3) Dermal Tissue System - Forms an outer protective covering of the plant. - Covers and protects the plant surface from drying out, pathogens, & insects.

3) Dermal Tissue System - Forms an outer protective covering of the plant.

- Covers and protects the plant surface from drying out, pathogens, & insects.

- Complex tissues make up this tissue system.

- Main Tissue Types: epidermis (primary) and periderm (secondary).

- The Dermal Tissue System also includes modified cells like guard cells, root hairs and cells that produce a waxy cuticle.

- Dermal Tissue System is found in the epidermis of early growth and periderm of later growth. It also found in the endodermis which is tightly packed layer of cells that surrounds the vascular cylinder in the root of a plant.

Three Tissue Systems Make Up the Plant Body

Leaf Cross Section Stem Cross Section Root Cross Section

Note: On the below cross sections, only dermal tissues are circled with red dots.

A) Epidermis Tissue (Cells)

The Complex Tissues of the Dermal Tissue System

Upper leaf surface of Sheppard's purse (Magnified 350 times)

Epidermis is the outer covering of the plant made of complex tissue.

The epidermis regulates gas exchange in and out of the plant.

The epidermis is usually one cell layer thick but 5-6 cells thick in succulent (cacti) plants.

Epidermal Cell Types: Epidermal, Guard Cells, Subsidiary Cell, Trichomes (hairs).

Epidermis Tissue (Cells) continued.Epidermal Cells are living but lack chloroplasts. They posses thick cell walls.

The outer “facing outward” surface is coated with cutin, a waxy substance forming an impermeable layer called the cuticle. Notice how a drop of water beads on a leaf just like water beading on your freshly waxed car. Only the shoot apex, root cap, and root hair surface lacks a cuticle.

Guard Cells are found in young stems, leaves, flower parts and rarely roots. They contain chloroplasts. Between each pair of guard cells is a small pore through which gases enter or leave; a pair of guard cells in addition to the pore constitute a stoma (plural, stomata). Guard cells are able to open and close.

Subsidiary Cells regulate the opening of guard cells.

Epidermis Tissue (Cells) continued.

Trichome Cells are short filaments of one or more cells extending from the epidermis. Trichomes are epidermal outgrowths (single or multicellular). Root hairs are trichomes that are extensions of single epidermal cells that increase root surface area in contact with soil water. In some leaves, elaborate multicellular trichomes may form. Some trichomes can store water, insulate heat or reflect sunlight.

Glandular

Hair in

Tobacco

B) Periderm Tissue (Cells)

The Complex Tissues of the Dermal Tissue System

Periderm is a protective tissue that replaces the epidermis after secondary growth is initiated. In similar words, the periderm is a protective layer that forms in older stems and roots. The periderm consists of cork (phellem), cork cambium (phellogen) and phelloderm.

Cork is dead a maturity and has suberin, a waxy substance embedded in its cell walls.(Parenchyma Cells)

Now let’s look at different plant parts and understand the cells and tissue systems involved. See next 4 Slides.

Clover Stem (Cross Section)

(Dermal Tissue System)

(Xylem and Phloem Cells: Vascular Tissue System)

(Made from Parenchyma Cells:

Ground Tissue System)

Corn Stem (Cross Section)

(Dermal Tissue System)

(Xylem and Phloem

Cells: Vascular Tissue System)

(Made from Parenchyma Cells:

Ground Tissue System)

Buttercup Root (Cross Section)

(Dermal Tissue System)

(Xylem and Phloem

Cells: Vascular Tissue System)

(Made from Parenchyma Cells:

Ground Tissue System)

Lilac Leaf (Side View)

(Dermal Tissue System)

(Xylem and Phloem Cells: Vascular Tissue System)

(Made from Parenchyma Cells:

Ground Tissue System)

Top of Leaf

Meristems: Where Cells Divide

Meristems – sites in the plant body where cells divide and where differentiation into specialized cells and tissues are initiated.

Growth – Increasing the size and number of cells. This includes cell division and cell enlargement.

Cell Differentiation – Cells become structurally and biochemically different in order to do different functions.

Meristems are not necessarily tissues. They are “areas.”

Primary GrowthPrimary growth allows for vertical growth to occur (For the shoots to grow up and the roots to grow down). The Apical Meristems are the shoot apical meristem (SAM) and root apical meristem (RAM). The apical meristems are located at the tip of roots and shoots. The apical meristems are the Zone of Cell Division. This cell division does not often occur forever. Plant growth is determined by genetics, nutrients, and structural limitations.

Right behind the Zone of Cell Division (further from the apex) is the Zone of Elongation. Here is where the cells elongate and are responsible for pushing the root down and the shoot up.

Even further from the apex is the Zone of Differentiation (PRIMARY MERISTEMS). This is where cells undergo specialization into the 3 Primary Meristems. These 3 Primary Meristems give rise to the 3 tissue systems that we covered.

PRIMARY MERISTEM TISSUES

1) Protoderm . . . . . differentiates into . . . . . . . . . . . . . Epidermis.

2) Procambium . . . differentiate into . . . Primary Xylem & Primary Phloem.

3) Ground Meristem . . differentiate into . . . Pith and Cortex of Stems and Mesophyll of Leaves.

Primary Growth of Shoot Tip

Primary Growth of Root Tip

Secondary meristems produce secondary tissues which increases the girth of a plant. In other words, secondary meristems allow for lateral or horizontal growth. While growing, this allows for an increase in thickness and circumference of stems and roots. Secondary growth is responsible for wood in trees. In woody plants, secondary growth is responsible for the gradual thickening of the roots and shoots formed from earlier primary growth.

Some plants lack secondary growth. In herbaceous (nonwoody) plants there is only primary growth because they only grow during one year’s time.

SECONDARY MERISTEM TISSUES

1) Cork Cambium . . . . . . differentiates into . . . . . . . . Periderm.2) Vascular Cambium . . . differentiates into . . . . . Secondary Xylem &

Secondary Phloem.

Secondary Growth

Diagram of a tomato plant showing the relative positions of the root apical meristem (RAM) and shoot apical meristem (SAM), the primary meristems (protoderm, ground meristem, and procambium), and the secondary meristems (vascular cambium and cork cambium in both the shoot and root system.

Summary of Meristems and the Tissues They Generate

* indicates Tissue from the Ground Tissue System.^ indicates Tissue from the Dermal Tissue System.# indicates Tissue from the Vascular Tissue System.

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BIO 141 Botany with Laboratory

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