Plant Tissue

Damnjanović Ivana

Permanent Tissues

Permanent tissues are non-meristematic.The following permanent tissues will be discussed:

Dermal tissue Xylem Phloem Secretory tissue

Dermal Tissue

-Outer covering-Protection

Dermal Tissue System (Outer Covering of Plant):

1) Epidermal Tissue (epidermis):• Forms outermost layer

Cuticle: Waxy covering• Reduces evaporation• Inhibits microorganism invasion

Root Hairs: extended root surface• Increase absorption

2) Peridermal Tissue (periderm):• Only in woody plants (“bark = dead cells”)• Protection; support

Epidermis

The epidermis can be from one to several cell layers thick.It covers all the parts of a plant; shoots, stems, leaves, and roots.Live cells

Structure Function

Layer of cells covering surface of entire plant.

Acts as a barrier to fungi and other microorganisms and pathogens.

Layer is thin and transparent.Allow for light to pass through, allowing for photosynthesis in the tissues below.

Epidermal tissues have abundant trichomes which are tiny hairs projecting from surface of epidermis.

Leaf trichomes trap water in the area above the stomata and prevent water loss.

Trichomes (hairs)Epidermal tissue

Special Dermal Cells – Trichomes & Root hairs

• Trichomes– Hairlike outgrowths of

epidermis – Keep leaf surfaces cool and

reduce evaporation

• Roots hairs– Tube extensions from

epidermal cells– Greatly increase the root’s

surface area for absorption

Root hairs are elongations of epidermal cells in the root.

Root hairs maximise the surface area over which absorption of water from the soil can occur.

Epidermal tissues in leaves are covered with a waxy cuticle.

The waxy outer layer on the epidermis prevents water loss from leaves.

Epidermal tissues contain guard cells containing chloroplasts.

Guard cells control the opening and closing of the pores known as stomata thus controlling water loss in plants.

Some plant epidermal cells can secrete poisonous or bad-tasting substances.

The bitter taste of the substances deter browsing and grazing by animals.

Epidermis continued: guard cells and stomata

Guard cells are bean shaped specialised epidermal cells found mainly on the lower surface of leaves which are responsible for regulating the size of the stoma opening.

Together, the stoma and the guard cells are referred to as stomata.

The stomata in the epidermis allow oxygen, carbon dioxide and water vapour to enter and leave the leaf. The guard cells also contain chloroplasts for photosynthesis.

Periderm

-Only in woody plants (“bark = dead cells”)-Protection; support-Lenticels

Plant Tissue - Vascular1) Xylem (dead at maturity):

Vessel Elements: Wide, tube-like cellsTracheids: Narrow, tube-like cells

Parenchyma cells

Xylem has the dual function of 1. supporting the plant and2. transporting water and dissolved mineral salts from the roots to the stems and leaves.

-The vessels and tracheids are non-living at maturity and are hollow to allow the transport of water- Both vessels and tracheids have lignin in their secondary walls, which provides additional strength and support.

-Tracheids have thick secondary cell walls and are tapered at the ends. -The thick walls of the tracheids provide support and tracheids do not have end openings like the vessels. -The tracheids' ends overlap with one another, with pairs of pits present which allow water to pass through horizontally from cell to cell.

2) Phloem (living at maturity)

A) Sieve Tubes: Wide, tube-like cells B) Companion Cells: support and regulate sieve tubes

2) Phloem (living at maturity)

- Moves water, sugar, amino acids & hormones

Phloem tissue is the living tissue responsible for transporting organic nutrients produced during photosynthesis (mainly as

the carbohydrate) to all parts of the plant where these are required

-The phloem tissue is made up of the following major types of cells:1. sieve elements: these are conducting cells which transport sucrose.2. parenchyma cells: which store food for transport in phloem.3. companion cells: are associated with parenchyma cells and control the activities of sieve tube elements, since the latter have no nuclei.

4. Fibres: unspecialised cells and supportive cells.

Secretory Tissues

Nectar (flowers) from nectaries Oils (peanuts, oranges, citrus) from accumulation

of glands and elaioplasts. Resins (conifers) from resin canals Macticifers (e.g., latex - milkweed, rubber plants,

opium poppy) Hydathodes (openings for secretion of water) Digestive glands of carnivorous plants (enzymes) Salt glands that shed salt (especial in plants

adapted to environments laden with salt).

The End