1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 35 Plant Structure, Growth, and Development

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: No two Plants Are Alike To some people, the fanwort is an intrusive weed, but to others it is an attractive aquarium plant This plant exhibits plasticity, the ability to alter itself in response to its environment

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4. In addition to plasticity, plant species have by natural selection accumulated characteristics of morphology that vary little within the species

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 35.1: The plant body has a hierarchy of organs, tissues, and cells Plants, like multicellular animals, have organs composed of different tissues, which are in turn are composed of cells

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Three Basic Plant Organs: Roots, Stems, and Leaves Basic morphology of vascular plants reflects their evolution as organisms that draw nutrients from below-ground and above-ground

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Three basic organs evolved: roots, stems, and leaves They are organized into a root system and a shoot system

8. LE 35-2 Shoot system Root system Reproductive shoot (flower) Terminal bud Node Internode Blade Vegetable shoot Terminal bud Petiole Axillary bud Stem Leaf Taproot Lateral roots

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Roots Functions of roots: – Anchoring the plant – Absorbing minerals and water – Often storing organic nutrients

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In most plants, absorption of water and minerals occurs near the root tips, where vast numbers of tiny root hairs increase the surface area

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12. Many plants have modified roots

13. LE 35-4a Prop roots.

14. LE 35-4b Storage roots.

15. LE 35-4c “Strangling” aerial roots.

16. LE 35-4d Buttress roots.

17. LE 35-4e Pneumatophores.

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stems A stem is an organ consisting of – An alternating system of nodes, the points at which leaves are attached – Internodes, the stem segments between nodes

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An axillary bud is a structure that has the potential to form a lateral shoot, or branch A terminal bud is located near the shoot tip and causes elongation of a young shoot

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many plants have modified stems

21. LE 35-5a Stolons.

22. LE 35-5b Storage leaves Bulbs. Stem Roots

23. LE 35-5c Tubers.

24. LE 35-5d Node Root Rhizomes. Rhizome

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Leaves The leaf is the main photosynthetic organ of most vascular plants

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Leaves generally consist of – A flattened blade and a stalk – The petiole, which joins the leaf to a node of the stem

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Monocots and eudicots differ in the arrangement of veins, the vascular tissue of leaves Most monocots have parallel veins Most eudicots have branching veins

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In classifying angiosperms, taxonomists may use leaf morphology as a criterion

29. LE 35-6a Simple leaf Axillary bud Petiole

30. LE 35-6b Compound leaf Axillary bud Petiole Leaflet

31. LE 35-6c Doubly compound leaf Axillary bud Petiole Leaflet

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some plant species have evolved modified leaves that serve various functions

33. LE 35-7a Tendrils.

34. LE 35-7b Spines.

35. LE 35-7c Storage leaves.

36. LE 35-7d Bracts.

37. LE 35-7e Reproductive leaves.

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Three Tissue Systems: Dermal, Vascular, and Ground Each plant organ has dermal, vascular, and ground tissues

39. LE 35-8 Dermal tissue Vascular tissue Ground tissue

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In nonwoody plants, the dermal tissue system consists of the epidermis In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The vascular tissue system carries out long- distance transport of materials between roots and shoots The two vascular tissues are xylem and phloem

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Xylem conveys water and dissolved minerals upward from roots into the shoots Phloem transports organic nutrients from where they are made to where they are needed

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The vascular tissue of a stem or root is collectively called the stele In angiosperms the stele of the root is a solid central vascular cylinder The stele of stems and leaves is divided into vascular bundles, strands of xylem and phloem

44. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tissues that are neither dermal nor vascular are the ground tissue system Ground tissue includes cells specialized for storage, photosynthesis, and support

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Common Types of Plant Cells Like any multicellular organism, a plant is characterized by cellular differentiation, the specialization of cells in structure and function

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some major types of plant cells: – Parenchyma – Collenchyma – Sclerenchyma – Water-conducting cells of the xylem – Sugar-conducting cells of the phloem

47. LE 35-9 PARENCHYMA CELLS Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 µm 80 µm Cortical parenchyma cells Collenchyma cells (in cortex of Sambucus, elderberry; cell walls stained red) (LM) COLLENCHYMA CELLS SCLERENCHYMA CELLS SUGAR-CONDUCTING CELLS OF THE PHLOEM WATER-CONDUCTING CELLS OF THE XYLEM 5 µm Fiber cells (transverse section from ash tree) (LM) 25 µm Sclereid cells in pear (LM) Cell wall Sieve-tube members: longitudinal view 30 µm 15 µm Companion cell Companion cell Sieve-tube member Plasmodesma Sieve plate Sieve plate with pores (LM) Nucleus Cytoplasm Sieve-tube members: longitudinal view (LM) Vessel elements with perforated end walls Vessel element Tracheids Pits Tracheids and vessels (colorized SEM) Tracheids Vessel 100 µm

48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 35.2: Meristems generate cells for new organs Apical meristems are located at the tips of roots and in the buds of shoots Apical meristems elongate shoots and roots, a process called primary growth

49. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lateral meristems add thickness to woody plants, a process called secondary growth There are two lateral meristems: the vascular cambium and the cork cambium The vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem The cork cambium replaces the epidermis with periderm, which is thicker and tougher

50. LE 35-10 Shoot apical meristems (in buds) Vascular cambium Cork cambium Lateral meristems Primary phloem Periderm Cork cambium Secondary xylem Primary xylem Pith Cortex Secondary growth in stems Secondary phloem Vascular cambium Primary phloem Primary xylem Cortex Primary growth in stems Epidermis Root apical meristems

51. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In woody plants, primary and secondary growth occur simultaneously but in different locations

52. LE 35-11 This year’s growth (one year old) Terminal bud Leaf scar Growth of two years ago (three years old) Last year’s growth (two years old) One-year-old side branch formed from axillary bud near shoot apex Leaf scar Bud scale Axillary buds Internode Stem Node Leaf scar Scars left by terminal bud scales of previous winters

53. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 35.3: Primary growth lengthens roots and shoots Primary growth produces the primary plant body, the parts of the root and shoot systems produced by apical meristems

54. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Primary Growth of Roots The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil Growth occurs just behind the root tip, in three zones of cells: – Zone of cell division – Zone of elongation – Zone of maturation Video: Root Growth in a Radish Seed (time lapse) Video: Root Growth in a Radish Seed (time lapse)

55. LE 35-12 Key Dermal Ground Vascular Epidermis Root hair Cortex Vascular cylinder Zone of maturation Zone of elongation Zone of cell division Apical meristem Root cap 100 µm

56. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The primary growth of roots produces the epidermis, ground tissue, and vascular tissue In most roots, the stele is a vascular cylinder The ground tissue fills the cortex, the region between the vascular cylinder and epidermis The innermost layer of the cortex is called the endodermis

57. LE 35-13 Key Dermal Ground Vascular Epidermis Cortex Vascular cylinder Transverse section of a typical root. In the roots of typical gymnosperms and eudicots, as well as some monocots, the stele is a vascular cylinder consisting of a lobed core of xylem with phloem between the lobes. 100 µm Endodermis Core of parenchyma cells Pericycle Xylem Phloem Endodermis Pericycle Xylem Phloem 50 µm 100 µm Transverse section of a root with parenchyma in the center. The stele of many monocot roots is a vascular cylinder with a core of parenchyma surrounded by a ring of alternating xylem and phloem.

58. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder

59. LE 35-14 Emerging lateral root 100 µm Cortex Vascular cylinder Epidermis Lateral root

60. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Primary Growth of Shoots A shoot apical meristem is a dome-shaped mass of dividing cells at the tip of the terminal bud It gives rise to a repetition of internodes and leaf- bearing nodes

61. LE 35-15 Developing vascular strand Axillary bud meristems 0.25 mm Leaf primordia Apical meristem

62. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tissue Organization of Stems In gymnosperms and most eudicots, the vascular tissue consists of vascular bundles that are arranged in a ring

63. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring

64. LE 35-16 Key Dermal Ground Vascular Epidermis Cortex A eudicot (sunflower) stem. Vascular bundles form a ring. Ground tissue toward the inside is called pith, and ground tissue toward the outside is called cortex. (LM of transverse section) Xylem Phloem Pith Vascular bundles Epidermis Vascular bundles 1 mm Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Ground tissue A monocot (maize) stem. Vascular bundles are scattered throughout the ground tissue. In such an arrangement, ground tissue is not partitioned into pith and cortex. (LM of transverse section) 1 mm

65. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tissue Organization of Leaves The epidermis in leaves is interrupted by stomata, which allow CO 2 exchange between the air and the photosynthetic cells in a leaf The ground tissue in a leaf is sandwiched between the upper and lower epidermis The vascular tissue of each leaf is continuous with the vascular tissue of the stem

66. LE 35-17 Key to labels Dermal Ground Vascular Guard cells Epidermal cells Stomatal pore Surface view of a spiderwort (Tradescantia) leaf (LM) 50 µm Upper epidermis Stoma Lower epidermis Palisade mesophyll Spongy mesophyll Air spaces Vein Guard cells Transverse section of a lilac (Syringa) leaf (LM) 100 µm Bundle- sheath cell Xylem Phloem Guard cells Vein Cuticle Sclerenchyma fibers Guard cells Cutaway drawing of leaf tissues

67. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 35.4: Secondary growth adds girth to stems and roots in woody plants Secondary growth occurs in stems and roots of woody plants but rarely in leaves The secondary plant body consists of the tissues produced by the vascular cambium and cork cambium

68. LE 35-18a Primary and secondary growth in a two-year-old stem Epidermis Cortex Growth Xylem ray Vascular cambium Primary phloem Pith Primary xylem Phloem ray Epidermis Cortex Vascular cambium Primary phloem Pith Primary xylem Vascular cambium Primary phloem Primary xylem Secondary phloem Secondary xylem First cork cambium Cork Growth Vascular cambium Primary phloem Secondary phloem Secondary xylem Periderm (mainly cork cambia and cork) Primary xylem Pith Vascular cambium Secondary phloem Secondary xylem (two years of production) Cork Bark Layers of periderm Most recent cork cambium

69. LE 35-18b 0.5 mm Vascular cambium Secondary phloem Secondary xylem Transverse section of a three-year- old Tilia (linden) stem (LM) Late wood Early wood 0.5 mm Cork cambium Cork Periderm Xylem ray Bark

70. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Vascular Cambium and Secondary Vascular Tissue The vascular cambium is a cylinder of meristematic cells one cell thick It develops from undifferentiated cells and parenchyma cells that regain the capacity of divide

71. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In transverse section, the vascular cambium appears as a ring, with regions of dividing cells called fusiform initials and ray initials The initials increase the vascular cambium’s circumference and add secondary xylem to the inside and secondary phloem to the outside

72. LE 35-19 Vascular cambium Types of cell division Accumulation of secondary growth

73. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings As a tree or woody shrub ages, the older layers of secondary xylem, the heartwood, no longer transport water and minerals The outer layers, known as sapwood, still transport materials through the xylem

74. LE 35-20 Growth ring Vascular ray Secondary xylem Heartwood Sapwood Vascular cambium Secondary phloem Layers of periderm Bark

75. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cork Cambia and the Production of Periderm The cork cambium gives rise to the secondary plant body’s protective covering, or periderm Periderm consists of the cork cambium plus the layers of cork cells it produces Bark consists of all the tissues external to the vascular cambium, including secondary phloem and periderm

76. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 35.5: Growth, morphogenesis, and differentiation produce the plant body The three developmental processes of growth, morphogenesis, and cellular differentiation act in concert to transform the fertilized egg into a plant

77. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molecular Biology: Revolutionizing the Study of Plants New techniques and model systems are catalyzing explosive progress in our understanding of plants Arabidopsis is the first plant to have its entire genome sequenced

78. LE 35-21 Cell organization and biogenesis (1.7%) DNA metabolism (1.8%) Unknown (36.6%) Carbohydrate metabolism (2.4%) Protein modification (3.7%) Electron transport (3%) Other biological processes (18.6%) Protein metabolism (5.7%) Signal transduction (2.6%) Protein biosynthesis (2.7%) Transcription (6.1%) Other metabolism (6.6%) Transport (8.5%)

79. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Growth: Cell Division and Cell Expansion By increasing cell number, cell division in meristems increases the potential for growth Cell expansion accounts for the actual increase in plant size

80. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Plane and Symmetry of Cell Division The plane (direction) and symmetry of cell division are immensely important in determining plant form If the planes of division are parallel to the plane of the first division, a single file of cells is produced

81. LE 35-22a Division in same plane Plane of cell division Division in three planes Cell divisions in the same plane produce a single file of cells, whereas cell divisions in three planes give rise to a cube. Single file of cells forms Cube forms Nucleus

82. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings If the planes of division vary randomly, asymmetrical cell division occurs

83. LE 35-22b Unspecialized epidermal cell An asymmetrical cell division precedes the development of epidermal guard cells, the cells that border stomata (see Figure 35.17). Unspecialized epidermal cell Asymmetrical cell division Guard cell “mother cell” Unspecialized epidermal cell Developing guard cells

84. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The plane in which a cell divides is determined during late interphase Microtubules become concentrated into a ring called the preprophase band

85. LE 35-23 Preprophase bands of microtubules Nuclei Cell plates 10 µm

86. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Orientation of Cell Expansion Plant cells rarely expand equally in all directions

87. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Orientation of the cytoskeleton affects the direction of cell elongation by controlling orientation of cellulose microfibrils within the cell wall

88. LE 35-24 Cellulose microfibrils 5 µm Vacuoles Nucleus

89. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Microtubules and Plant Growth Studies of fass mutants of Arabidopsis have confirmed the importance of cytoplasmic microtubules in cell division and expansion

90. LE 35-25 Wild-type seeding Mass fass mutant fass seeding

91. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Morphogenesis and Pattern Formation Pattern formation is the development of specific structures in specific locations It is determined by positional information in the form of signals indicating to each cell its location Polarity is one type of positional information In the gnom mutant of Arabidopsis, the establishment of polarity is defective

92. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

93. Morphogenesis in plants, as in other multicellular organisms, is often controlled by homeotic genes

94. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

95. Gene Expression and Control of Cellular Differentiation In cellular differentiation, cells of a developing organism synthesize different proteins and diverge in structure and function even though they have a common genome Cellular differentiation to a large extent depends on positional information and is affected by homeotic genes

96. LE 35-28 Cortical cells 20 µm

97. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Location and a Cell’s Developmental Fate A cell’s position in a developing organ determines its pathway of differentiation

98. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Shifts in Development: Phase Changes Plants pass through developmental phases, called phase changes, developing from a juvenile phase to an adult phase The most obvious morphological changes typically occur in leaf size and shape

99. LE 35-29 Leaves produced by adult phase of apical meristem Leaves produced by juvenile phase of apical meristem

100. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Genetic Control of Flowering Flower formation involves a phase change from vegetative growth to reproductive growth It is triggered by a combination of environmental cues and internal signals Transition from vegetative growth to flowering is associated with the switching-on of floral meristem identity genes

101. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plant biologists have identified several organ identity genes that regulate the development of floral pattern

102. LE 35-30 Normal Arabidopsis flower. Arabidopsis normally has four whorls of flower parts: sepals (Se), petals (Pe), stamens (St), and carpels (Ca). Pe Se Pe Se Pe Se Pe Ca St Abnormal Arabidopsis flower. This flower has an extra set of petals in place of stamens and an internal flower where normal plants have carpels.

103. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The ABC model of flower formation identifies how floral organ identity genes direct the formation of the four types of floral organs

104. LE 35-31a Sepals Petals Stamens A B C Carpels C gene activity B + C gene activity A + B gene activity A gene activity A schematic diagram of the ABC hypothesis

105. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An understanding of mutants of the organ identity genes depicts how this model accounts for floral phenotypes

106. LE 35-31b Active genes: Wild type Side view of organ identity mutant flowers Whorls: StamenPetal Carpel Sepal Mutant lacking A Mutant lacking B Mutant lacking C