Plant TissuesTissue – 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

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

Kinds of MeristemsBased 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.

Kinds of Permanent TissuesBased 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

Different Kinds of Simple Permanent Tissues

EpidermisExternal tissue consists of single layer of

living cellsServes 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 shapeIn terms of function, a protective tissueIn 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

epidermis

cortex

pith

vascular bundle

Different Kinds of Simple Permanent Tissues

EpidermisIn 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

Different Kinds of Simple Permanent Tissues

ParenchymaInternal tissueConsists of living cells with uniformly thin cell

wallsLarge intercellular spacesIn cross section, appear rounded Chlorenchyma – parenchyma with

chloroplastidsInvolved in food manufacturing and in food

storage

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.

epidermiscollenchyma

parenchyma

Different Kinds of Simple Permanent Tissues

CollenchymaAlso an internal tissueConsists 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

Collenchyma CellsCollenchyma 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.

Different Kinds of Simple Permanent Tissues

SclerenchymaAlso an internal tissueConsists 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

fibersgritty texture of sugar apple (atis) and chico due

to stone cellsStrengthening or supportive tissue

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

Different Kinds of Simple Permanent TissuesCork

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

epidermisphellem (cork)

cortical parenchyma

phellogen (cork cambium)

phelloderm

phellem

phellogen

phelloderm

BARKp

eri

derm

Plant Cell TypesPLANT CELL

TYPEPROTOPLASM

+/-, CELL LIVING OR DEAD

CELL WALL CHARACTERS FUNCTION

CELL THICKNESS CHEMICAL COMPOSITION

Parenchyma +, living Uniformly thin Cellulose, hemicellulosemay have cutin

Food storage, food manufacture

Collenchyma +, living Irregularly thick Cellulose, hemicellulose

Food storage, strengthening

Sclerenchyma 1. sclereid 2. fiber

-, dead Uniformly thick Cellulose, hemicellulose added suberin or lignin

Strengthening and support

CELL SHAPEPolyhedral to much branched sclerenchyma cellsLong and slender sclerenchyma cells

Kinds of Complex Permanent Tissues

PhloemFunction: mainly conductive or vascular tissueConducts dissolved organic food materialsConsists of the following cell types:

Phloem fibers Phloem parenchyma Sieve tube elements Companion cells

Kinds of Complex Permanent Tissues

Phloem: cell typesPhloem fibers

appear like ordinary schlerenchyma fibersPhloem parenchyma

appear like ordinary parenchyma cells

Kinds of Complex Permanent TissuesPhloem: 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

Kinds of Complex Permanent TissuesPhloem: 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

Kinds of Complex Permanent Tissues

Xylem or WoodFunction: mainly conductive or vascular tissueConducts water and mineral salts The main strengthening tissue of the plantConsists of the following cell types:

Xylem fibers Xylem parenchyma Vessel elements Tracheids

Kinds of Complex Permanent Tissues

Xylem: cell typesXylem fibers

appear like ordinary schlerenchyma fibersXylem parenchyma

structurally similar but much smaller than the ordinary parenchyma cells

Kinds of Complex Permanent TissuesXylem: 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

Kinds of Complex Permanent TissuesXylem: 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

xylem

phloem

vessel

vessel

air space

companion cell

sieve tube

bundle sheath

Cross section of a monocot stem

vascular bundle

phloem fiber

sieve tubecompanion cell

xylem parenchyma

xylem fiber

phloem parenchyma

vascular cambium

vessel

Tracheid (schlerenchyma)

Kinds of Complex Permanent TissuesMain 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-likeReticulate – the thickening is net-likePitted 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

reticulate

Plant TrichomesTrichomes or epidermal hairs

appendages of the epidermal cellsmay be unicellular or multicellularglandular and non-glandular structuresGlandular 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)

Plant Trichomes

Glandular TrichomesGlandular 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

Plant Trichomes

Non-glandular TrichomesBristles - stiff, sharp pointed hairs which may

be barb-like protuberances along the sides as in lipa

Scales - flattened structure as in alingaroStellate trichomes – star-like structure as in

ratilis and MallotusBranched trichomes (dendroid) – as in the

velvet dock

Glandular trichomes

Glandular trichomes - Enlarge terminal portions

Glandular trichomes - Enlarge terminal portions

Non-gladular