Plant Form

1. Plant Form Chapter 36

2. Plant Body Organization A vascular plant consists of: 1. Root system,which is underground -Anchors the plant, and is used to absorb water and minerals 2. Shoot system,which is above ground -Consists of supporting stems, photosynthetic leaves and reproductive flowers Each has an apex that extends growth

4. Plant Body Organization Plant cell walls consist of cellulose -Primary cell wall -Found in all cells -Cellulose fibers parallel to microtubules -Secondary cell wall -Found in some cells -Additional layers of cellulose and lignin -Increase mechanical strength of wall

5. Plant Body Organization

6. Plant Body Organization Roots, shoots and leaves contain three basic tissue systems: -Dermal tissue – For protection -Wax and bark -Ground tissue – For storage, photosynthesis and secretion -Vascular tissue – For conduction -Xylem – Water and dissolved minerals -Phloem – Nutrient-containing solution

7. Plant Body Organization Meristems are clumps of small cells with dense cytoplasm and large nuclei They act as stem cells do in animals -One cell divides producing a differentiating cell and another that remains meristematic

9. Plant Body Organization Apical meristems are located at the tips of stems and roots -Give rise to primary tissues which are collectively called the primary plant body -Threeprimary meristems -Protoderm Epidermis -Procambium 1o vascular tissue -Ground meristem Ground tissue

10. Plant Body Organization

11. Plant Body Organization (Cont.)

12. Plant Body Organization Lateral meristems are found in plants that exhibit secondary growth -Give rise to secondary tissues which are collectively called the secondary plant body -Woody plants have two types -Cork cambium Outer bark -Vascular cambium 2o vascular tissue

14. Plant Tissues As mentioned earlier, plants contain three main types of tissue -Dermal -Ground -Vascular

15. Dermal Tissue Forms the epidermis,which is usually one cell layer thick Covered with a fatty cutin layer constituting the cuticle Contains special cells, including guard cells, trichomes and root hairs

16. Dermal Tissue Guard cells are paired sausage-shaped cells -Flank a stoma,which is the passageway for oxygen and carbon dioxide Guard cell formation is the result of an asymmetrical cell division that produces: -A guard cell -A subsidiary cell -Aids in stoma opening and closing

17. Dermal Tissue

18. Dermal Tissue (Cont.)

19. Dermal Tissue (Cont.)

20. Dermal Tissue Trichomes are cellular or multicellular hairlike outgrowths of the epidermis -Keep leaf surfaces cool and reduce evaporation by covering stomatal openings -Some are glandular, secreting substances that deter herbivory Trichome patterning is under genetic control

21. Dermal Tissue

22. Dermal Tissue (Cont.)

23. Dermal Tissue Roots hairs are tubular extensions of individual epidermal cells -Greatly increase the root’s surface area and efficiency of absorption

24. Ground Tissue Consist of three types of cells -Parenchyma -Collenchyma -Sclerenchyma

25. Ground Tissue Parenchyma cells are the most common type of plant cell -May live for many years, functioning in storage, photosynthesis and secretion -Some contain chloroplasts and are called chlorenchyma Collenchyma cells provide support for plant organs, allowing bending but not breaking -Have living protoplasts and may live for many years

26. Ground Tissue Sclerenchyma cells have tough thick walls -Lack living walls at maturity -Two general types -Fibers: Long, slender cells that are usually grouped in strands -Sclereids: Variable shape; branched; may occur singly or in groups -Both strengthen tissues

27. Ground Tissue

28. Ground Tissue (Cont.)

29. Vascular Tissue Xylem -Constitutes the main water- and mineral-conducting tissue -Vessels: Continuous tubes of dead cylindrical cells arranged end-to-end -Tracheids: Dead cells that taper at the end and overlap one another -Vessels are shorter & wider than tracheids -And conduct water more efficiently

31. Vascular Tissue Xylem -Also conducts inorganic ions such as nitrates, and supports the plant body -Typically includes parenchyma cells in horizontal rows called rays -Function in lateral conduction and food storage Note: The diffusion of water vapor from a plant is termed transpiration

32. Vascular Tissue Phloem -Constitutes the main food-conducting tissue in vascular plants -Contains two types of elongated cells: sieve cells and sieve tube members -Living cells that contain clusters of pores called sieve areas or sieve plates -Sieve-tube members are more specialized -Associated with companion cells

34. Roots Roots have a simpler pattern of organization and development than stems Four regions are commonly recognized: -Root cap -Zone of cell division -Zone of elongation -Zone of maturation

36. Roots Root cap -Contains two types of cells that are formed continuously by the root apical meristem -Columella cells: Inner -Root cap cells: Outer and lateral -Functions mainly in protection of the delicate tissues behind it -Also in the perception of gravity

37. Roots Zone of cell division -Contains mostly cuboidal cells, with small vacuoles and large central nuclei -Derived from rapid divisions of the root apical meristem -Quiescent center cells divide very infrequently -Apical meristem daughter cells soon subdivide into the three primary tissues

38. Roots Zone of cell division -Patterning of these tissues begins in this zone -WEREWOLF (WER) gene -Suppresses root hair development -SCARECROW (SCR) gene -Necessary for differentiation of endodermal and ground cells

41. Roots Zone of elongation -Roots lengthen because cells become several times longer than wide -No further increase occurs above this zone

42. Roots Zone of maturation -The elongated cells become differentiated into specific cell types -Epidermal cells: Have very thin cuticle -Include root hair and nonhair cells -Cortex: Interior to the epidermis -Parenchyma cells used for storage

43. Roots Zone of maturation -Endodermis: Single-layered cylinder -Impregnated with bands of suberin called the Casparian strips -Stele:All tissues interior to endodermis -Pericycle: Multiple-layered cylinder -Gives rise to lateral (branch) roots or the two lateral meristems

44. Roots

47. Plant Tissue Differentiation

48. Modified Roots Most plants produce either/or: -Taproot system: Single large root with small branch roots -Fibrous root system: Many small roots of similar diameter Some plants, however, produce modified roots with specific functions -Adventitious roots arise from any place other than the plant’s root

49. Modified Roots Prop roots:Keep the plant upright Aerial roots: Obtain water from the air Pneumatophores: Facilitate oxygen uptake Contractile roots: Pull plant deeper into soil Parasitic roots: Penetrate host plants Food storage roots: Store carbohydrates Water storage roots: Weigh 50 or more kg Buttress roots: Provide considerable stability

50. Prop roots Aerial roots