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Chapter 35 Presentation
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  • Figure 35.1 Why does this plant have two types of leaves?
  • Figure 35.2 An overview of a flowering plant
  • Figure 35.3 Root hairs of a radish seedling
  • Figure 35.4 Modified roots
  • Figure 35.4 Modified roots
  • Figure 35.4 Modified roots
  • Figure 35.4 Modified roots
  • Figure 35.4 Modified roots
  • Figure 35.4 Modified roots
  • Figure 35.5 Modified stems
  • Figure 35.5 Modified stems
  • Figure 35.5 Modified stems
  • Figure 35.5 Modified stems
  • Figure 35.5 Modified stems
  • Figure 35.6 Simple versus compound leaves
  • Figure 35.6 Simple versus compound leaves
  • Figure 35.6 Simple versus compound leaves
  • Figure 35.6 Simple versus compound leaves
  • Figure 35.7 Modified leaves
  • Figure 35.7 Modified leaves
  • Figure 35.7 Modified leaves
  • Figure 35.7 Modified leaves
  • Figure 35.7 Modified leaves
  • Figure 35.7 Modified leaves
  • Figure 35.8 The three tissue systems
  • Figure 35.9 Do soybean pod trichomes deter herbivores?
  • Figure 35.10 Examples of differentiated plant cells
  • Figure 35.10 Examples of differentiated plant cells
  • Figure 35.10 Examples of differentiated plant cells
  • Figure 35.10 Examples of differentiated plant cells
  • Figure 35.10 Examples of differentiated plant cells
  • Figure 35.10 Examples of differentiated plant cells
  • Figure 35.10 Examples of differentiated plant cells
  • Figure 35.10 Examples of differentiated plant cells
  • Figure 35.10 Examples of differentiated plant cells
  • Figure 35.10 Examples of differentiated plant cells
  • Figure 35.11 An overview of primary and secondary growth
  • Figure 35.12 Three years’ growth in a winter twig
  • Figure 35.13 Primary growth of a root
  • Figure 35.14 Organization of primary tissues in young roots
  • Figure 35.14 Organization of primary tissues in young roots
  • Figure 35.14 Organization of primary tissues in young roots
  • Figure 35.14 Organization of primary tissues in young roots
  • Figure 35.15 The formation of a lateral root
  • Figure 35.15 The formation of a lateral root
  • Figure 35.15 The formation of a lateral root
  • Figure 35.16 The shoot tip
  • Figure 35.17 Organization of primary tissues in young stems
  • Figure 35.17 Organization of primary tissues in young stems
  • Figure 35.17 Organization of primary tissues in young stems
  • Figure 35.18 Leaf anatomy
  • Figure 35.18 Leaf anatomy
  • Figure 35.18 Leaf anatomy
  • Figure 35.18 Leaf anatomy
  • Figure 35.19 Primary and secondary growth of a stem
  • Figure 35.19 Primary and secondary growth of a stem
  • Figure 35.19 Primary and secondary growth of a stem
  • Figure 35.19 Primary and secondary growth of a stem
  • Figure 35.19 Primary and secondary growth of a stem
  • Figure 35.20 Secondary growth produced by the vascular cambium
  • Figure 35.21 Using dendrochronology to study climate
  • Fig 35.22 Anatomy of a tree trunk
  • Figure 35.23 Is this tree living or dead?
  • Figure 35.24 Arabidopsis thaliana
  • Figure 35.25 The plane and symmetry of cell division influence development of form
  • Figure 35.25a The plane and symmetry of cell division influence development of form
  • Figure 35.25b The plane and symmetry of cell division influence development of form
  • Figure 35.26 The preprophase band and the plane of cell division
  • Figure 35.27 The orientation of plant cell expansion
  • Figure 35.28 The fass mutant of Arabidopsis confirms the importance of cytoplasmic microtubules to plant growth
  • Figure 35.29 Establishment of axial polarity
  • Figure 35.30 Overexpression of a homeotic gene in leaf formation
  • Figure 35.31 Control of root hair differentiation by a homeotic gene
  • Figure 35.32 Phase change in the shoot system of Acacia koa
  • Figure 35.33 Organ identity genes and pattern formation in flower development
  • Figure 35.34 The ABC hypothesis for the functioning of organ identity genes in flower development
  • Figure 35.34 The ABC hypothesis for the functioning of organ identity genes in flower development
  • Figure 35.34 The ABC hypothesis for the functioning of organ identity genes in flower development
  • Transcript

    • 1. Chapter 35 Plant Structure, Growth, and Development
    • 2. Overview: Plastic Plants? <ul><li>To some people, the fanwort is an intrusive weed, but to others it is an attractive aquarium plant </li></ul><ul><li>This plant exhibits developmental plasticity , the ability to alter itself in response to its environment </li></ul>
    • 3. Fig. 35-1
    • 4. <ul><li>Developmental plasticity is more marked in plants than in animals </li></ul><ul><li>In addition to plasticity, plant species have by natural selection accumulated characteristics of morphology that vary little within the species </li></ul>
    • 5. Concept 35.1: The plant body has a hierarchy of organs, tissues, and cells <ul><li>Plants, like multicellular animals, have organs composed of different tissues , which in turn are composed of cells </li></ul>
    • 6. The Three Basic Plant Organs: Roots, Stems, and Leaves <ul><li>Basic morphology of vascular plants reflects their evolution as organisms that draw nutrients from below ground and above ground </li></ul>
    • 7. <ul><li>Three basic organs evolved: roots, stems, and leaves </li></ul><ul><li>They are organized into a root system and a shoot system </li></ul><ul><li>Roots rely on sugar produced by photosynthesis in the shoot system, and shoots rely on water and minerals absorbed by the root system </li></ul>
    • 8. Fig. 35-2 Reproductive shoot (flower) Apical bud Node Internode Apical bud Shoot system Vegetative shoot Leaf Blade Petiole Axillary bud Stem Taproot Lateral branch roots Root system
    • 9. Roots <ul><li>Roots are multicellular organs with important functions: </li></ul><ul><ul><li>Anchoring the plant </li></ul></ul><ul><ul><li>Absorbing minerals and water </li></ul></ul><ul><ul><li>Storing organic nutrients </li></ul></ul>
    • 10. <ul><li>A taproot system consists of one main vertical root that gives rise to lateral roots , or branch roots </li></ul><ul><li>Adventitious roots arise from stems or leaves </li></ul><ul><li>Seedless vascular plants and monocots have a fibrous root system characterized by thin lateral roots with no main root </li></ul>
    • 11. <ul><li>In most plants, absorption of water and minerals occurs near the root hairs , where vast numbers of tiny root hairs increase the surface area </li></ul>
    • 12. Fig. 35-3
    • 13. <ul><li>Many plants have modified roots </li></ul>
    • 14. Fig. 35-4 Prop roots “ Strangling” aerial roots Storage roots Buttress roots Pneumatophores
    • 15. Fig. 35-4a Prop roots
    • 16. Fig. 35-4b Storage roots
    • 17. Fig. 35-4c “ Strangling” aerial roots
    • 18. Fig. 35-4d Pneumatophores
    • 19. Fig. 35-4e Buttress roots
    • 20. Stems <ul><li>A stem is an organ consisting of </li></ul><ul><ul><li>An alternating system of nodes , the points at which leaves are attached </li></ul></ul><ul><ul><li>Internodes , the stem segments between nodes </li></ul></ul>
    • 21. <ul><li>An axillary bud is a structure that has the potential to form a lateral shoot, or branch </li></ul><ul><li>An apical bud , or terminal bud, is located near the shoot tip and causes elongation of a young shoot </li></ul><ul><li>Apical dominance helps to maintain dormancy in most nonapical buds </li></ul>
    • 22. <ul><li>Many plants have modified stems </li></ul>
    • 23. Fig. 35-5 Rhizomes Bulbs Storage leaves Stem Stolons Stolon Tubers
    • 24. Fig. 35-5a Rhizomes
    • 25. Fig. 35-5b Bulb Storage leaves Stem
    • 26. Fig. 35-5c Stolons Stolon
    • 27. Fig. 35-5d Tubers
    • 28. Leaves <ul><li>The leaf is the main photosynthetic organ of most vascular plants </li></ul><ul><li>Leaves generally consist of a flattened blade and a stalk called the petiole , which joins the leaf to a node of the stem </li></ul>
    • 29. <ul><li>Monocots and eudicots differ in the arrangement of veins , the vascular tissue of leaves </li></ul><ul><ul><li>Most monocots have parallel veins </li></ul></ul><ul><ul><li>Most eudicots have branching veins </li></ul></ul><ul><li>In classifying angiosperms, taxonomists may use leaf morphology as a criterion </li></ul>
    • 30. Fig. 35-6 (a) Simple leaf Compound leaf (b) Doubly compound leaf (c) Petiole Axillary bud Leaflet Petiole Axillary bud Leaflet Petiole Axillary bud
    • 31. Fig. 35-6a (a) Simple leaf Petiole Axillary bud
    • 32. Fig. 35-6b Compound leaf (b) Leaflet Petiole Axillary bud
    • 33. Fig. 35-6c Doubly compound leaf (c) Leaflet Petiole Axillary bud
    • 34. <ul><li>Some plant species have evolved modified leaves that serve various functions </li></ul>
    • 35. Fig. 35-7 Tendrils Spines Storage leaves Reproductive leaves Bracts
    • 36. Fig. 35-7a Tendrils
    • 37. Fig. 35-7b Spines
    • 38. Fig. 35-7c Storage leaves
    • 39. Fig. 35-7d Reproductive leaves
    • 40. Fig. 35-7e Bracts
    • 41. Dermal, Vascular, and Ground Tissues <ul><li>Each plant organ has dermal, vascular, and ground tissues </li></ul><ul><li>Each of these three categories forms a tissue system </li></ul>
    • 42. Fig. 35-8 Dermal tissue Ground tissue Vascular tissue
    • 43. <ul><li>In nonwoody plants, the dermal tissue system consists of the epidermis </li></ul><ul><li>A waxy coating called the cuticle helps prevent water loss from the epidermis </li></ul><ul><li>In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots </li></ul><ul><li>Trichomes are outgrowths of the shoot epidermis and can help with insect defense </li></ul>
    • 44. Fig. 35-9 Very hairy pod (10 trichomes/ mm 2 ) Slightly hairy pod (2 trichomes/ mm 2 ) Bald pod (no trichomes) Very hairy pod: 10% damage Slightly hairy pod: 25% damage Bald pod: 40% damage EXPERIMENT RESULTS
    • 45. <ul><li>The vascular tissue system carries out long-distance transport of materials between roots and shoots </li></ul><ul><li>The two vascular tissues are xylem and phloem </li></ul><ul><li>Xylem conveys water and dissolved minerals upward from roots into the shoots </li></ul><ul><li>Phloem transports organic nutrients from where they are made to where they are needed </li></ul>
    • 46. <ul><li>The vascular tissue of a stem or root is collectively called the stele </li></ul><ul><li>In angiosperms the stele of the root is a solid central vascular cylinder </li></ul><ul><li>The stele of stems and leaves is divided into vascular bundles , strands of xylem and phloem </li></ul>
    • 47. <ul><li>Tissues that are neither dermal nor vascular are the ground tissue system </li></ul><ul><li>Ground tissue internal to the vascular tissue is pith ; ground tissue external to the vascular tissue is cortex </li></ul><ul><li>Ground tissue includes cells specialized for storage, photosynthesis, and support </li></ul>
    • 48. Common Types of Plant Cells <ul><li>Like any multicellular organism, a plant is characterized by cellular differentiation, the specialization of cells in structure and function </li></ul>
    • 49. <ul><li>Some major types of plant cells: </li></ul><ul><ul><li>Parenchyma </li></ul></ul><ul><ul><li>Collenchyma </li></ul></ul><ul><ul><li>Sclerenchyma </li></ul></ul><ul><ul><li>Water-conducting cells of the xylem </li></ul></ul><ul><ul><li>Sugar-conducting cells of the phloem </li></ul></ul>
    • 50. Parenchyma Cells <ul><li>Mature parenchyma cells </li></ul><ul><ul><li>Have thin and flexible primary walls </li></ul></ul><ul><ul><li>Lack secondary walls </li></ul></ul><ul><ul><li>Are the least specialized </li></ul></ul><ul><ul><li>Perform the most metabolic functions </li></ul></ul><ul><ul><li>Retain the ability to divide and differentiate </li></ul></ul>BioFlix: Tour of a Plant Cell
    • 51. Fig. 35-10a Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 µm
    • 52. Collenchyma Cells <ul><li>Collenchyma cells are grouped in strands and help support young parts of the plant shoot </li></ul><ul><li>They have thicker and uneven cell walls </li></ul><ul><li>They lack secondary walls </li></ul><ul><li>These cells provide flexible support without restraining growth </li></ul>
    • 53. Fig. 35-10b Collenchyma cells (in Helianthus stem) (LM) 5 µm
    • 54. Sclerenchyma Cells <ul><li>Sclerenchyma cells are rigid because of thick secondary walls strengthened with lignin </li></ul><ul><li>They are dead at functional maturity </li></ul><ul><li>There are two types: </li></ul><ul><ul><li>Sclereids are short and irregular in shape and have thick lignified secondary walls </li></ul></ul><ul><ul><li>Fibers are long and slender and arranged in threads </li></ul></ul>
    • 55. Fig. 35-10c 5 µm 25 µm Sclereid cells in pear (LM) Fiber cells (cross section from ash tree) (LM) Cell wall
    • 56. Fig. 35-10d Perforation plate Vessel element Vessel elements, with perforated end walls Tracheids Pits Tracheids and vessels (colorized SEM) Vessel Tracheids 100 µm
    • 57. Fig. 35-10d1 Vessel Tracheids 100 µm Tracheids and vessels (colorized SEM)
    • 58. Fig. 35-10d2 Perforation plate Vessel element Vessel elements, with perforated end walls Tracheids Pits
    • 59. Water-Conducting Cells of the Xylem <ul><li>The two types of water-conducting cells, tracheids and vessel elements , are dead at maturity </li></ul><ul><li>Tracheids are found in the xylem of all vascular plants </li></ul>
    • 60. <ul><li>Vessel elements are common to most angiosperms and a few gymnosperms </li></ul><ul><li>Vessel elements align end to end to form long micropipes called vessels </li></ul>
    • 61. Fig. 35-10e Sieve-tube element (left) and companion cell: cross section (TEM) 3 µm Sieve-tube elements: longitudinal view (LM) Sieve plate Companion cells Sieve-tube elements Plasmodesma Sieve plate Nucleus of companion cells Sieve-tube elements: longitudinal view Sieve plate with pores (SEM) 10 µm 30 µm
    • 62. Fig. 35-10e1 Sieve-tube element (left) and companion cell: cross section (TEM) 3 µm
    • 63. Sugar-Conducting Cells of the Phloem <ul><li>Sieve-tube elements are alive at functional maturity, though they lack organelles </li></ul><ul><li>Sieve plates are the porous end walls that allow fluid to flow between cells along the sieve tube </li></ul><ul><li>Each sieve-tube element has a companion cell whose nucleus and ribosomes serve both cells </li></ul>
    • 64. Fig. 35-10e2 Sieve-tube elements: longitudinal view (LM) Sieve plate Companion cells Sieve-tube elements 30 µm
    • 65. Fig. 35-10e3 Sieve-tube element Plasmodesma Sieve plate Nucleus of companion cells Sieve-tube elements: longitudinal view Sieve plate with pores (SEM) 10 µm
    • 66. Concept 35.2: Meristems generate cells for new organs <ul><li>A plant can grow throughout its life; this is called indeterminate growth </li></ul><ul><li>Some plant organs cease to grow at a certain size; this is called determinate growth </li></ul><ul><li>Annuals complete their life cycle in a year or less </li></ul><ul><li>Biennials require two growing seasons </li></ul><ul><li>Perennials live for many years </li></ul>
    • 67. <ul><li>Meristems are perpetually embryonic tissue and allow for indeterminate growth </li></ul><ul><li>Apical meristems are located at the tips of roots and shoots and at the axillary buds of shoots </li></ul><ul><li>Apical meristems elongate shoots and roots, a process called primary growth </li></ul>
    • 68. <ul><li>Lateral meristems add thickness to woody plants, a process called secondary growth </li></ul><ul><li>There are two lateral meristems: the vascular cambium and the cork cambium </li></ul><ul><li>The vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem </li></ul><ul><li>The cork cambium replaces the epidermis with periderm, which is thicker and tougher </li></ul>
    • 69. Fig. 35-11 Shoot tip (shoot apical meristem and young leaves) Lateral meristems: Axillary bud meristem Vascular cambium Cork cambium Root apical meristems Primary growth in stems Epidermis Cortex Primary phloem Primary xylem Pith Secondary growth in stems Periderm Cork cambium Cortex Primary phloem Secondary phloem Pith Primary xylem Secondary xylem Vascular cambium
    • 70. <ul><li>Meristems give rise to initials , which remain in the meristem, and derivatives , which become specialized in developing tissues </li></ul><ul><li>In woody plants, primary and secondary growth occur simultaneously but in different locations </li></ul>
    • 71. Fig. 35-12 Apical bud This year’s growth (one year old) Bud scale Axillary buds Leaf scar Bud scar Node Internode One-year-old side branch formed from axillary bud near shoot tip Last year’s growth (two years old) Leaf scar Stem Bud scar left by apical bud scales of previous winters Leaf scar Growth of two years ago (three years old)
    • 72. Concept 35.3: Primary growth lengthens roots and shoots <ul><li>Primary growth produces the primary plant body , the parts of the root and shoot systems produced by apical meristems </li></ul>
    • 73. Primary Growth of Roots <ul><li>The root tip is covered by a root cap , which protects the apical meristem as the root pushes through soil </li></ul><ul><li>Growth occurs just behind the root tip, in three zones of cells: </li></ul><ul><ul><li>Zone of cell division </li></ul></ul><ul><ul><li>Zone of elongation </li></ul></ul><ul><ul><li>Zone of maturation </li></ul></ul>Video: Root Growth in a Radish Seed (Time Lapse)
    • 74. Fig. 35-13 Ground Dermal Key to labels Vascular Root hair Epidermis Cortex Vascular cylinder Zone of differentiation Zone of elongation Zone of cell division Apical meristem Root cap 100 µm
    • 75. <ul><li>The primary growth of roots produces the epidermis, ground tissue, and vascular tissue </li></ul><ul><li>In most roots, the stele is a vascular cylinder </li></ul><ul><li>The ground tissue fills the cortex, the region between the vascular cylinder and epidermis </li></ul><ul><li>The innermost layer of the cortex is called the endodermis </li></ul>
    • 76. Fig. 35-14 Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Xylem Phloem 100 µm Root with xylem and phloem in the center (typical of eudicots) (a) Root with parenchyma in the center (typical of monocots) (b) 100 µm Endodermis Pericycle Xylem Phloem 50 µm Key to labels Dermal Ground Vascular
    • 77. Fig. 35-14a1 Root with xylem and phloem in the center (typical of eudicots) (a) 100 µm Epidermis Cortex Endodermis Vascular cylinder Pericycle Xylem Phloem Dermal Ground Vascular Key to labels
    • 78. Fig. 35-14a2 Vascular Ground Dermal Key to labels Root with xylem and phloem in the center (typical of eudicots) (a) Endodermis Pericycle Xylem Phloem 50 µm
    • 79. Fig. 35-14b Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Key to labels Dermal Ground Vascular Xylem Phloem Root with parenchyma in the center (typical of monocots) (b) 100 µm
    • 80. <ul><li>Lateral roots arise from within the pericycle , the outermost cell layer in the vascular cylinder </li></ul>
    • 81. Fig. 35-15-1 1 Cortex Emerging lateral root Vascular cylinder 100 µm
    • 82. Fig. 35-15-2 Cortex Emerging lateral root Vascular cylinder 100 µm 2 Epidermis Lateral root 1
    • 83. Fig. 35-15-3 Cortex Emerging lateral root Vascular cylinder 100 µm Epidermis Lateral root 3 2 1
    • 84. Primary Growth of Shoots <ul><li>A shoot apical meristem is a dome-shaped mass of dividing cells at the shoot tip </li></ul><ul><li>Leaves develop from leaf primordia along the sides of the apical meristem </li></ul><ul><li>Axillary buds develop from meristematic cells left at the bases of leaf primordia </li></ul>
    • 85. Fig. 35-16 Shoot apical meristem Leaf primordia Young leaf Developing vascular strand Axillary bud meristems 0.25 mm
    • 86. Tissue Organization of Stems <ul><li>Lateral shoots develop from axillary buds on the stem’s surface </li></ul><ul><li>In most eudicots, the vascular tissue consists of vascular bundles that are arranged in a ring </li></ul>
    • 87. Fig. 35-17 Phloem Xylem Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Pith Cortex 1 mm Epidermis Vascular bundle Cross section of stem with vascular bundles forming a ring (typical of eudicots) (a) Key to labels Dermal Ground Vascular Cross section of stem with scattered vascular bundles (typical of monocots) (b) 1 mm Epidermis Vascular bundles Ground tissue
    • 88. Fig. 35-17a Sclerenchyma (fiber cells) Phloem Xylem Ground tissue connecting pith to cortex Pith Cortex Epidermis Vascular bundle 1 mm Cross section of stem with vascular bundles forming a ring (typical of eudicots) (a) Dermal Ground Vascular Key to labels
    • 89. Fig. 35-17b Ground tissue Epidermis Key to labels Cross section of stem with scattered vascular bundles (typical of monocots) Dermal Ground Vascular (b) Vascular bundles 1 mm
    • 90. <ul><li>In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring </li></ul>
    • 91. Tissue Organization of Leaves <ul><li>The epidermis in leaves is interrupted by stomata , which allow CO 2 exchange between the air and the photosynthetic cells in a leaf </li></ul><ul><li>Each stomatal pore is flanked by two guard cells , which regulate its opening and closing </li></ul><ul><li>The ground tissue in a leaf, called mesophyll , is sandwiched between the upper and lower epidermis </li></ul>
    • 92. <ul><li>Below the palisade mesophyll in the upper part of the leaf is loosely arranged spongy mesophyll , where gas exchange occurs </li></ul><ul><li>The vascular tissue of each leaf is continuous with the vascular tissue of the stem </li></ul><ul><li>Veins are the leaf’s vascular bundles and function as the leaf’s skeleton </li></ul><ul><li>Each vein in a leaf is enclosed by a protective bundle sheath </li></ul>
    • 93. Fig. 35-18 Key to labels Dermal Ground Vascular Cuticle Sclerenchyma fibers Stoma Bundle- sheath cell Xylem Phloem (a) Cutaway drawing of leaf tissues Guard cells Vein Cuticle Lower epidermis Spongy mesophyll Palisade mesophyll Upper epidermis Guard cells Stomatal pore Surface view of a spiderwort ( Tradescantia ) leaf (LM) Epidermal cell (b) 50 µm 100 µm Vein Air spaces Guard cells Cross section of a lilac ( Syringa) ) leaf (LM) (c)
    • 94. Fig. 35-18a Key to labels Dermal Ground Vascular Cuticle Sclerenchyma fibers Stoma Bundle- sheath cell Xylem Phloem (a) Cutaway drawing of leaf tissues Guard cells Vein Cuticle Lower epidermis Spongy mesophyll Palisade mesophyll Upper epidermis
    • 95. Fig. 35-18b Guard cells Stomatal pore Surface view of a spiderwort ( Tradescantia ) leaf (LM) Epidermal cell (b) 50 µm
    • 96. Fig. 35-18c Upper epidermis Palisade mesophyll Key to labels Dermal Ground Vascular Spongy mesophyll Lower epidermis Vein Air spaces Guard cells Cross section of a lilac ( Syringa ) leaf (LM) (c) 100 µm
    • 97. Concept 35.4: Secondary growth adds girth to stems and roots in woody plants <ul><li>Secondary growth occurs in stems and roots of woody plants but rarely in leaves </li></ul><ul><li>The secondary plant body consists of the tissues produced by the vascular cambium and cork cambium </li></ul><ul><li>Secondary growth is characteristic of gymnosperms and many eudicots, but not monocots </li></ul>
    • 98. Fig. 35-19 Primary and secondary growth in a two-year-old stem (a) Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Periderm (mainly cork cambia and cork) Primary phloem Secondary phloem Vascular cambium Secondary xylem Primary xylem Pith Pith Primary xylem Vascular cambium Primary phloem Epidermis Cortex Growth Vascular ray Primary xylem Secondary xylem Vascular cambium Secondary phloem Primary phloem First cork cambium Cork Secondary Xylem (two years of production) Vascular cambium Secondary phloem Most recent cork cambium Cork Bark Layers of periderm Growth Secondary phloem Vascular cambium Secondary xylem Bark Cork Late wood Early wood Cork cambium Periderm Vascular ray Growth ring Cross section of a three-year- old Tilia (linden) stem (LM) (b) 0.5 mm 0.5 mm
    • 99. Fig. 35-19a1 Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Primary and secondary growth in a two-year-old stem (a) Periderm (mainly cork cambia and cork) Secondary phloem Secondary xylem Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith
    • 100. Fig. 35-19a2 Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Primary and secondary growth in a two-year-old stem (a) Periderm (mainly cork cambia and cork) Secondary phloem Secondary xylem Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Vascular ray Secondary xylem Secondary phloem First cork cambium Cork Growth
    • 101. Fig. 35-19a3 Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Primary and secondary growth in a two-year-old stem (a) Periderm (mainly cork cambia and cork) Secondary phloem Secondary xylem Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Vascular ray Secondary xylem Secondary phloem First cork cambium Cork Growth Cork Bark Most recent cork cambium Layers of periderm
    • 102. Fig. 35-19b Secondary phloem Vascular cambium Secondary xylem Bark Early wood Late wood Cork cambium Cork Periderm 0.5 mm Vascular ray Growth ring Cross section of a three-year- old Tilia (linden) stem (LM) (b) 0.5 mm
    • 103. The Vascular Cambium and Secondary Vascular Tissue <ul><li>The vascular cambium is a cylinder of meristematic cells one cell layer thick </li></ul><ul><li>It develops from undifferentiated parenchyma cells </li></ul>
    • 104. <ul><li>In cross section, the vascular cambium appears as a ring of initials </li></ul><ul><li>The initials increase the vascular cambium’s circumference and add secondary xylem to the inside and secondary phloem to the outside </li></ul>
    • 105. Fig. 35-20 Vascular cambium Growth Secondary xylem After one year of growth After two years of growth Secondary phloem Vascular cambium X X X X X X P P P P C C C C C C C C C C C C C
    • 106. <ul><li>Secondary xylem accumulates as wood, and consists of tracheids, vessel elements (only in angiosperms), and fibers </li></ul><ul><li>Early wood, formed in the spring, has thin cell walls to maximize water delivery </li></ul><ul><li>Late wood, formed in late summer, has thick-walled cells and contributes more to stem support </li></ul><ul><li>In temperate regions, the vascular cambium of perennials is dormant through the winter </li></ul>
    • 107. <ul><li>Tree rings are visible where late and early wood meet, and can be used to estimate a tree’s age </li></ul><ul><li>Dendrochronology is the analysis of tree ring growth patterns, and can be used to study past climate change </li></ul>
    • 108. Fig. 35-21 RESULTS Ring-width indexes 2 1.5 0.5 1 0 1600 1700 1800 1900 2000 Year
    • 109. <ul><li>As a tree or woody shrub ages, the older layers of secondary xylem, the heartwood , no longer transport water and minerals </li></ul><ul><li>The outer layers, known as sapwood , still transport materials through the xylem </li></ul><ul><li>Older secondary phloem sloughs off and does not accumulate </li></ul>
    • 110. Fig. 35-22 Growth ring Vascular ray Secondary xylem Heartwood Sapwood Bark Vascular cambium Secondary phloem Layers of periderm
    • 111. Fig. 35-23
    • 112. The Cork Cambium and the Production of Periderm <ul><li>The cork cambium gives rise to the secondary plant body’s protective covering, or periderm </li></ul><ul><li>Periderm consists of the cork cambium plus the layers of cork cells it produces </li></ul><ul><li>Bark consists of all the tissues external to the vascular cambium, including secondary phloem and periderm </li></ul><ul><li>Lenticels in the periderm allow for gas exchange between living stem or root cells and the outside air </li></ul>
    • 113. Concept 35.5: Growth, morphogenesis, and differentiation produce the plant body <ul><li>Morphogenesis is the development of body form and organization </li></ul><ul><li>The three developmental processes of growth, morphogenesis, and cellular differentiation act in concert to transform the fertilized egg into a plant </li></ul>
    • 114. <ul><li>New techniques and model systems are catalyzing explosive progress in our understanding of plants </li></ul><ul><li>Arabidopsis is a model organism, and the first plant to have its entire genome sequenced </li></ul><ul><li>Studying the genes and biochemical pathways of Arabidopsis will provide insights into plant development, a major goal of systems biology </li></ul>Molecular Biology: Revolutionizing the Study of Plants
    • 115. Fig. 35-24 DNA or RNA metabolism (1%) Signal transduction (2%) Development (2%) Energy pathways (3%) Cell division and organization (3%) Transport (4%) Transcription (4%) Response to environment (4%) Protein metabolism (7%) Other biological processes (11%) Other cellular processes (17%) Other metabolism (18%) Unknown (24%)
    • 116. Growth: Cell Division and Cell Expansion <ul><li>By increasing cell number, cell division in meristems increases the potential for growth </li></ul><ul><li>Cell expansion accounts for the actual increase in plant size </li></ul>
    • 117. The Plane and Symmetry of Cell Division <ul><li>The plane (direction) and symmetry of cell division are immensely important in determining plant form </li></ul><ul><li>If the planes of division are parallel to the plane of the first division, a single file of cells is produced </li></ul>
    • 118. Fig. 35-25 Plane of cell division (a) Planes of cell division Developing guard cells Guard cell “ mother cell” Unspecialized epidermal cell (b) Asymmetrical cell division
    • 119. Fig. 35-25a Plane of cell division (a) Planes of cell division
    • 120. <ul><li>If the planes of division vary randomly, asymmetrical cell division occurs </li></ul>
    • 121. Fig. 35-25b Developing guard cells Guard cell “ mother cell” Unspecialized epidermal cell (b) Asymmetrical cell division
    • 122. <ul><li>The plane in which a cell divides is determined during late interphase </li></ul><ul><li>Microtubules become concentrated into a ring called the preprophase band that predicts the future plane of cell division </li></ul>
    • 123. Fig. 35-26 Preprophase bands of microtubules 10 µm Nuclei Cell plates
    • 124. Orientation of Cell Expansion <ul><li>Plant cells grow rapidly and “cheaply” by intake and storage of water in vacuoles </li></ul><ul><li>Plant cells expand primarily along the plant’s main axis </li></ul><ul><li>Cellulose microfibrils in the cell wall restrict the direction of cell elongation </li></ul>
    • 125. Fig. 35-27 Cellulose microfibrils Nucleus Vacuoles 5 µm
    • 126. Microtubules and Plant Growth <ul><li>Studies of fass mutants of Arabidopsis have confirmed the importance of cytoplasmic microtubules in cell division and expansion </li></ul>
    • 127. Fig. 35-28 (a) Wild-type seedling (b) fass seedling (c) Mature fass mutant 2 mm 2 mm 0.3 mm
    • 128. Morphogenesis and Pattern Formation <ul><li>Pattern formation is the development of specific structures in specific locations </li></ul><ul><li>It is determined by positional information in the form of signals indicating to each cell its location </li></ul><ul><li>Positional information may be provided by gradients of molecules </li></ul><ul><li>Polarity , having structural or chemical differences at opposite ends of an organism, provides one type of positional information </li></ul>
    • 129. <ul><li>Polarization is initiated by an asymmetrical first division of the plant zygote </li></ul><ul><li>In the gnom mutant of Arabidopsis , the establishment of polarity is defective </li></ul>
    • 130. Fig. 35-29
    • 131. <ul><li>Morphogenesis in plants, as in other multicellular organisms, is often controlled by homeotic genes </li></ul>
    • 132. Fig. 35-30
    • 133. Gene Expression and Control of Cellular Differentiation <ul><li>In cellular differentiation, cells of a developing organism synthesize different proteins and diverge in structure and function even though they have a common genome </li></ul><ul><li>Cellular differentiation to a large extent depends on positional information and is affected by homeotic genes </li></ul>
    • 134. Fig. 35-31 Cortical cells 20 µm
    • 135. Location and a Cell’s Developmental Fate <ul><li>Positional information underlies all the processes of development: growth, morphogenesis, and differentiation </li></ul><ul><li>Cells are not dedicated early to forming specific tissues and organs </li></ul><ul><li>The cell’s final position determines what kind of cell it will become </li></ul>
    • 136. Shifts in Development: Phase Changes <ul><li>Plants pass through developmental phases, called phase changes , developing from a juvenile phase to an adult phase </li></ul><ul><li>Phase changes occur within the shoot apical meristem </li></ul><ul><li>The most obvious morphological changes typically occur in leaf size and shape </li></ul>
    • 137. Fig. 35-32 Leaves produced by adult phase of apical meristem Leaves produced by juvenile phase of apical meristem
    • 138. Genetic Control of Flowering <ul><li>Flower formation involves a phase change from vegetative growth to reproductive growth </li></ul><ul><li>It is triggered by a combination of environmental cues and internal signals </li></ul><ul><li>Transition from vegetative growth to flowering is associated with the switching on of floral meristem identity genes </li></ul>
    • 139. <ul><li>Plant biologists have identified several organ identity genes (plant homeotic genes) that regulate the development of floral pattern </li></ul><ul><li>A mutation in a plant organ identity gene can cause abnormal floral development </li></ul>
    • 140. Fig. 35-33 (a) Normal Arabidopsis flower Ca St Pe Se Pe Pe Pe Se Se (b) Abnormal Arabidopsis flower
    • 141. <ul><li>Researchers have identified three classes of floral organ identity genes </li></ul><ul><li>The ABC model of flower formation identifies how floral organ identity genes direct the formation of the four types of floral organs </li></ul><ul><li>An understanding of mutants of the organ identity genes depicts how this model accounts for floral phenotypes </li></ul>
    • 142. Fig. 35-34 Sepals Petals Stamens Carpels (a) A schematic diagram of the ABC hypothesis A A + B gene activity B C A gene activity B + C gene activity C gene activity Carpel Petal Stamen Sepal Active genes: Whorls: Stamen Carpel Petal Sepal Wild type Mutant lacking A Mutant lacking B Mutant lacking C A A A A B B B B C C C C B B B B C C C C C C C C A A A A C C C C A A A A B B B B A A A A (b) Side view of flowers with organ identity mutations
    • 143. Fig. 35-34a Sepals Petals Stamens Carpels A B C A + B gene activity B + C gene activity C gene activity A gene activity (a) A schematic diagram of the ABC hypothesis Carpel Petal Stamen Sepal
    • 144. Fig. 35-34b Active genes: Whorls: Stamen Carpel Petal Sepal Wild type Mutant lacking A Mutant lacking B Mutant lacking C (b) Side view of flowers with organ identity mutations A A A A C C C C B B B B B B C C C C C C C C C C C C A A A A A A A A B B B B B A A A A B
    • 145. Fig. 35-UN1 Shoot tip (shoot apical meristem and young leaves) Axillary bud meristem Cork cambium Vascular cambium Lateral meristems Root apical meristems
    • 146. Fig. 35-UN2
    • 147. Fig. 35-UN3
    • 148. You should now be able to: <ul><li>Compare the following structures or cells: </li></ul><ul><ul><li>Fibrous roots, taproots, root hairs, adventitious roots </li></ul></ul><ul><ul><li>Dermal, vascular, and ground tissues </li></ul></ul><ul><ul><li>Monocot leaves and eudicot leaves </li></ul></ul><ul><ul><li>Parenchyma, collenchyma, sclerenchyma, water-conducting cells of the xylem, and sugar-conducting cells of the phloem </li></ul></ul><ul><ul><li>Sieve-tube element and companion cell </li></ul></ul>
    • 149. <ul><li>Explain the phenomenon of apical dominance </li></ul><ul><li>Distinguish between determinate and indeterminate growth </li></ul><ul><li>Describe in detail the primary and secondary growth of the tissues of roots and shoots </li></ul><ul><li>Describe the composition of wood and bark </li></ul>
    • 150. <ul><li>Distinguish between morphogenesis, differentiation, and growth </li></ul><ul><li>Explain how a vegetative shoot tip changes into a floral meristem </li></ul>

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