Tissues

1. Tissues Chapter 4

2. Outline • Organs and Tissues • Meristematic Tissues • Apical Meristems • Lateral Meristems • Intercalary Meristems • Tissues Produced by Meristems • Simple Tissues • Complex Tissues

3. Organs and Tissues • Plants have 3 or 4 major groups of organs: • Roots • Stems • Leaves • Flowers • Each organ composed of tissues • Tissue - group of cells performing similar function • May be more than one tissue per organ

4. Meristematic TissuesApical Meristems • Meristems -permanent regions of growth and active cell division • Apical Meristems -found at tips of roots and shoots • Roots and shoots increase in length as apical meristems produce new cells (=1° growth)

5. Meristematic TissuesApical Meristems • Primary (1°) meristemsdevelop from apical meristems • Protoderm • Ground Meristem • Procambium • 1° meristems produce primary tissues Diagram of longitudinal axis of a plant

6. Meristematic TissuesLateral Meristems • Lateral Meristems -produce 2° tissues that increase girth of roots and stems (=2° growth) • Vascular Cambium -produces tissues functioning primarily in support and conduction • Composed of thin cylinder of brick-shaped cells that extends length of stems and roots • Cork Cambium -lies outside vascular cambium just inside outer bark • Produces bark

7. Meristematic TissuesIntercalary Meristems • Grasses and related plants do not have vascular cambium nor cork cambium • Intercalary Meristems • In vicinity of nodes (leaf attachment area) • Add to stem length

8. Tissues Produced By MeristemsSimple Tissues • Simple Tissues -consist of only one kind of cell • Parenchyma -composed of parenchyma cells • Parenchyma cells • Thin, pliable walls • Usually 14-sided at maturity • Living cytoplasm, often containing large vacuoles and various secretions • May remain alive long time • Have spaces between them Parenchyma cells

9. Tissues Produced By MeristemsSimple Tissues • Types of parenchyma tissue and cells • Aerenchyma -parenchyma tissue with extensive connected air spaces, usually in aquatic plants • Chlorenchyma -parenchyma cells containing chloroplasts (photosynthesis) • Transfer Cells -develop irregular extensions of inner wall that greatly increase surface area of plasma membrane • Nectaries of flowers

10. Tissues Produced By MeristemsSimple Tissues • Collenchyma Tissue -contains collenchyma cells • Collenchymacells • Living cytoplasm • May remain alive long time • Cell walls thick, and with uneven thickness due to extra 1° wall in cell corners • Pliable and strong, thus providing flexible support Collenchyma cells

11. Tissues Produced By MeristemsSimple Tissues • Sclerenchyma Tissue -contains sclerenchyma cells • Sclerenchymacells • Thick, tough, 2° walls, normally impregnated with lignin • Dead at maturity • Function in support • Two types: sclereids and fibers • Sclereids – stone cells • Scattered in tissue • Cells long as wide Sclereids

12. Tissues Produced By MeristemsSimple Tissues • Fibers • Much longer than wide and contain lumen (tiny cavity) Fibers in cross section and longitudinal section

13. Tissues Produced By MeristemsComplex Tissues • Complex Tissues -composed of 2 or more kinds of cells • Vascular tissues include xylem and phloem • Xylem -chief conducting tissue for water and minerals absorbed by roots • Composed of parenchyma cells, fibers, vessels, tracheids and ray cells

14. Tissues Produced By MeristemsComplex Tissues • Vessels -made of vessel elements • Vessel elements • Open at each end, but may have perforation plate • Dead at maturity • Thick 2° cell walls • Many have spiral thickenings on cell walls Vessels elements Spiral thickenings on vessel walls

15. Tissues Produced By MeristemsComplex Tissues • Tracheids • Tapered at ends with pairs of pits that allow water to pass from cell to cell • Pits -areas without 2° cell wall • Dead at maturity • Thick 2° cell walls • May have spiral thickenings Tracheids Pit pairs • Rays -function in lateral conduction and food storage • Composed of long-lived parenchyma cells

16. Tissues Produced By MeristemsComplex Tissues • Phloem -conducts dissolved food materials produced by photosynthesis throughout plant • Composed of sieve tube members, companion cells, fibers, parenchyma cells and ray cells • Sieve Tube Members • Lack 2° cell walls and nuclei • Lay end to end to form sieve tubes • Walls have sieve plates with small pores • Callose forms callus plug - prevents leaking of contents when cell injured Phloem • Companion Cells -aid in conduction of food

17. Tissues Produced By MeristemsComplex Tissues • Epidermis - one cell-layer thick protective layercovering all plant organs • Composed mostly of parenchyma cells, guard cells of stomata, secretoryglands, and hairs Leaf cross section

18. Tissues Produced By MeristemsComplex Tissues • Cutin -fatty substance on surface of outer walls of epidermis forming cuticle • Wax secreted on cuticle • Cuticle and wax prevent water loss by evaporation • Resistant to bacteria and other disease organisms • Root epidermal cells produce root hairs • Increase absorptive area of root surface • Leaves have stomata bordered by pairs of guard cells

19. Tissues Produced By MeristemsComplex Tissues • Periderm -replaces epidermis when cork cambium begins producing new tissue • Constitutes outer bark • Primarily composed of cork cells • Dead at maturity • While still alive, cytoplasm secretes suberin(fatty substance) into walls • Makes cork cells waterproof and helps protect phloem Periderm with lenticel • Lenticels -loosely arranged pockets of parenchyma cells formed by cork cambium that protrude throughsurface of periderm

20. Tissues Produced By MeristemsComplex Tissues • Secretory Cells and Tissue • Secretory cells may function individually or as part ofsecretory tissue • Flower nectar • Citrus oils • Glandular hair mucilage • Latex • Resins

21. Review • Organs and Tissues • Meristematic Tissues • Apical Meristems • Lateral Meristems • Intercalary Meristems • Tissues Produced by Meristems • Simple Tissues • Complex Tissues