1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 35 Plant Growth and Development

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings No two Plants Are Alike To some,fanwort (Cabomba) is an intrusive weed, but to others it is an attractive aquarium plant Exhibits plasticity – Ability to alter itself in response to its environment Figure 35.1

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plant body: hierarchy of organs, tissues, cells

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Three Basic Plant Organs: Roots, Stems, and Leaves

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Organized into a root system and a shoot system Figure 35.2 Reproductive shoot (flower) Terminal bud Node Internode Terminal bud Vegetative shoot Blade Petiole Stem Leaf Taproot Lateral roots Root system Shoot system Axillary bud

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Roots Anchors the vascular plant Absorbs minerals and water Often stores organic nutrients

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Absorption of water and minerals occurs near the root tips  vast numbers of tiny root hairs increase the surface area of the root Figure 35.3

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Modified roots Figure 35.4a–e (a) Prop roots(b) Storage roots (c) “Strangling” aerial roots (d) Buttress roots (e) Pneumatophores

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Epiphytes Plants, e.g. tropical orchids, that grows on another plant upon which it depends for mechanical support but not for nutrients. Also called air plants.

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stems Nodes  leaf attachment Internodes  between nodes

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Axillary bud – Potential to form a lateral shoot, or branch Terminal bud – Causes elongation of a young shoot

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Modified stems Figure 35.5a–d Rhizomes. The edible base of this ginger plant is an example of a rhizome, a horizontal stem that grows just below the surface or emerges and grows along the surface. (d) Tubers. Tubers, such as these red potatoes, are enlarged ends of rhizomes specialized for storing food. The “eyes” arranged in a spiral pattern around a potato are clusters of axillary buds that mark the nodes. (c) Bulbs. Bulbs are vertical, underground shoots consisting mostly of the enlarged bases of leaves that store food. You can see the many layers of modified leaves attached to the short stem by slicing an onion bulb lengthwise. (b) Stolons. Shown here on a strawberry plant, stolons are horizontal stems that grow along the surface. These “runners” enable a plant to reproduce asexually, as plantlets form at nodes along each runner. (a) Storage leaves Stem Root Node Rhizome Root

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Leaves -Main photosynthetic organ

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blade and a stalk – The petiole, which joins the leaf to a node of the stem

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Monocots – parallel veins Dicots – branching veins

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 35.6a–c Petiole (a) Simple leaf. A simple leaf is a single, undivided blade. Some simple leaves are deeply lobed, as in an oak leaf. (b) Compound leaf. In a compound leaf, the blade consists of multiple leaflets. Notice that a leaflet has no axillary bud at its base. (c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets. Axillary bud Leaflet Petiole Axillary bud Leaflet Petiole

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Modified leaves Figure 35.6a–e (a)Tendrils. The tendrils by which this pea plant clings to a support are modified leaves. After it has “lassoed” a support, a tendril forms a coil that brings the plant closer to the support. Tendrils are typically modified leaves, but some tendrils are modified stems, as in grapevines. (b)Spines. The spines of cacti, such as this prickly pear, are actually leaves, and photosynthesis is carried out mainly by the fleshy green stems. (c)Storage leaves. Most succulents, such as this ice plant, have leaves modified for storing water. (d)Bracts. Red parts of the poinsettia are often mistaken for petals but are actually modified leaves called bracts that surround a group of flowers. Such brightly colored leaves attract pollinators. (e)Reproductive leaves. The leaves of some succulents, such as Kalanchoe daigremontiana, produce adventitious plantlets, which fall off the leaf and take root in the soil.

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3 Tissue Systems: Dermal, Vascular, and Ground Each plant organ has all 3 Figure 35.8 Dermal tissue Ground tissue Vascular tissue

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dermal – Consists of the epidermis and periderm

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vascular tissue – Transport between roots and shoots – 2 types tissues, xylem and phloem

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Xylem – Water and dissolved minerals upward from roots into the shoots Phloem – Organic nutrients from where they are made to where they are needed

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ground tissue – Various cells specialized for functions such as storage, photosynthesis, and support

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plant Cells Cellular differentiation, specialization of cells in structure and function

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell types Parenchyma, collenchyma, and sclerenchyma cells Figure 35.9 Parenchyma cells 60  m PARENCHYMA CELLS 80  m Cortical parenchyma cells COLLENCHYMA CELLS Collenchyma cells SCLERENCHYMA CELLS Cell wall Sclereid cells in pear 25  m Fiber cells 5  m

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water-conducting cells of the xylem and sugar- conducting cells of the phloem Figure. 35.9 WATER-CONDUCTING CELLS OF THE XYLEM Vessel Tracheids 100  m Tracheids and vessels Vessel element Vessel elements with partially perforated end walls Pits Tracheids SUGAR-CONDUCTING CELLS OF THE PHLOEM Companion cell Sieve-tube member Sieve-tube members: longitudinal view Sieve plate Nucleus Cytoplasm Companion cell 30  m 15  m

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Apical meristems – At the tips of roots and in the buds of shoots – Elongate shoots and roots through primary growth

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lateral meristems – Add thickness to woody plants through secondary growth

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Primary and secondary growth Figure. 35.10 In woody plants, there are lateral meristems that add secondary growth, increasing the girth of roots and stems. Apical meristems add primary growth, or growth in length. Vascular cambium Cork cambium Lateral meristems 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 Vascular cambium Secondary xylem Primary xylem Pith Shoot apical meristems (in buds) The cork cambium adds secondary dermal tissue. The vascular cambium adds secondary xylem and phloem.

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Woody plants – Primary and secondary growth occur simultaneously but in different locations Figure 35.11 This year’s growth (one year old) Last year’s growth (two years old) Growth of two years ago (three years old) One-year-old side branch formed from axillary bud near shoot apex Scars left by terminal bud scales of previous winters Leaf scar Stem Leaf scar Bud scale Axillary buds Internode Node Terminal bud

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Primary Growth of Roots Figure 35.12 Dermal Ground Vascular Key Cortex Vascular cylinder Epidermis Root hair Zone of maturation Zone of elongation Zone of cell division Apical meristem Root cap 100  m

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Primary tissues in young roots Figure 35.13a, b Cortex Vascular cylinder Endodermis Pericycle Core of parenchyma cells Xylem 50  m Endodermis Pericycle Xylem Phloem Key 100  m Vascular Ground Dermal Phloem 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. (b) 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. (a) 100  m Epidermis

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lateral roots Figure 35.14 Cortex Vascular cylinder Epidermis Lateral root 100  m 1 2 3 4 Emerging lateral root

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Primary Growth of Shoots A shoot apical meristem Figure. 35.15 Apical meristemLeaf primordia Developing vascular strand Axillary bud meristems 0.25 mm

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tissue Organization of Stems gymnosperms and eudicots – Vascular bundles arranged in a ring Figure 35.16a XylemPhloem Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Pith Epidermis Vascular bundle Cortex Key Dermal Ground Vascular 1 mm (a)A eudicot stem. A eudicot stem (sunflower), with vascular bundles forming a ring. Ground tissue toward the inside is called pith, and ground tissue toward the outside is called cortex. (LM of transverse section)

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ground tissue Epidermis Vascular bundles 1 mm (b)A monocot stem. A monocot stem (maize) with vascular bundles scattered throughout the ground tissue. In such an arrangement, ground tissue is not partitioned into pith and cortex. (LM of transverse section) Figure 35.16b Monocot stems – Bundles scattered

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tissue Organization of Leaves Epidermal barrier interrupted by stomata  CO 2 exchange The ground tissue in a leaf – Sandwiched between upper and lower epidermis Vascular tissue continuous with vascular tissue of stem

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Key to labels Dermal Ground Vascular Guard cells Stomatal pore Epidermal cell 50 µm Surface view of a spiderwort (Tradescantia) leaf (LM) (b) Cuticle Sclerenchyma fibers Stoma Upper epidermis Palisade mesophyll Spongy mesophyll Lower epidermis Cuticle Vein Guard cells Xylem Phloem Guard cells Bundle- sheath cell Cutaway drawing of leaf tissues(a) VeinAir spacesGuard cells 100 µm Transverse section of a lilac (Syringa) leaf (LM) (c) Figure 35.17a–c Leaf anatomy

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vascular Cambium The vascular cambium  secondary growth of vascular tissue

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vascular cambium Pith Primary xylem Secondary xylem Vascular cambium Secondary phloem Primary phloem Periderm (mainly cork cambia and cork) Pith Primary xylem Vascular cambium Primary phloem Cortex Epidermis Vascular cambium 4 First cork cambium Secondary xylem (two years of production) Pith Primary xylem Vascular cambium Primary phloem 2 1 6 Growth Primary xylem Secondary xylem Secondary phloem Primary phloem Cork Phloem ray 3 Xylem ray Growth Bark 8 Layers of periderm 7 Cork 5 Most recent cork cambium Cortex Epidermis 9 In the youngest part of the stem, you can see the primary plant body, as formed by the apical meristem during primary growth. The vascular cambium is beginning to develop. As primary growth continues to elongate the stem, the portion of the stem formed earlier the same year has already started its secondary growth. This portion increases in girth as fusiform initials of the vascular cambium form secondary xylem to the inside and secondary phloem to the outside. The ray initials of the vascular cambium give rise to the xylem and phloem rays. As the diameter of the vascular cambium increases, the secondary phloem and other tissues external to the cambium cannot keep pace with the expansion because the cells no longer divide. As a result, these tissues, including the epidermis, rupture. A second lateral meristem, the cork cambium, develops from parenchyma cells in the cortex. The cork cambium produces cork cells, which replace the epidermis. In year 2 of secondary growth, the vascular cambium adds to the secondary xylem and phloem, and the cork cambium produces cork. As the diameter of the stem continues to increase, the outermost tissues exterior to the cork cambium rupture and slough off from the stem. Cork cambium re-forms in progressively deeper layers of the cortex. When none of the original cortex is left, the cork cambium develops from parenchyma cells in the secondary phloem. Each cork cambium and the tissues it produces form a layer of periderm. Bark consists of all tissues exterior to the vascular cambium. 1 2 3 4 5 6 7 8 9 Secondary phloem (a) Primary and secondary growth in a two-year-old stem Primary and secondary growth of a stem Figure 35.18a

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Secondary phloem Vascular cambium Late wood Early wood Secondary xylem Cork cambium Cork Periderm (b) Transverse section of a three-year- old stem (LM) Xylem ray Bark 0.5 mm Figure 35.18b

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings With age older layers of secondary xylem (heartwood) no longer transport water and minerals Outer layers, (sapwood) – Transport materials through xylem

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Growth ring Vascular ray Heartwood Sapwood Vascular cambium Secondary phloem Layers of periderm Secondary xylem Bark Figure 35.20

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Periderm – Cork cambium  cork cells Bark – Tissues external to vascular cambium (secondary phloem and periderm)

44. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Growth, morphogenesis, and differentiation  plant body

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molecular Biology: Revolutionizing the Study of Plants New techniques and model systems catalyzing explosive progress in understanding of plants

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Arabidopsis – First plant to have genome sequenced Cell organization and biogenesis (1.7%) DNA metabolism (1.8%) Carbohydrate metabolism (2.4%) Signal transduction (2.6%) Protein biosynthesis (2.7%) Electron transport (3%) Protein modification (3.7%) Protein metabolism (5.7%) Transcription (6.1%) Other metabolism (6.6%) Transport (8.5%) Other biological processes (18.6%) Unknown (36.6%) Figure 35.21

47. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Growth: Cell Division and Cell Expansion Increasing cell number – Potential for growth Cell expansion – Actual increase in plant size

48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Morphogenesis and Pattern Formation Pattern formation – Development of specific structures in specific locations – Determined by positional information in the form of signals that indicate to each cell its location

49. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular differentiation – Depends on positional information – Affected by homeotic genes Figure 35.28 When epidermal cells border a single cortical cell, the homeotic gene GLABRA-2 is selectively expressed, and these cells will remain hairless. (The blue color in this light micrograph indi- cates cells in which GLABRA-2 is expressed.) Here an epidermal cell borders two cortical cells. GLABRA-2 is not expressed, and the cell will develop a root hair. The ring of cells external to the epi- dermal layer is composed of root cap cells that will be sloughed off as the root hairs start to differentiate. Cortical cells 20 µm

50. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Transition from vegetative growth  flowering – Switching-on of floral meristem identity genes