1. Plant Tissues
Lecture 3
March 7, 2018

2. Plant Growth and Development
Plant Development
Growth (an irreversible increase in size)
Morphogenesis (a particular shape or form of a plant)
Differentiation (cells with identical DNA become different from one another and from meristematic cells)
Plant grows through cell division and cell enlargement

3. Plant Growth and Development
Cellular differentiation: Under the control of gene expression and the fate of a plant cell is determined by it final position in the developing organ
Differentiation is referred to determination and competence.
Determination: Progressive commitment to become differentiated or produce progeny
Competency: The ability of a cell to develop in response to a specific signal (light)

4. Cell Wall
Chloroplast
Central Vacuole
Organelles
Plant Organs
Plant Tissues
Plant Cells
Whole Plants
Leaves
Stems
Roots
Flowers
Vascular System
Ground System
Dermal System
Guard Cells
Stomata
Epidermis
Sclerenchyma
Collenchyma
Xylem
Phloem
Parenchyma
Cuticle

5. The Primary Plant Body
Primary growth: close to the tips of roots and stems (meristems)
Extension of the plant body: vertical growth
Forms primary tissues= primary plant body
The root system anchors the plant and absorbs water and mineral from the soil
The shoot system including stems and leaves provides solar panels to absorbs sunlight to perform photosynthesis
Both root and shoot systems are made of different tissue systems.

6. Check Your Understanding
The primary activity of cells of meristematic tissues is ______________________.   A.  support B.  transport of water C.  photosynthesis D.  cell division E.   defense

7. Check Your Understanding
Primary meristems produce tissues that ________________.  
A.  increase the width of a plant B.  increase the mass of a plant C.  increase the length of a plant D.  lead to the production of bark E.  produce the cork cambium

8. Plant Tissues Tissues: structural and functional units
Tissue systems: larger units of principal tissues
3 tissue systems
Ground (fundamental) tissue system formed from ground meristem
Vascular tissue system formed from procambium
Dermal tissue system formed from protoderm

9. two or more types of cells
Plant Tissues
Ground tissue system:
Parenchyma, Collenchyma, Sclerenchyma
Vascular tissue system: Xylem and Phloem
Dermal tissue system: Epidermis and Periderm
Simple Tissues
only one type of cell
Complex Tissues
two or more types of cells

10. Ground Tissue System: Parenchyma Cells
Parenchyma cells: the most numerous cells in the plant body
Variable shape and size
Living at maturity, capable of cell division, mostly primary cell walls, but some have also secondary walls
Involved in regeneration and wound healing

11. Parenchyma cells
Parenchyma tissue: continuous masses in the primary plant body found in the cortex and pith of stems and roots, in leaf mesophyll
Rays, parenchyma cells found as:
Vertical strands of cells in the primary and secondary vascular tissues and horizontal strands in the secondary vascular tissues
Function
Photosynthesis, storage and secretion
Water movement and food transportation
Water-storage tissue in many succulents (Cactaceae)

12. Ground Tissue System: Collenchyma Cells
Collenchyma cells like parenchyma cells are living at maturity
Typically elongated
With unevenly thickened, nonlignified primary walls
Found as continuous cylinders beneath the epidermis in stems and petioles and bordering the veins in eudicot leaves
Typical supporting tissue of growing stems, leaves, and floral parts
Roots rarely have collenchyma

13. Ground Tissue System: Sclerenchyma Cells
Sclerenchyma cells as continuous masses or small group, individually or among other cells
Found in any or all parts of the primary and secondary plant bodies
Dead at maturity (due to lack of protoplast)
Having thick, often lignified secondary walls
Important strengthening and supporting elements in plant parts that no longer are elongated

14. Sclerenchyma Cells Two types of sclerenchyma: Fiber and sclereids
Fibers: long, slender cells as strands or bundles, vary in length ( mm in jute and 9-70 mm in flax)
Sclereids: variable in shapes and often branched, relatively short cells compared to the most fibers.
Found singly or aggregated throughout the ground tissue
Seed coats of many seeds, shells of nuts, the stone endocarp) of stone fruits (olives, peaches, cherries) ad gritty texture of pears

15. Check Your Understanding
Groups of cells that have a similar structure or common function are called ______________. A. tissues. B. meristems. C. differentiated cells. D. primary meristems. E. secondary meristems.

16. Check Your Understanding
Which of the following cell types can be used for photosynthesis? A. collenchyma cells B. parenchyma cells C. sieve-tube elements D. sclerenchyma cells E. vessel elements

17. Vascular Tissue System
Stele: vascular tissue of root or stem
Xylem: conducts waters and dissolved minerals upwards from roots
Tracheids
Vessel elements
Phloem: transports sugars (from photosynthesis) to roots and other are as of growth
Sieve-tube elements
Companion cells

18. Vascular Tissue System: Xylem
Xylem: principal water-conducting tissue
Involved in transportation of minerals, support and food storage
During the primary growth, it is derived from the procambium and in the secondary growth, the xylem is derived from the vascular cambium.
Tracheary elements: principal conducting cells of the xylem
Tracheids
Vessel elements
Vessel elements have perforation (area with no primary and secondary walls)
Perforation plates at the end walls where the vessel elements joined end- to-end to form long, continuous columns, or tubes called vessel
Both are elongated cells with secondary walls, no protoplast at maturity, have pits in their walls

19. Vascular Tissue System: Xylem
Tracheids only type of water- conducting cells in most seedless vascular plants and gymnosperms
Angiosperms have both vessel elements and tracheids
Vessel elements more efficient than tracheids but less safe due to not filter out the air bubbles

20. Vascular Tissue System: Xylem
Tracheids and vessel elements of protoxylem (primary xylem) vary in the thickening of cell walls
Form annular/ring-like or helical/spiral thickenings to be able to extend or stretch after cell differentiation
Amount of elongation affects the thickening of wall
Little elongation : non-extensible rather extensible elements
Much elongation: more annular or spiral thickenings

21. Metaxylem or Secondary Xylem
Metaxylem or secondary xylem: primary walls completely covered by secondary walls at the pit membranes and at the perforations of vessel element
Pitted elements; rigid and can’t be stretched
Tracheary element differentiation: programmed cell death (total elimination of protoplast)
Xylem tissue has parenchyma cells to store different substances
Xylem parenchyma cells: Vertical strands, but in the secondary xylem found in rays
Fibers in xylems living at maturity and serve a dual function of storage and support

22. Vascular Tissue System: Phloem
Phloem: principal food-conducting tissue
Transport of sugars, amino acids, lipids, micronutrients, hormones, the floral stimulus (florigen), proteins and RNAs
Route for movement of plant viruses
Protophloem formed first and meta-phloem differentiates later
Principal conducting cells of phloem: the sieve elements
Sieves: clusters of pores at sieve area that interconnect the protoplasts of adjacent sieve elements
Two types of sieve elements in seed plants:
Sieve cells (only type of food-conducting cell in gymnosperms)
Sieve-tube elements (only can be found in angiosperms)

23. Vascular Tissue System: Phloem
Sieve cells:
The sieve area pores are narrow
the sieve areas are uniform in structure on all walls and mostly concentrated on the overlapping ends of the long, slender sieve cell
Only type of food-conducting cell in gymnosperms

24. Vascular Tissue System: Phloem
Sieve- tube elements:
The sieve areas on some walls have larger pores than those on other walls of the same cell (Sieve plate)
Sieve plates located on the end walls
Sieve tubes: sieve-tube elements arranged end- on-end in longitudinal series
Sieve elements have living protoplasts at maturity
Selective breakdown (losing the Golgi apparatus, cytoskeleton, ribosomes)

25. Vascular Tissue System: Phloem
Companion cells: parenchyma cells associated with sieve-tube elements cell
Connects through a small pore on the side of the sieve-tube element and branch plasmodesmata on the companion cell side
Life-support system of the sieve-tube element by providing proteins, ATP and informational molecules
In gymnosperms, albuminous cells are parenchyma cells associated with the sieve cells
Fibers and sclereids are also present.

26. Check Your Understanding
Which of the following cell types is dead at maturity? 
A. collenchyma cells B. companion cells C. parenchyma cells D. all of these E. none of these

27. Check Your Understanding
Which of the following pairs of cells function together? 
A. companion cells and fibers B. companion cells and sieve tube elements C. guard cells and root hairs D. parenchyma cells and sclerenchyma cells E. sieve tube elements and vessel elements

28. Stele/Pith
Central column of ground tissue in stems and roots: Pith or central cylinder (stele)
3 types of stele
Protostele
Simplest and most ancient type
Solid cylinder of vascular tissue; phloem surrounds the xylem or interspersed within it
Found in seedless vascular plants such as club mosses, young stems of some other living group
It is the type of stele fond in most roots

29. Stele/Pith 2. Siphonostele
in the stems of most species of seedless vascular plants
Central pith surrounded by vascular tissues
Phloem forms outsides the cylinder of xylem or on both sides of it
3. Eustele
primary vascular cylinder
Evolved directly from protostele
Discrete strands around a pith

30. Dermal Tissue System
Epidermis: the dermal tissue system of leaves, floral parts, fruits, and seeds
Provide mechanical protection for the plant body by their compact arrangement
Cuticle made of cutin and wax minimizes water loss
Site of the light protection involved in circadian leaf movement and photoperiodic induction
Epidermal cells diverse both structurally and functionally

31. Dermal Tissue System
Guard cells: regulate opening/closing of the small epidermal pores (stomata) to manage the movement of gases and water into and outside
Trichomes: variety of functions
Root hairs are trichomes to facilitate the water and mineral absorption from the soil
Increase in leaf hairiness because of leaf trichomes lower leaf temperature and rates of water loss by increasing reflection of solar radiation
Many air plants absorbs water and minerals through their leaf trichomes
Trichomes provide a defense system against insects

32. Periderm
Replaces epidermis in stems and roots undergoing secondary growth
Arranged compactly but lenticels loosely arranged to provide air for the internal tissues of roots and stems
Protective cork (phellem): nonliving cells with heavily suberized walls at maturity
Cork cambium (phellogen)
Phelloderm: a living parenchyma-like tissue
Cork cambium forms cork tissue on its outer surface and phelloderm on its inner surface

33. Plant Tissues Arrangement in Plant Organs
Within the plant body, the various tissue are distributed in a radial pattern with specific arrangements depending on the plant part or plant taxon or both
The vascular tissues are embedded within the ground tissue with the dermal tissue forming the outer covering.
The relative distribution of the vascular and ground tissues is the main difference in patterns

34. Plant Tissues Arrangement in Plant Organs
Leaf
Vascular systems form vascular bundles (veins) embedded in mesophyll (photosynthetic ground tissue)
Stem
Pith (the region formed internal to the strands of vascular system)
Cortex (the region external to them)
Root
Vascular tissues form vascular cylinder (stele) surrounded by a cortex

35. Check Your Understanding
In which tissue would you find guard cells and stomata? 
A. epidermis B. ground tissue C. periderm D. phloem E. xylem

36. Check Your Understanding
True/False: Vessel elements are the conducting cells of the phloem. True/False: Meristems are localized regions of growth in plants.