Plant Tissues

1. Plant Tissues • Tissue – group of vegetative cells with one or more specific functions. • Two kinds based on state of development: • Meristematic tissues or Meristems • Actively engaged in cell division (production of new cells) • Enlarge and differentiate to become permanent tissues • Remain meristematic or repeatedly divide (initials) • Permanent tissues • Attained mature form and perform their specific functions • No longer divide and give rise to new cells • All are derived from meristematic tissues

2. Kinds of Meristems • Based on position or location within the plant body: • Apical meristems (promeristems) • Found at the tips or apices of stems and roots • Responsible for the increase in length of stems and roots • 3 meristematic zones: • Protoderm, Ground meristem, Procambium • Lateral meristems (or cambia) • Found along the sides of certain roots and stems • Responsible for the increase in width or diameter • Dicots have cambia whereas monocots have no cambia • Types: vascular cambium and cork cambium (phellogen) • Intercalary meristems • Found at the bases of young leaves and internodes • Considered temporary (short-lived) meristems

3. Kinds of Meristems • Based on origin, meristems may be classified as: • Primary meristems • Originate in the embryo and persist throughout the lifetime • Apical meristems or their meristematic zones • Intercalary and the vascular cambium • Secondary meristems • Derived from permanent tissues • Cork cambium • Living permanent tissues lining injured or wounded portions of plants become meristematic to heal the injured portions resulting in formation of “callus” or scar tissue.

4. Kinds of Permanent Tissues • Based on the number of cell types/kinds of cells: • Simple permanent tissues • for the most part consist of only one kind of cell • Composed of similar in structure and function • Complex permanent tissues • Consist of several kinds of cells working together as a unit in carrying out one or more specific functions

5. Different Kinds of SimplePermanent Tissues • Epidermis • External tissue consists of single layer of living cells • Serves as outermost tissue of leaves, young roots and young stems; also in old roots and old stems of monocot plants and herbaceous dicot plants • Appear cubical or rectangular in shape • In terms of function, a protective tissue • In leaves and stems: • 2 kinds of cells: • Ordinary epidermal cells • Guard cells (kidney-shaped) which occur in pairs and bound by tiny openings or pores called stomata

6. epidermis cortex vascular bundle pith

7. Different Kinds of SimplePermanent Tissues • Epidermis • In leaves and stems: • 2 kinds of cells: • Ordinary epidermal cells • Guard cells (kidney-shaped) which occur in pairs and bound by tiny openings or pores called stomata. • Outer wall is coated with a heavy waxy substance (cutin or cuticle) that prevents excessive transpiration or evaporation of water from the leaves and stems; roots not cutinized • Epidermal hairs (trichomes) for protective function

8. Different Kinds of SimplePermanent Tissues • Parenchyma • Internal tissue • Consists of living cells with uniformly thin cell walls • Large intercellular spaces • In cross section, appear rounded • Chlorenchyma – parenchyma with chloroplastids • Involved in food manufacturing and in food storage

9. Parenchyma Cells - Parenchyma cells are living cells with uniformly thin walls. They comprise the photosynthetic tissue of a leaf, the soft flesh of fruits, and the storage tissue of roots and seeds. - A widely distributed tissue located beneath the collenchyma between the vascular bundles (consisting of vascular tissues and at the center of the section. epidermis collenchyma parenchyma

10. Different Kinds of SimplePermanent Tissues • Collenchyma • Also an internal tissue • Consists of living cells with unevenly thickened walls– thin on the sides but thickened at the angles where two or more cells meet • Appear cubical or slightly rectangular and are more or less compactly arranged • A strengthening or support tissue; storage of food

11. Collenchyma Cells Collenchyma cells have unevenly thickened cell walls, which are their distinguishing characteristic. They form strands along veins in leaves and beneath the epidermis in stems to provide support and strength against the onslaught of strong winds and rains.

12. Different Kinds of SimplePermanent Tissues • Sclerenchyma • Also an internal tissue • Consists of dead cells when mature, with heavily thickened cell walls mainly due to the deposition of lignin • It may appear in the form of fibers or sclerids • Fibers –elongated cells with tapering ends occurring in groups; appear as cells with tiny empty cell cavities or cell lumina with heavy and uniformly thickened cell walls in cross section • Sclerids –irregularly-shaped cells and typically not elongated; various forms but the most common are stone cells (isodiametric and like sand particles occur singly or in groups) • Found in fruits: coconut shell is sclerids, coconut husk is fibers gritty texture of sugar apple (atis) and chico due to stone cells • Strengthening or supportive tissue

13. Sclerenchyma Cells - Sclerenchyma cells have thick and rigid cell walls. They serve as strengthening elements to support mature plant parts. - Found in groups of cluster among the parenchyma cells around the vascular tissues

14. Different Kinds of SimplePermanent Tissues • Cork • External tissue serving as outermost tissue or covering of old stems/roots of woody dicot plants • Consists of several layers of dead cells when mature • Cell walls are impregnated with waxy substance (suberin) – impermeable to substances, resulting to the death of cells upon reaching maturity • Rectangular in shape and arranged in layers in cross-section • Protective tissue

15. BARK epidermis phellem (cork) phellogen (cork cambium) phelloderm cortical parenchyma phellem phellogen phelloderm periderm

16. Plant Cell Types

17. Kinds of ComplexPermanent Tissues • Phloem • Function: mainly conductive or vascular tissue • Conducts dissolved organic food materials • Consists of the following cell types: • Phloem fibers • Phloem parenchyma • Sieve tube elements • Companion cells

18. Kinds of ComplexPermanent Tissues • Phloem: cell types • Phloem fibers • appear like ordinary schlerenchyma fibers • Phloem parenchyma • appear like ordinary parenchyma cells

19. Kinds of ComplexPermanent Tissues • Phloem: cell types • Sieve tube elements • conducting cells of the phloem • living, non-nucleated cell when mature • elongated in form and uniformly thin-walled with the end walls perforated to form sieve plates that are attached end-to-end forming long conducting tubes (sieve tubes) • consists of protoplasmic connections between adjacent cells - plasmodesmata

20. Kinds of ComplexPermanent Tissues • Phloem: cell types • Companion cells • parenchymatous cells which are always found beside the sieve tubes • small, elongated and nucleated living cells when mature • plasmodesmata have also been observed to occur between the companion cells and the sieve tubes

21. Kinds of ComplexPermanent Tissues • Xylem or Wood • Function: mainly conductive or vascular tissue • Conducts water and mineral salts • The main strengthening tissue of the plant • Consists of the following cell types: • Xylem fibers • Xylem parenchyma • Vessel elements • Tracheids

22. Kinds of ComplexPermanent Tissues • Xylem: cell types • Xylem fibers • appear like ordinary schlerenchyma fibers • Xylem parenchyma • structurally similar but much smaller than the ordinary parenchyma cells

23. Kinds of ComplexPermanent Tissues • Xylem: cell types • Vessel elements • main conducting cells of the xylem • Elongated in shape and dead when mature • Heavily thickened cell walls • Have relatively large cavities or lumina which generally appear rounded in cross section • Vessel elements are attached end-to-end with their end walls perforated to form long conducting tubes (xylem vessels) • Perforation plate – perforated wall having one or more openings

24. Kinds of ComplexPermanent Tissues • Xylem: cell types • Tracheids • simplest conducting cells of the xylem • dead cell when mature • elongated in shape and square-like in cross section with heavily thickened cell walls • Tracheary elements – consists of the vessel elements and the traceheids; have different types depending on how lignin is deposited on their cell walls

25. bundle sheath companion cell sieve tube vessel vessel air space phloem Cross section of a monocot stem xylem vascular bundle

26. phloem fiber phloem parenchyma sieve tube companion cell vascular cambium Tracheid (schlerenchyma) vessel xylem parenchyma xylem fiber

27. Kinds of ComplexPermanent Tissues • Main types of tracheary elements: • Annular type – thickening of the cell wall is in the form of rings • Spiral type – the thickening is in the form of a spiralling or helical structure • Scalariform – the thickening is ladder-like • Reticulate – the thickening is net-like • Pitted type – the uniformly thickened cell walls show the presence of more or less rounded depressions or pore-like structure (pitts) representing the non-lignifed portions of a wall

29. reticulate

30. Plant Trichomes • Trichomes or epidermal hairs • appendages of the epidermal cells • may be unicellular or multicellular • glandular and non-glandular structures • Glandular trichomes – consist of living cells and produce secretions • Types: glandular and stinging trichomes • Non-glandular trichomes – consist of dead cells and non-secretory • Kinds: bristles, scales, stellate, and branched (dendroid)

31. Plant Trichomes • Glandular Trichomes • Glandular trichomes • produce secretions in enlarged terminal portions • Examples: ratilis, oregano and malvarosa • Stinging trichomes • Consist of enlarged base containing secretion from which projects a stiff, slender structure that ends in a sharp point • Example: lipang kalabaw

32. Plant Trichomes • Non-glandular Trichomes • Bristles - stiff, sharp pointed hairs which may be barb-like protuberances along the sides as in lipa • Scales - flattened structure as in alingaro • Stellate trichomes – star-like structure as in ratilis and Mallotus • Branched trichomes (dendroid) – as in the velvet dock

34. Glandular trichomes

35. Glandular trichomes - Enlarge terminal portions

36. Glandular trichomes - Enlarge terminal portions

37. Non-gladular