1. Chapter 35 Plant Structure, Growth, and Development Dr. Wendy Sera Houston Community College Biology 1407

2. Overview: Are Plants Computers? Romanesco grows according to a repetitive program The development of plants depends on the environment and is highly adaptive © 2011 Pearson Education, Inc. Figure 35.1—Computer art?

3. Concept 35.1—Plants have a hierarchical organization consisting of organs, tissues, and cells Plants have organs composed of different tissues, which in turn are composed of different cell types A tissue is a group of cells consisting of one or more cell types that together perform a specialized function An organ consists of several types of tissues that together carry out particular functions © 2011 Pearson Education, Inc.

4. 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 –Plants take up water and minerals from below ground –Plants take up CO 2 and light from above ground Three basic organs evolved: roots, stems, and leaves They are organized into a root system and a shoot system © 2011 Pearson Education, Inc.

5. Reproductive shoot (flower) Apical bud Node Internode Apical bud Vegetative shoot Leaf Blade Petiole Stem Taproot Lateral (branch) roots Shoot system Root system Axillary bud Figure 35.2—An overview of a flowering plant.

6. Roots rely on sugar produced by photosynthesis in the shoot system, and shoots rely on water and minerals absorbed by the root system Monocots and eudicots are the two major groups of angiosperms © 2011 Pearson Education, Inc. The Three Basic Plant Organs, cont.

7. Roots A root is an organ with important functions: –Anchoring the plant –Absorbing minerals and water –Storing carbohydrates © 2011 Pearson Education, Inc.

8. Most eudicots and gymnosperms have a taproot system, which consists of: A taproot, the main vertical root Lateral roots, or branch roots, that arise from the taproot Most monocots have a fibrous root system, which consists of: Adventitious roots that arise from stems or leaves Lateral roots that arise from the adventitious roots. In most plants, absorption of water and minerals occurs near the root hairs, where vast numbers of tiny root hairs increase the surface area © 2011 Pearson Education, Inc. Roots, etc.

9. Figure 35.3—Root hairs of a radish seedling.

10. Many plants have root adaptations with specialized functions © 2011 Pearson Education, Inc. Roots, etc.

11. Prop roots Storage roots “Strangling” aerial roots Buttress roots Pneumatophores Figure 35.4—Evolutionary adaptations of roots.

12. 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 © 2011 Pearson Education, Inc.

13. An axillary bud is a structure that has the potential to form a lateral shoot, or branch An apical bud, or terminal bud, is located near the shoot tip and causes elongation of a young shoot Apical dominance helps to maintain dormancy in most axillary buds Many plants have modified stems (e.g., rhizomes, bulbs, stolons, tubers) © 2011 Pearson Education, Inc. Stems, cont.

14. Rhizomes Rhizome Bulbs Storage leaves Stem Stolons Tubers Root Stolon Figure 35.5— Evolutionary adaptations of stems.

15. Leaves The leaf is the main photosynthetic organ of most vascular plants Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem © 2011 Pearson Education, Inc.

16. Monocots and eudicots differ in the arrangement of veins, the vascular tissue of leaves –Most monocots have parallel veins –Most eudicots have branching veins In classifying angiosperms, taxonomists may use leaf morphology as a criterion Some plant species have evolved modified leaves that serve various functions © 2011 Pearson Education, Inc. Leaves, cont.

17. Simple leaf Axillary bud Petiole Compound leaf Leaflet Axillary bud Petiole Doubly compound leaf Axillary bud Petiole Leaflet Figure 35.6—Simple versus compound leaves.

18. Tendrils Spines Storage leaves Reproductive leaves Bracts Figure 35.7—Evolutionary adaptations of leaves.

19. Dermal, Vascular, and Ground Tissues Each plant organ has dermal, vascular, and ground tissues Each of these three categories forms a tissue system Each tissue system is continuous throughout the plant © 2011 Pearson Education, Inc.

20. Dermal tissue Ground tissue Vascular tissue Figure 35.8— The three tissue systems.

21. In nonwoody plants, the dermal tissue system consists of the epidermis A waxy coating called the cuticle helps prevent water loss from the epidermis In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots Trichomes are outgrowths of the shoot epidermis and can help with insect defense © 2011 Pearson Education, Inc. Dermal, Vascular, and Ground Tissues, cont.

22. The vascular tissue system carries out long- distance transport of materials between roots and shoots The two vascular tissues are xylem and phloem –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 © 2011 Pearson Education, Inc. Vascular Tissues

23. 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 © 2011 Pearson Education, Inc. Vascular Tissues, cont.

24. Tissues that are neither dermal nor vascular are the ground tissue system Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex Ground tissue includes cells specialized for storage, photosynthesis, and support © 2011 Pearson Education, Inc. Ground Tissue

25. Common Types of Plant Cells Like any multicellular organism, a plant is characterized by cellular differentiation, the specialization of cells in structure and function The major types of plant cells are: –Parenchyma –Collenchyma –Sclerenchyma –Water-conducting cells of the xylem –Sugar-conducting cells of the phloem © 2011 Pearson Education, Inc.

26. Parenchyma Cells Mature parenchyma cells – Have thin and flexible primary walls – Lack secondary walls – Are the least specialized – Perform the most metabolic functions – Retain the ability to divide and differentiate © 2011 Pearson Education, Inc.

28. Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60  m Figure 35.10—Exploring: Examples of Differentiated Plant Cells

29. Collenchyma Cells Collenchyma cells are grouped in strands and help support young parts of the plant shoot They have thicker and uneven cell walls They lack secondary walls These cells provide flexible support without restraining growth © 2011 Pearson Education, Inc.

30. Collenchyma cells (in Helianthus stem) (LM) 5  m Figure 35.10—Exploring: Examples of Differentiated Plant Cells

31. Sclerenchyma Cells Sclerenchyma cells are rigid because of thick secondary walls strengthened with lignin They are dead at functional maturity There are two types: –Sclereids are short and irregular in shape and have thick lignified secondary walls –Fibers are long and slender and arranged in threads © 2011 Pearson Education, Inc.

32. Cell wall Sclereid cells in pear (LM) Fiber cells (cross section from ash tree) (LM) 25  m 5  m Figure 35.10— Exploring: Examples of Differentiated Plant Cells

33. Water-Conducting Cells of the Xylem The two types of water-conducting cells, tracheids and vessel elements, are dead at maturity Tracheids are found in the xylem of all vascular plants Vessel elements are common to most angiosperms and a few gymnosperms Vessel elements align end to end to form long micropipes called vessels © 2011 Pearson Education, Inc.

34. Vessel Tracheids 100  m Tracheids and vessels (colorized SEM) Perforation plate Vessel element Vessel elements, with perforated end walls Pits Tracheids Figure 35.10— Exploring: Examples of Differentiated Plant Cells

35. Sugar-Conducting Cells of the Phloem Sieve-tube elements are alive at functional maturity, though they lack organelles Sieve plates are the porous end walls that allow fluid to flow between cells along the sieve tube Each sieve-tube element has a companion cell whose nucleus and ribosomes serve both cells © 2011 Pearson Education, Inc.

36. Sieve-tube element (left) and companion cell: cross section (TEM) Sieve-tube elements: longitudinal view Sieve plate 3  m Companion cells Sieve-tube elements Plasmodesma Sieve plate Nucleus of companion cell Sieve-tube elements: longitudinal view (LM) 30  m 15  m Sieve plate with pores (LM)

37. Concept 35.2: Meristems generate cells for primary and secondary growth A plant can grow throughout its life; this is called indeterminate growth Some plant organs cease to grow at a certain size; this is called determinate growth © 2011 Pearson Education, Inc.

38. Meristems are perpetually embryonic tissue and allow for indeterminate growth Apical meristems are located at the tips of roots and shoots and at the axillary buds of shoots Apical meristems elongate shoots and roots, a process called primary growth © 2011 Pearson Education, Inc. Meristems

39. 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 © 2011 Pearson Education, Inc. Meristems, etc.

40. Shoot tip (shoot apical meristem and young leaves) Axillary bud meristem Root apical meristems Vascular cambium Cork cambium Lateral meristems Primary growth in stems Epidermis Cortex Primary phloem Primary xylem Pith Secondary growth in stems Cork cambium Cortex Primary phloem Secondary phloem Vascular cambium Secondary xylem Primary xylem Pith Periderm Figure 35.11—An overview of primary and secondary growth.

41. Meristems give rise to: –Initials, also called stem cells, which remain in the meristem –Derivatives, which become specialized in mature tissues In woody plants, primary growth and secondary growth occur simultaneously but in different locations © 2011 Pearson Education, Inc. Meristems, etc.

42. Apical bud This year’s growth (one year old) Last year’s growth (two year old) Growth of two years ago (three years old) One-year-old side branch formed from axillary bud near shoot tip Bud scale Axillary buds Leaf scar Bud scar Node Internode Leaf scar Stem Bud scar Leaf scar Figure 35.12—Three years’ growth in a winter twig.

43. Flowering plants can be categorized based on the length of their life cycle –Annuals complete their life cycle in a year or less –Biennials require two growing seasons –Perennials live for many years © 2011 Pearson Education, Inc. Meristems, etc.

44. Concept 35.3: Primary growth lengthens roots and shoots Primary growth produces the parts of the root and shoot systems produced by apical meristems © 2011 Pearson Education, Inc.

45. 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 differentiation, or maturation © 2011 Pearson Education, Inc. Video: Root Growth in a Radish Seed (Time Lapse)

46. Epidermis Cortex Root hair Vascular cylinder Zone of differentiation Zone of elongation Zone of cell division (including apical meristem) Key to labels Root cap Dermal Ground Vascular Mitotic cells 100  m Figure 35.13— Primary growth of a root.

47. The primary growth of roots produces the epidermis, ground tissue, and vascular tissue In angiosperm roots, the stele is a vascular cylinder In most eudicots, the xylem is starlike in appearance with phloem between the “arms” In many monocots, a core of parenchyma cells is surrounded by rings of xylem then phloem © 2011 Pearson Education, Inc. Primary Growth of Roots, etc.

48. Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Xylem Phloem Endodermis Pericycle Xylem Phloem Dermal Ground Vascular Key to labels 50  m 100  m (a) (b)Root with parenchyma in the center (typical of monocots) Root with xylem and phloem in the center (typical of eudicots) Figure 35.14— Organization of primary tissues in young roots.

49. The ground tissue, mostly parenchyma cells, fills the cortex, the region between the vascular cylinder and epidermis The innermost layer of the cortex is called the endodermis The endodermis regulates passage of substances from the soil into the vascular cylinder © 2011 Pearson Education, Inc. Primary Growth of Roots, etc.

50. Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder © 2011 Pearson Education, Inc. Primary Growth of Roots, etc.

51. Emerging lateral root Cortex Vascular cylinder Pericycle 100  m Epidermis Lateral root 321 Figure 35.15—The formation of a lateral root.

52. Primary Growth of Shoots A shoot apical meristem is a dome-shaped mass of dividing cells at the shoot tip Leaves develop from leaf primordia along the sides of the apical meristem Axillary buds develop from meristematic cells left at the bases of leaf primordia © 2011 Pearson Education, Inc.

53. Shoot apical meristem Leaf primordia Young leaf Developing vascular strand Axillary bud meristems 0.25 mm Figure 35.16— The shoot tip.

54. Tissue Organization of Stems Lateral shoots develop from axillary buds on the stem’s surface In most eudicots, the vascular tissue consists of vascular bundles arranged in a ring In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring © 2011 Pearson Education, Inc.

55. Sclerenchyma (fiber cells) Phloem Xylem Ground tissue connecting pith to cortex Pith Cortex Vascular bundle Epidermis 1 mm Vascular bundles Epidermis Ground tissue Dermal Ground Vascular Key to labels (a) (b) Cross section of stem with vascular bundles forming a ring (typical of eudicots) Cross section of stem with scattered vascular bundles (typical of monocots) Figure 35.17—Organization of primary tissues in young stems.

56. Tissue Organization of Leaves The epidermis in leaves is interrupted by stomata, which allow CO 2 and O 2 exchange between the air and the photosynthetic cells in a leaf Each stomatal pore is flanked by two guard cells, which regulate its opening and closing The ground tissue in a leaf, called mesophyll, is sandwiched between the upper and lower epidermis © 2011 Pearson Education, Inc.

57. The mesophyll of eudicots has two layers:  The palisade mesophyll in the upper part of the leaf  The spongy mesophyll in the lower part of the leaf; the loose arrangement allows for gas exchange © 2011 Pearson Education, Inc. Tissue Organization of Leaves, etc.

58. The vascular tissue of each leaf is continuous with the vascular tissue of the stem Veins are the leaf’s vascular bundles and function as the leaf’s skeleton Each vein in a leaf is enclosed by a protective bundle sheath © 2011 Pearson Education, Inc. Tissue Organization of Leaves, etc.

59. Key to labels Dermal Ground Vascular Cuticle Bundle- sheath cell Xylem Phloem Sclerenchyma fibers Stoma Upper epidermis Palisade mesophyll Spongy mesophyll Lower epidermis Cuticle Vein Guard cells (a) Cutaway drawing of leaf tissues (b) (c)Cross section of a lilac (Syringa) leaf (LM) Surface view of a spiderwort (Tradescantia) leaf (LM) Guard cells Stomatal pore Epidermal cell Vein Air spaces Guard cells 50  m 100  m Figure 35.18—Leaf anatomy.

60. Concept 35.4: Secondary growth increases the diameter of 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 Secondary growth is characteristic of gymnosperms and many eudicots, but not monocots © 2011 Pearson Education, Inc.

61. Primary and secondary growth in a two-year-old woody stem (a) Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Primary xylem Vascular cambium Primary phloem Cortex Epidermis Periderm (mainly cork cambia and cork) Secondary phloem Secondary xylem Vascular ray Growth Secondary xylem Secondary phloem First cork cambium Cork Growth Cork Bark Most recent cork cambium Layers of periderm

62. Secondary xylem 0.5 mm Secondary phloem Vascular cambium Late wood Early wood Vascular ray Growth ring Bark Cork cambium Cork Periderm (b) Cross section of a three-year- old Tilia (linden) stem (LM) 0.5 mm

63. The Vascular Cambium and Secondary Vascular Tissue The vascular cambium is a cylinder of meristematic cells one cell layer thick It develops from undifferentiated parenchyma cells In cross section, the vascular cambium appears as a ring of initials (stem cells) –The initials increase the vascular cambium’s circumference and add secondary xylem to the inside and secondary phloem to the outside © 2011 Pearson Education, Inc.

64. Vascular cambium Growth Secondary xylem Secondary phloem Vascular cambium After one year of growth After two years of growth Figure 35.20—Secondary growth produced by the vascular cambium.

65. Elongated initials produce tracheids, vessel elements, fibers of xylem, sieve-tube elements, companion cells, axially oriented parenchyma, and fibers of the phloem Shorter initials produce vascular rays, radial files of parenchyma cells that connect secondary xylem and phloem © 2011 Pearson Education, Inc. The Vascular Cambium and Secondary Vascular Tissue, etc.

66. Secondary xylem accumulates as wood and consists of tracheids, vessel elements (only in angiosperms), and fibers Early wood, formed in the spring, has thin cell walls to maximize water delivery Late wood, formed in late summer, has thick- walled cells and contributes more to stem support In temperate regions, the vascular cambium of perennials is inactive through the winter © 2011 Pearson Education, Inc. The Vascular Cambium and Secondary Vascular Tissue, etc.

67. Tree rings are visible where late and early wood meet, and can be used to estimate a tree’s age Dendrochronology is the analysis of tree ring growth patterns and can be used to study past climate change © 2011 Pearson Education, Inc. The Vascular Cambium and Secondary Vascular Tissue, etc.

68. 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 Older secondary phloem sloughs off and does not accumulate © 2011 Pearson Education, Inc. The Vascular Cambium and Secondary Vascular Tissue, etc.

69. Growth ring Vascular ray Secondary xylem Heartwood Sapwood Vascular cambium Bark Secondary phloem Layers of periderm Figure 35.22—Anatomy of a tree trunk.

70. The Cork Cambium and the Production of Periderm Cork cambium gives rise to two tissues:  Phelloderm is a thin layer of parenchyma cells that forms to the interior of the cork cambium  Cork cells accumulate to the exterior of the cork cambium Cork cells deposit waxy suberin in their walls, then die Periderm consists of the cork cambium, phelloderm, and cork cells it produces © 2011 Pearson Education, Inc.

71. Lenticels in the periderm allow for gas exchange between living stem or root cells and the outside air Bark consists of all the tissues external to the vascular cambium, including secondary phloem and periderm © 2011 Pearson Education, Inc.

72. Concept 35.5: Growth, morphogenesis, and cell differentiation produce the plant body Cells form specialized tissues, organs, and organisms through the process of development Developmental plasticity describes the effect of environment on development –For example, the aquatic plant fanwort forms different leaves depending on whether or not the apical meristem is submerged © 2011 Pearson Education, Inc.

73. Figure 35.24—Developmental plasticity in the aquatic plant Cabomba caroliniana.

74. Development consists of growth, morphogenesis, and cell differentiation Growth is an irreversible increase in size Morphogenesis is the development of body form and organization Cell differentiation is the process by which cells with the same genes become different from each other © 2011 Pearson Education, Inc.

75. New techniques and model organisms are catalyzing explosive progress in our understanding of plants Arabidopsis is a model organism and the first plant to have its entire genome sequenced Arabidopsis has 27,000 genes divided among 5 pairs of chromosomes Model Organisms: Revolutionizing the Study of Plants © 2011 Pearson Education, Inc.

77. Arabidopsis is easily transformed by introducing foreign DNA via genetically altered bacteria Studying the genes and biochemical pathways of Arabidopsis will provide insights into plant development, a major goal of systems biology © 2011 Pearson Education, Inc.

78. Morphogenesis and Pattern Formation Pattern formation is the development of specific structures in specific locations Two types of hypotheses explain the fate of plant cells –Lineage-based mechanisms propose that cell fate is determined early in development and passed on to daughter cells –Position-based mechanisms propose that cell fate is determined by final position © 2011 Pearson Education, Inc.

79. Experiments suggest that plant cell fate is established late in development and depends on cell position In contrast, cell fate in animals is largely lineage- dependent © 2011 Pearson Education, Inc. Morphogenesis and Pattern Formation, cont.

80. Hox genes in animals affect the number and placement of appendages in embryos A plant homolog of Hox genes called KNOTTED-1 does not affect the number or placement of plant organs KNOTTED-1 is important in the development of leaf morphology © 2011 Pearson Education, Inc. Morphogenesis and Pattern Formation, cont.

81. Figure 35.30—Overexpression of a Hox-like gene in leaf formation.