8

9. Shoot Apical Meristem Central Zone -- Metaphysically equivalent to quiescent center Central Zone -- Metaphysically equivalent to quiescent center Peripheral zone – mitotically active Peripheral zone – mitotically active Protoderm – L1 Protoderm – L1 Procambium and part of ground meristem (cortex & maybe pith) – peripheral meristem Procambium and part of ground meristem (cortex & maybe pith) – peripheral meristem Rest of ground meristem (pith) – pith meristem Rest of ground meristem (pith) – pith meristem 9

10. Root vs Stem Development No regions in stem like in root No regions in stem like in root SAM produces phytomeres so rapidly -- tissues initially indistinguishable SAM produces phytomeres so rapidly -- tissues initially indistinguishable  On cell elongation, nodes/internodes recognizable Intercalary meristem – meristem between 2 or more differentiated regions Intercalary meristem – meristem between 2 or more differentiated regions  Activity localized SAM gives rise to same meristems as in root SAM gives rise to same meristems as in root  Protoderm, procambium and ground meristem Thickening – periclinal divisions and cell enlargement Thickening – periclinal divisions and cell enlargement 10

11. Primary Structure Variation Variation  Cortex around a central pith o Continuous cylinder of vascular tissue o Tilia americana o Cylinder of discrete strands/bundles o Sambucus canadensis, Ranunculus, and Medicago sativa  Pith and cortex not separable o Scattered vascular bundles o Zea mays 11

12. Primary Structure

15. Vascular Cylinder Vascular bundles separated by ground meristem Vascular bundles separated by ground meristem  Interfascicular regions – connect cortex and pith  Cortex – parenchyma and collenchyma 1º phloem – outer cells of procambium 1º phloem – outer cells of procambium 1º xylem – inner cells of the procambium 1º xylem – inner cells of the procambium Vascular cambium – single layer of cells between Vascular cambium – single layer of cells between  meristematic 15

16. Vascular Tissues Fibers develop after internode elongation Fibers develop after internode elongation First formed 1º xylem and 1º phloem stretched & destroyed during elongation First formed 1º xylem and 1º phloem stretched & destroyed during elongation

17. Vascular Tissues First formed 1º xylem and 1º phloem stretched & destroyed during elongation First formed 1º xylem and 1º phloem stretched & destroyed during elongation  Protoxylem lacuna

18. Vascular Tissues of Stem & Leaf Inexorably tied together – from the beginning, continuous with stem Inexorably tied together – from the beginning, continuous with stem 18

19. Vascular Tissues of Stem & Leaf 19 ← Triticum meristem

20. Vascular Tissues Leaf trace extends from stem bundle to the leaf Leaf trace extends from stem bundle to the leaf Leaves can have multiple leaf traces Leaves can have multiple leaf traces Sympodium – stem bundle and all associated leaf traces Sympodium – stem bundle and all associated leaf traces Branch trace – to buds Branch trace – to buds

21. Leaf Traces & Leaf Gaps Some sympodia interconnected; some independent Some sympodia interconnected; some independent Generally 2 branch traces/bud Generally 2 branch traces/bud

22. Phyllotaxy Opposite, alternate or whorled Opposite, alternate or whorled  Opposite: MADCap Horse ….. Remember Fibonacci? ….. Remember Fibonacci?  First available space o As soon as there’s enough space …..  Physiological field hypothesis o Each new bud surrounded by a “zone of inhibition”  Biophysical forces o Pressure causes buckling in tunica o Expansin genes expressed at sites of primordium initiation 22

23. Morphogenesis Primary event – expansion of tissue Primary event – expansion of tissue  Subdivided by cell division  Think tunica-corpus …… 23

24. Leaf Morphology Blade (lamina) Petiole Stipules sheath

25. Leaf Morphology Simple vs Compound Simple vs Compound  Simple may be lobed 25

26. Simple vs Compound Leaves -- lateral buds Leaflets -- same plane

27. Habitat Forms Mesophytes Mesophytes  Size varies; thin cuticle; numerous stomates  Palisade/spongy; bundle sheath cells 27

28. Habitat Forms Hydrophytes Hydrophytes  Large thin leaves; aerenchyma  Thin cuticle; stomates on upper surface  Epidermis photosynthetic 28

29. Habitat Forms Xerophytes Xerophytes  Small thick leaves  Often sunken stomates  Thick cuticle 29

30. Mesophyll Specialized for photosynthesis Specialized for photosynthesis  Generally – spongy parenchyma & pallisade parenchyma 30

31. Vascular Tissue Permeates lamina Permeates lamina Branching patterns often characteristic Branching patterns often characteristic  Monocot vs dicot Xylem on top Xylem on top  Why????? Minor veins vs Major veins Minor veins vs Major veins Vascular bundles & bundle sheath cells Vascular bundles & bundle sheath cells  Protection  Filtering  Bundle sheath extensions – conduits to epidermis? 31

32. Grasses and C4 photosynthesis Different Anatomy Different Anatomy  No pallisade mesophyll – Krantz anatomy  Mesophyll rings around bundle sheath cells o Mestome sheath in C3 – thick walls  Distance between veins 32

33. Bulliform Cells In grasses – appear to function in folding/rolling of leaves – changes in turgor pressure In grasses – appear to function in folding/rolling of leaves – changes in turgor pressure

34. Leaf Development Chimera – different genotypes Chimera – different genotypes  Only apical meristem – Coleus and Croton 34

35. Leaf Development Founder cells Founder cells  10-15 cells/layer in Arabidopsis  L1, L2, and L3 First change is a Leaf Buttress First change is a Leaf Buttress Buttress → Leaf primordium Buttress → Leaf primordium 35

36. Leaf Development Tissue derives from only two tunica layers Tissue derives from only two tunica layers  L1 – epidermis  L2 & L3 – internal tissues Intercalary growth Intercalary growth  Cell division  Cell enlargement Determinate – stops at the tip first Determinate – stops at the tip first 36

37. Vascular Development Differentiation of midvein from procambium Differentiation of midvein from procambium Major veins develop “upward” with the procambium Major veins develop “upward” with the procambium Minor veins – from margin in toward midveins! Minor veins – from margin in toward midveins! 37

38. Sun and Shade Leaves Sun Leaves – Smaller & Thicker Sun Leaves – Smaller & Thicker  Palisade parenchyma  Vascular system more extensive  Internal surface area to leaf blade much higher 38

39. Leaf Abcission Fall Color! Fall Color! Two layers Two layers  Separation layer – poorly developed cell wall thickenings  Protective layer – isolates leaf from plant – leaf scar Enzymes break down cell walls Enzymes break down cell walls  Weakening middle lamella  Hydrolysis of cell walls 39

40. Root/Shoot Transition Distribution and arrangement of stele very different! Distribution and arrangement of stele very different!  Solid cylinder → discrete vascular bundles Transition initiated during embryogenesis Transition initiated during embryogenesis One example ….. One example ….. 40

41. Floral Development Ends meristematic activity of shoot apex Ends meristematic activity of shoot apex Transformation from vegetative to reproductive Transformation from vegetative to reproductive Lots of environmental factors Lots of environmental factors  Day length, temperature, etc. Increase in mitotic activity Increase in mitotic activity Major changes in organization Major changes in organization 41

42. Floral Development a=floral apex; b=bract; s=sepals; p=petals; st=stamens; c=carpel

44. Genetics of Floral Development 3 genes – A, B, C 3 genes – A, B, C

46. Stem & Leaf Modifications Tendrils Tendrils  Modified stems – grape  Modified leaves – peas Cladophylls Cladophylls  Stems that look like leaves Spines, thorns & prickles Spines, thorns & prickles  Spines – modified leaves  Thorns – modified stems  Prickles – epidermal outgrowths 46

47. Stem & Leaf Modifications Food Storage Food Storage  Tubers – aka Taters, precious!  Onions  Gladiolus  Kohlrabi Water storage Water storage  Cactus  Agave/ Aloe 47