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 Tissues Apical 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 Tissues Apical Meristems  Primary (1°) meristems develop from apical meristems Protoderm Ground Meristem Procambium  1° meristems produce primary tissues Diagram of longitudinal axis of a plant

6. Meristematic Tissues Lateral 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 Tissues Intercalary 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 Meristems Simple Tissues  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  Simple Tissues - consist of only one kind of cell

9. Tissues Produced By Meristems Simple 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 Meristems Simple Tissues  Collenchyma Tissue - contains collenchyma cells Collenchyma cells −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 Meristems Simple Tissues  Sclerenchyma Tissue - contains sclerenchyma cells Sclerenchyma cells −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 Meristems Simple Tissues −Fibers – Much longer than wide and contain lumen (tiny cavity) Fibers in cross section and longitudinal section

13. Tissues Produced By Meristems Complex 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 Meristems Complex 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 Meristems Complex 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  Rays - function in lateral conduction and food storage – Composed of long-lived parenchyma cells Tracheids Pit pairs

16. Tissues Produced By Meristems Complex Tissues  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  Phloem - conducts dissolved food materials produced by photosynthesis throughout plant Composed of sieve tube members, companion cells, fibers, parenchyma cells and ray cells  Companion Cells - aid in conduction of food

17. Tissues Produced By Meristems Complex Tissues  Epidermis - one cell-layer thick protective layer covering all plant organs Composed mostly of parenchyma cells, guard cells of stomata, secretory glands, and hairs Leaf cross section

18. Tissues Produced By Meristems Complex 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 Meristems Complex Tissues 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 - replaces epidermis when cork cambium begins producing new tissue Periderm with lenticel Lenticels - loosely arranged pockets of parenchyma cells formed by cork cambium that protrude through surface of periderm

20. Tissues Produced By Meristems Complex Tissues  Secretory Cells and Tissue Secretory cells may function individually or as part of secretory 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