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Today: Introduction to Plant Anatomy

Today: Introduction to Plant Anatomy. Plant Morphology Reflects the demands of two very different environments: Soil and Air. Intro to Plant Anatomy. The Root System. Functions: ???. Root Systems.

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Today: Introduction to Plant Anatomy

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  1. Today: • Introduction to Plant Anatomy

  2. Plant Morphology Reflects the demands of two very different environments:Soil and Air Intro to Plant Anatomy

  3. The Root System Functions: ???

  4. Root Systems Monocots: typically have fibrous root systems (mats of thin roots below the soil surface) Dicots: typically have a taproot system (one large vertical root with smaller lateral roots)

  5. Root Modifications Both Monocots and Dicots use root hairs at the root tips. Why??

  6. Root Modifications Both may have adventitious roots arising from stems or leaves

  7. Many Modified Shoots Look Like Roots! Axillary buds Swollen Ends of Rhizomes! Leaves Stem Roots

  8. Plant Organs are Composed of 3 Tissues: 1. Dermal Tissue 2. Vascular Tissue 3. Ground Tissue

  9. 1. Dermal Tissue (Epidermis) • Single layer of tightly-packed cells • Covers and protects young plant parts • May have other specialized functions: Example: Root hairs or the Cuticle secreted by leaves and stems

  10. 2. Vascular Tissue • Transports materials between roots and shoots • Composed of xylem and phloem

  11. 2. Vascular Tissue Wood is composed primarily of vessels and tracheids

  12. Plant Cell Walls: A Quick Review Note the thick, secondary wall!

  13. 2. Vascular Tissue: Xylem • Tracheids have secondary walls hardened with lignin, allowing them to function in support • Water is transported through pits in the secondary cell wall. • Vessel elements are wider, shorter, and have thinner walls. They align end to end to form “pipes” or xylem vessels.

  14. 2. Vascular Tissue: Phloem Sugars and other organic molecules and ions are transported through chains of specialized cells- the sieve tube members.

  15. 2. Vascular Tissue: Phloem Sieve-tube members are alive, but have no nucleus or ribosomes! Each sieve-tube has a nonconductingcompanion cell connected by plasmodesmata

  16. 3. Ground Tissue Ground tissue is tissue that is neither dermal or vascular! Functions include photosynthesis, storage and support. In dicot stems (above), ground tissue is divided into pith (C) inside the vascular tissue and cortex (D), outside the vascular tissue

  17. Cell Types All plant tissues are composed of three basic cell types: 1. Parenchyma Cells 2. Collenchyma Cells 3. Sclerenchyma Cells

  18. Cell Types: Parenchyma Cells • Thin, flexible primary walls • Typically no secondary wall • Large central vacuole • Typically generalists! But sieve-tube members (phloem) are also parenchyma cells

  19. Cell Types: Parenchyma Cells Developmentally important, and used in repair and replacement! Can generate an entire plant from a parenchyma cell!

  20. Collenchyma Cells • Thicker (but uneven) primary walls • Grouped in strands or cylinders to support young plant shoots • Provide support without restraining growth (no lignin!)

  21. Sclerenchyma Cells • Thick secondary walls (with lignin) • Many are dead at functional maturity Example: vessel elements and tracheids • Fibers and sclereids are sclerenchyma cells specialized entirely for support.

  22. Shoot Anatomy Shoots are composed of stems and leaves, and may be vegetative or reproductive Stems are alternating nodes (where leaves are attached) and internodes (stem segments between nodes)

  23. Shoot Anatomy At the intersection of each leaf and the stem is an axillary bud with the potential to form a vegetative branch. Most axillary buds of a young shoot are dormant.

  24. Shoot Anatomy Growth of a young shoot is typically concentrated at the terminal bud (apex) Presence of the terminal bud helps inhibit growth of axillary buds (apical dominance)

  25. Leaves Most leaves are composed of a flattened bladeand a stalk, the petiole

  26. So what’s this? One petiole…. No axillary buds…

  27. Leaves Many leaves are specialized for functions besides photosynthesis!

  28. Plant Anatomy: A Quick Review

  29. Tissue Systems in a Leaf

  30. The Leaf Ground Tissue In dicots, two distinct regions of mesophyll: 1. Palisade Parenchyma- columnar cells 2. Spongy Parenchyma- multiple air spaces (esp. near stomata) Lots of surface area! Hmm….

  31. Plant Growth • Most plants have indeterminate growth • May be annual, biennial, or perennial CREDIT: "Falling an old-growth redwood, 1985." Photo by Karen Tillson for "Timber and Forests: Post war to Present," a California Local Legacies project.

  32. Plant Growth Indeterminate growth is possible because of meristems, regions of perpetually embryonic tissues • Growth in Roots • Growth in Shoots

  33. Plant Growth Elongation of roots and shoots from the apical meristems is called primary growth Progressive thickening of roots and shoots as a product of lateral meristems is called secondary growth Both occur simultaneously in woody plants!

  34. Revisiting Roots What did you notice when you drew the root tip??

  35. Primary Growth in Roots

  36. A Typical Dicot Root

  37. A Typical Monocot Root

  38. Primary Growth in Roots Lateral roots form from the outermost layer of the stele, the pericycle

  39. Secondary Growth of Roots Two lateral meristems create secondary growth: 1. The Vascular Cambium- produces secondary xlyem (wood) and phloem 2. The Cork Cambium- produces a tough thick covering, the periderm, that replaces the epidermis (and is impermeable to water!!)

  40. Primary Growth in Shoots Apical Meristem Leaf Primordia Axillary bud meristems

  41. Primary Growth in Shoots Apical meristem gives rise to protoderm, procambium and ground meristem

  42. Primary Tissues In Stems Vascular tissue is packed in vascular bundles

  43. Primary Tissues In Stems Vascular tissue is packed in vascular bundles

  44. Secondary Growth in Shoots Vascular cambium= cylinder of meristematic cells Originates from parenchyma cells that regain the capacity to divide

  45. Secondary Growth in Shoots

  46. Secondary Growth in Shoots Each time a cambium cell divides (C), one daughter cells continues as an initial, the other becomes the derivative (D)

  47. Secondary Growth in Shoots As the diameter increases, a second lateral meristem, the cork cambium, develops from parenchyma cells in the cortex

  48. Secondary Growth in Shoots Dead cork cells (from the cork cambium) provide a barrier to water loss, physical damage, and pathogens

  49. Secondary Growth in Shoots Original cork cambium is a fixed size! New cork cambium must continually form deeper in the cortex, and eventually from the secondary phloem. (So only the youngest secondary phloem functions in sugar transport!)

  50. Bark Bark = all tissues external to the vascular cambium (secondary phloem, cork cambium, and cork)

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